Moon Mission

National Maritime Museum SMART-1

The mission

Artist's concept of the SMART-1 spacecraft. Image: (c) ESA

Europe's first mission to the Moon launched successfully at 23.14 UT on 27 September 2003 on board an Ariane 5 launch vehicle departing from the Kourou spaceport in French Guiana. It is now on its way to the Moon following testing of its ion engine. Its leisurely 18 month journey will allow testing en route of advanced technologies for future space missions. The European Space Agency (ESA) has a commitment to develop small, low cost space probes under the auspices of the Small Missions for Advanced Research in Technology (SMART) programme. SMART-1 will orbit the Moon for a minimum period of six months. In the process it will flight-test a variety of new deep space technologies. At the same time the spacecraft will be used to investigate unanswered questions such as the origin of the Moon and the suspected existence of ice in the craters around the lunar South Pole.

Electric propulsion

Artist's concept of a solar-electric propulsion craft in operation. Image: (c) ESA

Travelling through space using electric propulsion may be the key to future space exploration, particularly within our solar system. Electric or ion propulsion uses solar panels to convert sunlight into electrical energy. Inside the drive system, a negatively charged cathode emits electrons. These are attracted into a positively charged anode chamber. The electrons are trapped inside this chamber using a magnetic field. Atoms of xenon gas are then added to the chamber where they collide with the electrons. This dislodges additional electrons from the xenon atoms to form ions. These positively charged particles are repelled by the anode and are expelled from the spacecraft in an ion beam. The ejection of the ions creates a gentle acceleration and drives the spaceship forward. Ion propulsion is cheaper, lighter, easier and quicker to adjust than conventional chemical rockets. The engines can operate at high efficiency for long periods and drive spacecraft to high speeds, cutting down journey times to more distant targets

(although not the Moon – chemical engines can send probes there within a few days). SMART-1 is ESA's first spacecraft to use this propulsion system but several NASA probes including Stardust already employ ion engines.

Lunar science with SMART-1 SMART-1 will examine the Moon with a suite of instruments. For example, the Asteroid Moon micro-Imager Experiment (AMIE) camera will be used to study the Moon’s topography. It has a field view of 5° wide and observes in visible and near-infrared light. AMIE will view regions from different angles and under different lighting conditions to better understand the evolution of the lunar surface. SMART-1's most complex task is to peer into the dark regions around the poles, looking for signs of water ice, the possibility of frozen carbon dioxide and carbon monoxide. No light falls directly on to the areas that are to be targeted but rays reflected from nearby crater rims may light the ice sufficiently for it to be detected in the infrared. Many astronomers believe the Moon coalesced out of the debris from a collision between the early Earth and an asteroid the size of Mars. Compared with the Earth, the Moon should have a lower proportion of iron and the heavy elements found in the terrestrial core and a higher proportion of the lighter elements found in the Earth's crust. Atoms of different elements on the lunar surface absorb X-rays from the Sun. The X-rays are re-emitted with a characteristic signature of the element that absorbed them. The Demonstration of Compact Imaging X-ray Spectrometer (D-CIXS) instrument on the probe detects these re-emitted X-rays and measures the elemental composition of the lunar crust. A successful SMART-1 should give an impetus to ESA's programme to explore the solar system and observe the wider universe – projects ranging from gravitational wave detectors to probes that will land on Mercury.

Robert Massey and Heather Campbell, July 2003 http://www.nmm.ac.uk/conWebDoc/8084