Ariadna Brochure

ARIADNA Brochure Completed Studies 2003-2007

Released in June 2008 Advanced Concepts Team European Space Agency

Page 2 of 45

Ariadna Brochure June2008

Introduction to ARIADNA The future exploration of the Solar System and utilisation of space requires the development of new technologies and concepts. Ariadna is an initiative of the European Space Agency (ESA) to establish a link with the European academic community in advanced space technology research. Its main objective is to enhance cooperation and facilitate research partnerships with universities and research departments linked to universities. With its contracts mechanism, Ariadna stimulates research on enabling space research areas and on the development of new design methods. Subjects include theoretical physics, power systems, propulsion, trajectory design and optimisation, informatics and applied mathematics, biomimetics, and other subjects in which both space systems engineering skills and specific theoretical knowledge are required. Ariadna encompasses two types of announcements to award the contracts to universities: 1. The Calls for Proposals consist of announcements of specific assessment studies, in which the topic of research and tasks to be performed have been previously defined by ESA’s Advanced Concepts Team (ACT) and relate to the team’s basic research categories, and for which the need for a short, focused evaluation has been identified. 2. Where Calls for Proposals invite interested parties to submit study proposals on very specific topics and complying with a set of well defined tasks, these may be complemented by Calls for Ideas, where research groups are invited to submit ideas for their own proposals relating to a general theme or problem, specified by the ACT. In this case, and after a preliminary selection has taken place researchers will be expected to work in collaboration with the other participants in the Call for Ideas contributing to a comprehensive, multidisciplinary review of the proposed theme. This brochure presents the Ariadna studies that have been completed so far since the beginning of the Ariadna scheme. For each of them the motivations, contractual details, and main results are described.

Ariadna Brochure June 2008

Page 3 of 45

Page 4 of 45

Ariadna Brochure June2008

Table of Contents Introduction to ARIADNA ......................................................................................................................................................................................... 3 Table of Contents ................................................................................................................................................................................................... 5 Theoretical Study of the Interaction of Mesoscopic Systems with Gravity (Study 03/1301)....................................................................................... 7 Laser power beaming feasibility: non-mechanical beam steering options, laser phase-locking and control (Study 03/2201) .................................... 8 Advanced Global Optimisation Tools for Mission Analysis and Design (Study 03/4101)........................................................................................... 9 Study on Libration Points of the Sun and the Interstellar Medium for Interstellar Travel (Study 03/4102) ............................................................. 10 Assessment of Mission Design Including Utilisation of Libration Points and Weak Stability Boundaries (Study 03/4103) ........................................ 11 Feasibility Study for a Spacecraft Navigation System Relying on Pulsar Timing Information (Study 03/4202)........................................................ 12 Natural Language Technique in Support to Spacecraft Design (Study 03/5101) .................................................................................................... 13 Electroactive Polymer-Based Artificial Muscles as an Alternative to Space Mechanisms (Study 03/6101) ................................................................ 14 Biologically Inspired Solutions for Robotic Surface Mobility (Study 03/6201)........................................................................................................ 15 Mammalian Hibernation: Relevance to a Possible Hypo-metabolic State (Study 03/6501)..................................................................................... 16 Environmental Impacts of High Power Density Microwave Beams on Different Atmospheric Layers (Study 03/9102).............................................. 17 Lorentz-invariant description of the Feigel process for the extraction of momentum from the vacuum (Study 04/1201)......................................... 18 The relativistic double-embedding problem for the Solar System (Study 04/1302)................................................................................................ 19 Biomass-based Fuel Cells for Manned Space Exploration (Study 04/2301)............................................................................................................ 20 Sponge Iron Process for Manned Space Exploration (Study 04/2302)................................................................................................................... 21 Helicon Double Layer Thruster Concept for High Power Nuclear Electric Propulsion Missions (Study 04/3101)........................................................ 22 Assessment of Open Magnetic Fusion for Space Propulsion (Study 04/3102) ........................................................................................................ 23 A search for an invariant relative satellite motion (Study 04/4104)...................................................................................................................... 24 Assessing the accuracy of interval arithmetic estimates in space flight mechanics (Study 04/ 4105)...................................................................... 25 Mechanisms - Biologically inspired joints for innovative articulations concepts (Study 04/6201)............................................................................ 26 Numerical simulation of the Helicon Double Layer Thruster Concept (Study 05/3201)........................................................................................... 27 Advanced Concepts of Electromagnetic Generation, Confinement and Acceleration of High Density Plasma for Propulsion (Study 05/3202) ........... 28 Electrodynamic tether microsats at the giant planets (Study 05/3203) ................................................................................................................. 29 Spiral Trajectories in Global Optimisation of Interplanetary and Orbital Transfers (Study 05/4106)....................................................................... 30 Electrostatic forces for satellite swarm navigation and reconfiguration (Study 05/4107)....................................................................................... 31 The Flower Constellation Set and its possible applications (Study 05/4108).......................................................................................................... 32 Space Webs (Study 05/4109).............................................................................................................................................................................. 33 The application of clouds for modelling uncertainties in robust space system design (Study 05/5201)................................................................... 34 Bio-inspired distributed system for thermal (or particles) transport (Study 05/6203) ............................................................................................ 35 Strain sensors inspired by campaniform sensilla (Study 05/6401) ....................................................................................................................... 36 Non invasive brain-machine interfaces (Study 05/6402)...................................................................................................................................... 37 Global Trajectory Optimisation: Can We Prune the Solution Space when Considering Deep Space Maneuvers? (Study 06/4110)............................. 38 Advanced Injectors for Chemical Rockets Inspired by Ink-jet Printing Technology (Study 06/3101) ....................................................................... 39 Attaching Mechanisms and Strategies Inspired by Spiders' legs (Study 06/6201).................................................................................................. 40 Bio-inspiration from Plants' Roots (Study 06/6301) ............................................................................................................................................. 41 Microstructured Radiators (Study 06/9501)......................................................................................................................................................... 42 Efficient Usage of Self Validated Integrators for Space Applications (Study 07/5202)............................................................................................ 43 Evolving a Collective Consciousness for a Swarm of Pico Satellites (Study 07/8101).............................................................................................. 44 Keep in touch!! .................................................................................................................................................................................................... 45

Ariadna Brochure June 2008

Page 5 of 45

Page 6 of 45

Ariadna Brochure June2008

Theoretical Study of the Interaction of Mesoscopic Systems with Gravity (Study 03/1301) Motivation The interaction of mesoscopic quantum systems with gravity has repeatedly been the realm of speculations and experimental claims of gravitational anomalies. Recently, it has been suggested that there might be an enhanced gravitational interaction in superconductors. Depending on the assumed coupling scheme, this could either change the effective mass of the superconducting electrons or facilitate the conversion of electromagnetic waves into gravitational waves. This work constitutes a review assessing how far the two purported processes – which could have important technological consequences - find support through our knowledge of semi-classical gravity and quantum gravity. Study details ACT researchers: Andreas Rathke Academic research centre: Universitat zu Koln (DE) Duration: 2 months Results There have been repeated speculations about large quantum effects in the coupling of a quantum system to gravity. Such effects could lead to violations of the weak equivalence principle (all bodies fall equally fast) or to the generation of gravitational waves in superconductors or BoseEinstein condensates. A review was undertaken, showing that already at the level of the description of a single fermion (e.g. electron) in a combined electromagnetic and gravitational field, severe gaps in our understanding were identified. The necessary steps to fill these gaps were identified and described. All theoretical considerations that predict gravitational anomalies use these gaps in the formalism to postulate enhanced couplings. However there is no stringent theoretical justification for any of these. The study showed confirmed the current cautious approach to these anomalies and their claimed applications, e.g. in “breakthrough propulsion systems”. Highlights The ideas regarding the generation (and detection) of gravitational effects via quantum systems should be considered theoretically in order to gain a better understanding of the exact coupling strength; only in this way, it is possible to assess the outcome of experiments conducted to this end. According to the study there does not seem to be evidence for the inclusion of the gravitomagnetic fields on experimental grounds. The classical coupling scheme discussed in the study yields interactions which can be neglected. The study recommends investigating further these topics in a theoretical context to arrive at quantum coupling mechanisms which could lead to experimental results.

Ariadna Brochure June 2008

Page 7 of 45

Laser power beaming feasibility: non-mechanical beam steering options, laser phase-locking and control (Study 03/2201) Motivation In the frame of solar power from space concepts, most of the concepts use microwave frequencies for wireless power transmission (Space to Earth as well as to planetary surfaces). Wireless power transmission via lasers is often regarded as too advanced, since efficiencies are still considered too low. For space-to-space laser power transmission applications, the fiber laser option would offer many advantages, especially small emitting and receiving antennas. One of the major drawbacks of laser with respect to microwave systems apart from the low efficiencies is the need of moving parts to steer the beam. This study therefore investigated the principal feasibility of laser beam steering by phase locking and phase control of an array of multiple lasers (e.g. laser diodes). It was intended to identify theoretical solutions and eventually compare different technical approaches to the problem. Study details ACT researchers: Leopold Summerer Academic research centre: University of Kaiserslauten (DE) Duration: 2 months Results The fast progress and breakthrough rhythm of the years 1985-1995 on diode-laser phase locking could not be sustained as expected since then, essentially due to principal physics limitations of diodes (complex spatio-temporal behaviours); current techniques don’t allow yet the simulation of diode arrays. While the output power of diode lasers improved by more than one order of magnitude within the last 20 years (broad area lasers or arrays from 200 mW to 4 Watts, laser bars from 5 Watts to 70 Watts), the experimental results with phase-locking kept more or less constant at a few hundred mW for arrays and ~1W for laser bars, since phase locking works only at the laser threshold. Recent research indicates that wavelength multiplexing approaches might be more promising than phase locking concepts; 1-dimensional beam steering is theoretically possible but experimental data is still lacking; 2-dimensional electronic beam steering is in principle possible but with very high complexity. Fibre lasers seem to be most promising for laser power transmission applications and can in principle be integrated into a solar-pumped system. Publications • C.A. Schäfer, O. Matoba, N. Kaya, ”Non-mechanical laser beam steering with a liquid crystal spatial light modulator”, IAC-05-C3.2.10, 2005. • C. A. Schäfer, N. Kaya, ”Lunar Polar Mission applying Laser Power Transmission”, IAC-05-A3.4.09. 2005. • C. A. Schäfer, O. Matoba, N. Kaya, ”Tracking system by phase conjugation for laser energy transmission”, SPIE - Photonics West, 2007 (submitted). Highlights Following the study, one of the students of the University of Kaiserslauten went on to make a PhD on the subject and has not only theoretically but even experimentally demonstrated a completely new method of 2-dimensional electronic laser beam steering.

Page 8 of 45

Ariadna Brochure June2008

Advanced Global Optimisation Tools for Mission Analysis and Design (Study 03/4101) Motivation The importance of having an effective and efficient global optimisation approach, well known, understood and studied in many other fields, is also emerging in the space field with studies on optimisation methods to obtain a solution or even just a first guess solution to complex problems. In general, global optimisation techniques can be classified in two main groups: deterministic (systematic) and stochastic (or heuristic) approaches. Among deterministic methods promising area of research are interval analysis based methods, branch and bound approaches, tunneling techniques and quantum optimisation. Among stochastic methods evolution programming and clustering techniques appear to be the most promising. It is however likely that an already existing approach is not suitable or cannot directly be applied without a proper implementation. Therefore the study objectives are the identification of the most common classes of problems in mission analysis, the analysis of the nondeterministic-polynomial complexity of each class, the assessment of the most suitable global approach to solve the classes of problems commonly encountered in mission analysis, and the development of an innovative approach specifically dedicated to mission analysis if necessary. Study details ACT researchers: Dario Izzo, Massimiliano Vasile Academic research centre: University of Reading (UK) and University of Glasgow (UK) Duration: 6 months Results Multiple Gravity Assist, Low Thrust and Fuzzy Boundary transfers have been investigated and different global optimisers have been tested on each problem. Differential Evolution was found to be the most efficient heuristic global optimiser for problems related to mission analysis and design. For the simple Multiple Gravity Assist problem an efficient pruning technique allows to reach the global optimum with fairly high chances and to obtain an algorithm whose complexity grows only linearly with the number of swing-bys used. The use of advanced global optimisation algorithms in mission analysis and design problems drastically improves the efficiency of the search. Simple Genetic Algorithms are outperformed by advanced global optimisation techniques such as Multilevel Coordinate Search or Fast Evolutionary Programming. The objective function structure is linked to the particular technique to be used to locate the global optimum. Publications • Izzo D., Becerra V.M., Myatt D.R., Nasuto S.J., Bishop J.M., “Search Space Pruning and Global Optimisation of Multiple Gravity Assist Spacecraft Trajectories”, Journal of Global Optimisation 38, pp.283-296, 2007. • Izzo D., “Advances In Global optimisation For Space Trajectory Design”, Paper ISTS 2006-d-45, 25th International Symposium on Space Technology and Science, Japan, 2006. • Becerra V.M., Myatt D.R., Nasuto S.J., Bishop J.M., Izzo D., “An Efficient Pruning Technique for the Global Optimisation of Multiple Gravity Assist Trajectories”, Proceedings of the GO 2005 Conference, Almeria, Spain, October 2005. • Di Lizia P., Radice G., Izzo D., Vasile M., “On the Solution of Interplanetary Trajectory Design Problems by Global Optimisation Methods”, Proceedings of the GO 2005 Conference, Almeria, Spain, October 2005. Highlights In this pioneering study, trajectory design was put for the first time systematically into the perspective of global optimisation. The results paved the way to a now very active research field that is being pursued by a number of international groups. Among the many global optimisation algorithms tried out, Differential Evolution and Particle Swarm Optimisation were found to be the most effective in connection with a variety of problems ranging from multiple gravity assists to deep space maneuvers to low-thrust trajectory optimisation. Ariadna Brochure June 2008

Page 9 of 45

Study on Libration Points of the Sun and the Interstellar Medium for Interstellar Travel (Study 03/4102) Motivation Recent studies on restricted 3 and 4 body problems have opened the way to innovative type of transfer trajectories within the solar system exploiting the dynamics of Lagrangian points. If a great deal of effort has been put so far in the understanding of the dynamics of these points and in the exploitation of their characteristics in the design of missions in the solar system, the effect of the interaction of the gravity fields of n bodies in the galaxy is less clear and in particular the interaction of the gravity field of the solar system, as a whole, with the neighboring stellar systems. In addition, it should be noted that if those points can be identified, it would be interesting to look for its implication in the dynamics of any astronomical bodies in the interstellar medium which could be trapped either around them or through them. Therefore this study aims at a preliminary investigation of the n-body dynamics involving the solar system and the other stars of our galaxy. Furthermore, in the case in which critical points (either stable or unstable) or periodic solutions could be found for this dynamics within the study, a preliminary investigation of their use for interstellar travels or mission at the limits of the solar system constituted a supplementary objective of the study. Study details ACT researchers: Dario Izzo, Massimiliano Vasile Academic research centre: University of Padova (IT) and University of Glasgow (UK) Duration: 2 months Results The Solar System neighborhood behaves essentially as a system of non-interacting particles. The long debated relationship between Proxima Centauri and Alpha Centauri A/B is probably nothing but a hyperbolic passage of the former in the gravitational field of the latter. No libration point exists between the Sun and the Centauri system. The two fixed-point dynamics is not able to describe interstellar travel in our Solar System neighborhood. No known dynamic paradigms such as the existence of weak stability regions may be applied to the cruise phase of an interstellar travel, no critical point of libration exist between nearby stars. Light extinction, due to scattering and absorption of photons by interstellar matter, does not significantly reduce the stellar luminosity so that dust particle motion is influenced by light pressure at positions of temporary dynamic stability. Highlights This short study closed the debate about the relationship between Proxima Centauri and Alpha Centauri A/B by excluding the possibility that in the near Sun interstellar medium there could be dynamic phenomena similar to the weak stability boundary that could be used during a realistic interstellar mission.

Page 10 of 45

Ariadna Brochure June2008

Assessment of Mission Design Including Utilisation of Libration Points and Weak Stability Boundaries (Study 03/4103) Motivation Recent studies on restricted three- and four-body problems have paved the way to innovative types of transfer trajectories within the solar system exploiting the dynamics of Lagrangian points. A complete and clear understanding of all potential utilizations of libration points and weak stability boundaries (WSB) in relation to their dynamic characteristics was however still missing. An assessment at mission design level is required to identify the most interesting uses of these regions either as gateways or as stationary points. In fact, the convenience of locating a spacecraft in orbits around a libration point or of exploiting WSB for escape or capture could be limited in relation to other mission requirements though the cost in terms of propellant consumption could be reduced with respect to other designs. In summary the study aimed at identifying the most interesting uses of libration points either as gateways for interplanetary missions or as stationary points and at assessing - from a mission design point of view - the actual convenience (time, launch window, cost, complexity, etc…) of using libration points. Study details ACT researchers: Dario Izzo, Massimiliano Vasile Academic research centre: Universitat Politecnica de Catalunya (ES) and Politecnico di Milano (IT) Duration: 2 months Results The use of a precompiled database about the dynamic behavior at energy level close to the one of a libration point, and in particular containing the invariant curves associated to each libration point in our solar system, allows the design of a fast and efficient tool that might be used in future as a standard tool for mission analyst. Interplanetary trajectories may be performed by exploiting the interconnections formed by different manifolds coming from different libration points. The transfer time would, though, dramatically increase. An appropriate choice of the lunar phase may lower the cost of transfer from two Earth orbits without changing the transfer time. Though the state of the art is quite satisfactory in mission design using libration points’ dynamic features, there is still work to be done in connection, for example, with the combined use of low-thrust propulsion and Weak Stability Boundary transfers. Publications • Topputo, F., Vasile, M., Bernelli-Zazzera, F., "Interplanetary and Lunar Transfers using Libration Points Authors", Proceedings of the 18th International Symposium on Space Flight Dynamics (ESA SP-548), jointly organized by the German Space Operations Center of DLR and the European Space Operations Centre of ESA, 11-15 October 2004, Munich, Germany. Highlights This study also provided a broad overview of possible algorithms and tools to deal with the so-called Interplanetary Highways, which are low energy transfers between planets that get continuously created and destroyed by the celestial movements.

Ariadna Brochure June 2008

Page 11 of 45

Feasibility Study for a Spacecraft Navigation System Relying on Pulsar Timing Information (Study 03/4202) Motivation The planetary exploration missions currently under study by ESA underline the need for improved spacecraft positioning systems. Candidate sources for providing positioning signals are millisecond pulsars, whose position is known up to the precision of 0.1 arcseconds: the extreme constancy of pulsar signal timing (exceeding even that of atomic clocks), has already been applied for means of positioning by using it to tie together the coordinate systems of radio astronomy and that of visible astronomy. Although based on a simple principle, the actual realization of a positioning system based on pulsar timing faces severe technical challenges: first at all the very low luminosity of millisecond pulsars requires high-sensitivity radio antennas, which however have to obey the mandatory weight and power-consumption limitations for space systems, and the changes of arrival time will be tiny for small changes of the spacecraft position due to the large distance of the pulsars. The goal of the study is therefore to investigate the feasibility of a spacecraft navigation system based on (millisecond) pulsar timing, with targeted positioning precision of 106 m, and to compare it with both the current state of technology and the sensitivities achievable by envisaged technological progress. An investigation of the usability of the X-ray signals from pulsars for navigation purposes would be desirable. Study details ACT researchers: Torsten Bondo, Andreas Rathke Academic research centre: Universitat Politecnica de Catalunya (ES) Duration: 2 months Results Radio pulsars offer the most reliable timing standard ever. Hence their radio beacon might serve as a natural Galileo system for deep space. The feasibility of this idea was assessed by an interdisciplinary team (telecommunications engineers and astrophysicists). Accuracies of 500 km are achievable with 3.5 m diameter antennas and integration times of a few minutes. Hence the system is not attractive for Solar system exploration. It will however become an attractive option for travels further away, e.g. to the Oort cloud and beyond. Highlights Two years after this study was concluded, the results of a US DARPA study on the same topic were published with substantial media echo. The US study came to slightly different, much more optimistic conclusions. As a main difference, the DARPA study considered X-ray pulsars as more promising candidates than radio pulsars.

Page 12 of 45

Ariadna Brochure June2008

Natural Language Technique in Support to Spacecraft Design (Study 03/5101) Motivation The aim of the study was to assess and produce an "intelligent advisor" tool for spacecraft designers. The advisor would capture pieces of information needed during the design process, and it would retrieve relevant data by browsing both internal and external sources of information. The main study tasks were the definition of a suitable system architecture, the identification of its main components and the representation of the spacecraft ontology (i.e. the "knowledge" of the particular domain). Study details ACT researchers: Mihály Csaba Markót Academic research centre: University of Rome Tor Vergata (IT) Duration: 4 months Results First steps toward the implementation of an “intelligent advisor” tool for spacecraft design. The advisor captures information needed during the design process and retrieves related/relevant support data by browsing both internal and external sources of information. The core part of the suggested system architecture is an Information Retrieval (IR) engine and a Document Clusterer. An Information Need Extractor is used to get the information needs by processing implicit or explicit requests and to feed them into the IR module. The main modules utilize the space mission ontology and generic linguistic knowledge bases. The mission ontology is intended to be built from a domain corpus with the involvement of domain experts. The retrieved and clustered documents can serve also as a feedback to further refine the ontology. During the study period a preliminary ontological knowledge base (KB) was constructed. Design related terms and verbal expressions were extracted from a document corpus provided by ACT, and the extracted results were validated (filtered) by ESA experts. To make the validation tasks easier a Web-based validator interface software has been developed. Publications • M.T. Pazienza, M. Pennacchiotti, F.M. Zanzotto, “Terminology extraction: an analysis of linguistic and statistical approaches”, in Knowledge Mining, S.Sirmakessis (Ed.), Series: Studies in Fuzziness and Soft Computing, Vol.185, Springer Verlag, 2005. • M.T. Pazienza, M. Pennacchiotti, M. Vindigni, F. M. Zanzotto, “AI/NLP technologies applied to spacecraft design”, in Proceedings of the 18th International Conference on Industrial & Engineering Applications of Artificial Intelligence & Expert Systems, 2005. Highlights The study conceived an intelligent advisor architecture for the specific and practical scenario of the ESA Concurrent Design Facility. In order to estimate its validity, the architecture was tested over a corpus of spacecraft design documents, consisting of a collection of 32 ESA reports, tutorials and glossaries, forming 4.2 MB of textual material (about 673000 words). Extracted terms and relational patterns have been manually validated by a pool of ESA experts.

Ariadna Brochure June 2008

Page 13 of 45

Electroactive Polymer-Based Artificial Muscles as an Alternative to Space Mechanisms (Study 03/6101) Motivation Unlike existing linear actuators that could be considered roughly analogous to muscle (such as hydraulics for example), the muscle is a highly nonlinear, time variant and multivariate component of the animal system. These essential characteristics of nonlinearity, time-variable, repeatable performance and exquisite level of control make the imitation of living muscle a difficult engineering challenge. On the other hand range of speed and precision of muscle actuation are evident benefits of achieving a high-performance artificial muscle. The objective of this study is the development of Electroactive Polymer (EAP)-based mechanisms that have potential for application as artificial muscles in future space missions. Of particular interest are the performance characteristics of different types of EAP/EAP-based mechanisms, bearing in mind the wide range of envisaged future scenarios where artificial muscles will be applied, such as smart structures, mechanisms, and autonomous agents. Study details ACT researchers: Mark Ayre Academic research centre: University of Pisa (IT), University of Reading (UK) Duration: 2 months Results The various electro active materials were assessed for their suitability for space applications as actuators. The assessment included a look at actuation characteristics (stress, strain, repeatability etc.) and also their survivability in the space environment (transition temperatures, susceptibility to radiation etc.). Dielectric elastomers were concluded to be suitable candidates due to their wide operating temperature range, their relative tolerance of radiation, and their ability to operate in ‘dry’ environments. Publications • Ayre, M. R., De Rossi, D., Carpi, F., Jeronimidis, G., Gaudenzi, P., Tralli, A., Zolesi, V., "Electroactive Polymers for actuation and sensing in space applications" Proceedings of IAC 2004, Vancouver, Canada, 2004. Highlights Subsequent ESA study focused on the EAPs identified during this Ariadna

Page 14 of 45

Ariadna Brochure June2008

Biologically Inspired Solutions for Robotic Surface Mobility (Study 03/6201) Motivation The possible advantages of biomimetic locomotion are a robust response to obstacles, the ability to position the body of the robot with a high degree of accuracy, and rapid movement over complex and unpredictable terrain: wheeled vehicles in fact are obviously superior when the terrain is relatively smooth, but have difficulties when encountering natural uneven terrains with many substrates, whereas legged animals can traverse such environments rapidly. Identification and development of promising techniques of locomotion in planetary environments is therefore a priority. This study focuses on the identification and conceptual development of one or more innovative concepts inspired by natural systems for planetary surface locomotion. The correct mode of locomotion is obviously environment-dependent, and the suitability of proposed techniques must be justified in the context of the environment in which they operate. Investigation of the use of already-present environmental features to aid the locomotion is considered. Study details ACT researchers: Mark Ayre Academic research centre: Helsinki University of Technology, (F) Duration: 4 months Results Different ways of using environmental ‘free’ energy to power both the locomotion and subsystems of novel Martian scouts. A tumbleweed style configuration was adopted to allow wind-driven locomotion. An active ballast system was developed to also allow directional active motion of the rover in windless conditions, and also to act as a power generator during high-wind periods. Highlights Triggered by this concept study, Helsinki University of Technology developed a full scale prototype.

Ariadna Brochure June 2008

Page 15 of 45

Mammalian Hibernation: Relevance to a Possible Hypo-metabolic State (Study 03/6501) Motivation Hibernators exist in every phylum, and the behavioral and physiological mechanisms that animals use to hibernate are as diverse as the animals themselves. Because of their phenotypical/genotypical similarity to humans (belonging to the mammalian class), mammalian hibernation mechanisms are considered to hold the most promise in application to human hibernation and the ability to induce a hypo-metabolic state within astronauts during long-term space voyages would have a considerable effect on Life Support System resource requirements. There exist many different behavioral and physiological mechanisms peculiar to specific species, but there also exists a wide range of common behaviors and mechanisms that characterize mammalian hibernators as a whole. The objective of the study is to perform a review of knowledge gained to date concerning the mechanisms used by mammalian hibernators and winter sleepers. The review covers general hibernation strategies common to all hibernators and general mechanisms of winter sleepers as well. For every mechanism identified, the suitability/practicality of applying similar mechanisms to human hibernation should be explored and gauged. Of particular interest is to explore the potential suitability of hibernation and winter sleep to the human case, and a principal result from the study should be a reasoned argument in favour of one of these principle mechanisms. Study details ACT researchers: Mark Ayre, Massimiliano Vasile Academic research centre: University of Verona, Pavia and Urbino (IT) Duration: 2 months Results Hypometabolism was considered in application to astronauts to reduce both consumables and psychological burdens during long-duration deep space missions. Natural mammalian hibernation was reviewed and assessed for application to humans using a variety of techniques (pharmacological, genetic etc.). DADLE (an encephalin, similar to the Hibernation Induction Trigger molecules used by natural hibernators) was identified as the best short term avenue of research. Use of hibernation at a systems level was investigated as well, by assessing trip-times, and system-level impacts. Publications • Ayre, M. R., Vasile, M., "Perspectives on hibernation applied to human space exploration" ESF Exploratory Workshop on Mammalian Hibernation, Manburg, Germany, November 2003. • Ayre, M. R., "Hypometabolic stasis in astronauts for long term space flight - insights from fundamental research" Proceedings of IAC 2004, Vancouver, Canada, 2004. • Ayre, M. R., Morpheus "Hypometabolic Stasis for Long-term Spaceflight" Journal of the British Interplanetary Society, Vol. 57, no.9/10, 2004. Highlights Based on research roadmaps in the medical field, inducing a hypo-metabolic state in humans seems to be feasible in the long term. The study recommends a re-assessment in 5-10 years time.

Page 16 of 45

Ariadna Brochure June2008

Environmental Impacts of High Power Density Microwave Beams on Different Atmospheric Layers (Study 03/9102) Motivation In the frame of solar power from space concepts (Solar Power Satellites, Space Solar Power Stations, Solar Power Platforms, etc), most current concepts use wireless power transmission via microwave frequencies from in-space power stations (LEO, GEO, Lagrangian points, Moon) to Earth-based receiver sites. Two frequencies – both reserved by the ITU for ISM applications – are currently considered: 2.45 and 5.8 GHz. Theory predicts an about 2-3% transmission loss in the Earth ionosphere. (Preliminary experiments were done until now only in the 2.45 GHz range with Japanese sounding rockets.) This study intended to investigate the mechanisms underlying the absorption processes and their influence on beam quality, and to elaborate a model simulating these effects. The study was also to look at potential local/regional/global effects in the ionosphere in case of large SPS constellations as proposed in the frame of the NASA SPS Fresh Look Study and the ESA SE&U study. A significant portion of the work was expected to be derived from other atmospheric studies, including telecommunication applications. Study details ACT researchers: Leopold Summerer Academic research centre: Leicester University (UK) Duration: 2 months Results The study made a comprehensive, quantitative comparison of all different interaction mechanisms. Effects considered include absorption due to ionospheric electron collisional effects and beam fluctuations (scintillations) due to the presence of ionospheric plasma density irregularities (normal and extreme conditions considered). Potentially important nonlinear interactions between high power electromagnetic modes and the ionospheric plasma are dealt with. Beam power fluctuations are the single most important parameter with regard to detrimental effects (due both to naturally occurring ionospheric plasma density irregularities, as well as those which can be excited by the SPS beam through instability and nonlinear feedback effects). Estimations lead to potential amplitude fluctuations of close to 100% on 2.48 GHz signals, with somewhat smaller fluctuation levels on 5.8 GHz. Highlights Some model parameters needed extrapolations since these ranges of energy densities are usually not studied.

Ariadna Brochure June 2008

Page 17 of 45

Lorentz-invariant description of the Feigel process for the extraction of momentum from the vacuum (Study 04/1201) Motivation Several futuristic concepts of space propulsion rely on the properties of the quantum vacuum (Alcubierre bubbles, use of vacuum forces directly for propulsion), and in the last few years the understanding of the quantum vacuum in the presence of external fields has made considerable progress in areas, which seem relevant for the above ideas. Recently A. Feigel has demonstrated that in the presence of media with certain electromagnetic properties, momentum can be extracted from the vacuum of quantum electrodynamics. The result fits well into the recent findings on the existence of a UV cut-off in vacuum forces since also the extraction of momentum is limited by UV effects. Some doubt however remains about the reliability of Feigel's result due to the fact that the calculations were conducted in non-covariant fashion. The aim of this study is to reconsider the situation discussed by Feigel using the Lorentz-invariant representation of electrodynamics. In this way the result of Feigel should be either recovered or, if discrepancies arise, their origin shall be discussed and a reliable result shall be derived. Study details ACT researchers: Andreas Rathke Academic research centre: University of Cologne (DE) and University of Grenoble (FR) Duration: 2 months Results Generally covariant and Lorentz invariant description of Feigel process were derived using classical electrodynamics’ and quantum field approaches respectively. Further technical improvement of Feigel theoretical approach was performed, including the use of recent developed regularization techniques to avoid divergence. Both approaches show that momentum cannot be extracted from quantum vacuum fluctuations in the way stated by Feigel’s original work conclusions. However, analysis showed that this effect is in principle possible where electric and magnetic fields are increased slowly from zero, though experimental verification is thought to be out of reach. Where a strong isotropic classical radiation field is present, rather than a vacuum, both analyses conclude that motion may be induced in magnetoelectric media in a manner similar to that suggested by Feigel. Experimental setup was analyzed and proposed for verification of the case using classical radiation. Highlights The Feigel process, which claims to extract momentum from a very specifically tuned vacuum state, was critically reviewed. Not surprisingly it was found that a technological application of such an effect cannot exist. Both studies obtained results that differ from the original work by Feigel and show that the effect, if present, is much smaller than originally claimed. A situation similar to the Casimir effect is encountered: in very special situations an effect might be seen but due to theoretical and practical constraints it will never yield technological applications at a macroscopic level.

Page 18 of 45

Ariadna Brochure June2008

The relativistic double-embedding problem for the Solar System (Study 04/1302) Motivation Current interplanetary missions have already exceedingly high requirements on the maximally allowed unmodeled disturbance forces. From the smallness of the relevant disturbances, the cosmological state of the universe results in having a potential influence on spacecraft trajectories, which may become relevant for planned future space missions. Unfortunately, determining the impact of the cosmic expansion on the local dynamics of the Solar system is not trivial at all, because in extension of the Einstein-Straus problem a proper treatment requires to embed both the Schwarzschild metric of the solar system into that of the Galaxy, and to embed the Schwarzschild metric of the Galaxy into the Cosmic background solution. The aim of this study is to obtain a solution to this double embedding problem both for the Sitter universe and for closed, flat and open Friedman universes. The results shall encompass both the effective metric for Solar system and a calculation of the accelerations induced by the cosmic background solution on interplanetary spacecraft. Study details ACT researchers: Andreas Rathke Academic research centre: University of Freiburg (DE) Duration: 2 months Results Several approaches were investigated to solve the double embedding problem for the solar system, and thus to assess the effect of cosmological expansion on a local scale and in particular its relevance to the measured Pioneer anomaly. An extensive literature review showed no result: the one aiming to find a theorem like the statement based on a realistic and exact solution to Einstein’s equations which asserted that cosmological expansion is irrelevant to local dynamics. Both kinematical and dynamic effects, when studied in a fully relativistic treatment and using an improved Newtonian formulation respectively, were found to have potential effects, but many orders of magnitude smaller than the scale of the Pioneer anomaly. Highlights Could deviations from Newton’s gravitational law or even general relativity (most prominently the Pioneer anomaly) be explained from the expansion of the universe? An extensive literature review showed that an analytical solution to this question within general relativity is not known. Estimates of this effect - mostly within the Newtonian approach - showed that there exists an influence of the global cosmological expansion on local dynamics. However, these effects are far too small to explain the deviations that are currently under discussion.

Ariadna Brochure June 2008

Page 19 of 45

Biomass-based Fuel Cells for Manned Space Exploration (Study 04/2301) Motivation The increasing quantity of greenhouse gases in the atmosphere and the decrease in fossil fuels availability are driving the investigation of alternative energy sources for Earth applications. Among others, different processes for the conversion of biomass into useful fuels are under development or have been implemented in various countries. The transfer of this technology to space represents a promising approach in the frame of in-situ resources utilisation projects, in view of the ambitious plans for future manned exploration of Mars and the Moon. Besides the regeneration of consumables, human faeces represents a potential source of methane and hence hydrogen, which can be used as fuel in a fuel cell, or in propellant gas mixtures. Such a process would at the same time provide fuel from available resources, reducing fuel transportation from Earth, and contribute to waste disposal. The object of this study is the exploration of different routes for the production of fuels for a fuel cell from organic waste, and in particular from human excrements, during manned exploration of the Moon and Mars. A trade-off between the processes will be performed and discussed. Study details ACT researchers: Tiziana Pipoli Academic research centre: University of Wageningen (NL) and University of Helsinki (FI) Duration: 4 months Results This study performed a preliminary assessment of conversion of biomass to fuels for energy generation during manned missions and as an alternative to other waste handling approaches. Different routes to conversion were investigated: photo catalytic, photo biological and thermo catalytic. Key issues were identified and further work suggested. Overall system energy balance was investigated for both microbial fuel cells with separate waste decomposition process: waste decomposition + biogas treatment + fuel cell. In the two preliminary test cases, the system was found to be only marginal net energy consumer. System mass and volume estimates were made. Publications • T. Pipoli, “Feasibility of Biomass-based Fuel cells for Manned Space Exploration”, Seventh European Space Power Conference -espc 2005- 913 May, 2005 Stresa – Italy. Highlights A waste treatment system using biological fuel cells to degrade waste can have zero net energy. This means that the waste treatment does not cost the life support system any energy. With more development work, systems with positive net energy could probably be made and so the waste management system would be an energy producer instead of an energy consumer.

Page 20 of 45

Ariadna Brochure June2008

Sponge Iron Process for Manned Space Exploration (Study 04/2302) Motivation The Sponge Iron Process (RESC) is a well-known technology for the production of hydrogen where carbon monoxide level in the obtained hydrogen is very low (<10 ppm). The hydrogen produced has a purity grade compliant with the requirements of fuel cell noble metal catalysts, which would be otherwise irreversibly poisoned. The process is therefore very interesting for production and purification of hydrogen for fuel cell applications. Since iron oxides are present in the regolith of both the Moon and Mars, the process is promising in the frame of In Situ Utilization Resources for space exploration, and the technology might be transferred to the space sector. Goals of this study are: to assess the feasibility of the process during exploration missions of the Moon and Mars taking into account the environmental conditions and the need for process automatization; to optimize the process parameters for the abovementioned specific applications; to define the lifetime of the iron oxide and the efficiency of the process; to estimate the overall energy balance. Study details ACT researchers: Tiziana Pipoli Academic research centre: University of Graz (AT) Duration: 6 months Results The possibilities and limitations of utilizing the sponge iron reaction with different applications in mission to the surface of the Moon and Mars have been investigated. A mathematical model of the complete RESC cycle has been developed for systems analysis and performance prediction, including modeling of the hydrocarbon reformer, the Sponge iron reactor (SIR) and the complete RESC plant. Four different applications of the sponge iron reaction have been considered and were investigated with a detailed thermodynamic model: the production of pure cell grade hydrogen from different hydrocarbon species, the extraction of oxygen from lunar regolith, the production of hydrogen with carbon monoxide and SIR reducing agent, and the storage of hydrogen by means of a REDOX reaction of a contact mass. Publications • Pipoli, T., Summerer, L., Ongaro, F., “Hydrogen production technologies for space and terrestrial applications”, 2nd European Hydrogen Energy Conference, Zaragoza, Spain, November 2005. Highlights Using the sponge iron process in combination with solid oxide fuel cells gives the opportunity to use in-situ resources for hydrogen production. The overall hydrocarbon to electricity conversion efficiency is over 45% which makes this an interesting process to consider for exploration missions.

Ariadna Brochure June 2008

Page 21 of 45

Helicon Double Layer Thruster Concept for High Power Nuclear Electric Propulsion Missions (Study 04/3101) Motivation The Helicon source is a device capable of high-efficiency plasma generation. These helicon-type thruster concepts are entirely scalable to high power (kW to MW) operations, but scaling is a challenging task since non-linear interactions between plasma flow, magnetic and electric fields at higher energies are difficult to predict and small-scale instabilities arising may cause a reduction in thrust efficiency. Despite the significant challenges to be overcome, the potential for helicon-type thrusters operating at high power levels make them an attractive choice for propelling large spacecraft requiring high delta-V and acceptable transfer times. This study shall focus on the investigation of the novel Helicon Double Layer Thruster (HDLT) concept and provide a means for ESA and European academia to further collaborating with the Australian National University who are leading the development of this promising technology. The study should investigate the scaling of the helicon double layer thruster for high power interplanetary space missions. Study details ACT researchers: Roger Walker Academic research centre: Laboratoire de Physique et des Technologies des Plasmas (LPTP) and CNRS Ecole Polytechnique (FR) Duration: 4 months Results The concept appears to be promising for future high power electric propulsion, but needs to be investigated further. The original concept (strongly diverging magnetic field in pure argon) has been tested experimentally in a helicon reactor installed at LPTP. The double layer has been found in the same parameter space as at the Australian National University, thus verifying their findings. The specific impulse and thrust derived from flux and energy measurements in LPTP reactor are rather low at 900s and 20 micro-N, but it is expected than these values can be improved considerably with further research. The effect of adding an electronegative gas has also been investigated experimentally. In that case the double layer was easily formed, with or without magnetic field. However, it was unstable in a wide parameter range. Performance estimates suggest that it is less promising than original HDLT concept. Further numerical simulation and experimental work needs to focus on scaling to higher power and proving that the HDLT can function in free space vacuum conditions. Publications • R. Walker, N. Plihon, P. Chabert, J.L. Raimbault: “Experimental Studies of Helicon Double Layers for Future High Power Plasma Propulsion”, Proceedings of 42nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Sacramento, California, USA, July 9-12, 2006. Highlights The study was able to reproduce the double layer with a laboratory-based helicon reactor in France and replicated the original results obtained by the Australian National University, thus providing important verification of this complex plasma phenomenon and identifying critical issues on high power scaling and existence in the space environment to be investigated with numerical simulation codes.

Page 22 of 45

Ariadna Brochure June2008

Assessment of Open Magnetic Fusion for Space Propulsion (Study 04/3102) Motivation One alternative method of propulsion concept which is still at a relatively early stage of development is the direct use of energy from fusion reactions to drive a spacecraft. Only relatively recently some work has begun to focus on the detailed design of a space-propulsion-specific reactor and the impact of these designs on the potential performance and mission capability of such engines. Some concept evaluation work has been performed at a variety of different levels into concepts which employ closed chamber, toroidal confinement reactors, open confinement systems and inertial confinement devices. The preliminary results of this work have shown that open magnetic configurations have a number of advantages in terms of their use in space. The main objectives of this study are evaluation of the current status of practical research into fusion confinement systems, specifically open magnetic configurations, and identify new concepts where possible; the identification of most promising concepts for space propulsion applications; a brief consideration on how civilian and space research on fusion technology may influence one each other. Study details ACT researchers: Roger Walker Academic research centre: University of Rome “La Sapienza” and ENEA Frascati (IT) Duration: 2 months Results Open magnetic mirror configurations show potential for fusion propulsion. However, tandem mirror concepts require sophisticated techniques for end plugging and have been limited so far to low plasma density operations. Gasdynamic mirrors are simpler, but require either very long systems or very high density values that increase neutron wall load well beyond those sustainable with medium-term material development. Field Reserved Configurations are promising, but their stability approaching fusion conditions must be demonstrated and problems exist with plasma sustainment and confinement. Spheromaks are suitable for fusion propulsion, but their capability to achieve fusion conditions is not so good and they suffer problems with plasma stability and maintaining an effective laminar dynamo for adequate energy confinement. Research by the fusion community is needed to solve these issues. Significant technological advances need to be made in materials in order to substantially lower the specific mass of subsystems, e.g. breeding blankets, magnets, radiators, plasma heating etc. Highlights A very comprehensive and thorough review was made by a highly qualified and experienced study team into the state-of-the-art of fusion reactors concepts and related technologies/materials suitable for space propulsion applications, leading to highlighting the most interesting candidate concepts and their critical issues, necessary technology developments, and future studies of technical solutions.

Ariadna Brochure June 2008

Page 23 of 45

A search for an invariant relative satellite motion (Study 04/4104) Motivation Relative satellite motion plays an important role in the design of a number of advanced space mission concepts. Mission design methods would greatly benefit from a better understanding of relative motion dynamics. It is in particular of great interest to understand whether there are solutions to the equations governing the relative dynamic between two or more satellites that are naturally periodic when a complete dynamic model is accounted for, and to what extent space missions benefit from these solutions. Some results are already available in the literature and taking into account the sole average differential J2 effect. Invariants orbits, could, though, exist also in a more complete dynamic model. The objective of this study is to search for periodic solutions to the equations describing the relative motion dynamics accounting for a dynamic model as complete as possible and to investigate the impact that these solutions may have in real space missions. Mission concepts based on drag controlled relative dynamics and eccentricity effects should be accounted for. Study details ACT researchers: Dario Izzo Academic research centre: University of Rome (IT) and University of Reading (UK) Duration: 4 months Results The two teams focused on different algorithmic implementations of the periodic motion search. Surprisingly new special inclinations were discovered, namely near 49.1 deg in Low Earth Orbit, where a weak effect of the orbital perturbations allows for a quasi-periodic relative motion. These trajectories, when used as a reference for the orbital control system of each spacecraft, allow for great fuel savings. Publications • Sabatini, M., Izzo, D., and Bevilacqua, R., “Special Inclinations Allowing Minimal Drift Orbits for Formation Flying Satellites”, Journal of Guidance Control and Dynamics, 31(1), pp.94-100, 2008. • Sabatini, M., Bevilacqua, R., Pantaleoni, M., Izzo, D., “A Search for Invariant Relative Satellite”, Motion Journal of Nonlinear Dynamics and Systems Theory. • Becerra V.M., Biggs, J.D., Nasuto S.J., Ruiz V.F., Holderbaum W., Izzo D., “Using Newton's Method to Search for Quasi-Periodic Relative Satellite Motion Based on Nonlinear Hamiltonian Models”, 7th International Conference On Dynamics and Control of Systems and Structures in Space (DCSSS) 2006, 16th–20th July - The Old Royal Naval College, Greenwich, London, England. • Sabatini M., Izzo D., Palmerini G., “Analysis and control of convenient orbital configuration for formation flying missions”, Paper AAS 06120, AAS/AIAA Space Flight Mechanics Conference, Tampa, Florida, 2006. • Sabatini M., Bevilacqua R., Pantaleoni M., Izzo D., “Periodic relative motion of formation flying satellites”, Paper AAS 06-206, AAS/AIAA Space Flight Mechanics Conference, Tampa, Florida, 2006. Highlights The relative satellite motion dynamics is studied for the first time with non averaged techniques. The search for closed bounded orbits brings to the discovery of a new critical inclination, namely around 49.1 degrees, where the relative dynamics is quasi-periodic allowing for huge savings in terms of control effort.

Page 24 of 45

Ariadna Brochure June2008

Assessing the accuracy of interval arithmetic estimates in space flight mechanics (Study 04/ 4105) Motivation Interval arithmetic, started from the pioneering works by Moore and Sunaga, has recently been applied to space related issues. Taylor model technique is quite debated within the interval community and needs further comparative studies with existing verified techniques; a more useful approach to this problem could be that of considering the disturbances as unmodeled forces belonging to some predefined interval vector, or to include in the model effects due to solar radiation pressure or J2 effects for Earth Orbit applications. Applications could range from collision avoidance of NEOs to limiting the search space in a lost-in-space situation to many other interesting cases. In the framework of interval integration techniques, this study proposes to estimate the resulting interval overestimation in the position of a spacecraft over time when different techniques are applied to different problems. The initial conditions of the spacecraft have to be considered as intervals (orbit determination errors) together with the disturbance forces (modeling uncertainties). The simple keplerian case should be assessed first by means of basic interval arithmetic (using the simpletic transition matrix given by Lagrange coefficients); a verified integration technique should then be used to introduce disturbances both as intervals and as modeled effects. Study details ACT researchers: Mihály Csaba Markót, Dario Izzo Academic research centre: Politecnico di Milano (IT) Duration: 4 months Results Interval techniques were applied to analytical solutions available for the simple two-body dynamic model. The numerical integration of the motion was faced by the available interval integrators, whose performances were tested concerning both the possibility of obtaining validated solutions and the opportunity of propagating uncertainties. The motion of asteroids in the more complete and complex n-body dynamic model was investigated, together with the accuracy of the interval integrators in propagating uncertainties on dynamic model parameters related to the modeling of non-gravitational perturbations. The validated integration of motion during aero-capture manoeuvres (as an interesting space-related application deeply affected by model uncertainties) was also investigated. Highlights The results proved that the tested existing general rigorous solvers with their default setup are not comparable with the non rigorous ones due to the overestimation. However, the study is a good initiative to point out the need of specialized reliable methods in space flight mechanics.

Ariadna Brochure June 2008

Page 25 of 45

Mechanisms - Biologically inspired joints for innovative articulations concepts (Study 04/6201) Motivation Despite the dramatic improvements in the fields of materials, actuators, and control strategies, the vast majority of articulated systems are based on conventional linear or rotational rigid couplings (typically ball bearing rigid pinned hinges). The typical natural animal-world solution for achieving articulated systems are different from the “rigid pinned hinge” concept, not only as far as the materials are concerned, but also for the geometries of the coupled surfaces and for the trajectories allowed to the articulated members. It is believed that innovative articulations / joints concepts, inspired by animal-like forms could be exploited by the current research programs in the field of innovative actuation concepts, and could mimic to a much higher extent human motion, in particular a natural motion in general. This study assesses the feasibility, practical implications and potentials of adopting innovative, animal or human-like articulation concepts in the frame of robotic or more generally articulated structures. The purpose is to exploit synergies with innovative actuation type concepts which can reproduce the muscular functionality, and achieve superior performances in terms of higher degree of natural motion mimicking. Study details ACT researchers: Carlo Menon, Mark Ayre Academic research centre: University of Bologna (IT), TU Delft (NL) Duration: 6 months Results State of the art of mechanical joints, their limits and the needs of high performing systems were analyzed. Environment interaction and novel paradigms in machine design were discussed. Joints as passive mechanisms and as real organs were analyzed together with their key elements for functional stability. Existing biologically inspired mechanisms were considered and discussed. Novel types of bio-inspired joints were synthesized. Kinematical, dynamic and stiffness analyses were performed. Publications • R. van der Linde and C. Menon, “Novel bio-inspired mechatronic articulation with potential for use in space”, 57th IAC Conference, Valencia, Spain, 2006. • C. Menon, M. Markot, R. Vertechy and V. Parenti-Castelli, “Geometrical optimisation of parallel mechanisms based on natural frequency evaluation: application to a bio-inspired system for future space applications”- in preparation for journal submission. • R.Vertechy, C. Menon & V. Parenti-Castelli, “Design of a novel 2DOF joint inspired by the human knee for future space applications” - in preparation for journal submission. Highlights One patent has been filed in France sponsored by ESA.

Page 26 of 45

Ariadna Brochure June2008

Numerical simulation of the Helicon Double Layer Thruster Concept (Study 05/3201) Motivation The study was focused on investigating the formation, stability and characteristics of the double layer in plasma thrusters in laboratory and space-like conditions, through the development of a numerical code. Double-layers are electrostatic structures able to support a potential jump in a narrow spatial region of plasmas. Methodology The modelling approach was based on three different numerical models: a) a global numerical model of the plasma source, b) a 1-D code of the entire system, c) a 2-D open source code, XOOPIC, of the entire system. The global model was used to simulate the plasma source behaviour, it provided the other two codes with the source ionization rate, plasma density and electron temperature. A 1-D code named PPDL was developed specifically for this purpose. It is a hybrid code with Boltzmann electrons and driftkinetic ions, inclusion of dominant 2-D effects and high computational efficiency through implicit nonlinear Boltzmann solver. With the XOOPIC was necessary to perform fully electromagnetic simulations with kinetic electrons, resulting in long computational times. The effects of the source walls characteristics and geometry, DL formation and stability, influence of magnetic field and neutral pressure, ions’ beam divergence, flux detachment, thrust and specific impulse were evaluated. The 1-D and 2-D code results were compared and validated with experimental data provided by literature. Study details ACT researcher fellowship: Cristina Bramanti Academic research centre: CISAS G. Colombo, Padova, Italy Duration: 4 months Results The numerical analysis indicates that the formation of the potential drop is mainly due to the plasma expansion and subsequent density reduction immediately downstream, rather than a double layer, and that it happens when a particular “dimensional” threshold, defined by chamber pressure, source density, source-chamber dimension and expansion rate (ion density reduction), is reached. The jump of the potential has not been seen as deep as reported by the measurements but an ion flux having twice the velocity of the ions sound speed has been obtained. The source walls, in particular the left one, have a great influence on the potential reached by the plasma. A conducting left wall biased at a sufficiently high potential can significantly increase the value registered inside the source tube and, sometimes, influence the stabilization of the plasma density there. By increasing the neutral pressure, the potential jump reduces whereas an electrically biased wall can increase its amplitude. Publications • Manente, M., Carlsson, J., Bramanti, C., Pavarin, D., and Angrilli, F.,“Numerical Simulation Of The Helicon Double Layer Thruster Concept”, Proceedings of the 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference {\&} Exhibit, Cincinnati, Ohio, USA, 2007. • Musso, I., Manente, M., Carlsson, J., Giacomuzzo, C.,, Pavarin, D., Angrilli, F., and Bramanti, C., “2D OOPIC Simulation Of The Helicon Double Layer”, Proceedings of the 30th International Electric Propulsion Conference, Florence, Italy, 2007. • Manente, M., Carlsson, J., I. Musso,, Bramanti, C., and Giacomuzzo C., Pavarin, D., “1D Simulation Of The Helicon Double Layer”, Proceedings of the The 30th International Electric Propulsion Conference, Florence, Italy, 2007. Highlights Although at an early stage of laboratory experimentation, results indicate that there exists a potential for helicon radio-frequency plasma thrusters to operate at low to high power levels to produce a high continuous thrust, moderating high specific impulse with reasonable efficiency (up to 60%). This type of thruster has the additional advantage of requiring no high-current cathode, acceleration grids or neutralizer that presently limit the operating lifetime in other electric thrusters, allowing longer missions. Ariadna Brochure June 2008

Page 27 of 45

Advanced Concepts of Electromagnetic Generation, Confinement and Acceleration of High Density Plasma for Propulsion (Study 05/3202) Motivation The purpose of this study is to take advantage of the advanced numerical simulation codes developed by the nuclear fusion community for fusion plasmas in order to improve penetration of radiofrequency (RF) waves from the Ion Cyclotron Resonance (ICR) antenna into the dense plasma coming from the helicon source region. Methodology For the first time the 3D numerical simulation code, TOPICA, already developed by the University of Turin, was applied to modelling the RF antennas in space thrusters comprising of a helicon plasma source, a confining magnetic field structure enclosing a plasma heating section, and a magnetic nozzle. TOPICA is a self-consistent code, which was originally conceived for plasma facing antennas operating in tokamaks, and recently extended to handle cylindrically symmetric plasmas. The simulations aimed at improving the penetration and coupling of the RF waves with the magnetized plasma in order to enhance plasma heating and axial thrust. The results of TOPICA have been used as inputs of a system-level modelling, which was developed by the University of Padova. This combination enabled to optimize the design parameters: antenna shape, generators, matching circuits, as well as the ensuing required power, mass and other physical quantities, including magnetic field for confinement. Study details ACT researcher fellowship: Cristina Bramanti Academic research centre: Dipartimento di Elettronica, Politecnico di Torino, Torino, Italy and CISAS G. Colombo, Padova, Duration: 4 months Results TOPICA was modified to handle the specific geometry and plasma parameters of the thruster; it allowed the evaluation of the ICRH antenna parameters (strictly related to the antenna shape and plasma composition) and power penetration into the plasma. The zero-dimensional global model provided for the relevant global system parameters, necessary to assess the engine performance. The predictions of the global modeling were likewise validated against published experimental values, while TOPICA results for the parameters of the ICRH antenna of the booster unit were validated against published measured data (for the so-called coupling resistance). The results of the model gave the indication of the values of plasma parameters that should be expected during the experiment, and also the requirements for the needed diagnostics. In this respect, a prototypical optimisation exercise confirmed that the use of Argon as propellant is preferable to other lighter gases, mainly because it can be ionized with significantly lower power. Publications • Lancellotti, V., Maggiora, R., Vecchi, G., Pavarin, D., Rocca, S., and Bramanti, C., “Analysis of RF thrusters with TOPICA and a global systemlevel model”, Proceedings of the 30th International Electric Propulsion Conference, Florence, Italy, 2007. • Lancellotti, V., Maggiora, R., Vecchi, G., Pavarin, D., Rocca, S., and Bramanti, C., “Radiofrequency Plasma Thrusters: Modeling Of Ion Cyclotron Resonance Heating And System Performance”, Proceedings of the 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference Exhibit, Cincinnati, Ohio, USA, 2007. Highlights The developed tool set as a whole can be used, for instance, to investigate the feasibility of a low-power (a few kW) system and then to address its scaling to high power. Because of the reduced computational load of the zero-dimensional model, evolutionary algorithms can be employed to optimize the model. With this approach, it was possible to compute optimal values of power partition, mass flow rate, type of propellant, magnetic field and dimensions of the thrusters. Page 28 of 45

Ariadna Brochure June2008

Electrodynamic tether microsats at the giant planets (Study 05/3203) Motivation A full study of the complex Jovian system, particularly moons Europa and Io and Jupiter itself, is a central goal in space science. An alternative novel mission concept based on conductive tethers providing both power and propulsion at Jupiter to allow a costeffective tour of the Jovian system including rendezvous with the moons Io and Europa was assessed during the study. The use of electrodynamic bare tethers in exploring the Jovian system by tapping its rotational energy for power and propulsion was studied. The Jovian system is particularly appropriate for the use of ED-tethers in thrusting, as well as dragging, producing power either way. Operating conditions require plasma beyond the stationary radius as to i) be dense enough, and ii) co-rotate with the planet. The thin tether is left bare of insulation, allowing it to collect electrons over the segment coming out positively polarised, as a giant cylindrical Langmuir probe in the orbital-motion-limited (OML) regime. Study details ACT researcher fellowship: Cristina Bramanti Academic research centre: Universidad Politecnica di Madrid Duration: 4 months Results Capture and evolution to a low elliptical orbit near Jupiter, and capture into low circular orbits at moons Io and Europa were analysed. Different mission scenarios were assessed in terms of radiation environment, trip time, spacecraft/tether mass, power and tether characteristics (mechanical, thermal and electrical) together with the long term effect of the Lorentz torque on the tether spin, and a detailed power strategy allowing the use of energy generated and stored during high-current orbit phases to power electric propulsion at the critical thrust needed for the Io-orbit mission. Mission 1. Frequent Galilean Moons Flybys A tethered spacecraft could rapidly and frequently visit Galilean moons. Elliptical orbits with (capture) perijove at about rp = 1.5 RJ and apojoves down at the Io, Europa and Ganymede orbits, are in resonances 1:2, 4:9, and 2:5 with the respective moons. For the design tape, about 25 slow flybys of Io could take place before the accumulated radiation dose exceeds 3 Mrad(Si) with 10 mm Al shield thickness, for a total mission duration of over five months after capture. The respective number of flybys for Ganymede would be 12, with total duration of about 9 months. Mission 2. Jupiter Capture A tethered SC could acquire a safe, low circular orbit around Jupiter (below the radiation belts) and manoeuvre to get an optimal altitude, with no major radiation effects, in just over 4½ months after capture. An 80-km-long, 0.05-mm-thick tape, and several centimeters wide, could survive 1 year in the Jovian environment with probability very close to unity, allowing all three missions here. Mission 3. Io Low Orbit By thrusting at the apojove once down at the Io torus, in order to raise the perijove from the plasmasphere, a tethered SC could acquire a low circular orbit around moon Io in about 4 months, or 8 months after capture. This corresponds, however, to well over one hundred apojove passes, torus thrusting being weak; the accumulated radiation dose, about 7.5 Mrad (Si), poses a critical issue. Publications • Sanmartin, J.R., Charro, M., Lorenzini, E., Garrett, H., Bramanti, C., and Bombardelli, C., "Electrodynamic Tether at Jupiter. 2. Tour Missions after Capture", Proceedings of 10th Spacecraft Charging Technology Conference, Biarritz, France, 2007. • Sanmartin, J.R., Charro, M., Lorenzini, E., Garrett, H., Bramanti, C., and Bombardelli, C., “Electrodynamic Tether at Jupiter. 1. Capture operations and Constrains”, Proceedings of European Geophysical Union Conference, Vienna, Austria, 2007. Highlights During the study, three mission scenarios for exploring the Jovian system based on the use ED tether were evaluated and demonstrated to have potential. Basic standing issues concern high radiation dose and model uncertainties in plasma density. Ariadna Brochure June 2008

Page 29 of 45

Spiral Trajectories in Global Optimisation of Interplanetary and Orbital Transfers (Study 05/4106) Motivation Exponential sinusoids are the most surprising non-conic solutions to the planetary transfer problem and represent more than an efficient numerical approach aiming at finding a low-thrust solution. The practical use of these solutions is not suitable to be incorporated into a formalization of the Multigenetic Algorithm (MGA) problem as a global optimisation problem, but a different theoretical approach allows for this kind of formalization and enables the possibility of using the results and techniques derived for the simpler ballistic MGA. The enabling theoretical result (solution of Lambert’s problem for the exponential sinusoids) has yet to be embedded into a design tool to verify its ability to locate useful first guess trajectories. The objective of this study is to embed the Lambert’s problem solution for exponential sinusoids into a global optimisation algorithm in order to produce fast and efficient first guess trajectories for the interplanetary trajectory problem. The study should also determine to what extent the use of these special solutions in connection with global optimisation techniques is able to locate trajectories close to a real optimum. Study details ACT researcher fellowship: Dario Izzo Academic research centre: University of Glasgow Duration: 4 months Results The use of exponential sinusoids for zero revolution transfers is equivalent to the use of Lambert’s problem solution. Exponential sinusoids are thus convenient only for multiple revolution transfers. It is possible to embed the exponential sinusoids into a global optimisation scheme also with fly-bys. Publications • Schutze, O., Vasile, M. , Junge, O., Dellnitz, M. and Izzo, D., "Designing Optimal Low Thrust Gravity Assist Trajectories Using Space Pruning and a Multi-Objective Approach", Engineering Optimisation, (submitted August 2007). Highlights Exponential sinusoids for no revolution transfers are equivalent, in a global optimisation scheme, to the use of Lambert solutions.

Page 30 of 45

Ariadna Brochure June2008

Electrostatic forces for satellite swarm navigation and reconfiguration (Study 05/4107) Motivation A number of studies have recently addressed the dynamic modeling of what have been called Coulomb satellites, i.e. groups of satellites whose electric charge is controlled in order to achieve a certain relative dynamic exploiting the inter-satellite electrostatic forces. It is quite likely that if these forces will ever be used to activate “bindings” between orbiting satellites and to control their relative motion or positioning, these will be coupled with other kinds of propulsion systems able to control the absolute position of the satellites. This kind of hybrid actuation has not been studied before, but it could allow to efficiently navigate a swarm of satellites and to allow for their reconfiguration and formation keeping with a minimal amount of propellant. This study should investigate the possibility of combining inter-satellite electrostatic forces with standard propulsion systems in order to achieve a fully controllable system. The controller, when possible, should exploit the electrostatic forces, while the standard propulsion system could provide the complete controllability of the system at the cost of using some propellant. Study details ACT researcher fellowship: Dario Izzo Academic research centre: University of Bremen Duration: 4 months Results The hybrid propulsion system proposed in this study allows for significant fuel savings during certain types of manoeuvres where the formation center of mass does not move significantly. It is possible to make a simple modification of an ion engine as to control the spacecraft charge within the bandwidth required. The resulting charge control system is very stable with respect to plasma fluctuations and other disturbances. Publications • Saaj, C.M., Lappas, V., Richie, D., Schaub, H., and Izzo, D., “Hybrid Propulsion System for Spacecraft Swarm Aggregation using Coulomb Force”, Journal of the British Interplanetary Society, 2007. • Izzo, D. and Pettazzi, L., “Self-assembly of large structures in space using intersatellite Coulomb forces”, Paper IAC-06-C3.4/D3.4.07, 57th International Astronautical Congress, Valencia, Spain, 2006. • Pettazzi, L., Izzo, D., and Theil, S., “Swarm navigation and reconfiguration using electrostatic forces”, 7th International Conference On Dynamics and Control of Systems and Structures in Space (DCSSS). The Old Royal Naval College, Greenwich, London, England, 2006. Highlights A simple modification of an ion engine allows controlling the spacecraft charge with the bandwidth required to exploit inter-spacecraft Coulomb forces advantageously together with the low thrust forces.

Ariadna Brochure June 2008

Page 31 of 45

The Flower Constellation Set and its possible applications (Study 05/4108) Motivation In May 2003 a group of researchers from Texas A&M University lead by Prof. Daniele Mortari proposed the novel concept of Flower Constellation Set, a set that contains a large number of interesting constellations such as the JOCOS, LOOPUS, and COBRA and a great number of new and unexplored constellation geometries that have many interesting yet still poorly understood properties. The set is mathematically defined by only eight parameters, five integers and three real numbers that completely characterize it. Much work still has to be done to fully understand the benefits of adopting this novel viewpoint. The main objective of this study is to carry out a critical review of the Flower Constellation concept with respect to the applications that have been proposed and to study the possibility of optimising the design of a flower constellation. Some particular application should be investigated such as radio-occultation constellations, continuous Earth coverage constellations or space interferometry constellations. Study details ACT researcher fellowship: Dario Izzo Academic research centre: University of Rome Tor Vergata Duration: 6 months Results Flower constellations often have superior performances with respect to standard constellations. The design methodology for this type of constellation can be easily implemented, and takes advantage of a number of analytical results otherwise unavailable to the system engineer. A number of new concepts and geometries are enabled with the use of this type of constellations Flower constellation should be considered for the next generation of Galileo as they might offer substantial performance improvements. Publications • De Sanctis, M., Rossi, T., Lucente, M., Ruggieri, M., Bruccoleri, C., Mortari, D., and Izzo, D., “Flower Constellation of Orbiters for Martian Communication”, IEEE Aerospace Conference, Big Sky, Montana, 2007. • De Sanctis, M., Rossi, T., Lucente, M., Ruggieri, M., Bruccoleri, C., Mortari, D., and Izzo, D., “Flower Constellation for Telemedicine services”, Tyrrhenian International Workshop on Digital Communications (to appear on a Springer book, 2007), 2006. Highlights Flower constellation should be considered for the next generation of Galileo satellites as they might offer substantial performance improvements.

Page 32 of 45

Ariadna Brochure June2008

Space Webs (Study 05/4109) Motivation The deployment and stabilization of a net in space (space web) is a complex phenomenon that has only recently been given some attention triggered by a possible application to deploy very large antennas. A net provides a credible alternative to formation flying and, at smaller scale, to inflatable structures for the deployment of large structures in space, and has the additional advantages of a safety structure in case of temporary loss of control, the ability to reconfigure antenna elements, and in principle the possibility of reduced need for active shape and position control measures. Because a space web may be regarded as a “two dimensional tether”, some inspiration on their modeling may be drawn from the large number of publications available on tethers. The study intends to understand the dynamics of the deployment and stabilization of a net in a space environment, including both, the rotational as well as the active tension control case. Study details ACT researcher fellowship: Dario Izzo Academic research centre: Royal Institute of Technology - Stockholm, University of Glasgow Duration: 4 months Results The centrifugal deployment of a net cannot be controlled by tethers tension alone. It is possible, in principle, to aid the net deployment using the interaction with an external magnetic field but very difficult as the resulting force is tiny. The movement of robots on a rotating net brings forth instability issues that need to be accounted for not to compromise the entire concept. Publications • Gardsback, M., Tibert, G., and Izzo, D., “Design Considerations and Deployment Simulations of Spinning Space Webs”, Paper AIAA 20071829, 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Honolulu, Hawaii, 2007. • Bergamin, L. and Izzo, D., “Comments on Deployment and Control of Charged Space Webs”, European Space Agency, the Advanced Concepts Team, ACT technical report (DCMTSALF07), 2007. Highlights The net topology (its mesh) has an important influence on the centrifugal net deployment performances and needs to be chosen carefully.

Ariadna Brochure June 2008

Page 33 of 45

The application of clouds for modelling uncertainties in robust space system design (Study 05/5201) Motivation The currently mainly deterministic space system design and operation development approach needs to be advanced to a probabilistic approach to better allow for a robust system optimisation. A promising method to achieve such a goal is based on the concept of clouds: clouds capture useful properties of probabilistic and fuzzy uncertainties, and are able to handle multivariate uncertainty problems in algorithmic ways by reducing the necessary calculations to global optimisation and constraint satisfaction problems. This study aims to formulate sample space design applications, to investigate the possibility of modeling the system intrinsic, epistemic uncertainties by clouds, to quantify the reliability of a spacecraft design, to verify the robustness of possibly existing solutions of the sample design cases, and to propose “safe” designs as alternative solutions, using global optimisation techniques. Study details ACT researcher fellowship: Daniela Girimonte Academic research centre: University of Wien Duration: 4 months Results The underlying system model provided by the expert is given as black-box model, and all currently available uncertainty information on the input are variables of the model. The uncertainty information can be provided on the one hand as bounds or marginal probability distributions on the uncertain variables. On the other hand, the engineers can adaptively improve the uncertainty model, even if their expert knowledge is only little formalized, by adding correlation constraints to exclude scenarios deemed irrelevant for the worst-case analysis. The information can also be provided as real sample data, if available. Parameterized by given confidence levels, the clouds provide a nested collection of regions of relevant scenarios affecting the worst-case for a given design and thus produce safety constraints for the optimisation. Heuristic optimisation techniques have been developed taking advantage of inherent characteristics of spacecraft design problems, e.g., discrete design choices. The results of the optimisation are returned to the expert, who is given an interactive possibility to provide additional uncertainty information afterwards and re-run the procedure, adaptively improving the uncertainty model. Publications • M. Fuchs, D. Girimonte, D. Izzo, and A. Neumaier, “Robust and autonomous space system design”, Submitted invited book chapter, 2007. • M. Fuchs, A. Neumaier, and D. Girimonte, “Uncertainty modeling in autonomous robust spacecraft system design”, Proceedings in Applied Mathematics and Mechanics, 15 October 2007. Highlights The developed methods offer an exciting new approach to face the highly complex problem of robust and autonomous system design. This approach is easily understandable, reliable and computationally realizable. In a case study on the background of the NASA’s Mars Exploration Rover mission the methods apply to real-life problems of early phase spacecraft system design.

Page 34 of 45

Ariadna Brochure June2008

Bio-inspired distributed system for thermal (or particles) transport (Study 05/6203) Motivation Some bio-perceptive systems have the particular characteristic to be distributed along surfaces and not localized in small areas. This feature makes it possible to have efficient actuators that do not influence the shape and the macroscopic characteristics of organs in which they are located. Several distributed systems exist in nature with multiple functions for the different uses (ovum moving in the oviducts, for example, or peristaltic wave motion in the intestine to transport food and digest it). One of the most used devices for thermal control in spacecraft is the heat-pipe, a device based on natural convection inside sealed tubes having different temperatures at their ends. The possibility to have miniaturized actuators distributed on heat pipe surfaces able to realize forced air convection is a very appealing and compelling solution. This study aims to assess the feasibility of bio-inspired distributed systems for thermal transport. Study details ACT researcher fellowship: Carlo Menon Academic research centre: University of Pisa Duration: Medium Study (4 months, 25KEUR) Results The main goal of the study was to conceive possible new solutions, inspired by natural systems, for structures embedding distributed actuators for transport of small and lightweight particles, to be used for possible space operations. Some preferred concepts for possible designs of new distributed transport systems were proposed. They were inspired by peristalsis-like motions and consist of distributed actuating structures made of one specific category of electroactive polymers, namely dielectric elastomers. One of the considered solutions was selected among the others, according to its relatively superior simplicity. Prototype samples of a scaled model of an elementary actuation unit suitable for assembling the candidate system were fabricated. Each unit consists of a silicone-made cylindrical hollow dielectric elastomer actuator, working in radial mode. Actuation properties of such units were preliminarily investigated, by performing elementary electromechanical bench tests. Publications • C. Menon, F.Carpi and D. de Rossi, “Concept design of novel bio-inspired distributed actuators for space applications”, Acta Astronautica. • C. Menon, F.Carpi and D. de Rossi, “Concept design of novel bio-inspired distributed actuators for space applications”, 57th IAC Conference, Valencia, Spain, 2006. • F.Carpi, C. Menon and D. de Rossi, “Design of novel bio-inspired distributed actuators for space applications”, 3rd World Congress on Biomimetics, Artificial Muscles and Nano Bio: Scientists meet the Doctors, Lausanne, Switzerland, 2006. Highlights Among the different kinds of EAPs, the dielectric polymers are the most promising. This technology might be mainly applied for micro-fluidic applications.

Ariadna Brochure June 2008

Page 35 of 45

Strain sensors inspired by campaniform sensilla (Study 05/6401) Motivation Biological sensitive mechanoreceptors are inherently small, light and embedded in insect bodies. In particular, campaniform sensilla are used by insects as natural strain sensors: when the sensor is strained, a train of impulses is propagated to the central nerve system and insects can use these signals as feedback for their locomotion control. Embedded strain sensors are of interest for many space applications especially when slender structures are used (solar panels, booms, solar sails etc.) or structural frames must be monitored during hazardous mission phases. Therefore, they are suitable to be used in unlocking systems, docking mechanisms, limit switch devices, robotic arms, etc. This study aims to assess the feasibility of a strain sensor inspired by campaniform sensilla of insects. After a careful review on campaniform sensillum natural sensors, the study should focus on the design of a new-engineered strain sensor which synthesizes the main characteristics of the natural sensor. Study details ACT researcher fellowship: Carlo Menon Academic research centre: University of Bath Duration: 4 months Results The campaniform sensillum is a displacement sensor found in the external skeleton (cuticle) of insects, lobsters, spiders, etc. It is a hole extending itself through the cuticle arranged such that its shape changes in response to loads. In specific directions the shape change is rotated through 90° by the suspension of a bell-shaped cap whose deflection is detected by a cell beneath the cuticle. It can be sensitive to displacements of the order of 1 nm. The essential morphology – a hole formed in a plate of fibrous composite material – was modelled by Skordos et al. (2002) who showed that global deformation of the plate (which can be flat, curved or a tube) induces higher local deformation of the hole due to its locally higher compliance. Further developments reported here show that this approach can be applied to groups of holes relative to their orientation. The morphology of the sensillum in insects suggests that greater sensitivity can be achieved by arranging several holes in a regular pattern; that if the hole is oval it can be ‘aimed’ to sense specific strain directions; and that either by controlling the shape of the hole or its relationship with other holes it can have a tuned response to dynamic strains. A silicon MEMS device based on the campaniform sensillum is being developed in The Netherlands. Publications • Vincent, J.F.V., Clift, S.E., and Menon, C., “Biomimetics of Campaniform Sensilla: Measuring Strain from the Deformation of Holes”, Journal of Bionic Engineering, pp.63-76, 2007. • C. Menon, J.Vincent, S. Clift and S. Hood, “Novel concept inspired by campaniform sensilla for the design of strain sensors used in space applications”, 57th IAC Conference, Valencia, Spain, 2006. • C. Menon, J.Vincent, S. Clift and S. Hood, “Novel concept inspired by campaniform sensilla for the design of strain sensors used in space applications”, Acta Astronautica.

Page 36 of 45

Ariadna Brochure June2008

Non invasive brain-machine interfaces (Study 05/6402) Motivation Controlling and guiding computer-based systems using human brain signals now seems to become reality. The available technology allows implementing, in almost real-time, processes which measure neuron’s activity, convert their signals, and elaborate their output to the purpose of controlling mechanical systems. The advantages for astronauts of using non-invasive brainmachine interfaces are numerous: for example commands could be sent with high accuracy and without any output delays, and, moreover, multi-teleoperations could simultaneously be performed using one single brain-machine interface. This would maximise the efficiency of astronaut activity that is of primary interest. Purpose of this study is to survey literature about brain-machine interfaces (BMI). All existing interfaces were considered with emphasis to non-invasive interfaces. The study also suggested a future time scale for the development of non-invasive brain-machine interfaces. Study details ACT researcher fellowship: Carlo Menon Academic research centre: University of Pisa Scuola Superiore Sant’Anna, University of Pisa ‘E. Piaggio’, EPFL/IDIAP Duration: 2 months Results BMIs are a promising approach to overcome negative effects of microgravity on machine operation. EEG-based BMIs have a principal lack of spatial resolution due to the surface electrodes on the scalp of the subject. MAG-based BMIs would provide better resolution as it can focus inside the skull, however, the machines are currently extremely costly and not at all portable. EEG-based BMIs are easy to use, relatively cheap and portable, hence we decided to test them on a parabolic flight campaign. Publications • C. de Negueruela, M. Broschart, C. Menon, J.del R. Millán, “Brain-Computer Interfaces for Space Applications” (submitted). • C. Menon, C.de Negueruela, J.del R.Millán, O.Tonet, F.Carpi, M.Broschart, P.Ferrez, A.Buttfield, P.Dario, L.Citi, C.Laschi, M.Tombini, F.Sepulveda, R.Poli, R.Palaniappan, F.Tecchio, P.M.Rossini, D.De Rossi, “Prospects of Brain-Machine Interfaces for space system control”, Acta Astronautica (submitted). • Broschart, M., De Negueruela, C., Millan, J. d. R., and Menon, C., “Augmenting Astronauts Capabilities through Brain-Machine Interfaces”, Workshop on Artificial Intelligence for Space Applications at 20th International Joint Conference on Artificial Intelligence (IJCAI), Hyderabad, India, 2007. • Rossini, L., Seidl, T., Izzo, D., and Summerer, L., “Beyond astronauts capabilities: a critical review”, Proceedings of the 58th International Astronautical Conference, Hyderabad, 2007. Highlights Participation in the ESA parabolic flight campaign (Dec 2007), organized by Tobias Seidl.

Ariadna Brochure June 2008

Page 37 of 45

Global Trajectory Optimisation: Can We Prune the Solution Space when Considering Deep Space Maneuvers? (Study 06/4110) Methodology This study considers differential algebraic techniques as an effective tool to attach the pruning of gravity assisted trajectories when deep space manoeuvres (DSM) are considered. As far as differential algebra (DA) is used, the objective function and the constraints of the problem are represented by Taylor series of desired order, over boxes in which the design domain is split. Thanks to the polynomial representation of the function and the constraints, a course grid can be used and an efficient design space pruning can be performed. Furthermore, once the domain has been pruned, a suitable manipulation of the polynomials can ease the subsequent local optimisation process, therefore avoiding the use of any stochastic optimiser. These two aspects, connected with an efficient management of the list of boxes in which the design space can be decomposed, make differential algebraic techniques a powerful tool for the design of multiple gravity assist transfers including deep space manoeuvres, therefore supporting the achievement of a further step to fully automate the trajectory design problem. Study details ACT researcher: Tamás Vinkó Academic research centre: Politecnico di Milano/Aerospace Engineering Department Duration: 6 months Results A version of the pruning algorithm GASP has been implemented in the DA frame, demonstrating the effectiveness of DA techniques applied to space trajectory optimisation problems. The previous algorithm has been extended to manage DSM, showing the possibility of effectively prune the solution space when DSM are considered. Promising alternative strategies for the pruning of GA-DSM transfers have been investigated. An attempt to approach the global interplanetary transfer optimisation problem in a validated manner has been performed. Highlights A version of the classical pruning algorithm GASP, based on the use of differential algebraic techniques, has been implemented. This algorithm demonstrates that the DA formalism represents a promising technique to deal with global space trajectory optimisation problems. This algorithm has been further extended to manage DSM, so answering to the main question of the study: it is possible to prune the solution space when DSM are considered? In the second part of the study, a new strategy for the global optimisation of GA-DSM transfers has been formulated and an attempt to face the global optimisation problem in a validated manner has been made.

Page 38 of 45

Ariadna Brochure June2008

Advanced Injectors for Chemical Rockets Inspired by Ink-jet Printing Technology (Study 06/3101) Motivation: The injectors in a chemical rocket motor constitute a key in determining the efficiency of the reactions within the combustion chamber, ultimately affecting the performance of the motor, heat loads, etc. Critical to achieving good performance is the atomization process, whereby the propellant and oxidizer are transformed into small droplets; in essence the size of these drops determines the mixing process and evaporation rates, which have a profound influence on the combustion reactions. The purpose of this study was to assess several innovative injector designs in chemical rocket motors inspired by alternative technologies. Study details : ACT researcher: Cristina Bramanti Academic research centre: University of Southampton, UK Duration: 4 months Results: Inkjets were assessed as a possible method of injecting fuel into a bipropellant rocket engine. It was found that the surface tension effects that normally prevent unwanted ink escaping can only resist fuel pressures differences of the order of 0.05 bars for typical nozzle sizes. This means that unless the fuel pressure could be closely matched to the combustion chamber and fluctuations in chamber pressure were much reduced, there would be a need for valves. From considering the physics of devices it was found that the actuation technologies (piezoelectric, electrostatic; thermal-bubble consumes too much power) place limits on the maximum flow rates and blocking pressures of the inkjets. It was found that while inkjets are capable of suitable flow rates, none of the actuation technologies can also supply sufficient pressure. The only situation in which inkjets can generate sufficient pressure is if fuel pressure matched chamber pressure, and the chamber pressure fluctuations (from combustion instabilities) were reduced to less than 0.05 bars. Piezoelectric injectors were examined. The precise control over the injectors means that this type of technology offers the possibility of full throttling control, varying the mass flow rate (hence the thrust) from zero up to its maximum value, along with active control of combustion instabilities, and increased efficiency. The pressures found in diesel engines are very high (of order 1000 bars). Calculations show that at much lower pressures (e.g. 12 bars pressure difference for a 100µm nozzle) it would still be possible to atomize NTO and MMH fuels into droplets much smaller than nozzle diameters. A design concept was proposed, along with some basic calculations to show its expected performance. The use of a membrane actuated atomizer was investigated. This kind of injector will reduce the breakup length of about 4 times allowing reducing the combustion chamber length, hence saving mass, or increasing the combustion efficiency. No reduction should be expected in the droplet diameter if compared to a conventional injector. Experimental work is required to confirm the theoretical prediction and to effectively measure the droplet size and break up length. Electrospray injectors were studied. This kind of injection shows very attractive performances like no need of pressure drop along the injector plate, low power consumption, extremely small droplet, active control on mass flow rate and droplet size hence the possibility of performing throttling control and active instabilities control. Unknown are the effects that the charged droplets will have on combustion, nore is known how this kind of injector will work with an applied pressure drop and if this will still be required to prevent the propagation of combustion instabilities upstream. Further theoretical and experimental work is required. Publications • P. Glynne-Jones, M. Coletti, C. Bramanti, S. Gabriel, “Advanced Injectors for Chemical Rockets Inspired by Alternative Technologies”, Proceedings of the 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference Exhibit, Hartford, Connecticut, USA, 2008. Highlights Control over drop size distributions, injection rates, and geometrical distribution of fuel and oxidizer sprays in bi-propellant rocket engines has the potential to produce more efficient, more stable, less polluting rocket engines. This control also offers the potential of an engine that can be throttled, working efficiently over a wide range of output thrusts.

Ariadna Brochure June 2008

Page 39 of 45

Attaching Mechanisms and Strategies Inspired by Spiders' legs (Study 06/6201) Methodology Spiders are capable of efficiently operating and agilely moving in unstructured environments. Spiders can climb on vertical surfaces, go upside-down, build webs and can also walk on them. There are several engineering prototypes of bio-spider systems but they are mainly based on macroscopic observations of the animal's design. A closer look to the climbing abilities and to the attaching mechanisms together with a proper evaluation of the strategies used for locomotion leads to possible biomimetic applications. In particular, studying the biology of the spiders and the biomimesis of the dry-adhesive systems, mechanical and engineering directives and constraints in order to replicate these natural elements can be found. Moreover, a joint evaluation of the kinematic abilities and of the attaching and detaching procedures can lead to a suitable kinematic model and a simulated analysis for a future climbing spider prototype. Study details ACT researcher: Tobias Seidl Academic research centre: Department of Electrical, Mechanical and Management Engineering of the University of Udine (Italy) Duration: 6 months Results The study contains an accurate survey on attaching mechanisms and on locomotion strategies of spiders and engineering prototypes. In addition, the group defined the mechanical and physical requirements and characteristics of the attaching devices. Several different production techniques were assessed in relation to their feasibility concerning achieving dry attachment in the space environment. A large portion of the report contains work on the kinematic model and a simulator of a spider system that take into account both the climbing abilities and the locomotion strategies of the arachnid. Publications • Gasparetto A, Vidoni R, Seidl T. “Kinematic study of the spider locomotor system in a biomimetic perspective” (submitted to IEEE/RSJ IROS2008) Highlights The spiders’ biology has been investigated and a spider model for a biomimetic space application has been developed. Taking into account the attaching and detaching behaviour, the structure of the legs, the mobility and the locomotion strategies of the real spider, a suitable biomimetic model has been defined and implemented in a kinematic simulator. Such a simulator controls the locomotion and the overall degree of adhesion of the system, resulting in important constraints and directives for a future climbing spider-prototype.

Page 40 of 45

Ariadna Brochure June2008

Bio-inspiration from Plants' Roots (Study 06/6301) Methodology Plants are dynamic and highly sensitive organisms, actively and competitively foraging for limited resources both above and below ground, and they are also organisms which accurately compute the circumstances, use sophisticated cost–benefit analysis, and take defined actions to mitigate and control diverse environmental insults. In order to exploit distributed environmental resources, plants develop a network of growing and branching root apices, which efficiently explore and mine mineral and water. Planetary and asteroids’ soil exploration represents a very important and challenging space application. Plant-inspired robots or plantoids distributed on the planetary surface and able to explore soils could be a very appealing solution to a variety of problems in planetary exploration. The present study covers: a definition of realistic scenario where the plantoid will operate, a review of plants that may enable new strategies for planetary exploration, an assessment of technologies envisaged for the plantoid robot, and a review on the anchorage systems. Study details ACT researcher: Tobias Seidl Academic research centre: Scuola Superiore Sant’Anna, CRIM/ARTS Laboratories, Pisa, Italy; University of Florence, LINV, Dipartimento di Ortoflorofrutticoltura, Florence, Italy Duration: 4 months Results Identification of possible space scenarios for a robot inspired by plants’ roots. Deep review of plant beings from a “biomechatronic” viewpoint, including sensors, actuators, intelligence, control and behaviour, which may enable new strategies for planetary exploration. Assessment of technologies envisaged for the plantoid robot, with special attention to actuation solutions, suitable materials and assessment of power consumption of a system inspired to plant behaviour. A preliminary mechatronic system design inspired from plant’s roots for subsurface analysis of chemical-physical parameters for future space applications. Highlights The osmotic expansion in plants has inspired the design of a new class of electrochemical actuators able to fit these requirements: - Very low power consumption; - Actuators response with high modulation capability; - Slow actuation; - High pressure actuation. The osmotic pressure is controlled in a “cell” containing liquid or gel matrix, by applying a small electrical current, and using the resulting pressure to induce an actuation based on the proposed root architecture.

Ariadna Brochure June 2008

Page 41 of 45

Microstructured Radiators (Study 06/9501) Motivation The control of the thermal emissivity of a surface by means of micro- and nanostructures has become an important topic in the last years. This includes the enhancement of thermal emissivity as well as the control of its spatial distribution. Such techniques could become extremely important in the thermal control of spacecraft, as they aim to engineer thermal radiation, which is the only thermal exchange with the environment available in space and for which no similar control mechanisms existed so far. Methodology In two studies the possibilities to modify the radiative properties of surfaces by means of microstructures was investigated. One of them gave an overview of the current state of the art, describing the potential and the risks of different concepts of coherent emission. In this study, the impact of space environment on the functional efficiency was assessed as well. In a second study a reverse engineering approach to multi-layered structure was investigated. The objective was to find the optimal solution of a multi-layered structure given certain thermal properties as well as a choice of materials. Here, different scenarios of coherent emission were taken as specific examples. Study details ACT researcher: Luzi Bergamin, José Llorems Academic research centre: Ecole Centrale Paris and Université de Nantes Duration: twice 2 months Results The first study showed that coherent thermal emission from microstructured surfaces, in particular lamellar gratings, is very sensible to polarization. Hence, a different concept known as Salisbury’s screen has been shown to present a better choice for both radiative cooling and directional heating. Comparison of the efficiency of Salisbury’s screen with planar radiators has been analysed and an enhancement of the emissivity of more than 90% compared to the plane radiator has been demonstrated. Furthermore, the key issues of scalability and robustness were considered, showing that the effect of charging on microstructured radiators is negligible. It is expected that the effect of cosmic radiation will be negligible as well. The second study attacked the inverse engineering problem by means of a genetic algorithm. In this study the combination of three materials, a pair of materials respectively with high and low refractive index, complemented by a polar material or a metal, was investigated. It was shown how it is possible to find good solutions of multilayered structures for coherent emission (quasi-isotropic as well as directional emission) within reasonable time. In a further step, the temperature dependence was added as a new parameter. Publications • Ben-Abdallah P., Llorens J.M., Bergamin L., Vinko T., “Reverse Engineering Design of Directional Microstructured Radiators”, 6th ESA Round Table on Micro & Nano Technologies for Space Applications, Noordwijk, The Netherlands, 2007. Highlights Both studies mainly highlighted the current status in the field of coherent thermal emission and pointed out its potential for ESA. The approach could also find broad applications in others fields of thermal sciences. For example, one can consider ab initio design of functional materials to improve the performance of numerous optical technologies such as the thermo-photovoltaic energy conversion, infrared spectroscopy or radiative cooling. The rational design of materials also finds numerous ramifications and applications in others fields of physics. For instance, it could be used to sculpt the transport properties of nano-composite materials by considering some of their energy carriers (electrons, photon, phonons, magnons, excitons,…) as waves moving in a scattering network. In particular, our work opens interesting prospects for thermoelectric conversion by providing a method to achieve materials with high figure of merit, i.e. with high electric conductivity and small thermal conductivity. Page 42 of 45

Ariadna Brochure June2008

Efficient Usage of Self Validated Integrators for Space Applications (Study 07/5202) Motivation There are several problems in Astrodynamics where the effects of uncertainties in the initial data are critical. A recent example of this is given by the asteroid Apophis, that will have close approaches with the Earth in the years 2029 and 2036. Although it has already been ruled out the possibility of collision in 2029, the lack of precision of the actual measurements of the orbit of Apophis does not allow to discard completely a possible collision with the Earth in 2036. Methodology A method to propagate uncertainties in the initial conditions and parameters is offered by self validated integration methods, based on interval arithmetics and rigorous estimates for the errors. Already available general solvers are able to implement these methods for general ODEs, but previous Ariadna studies have shown that they produce very pessimistic results in the sense of a very large overestimation of the enclosure for the true solution. The aim of this study is to implement these methods for some concrete astrodynamic problems, taking advantage of the selected problem structure. The considered problems are the propagation of the asteroid Apophis and a transfer of a low thrust probe. Study details ACT researcher: Tamás Vinkó Academic research centre: University of Barcelona Duration: 6 months Results Several versions of Moore’s approach, like Lohner method and variants, have been implemented. As a result, it is clear that they are suitable when the size of the initial set of data is very small and the time interval of the integration is moderate. A non-validated N-body Taylor integrator, fast and rather accurate, has been implemented. It provides evidence on the true size of the propagated box. Highlights A new validated step size control strategy has been developed, and tested for the Kepler problem. It allows for much larger time steps and, hence, much shorter computing times. Validated integrations of the motion of an asteroid or a probe, using the JPL ephemeris for the motion of the solar system, have been implemented. Comparison of the propagated boxes using validated and non-validated methods clearly shows the role of wrapping, which can be decreased by using higher order variational and suitable representations of the intervals. It allows also help to realise the importance of the dependence problem.

Ariadna Brochure June 2008

Page 43 of 45

Evolving a Collective Consciousness for a Swarm of Pico Satellites (Study 07/8101) Methodology Multi-agent systems whose control structures are designed by using the principles of swarm intelligence seem to be among the most promising technologies for the design of autonomous vehicles to undertake missions in the space. To study the potentialities of this approach, a distributed control strategy was developed for a swarm of satellites to autonomously form a lattice in orbit around a planet. The algorithm is based on the artificial potential field approach and follows the principles of swarm intelligence: interactions among satellites are only local and no explicit communication is needed. The control parameters were obtained with a genetic algorithm to maximize the precision of the formed lattice. Study details ACT researcher: Dario Izzo Academic research centre: Université Libre de Bruxelles/IRIDIA, CoDE Duration: 4 months Results Distributed control strategy for a swarm of satellites. Precision does not depend on the number of satellites used, convergence achieved from all initial distributions of satellites. Reuse of known results in crystallography. Optimization of the control parameters. Publications • Carlo Pinciroli, Mauro Birattari, Elio Tuci, Marco Dorigo, Marco Del Rey Zapatero, Tamas Vinko, Dario Izzo. “Self-Organizing and Scalable Shape Formation for a Swarm of Pico Satellites”. NASA/ESA Conference on Adaptive Hardware and Systems (AHS-2008). IEEE Computer Society, Washingotn DC, USA. • Carlo Pinciroli, Mauro Birattari, Elio Tuci, Marco Dorigo, Marco Del Rey Zapatero, Tamas Vinko, Dario Izzo. “Lattice Formation in Space for a Swarm of Pico Satellites”. The Sixth International Conference on Ant Colony Optimization and Swarm Intelligence (ANTS 2008). LNCS, Springer, Berlin, Germany. Highlights A distributed control strategy was developed for a swarm of satellites to autonomously form a bi-dimensional hexagonal lattice in orbit around a planet. Experimental evaluation shows that the precision does not depend on the number of satellites used, and that convergence is achieved from all initial distributions of the satellites. The method employed to design the strategy exploits known results in crystallography, which may open a new way for conceiving lattice formation. The control parameters have been evolved to optimize the precision of the final lattice.

Page 44 of 45

Ariadna Brochure June2008

Keep in touch!! For more information about the ongoing studies performed in the frame of the Ariadna scheme, about the Call for Proposals releases, or about the Advanced Concepts Team activities, visit our webpages: www.esa.int/act

To stay in touch with the activities of the ACT, you can also subscribe to: •

Our Newsletter

You are a researcher... ...and you are interested in being updated with news about ACT research activities and Ariadna calls and studies? you are planning to cooperate scientifically with the ACT via the Ariadna scheme or via personal cooperations with the ACT researchers? We invite you to subscribe (http://atlas.estec.esa.int/Ariadna/users/register/index_info.php) to our Ariadna database: you will then receive the Ariadna Newsletter which will inform you about the new research projects, events and work opportunities in the group. You are not a researcher... ...and you are interested in the ACT's research activities, events and initiatives? Subscribe (http://esamultimedia.esa.int/docs/subscribers/subscribersACT.html) to our mailing list: you will receive the Ariadna Newsletter and be updated of all ACT's events. •

Our RSS Feed

Our feed provides you with a fast access to the ACT news published in the (http://www.esa.int/gsp/ACT/index.htm) Copy/paste our link into your favourite RSS reader: [http://www.esa.int/gsp/ACT/act_rss.xml] •

ACT

home

page

Our Podcasts

You can also subscribe to the ACT Podcasts Series by copying the following address into your podcast software: http://www.esa.int/gsp/ACT/podcast/podcast.xml If you're using iTunes you can subscribe by following this link: [iTunes] (http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?id=123292908 )

Ariadna Brochure June 2008

Page 45 of 45