Official Nasa Communication Nearpk

National Aeronautics and Space Administration Near Earth Asteroid Rendezvous (NEAR) Press Kit February 1996 CONTENTS

1.0 Press Release 2.0 NEAR Science Objectives 3.0 Asteroids and Meteorites 4.0 Near-Earth Asteroids 5.0 433 Eros 6.0 253 Mathilde 7.0 NEAR Science Team 8.0 Instruments 8.1 Multispectral Imager (MSI) 8.2 Near-Infrared Spectrograph (NIS) 8.3 X-Ray/Gamma Ray Spectrometer (XGRS) 8.4 NEAR Laser Rangefinder (NLR) 8.5 Magnetometer (MAG) 8.6 Radio Science Experiment (RS) 9.0 Mission Profile: Launch Phase 10.0 Mission Profile: Cruise Phase 10.1 Mathilde Flyby 10.2 Deep Space Maneuver 10.3 Earth Swingby 11.0 Mission Profile: Asteroid Approach 12.0 Eros Rendezvous/Science Operations 13.0 Spacecraft Description .....13.1 Mechanical Subsystem 13.2 Propulsion Subsystem 13.3 Power Subsystem 13.4 Guidance and Control Subsystem 13.5 Telecommunication Subsystem 13.6 Command and Data Handling Subsystem 14.0 NEAR Spacecraft Processing 15.0 Delta II Launch Vehicle 16.0 Launch Vehicle Processing 17.0 Mission Operations System 18.0 Data Analysis/Archiving 19.0 Discovery Program

20.0 NEAR on the NET 21.0 Public Affairs Contacts 1.0 NASA PRESS RELEASE 96-24 NEAR EARTH ASTEROID RENDEZVOUS SET FOR FEBRUARY LAUNCH The NEAR (Near Earth Asteroid Rendezvous) spacecraft -the first asteroid orbiter of the Space Age -- is scheduled for launch in February 1996 aboard a Delta II rocket from Cape Canaveral, FL. NEAR will rendezvous in 1999 with the asteroid 433 Eros, the smallest solar system body to be orbited by a spacecraft. The year-long rendezvous represents the first long-term, close-up look at an asteroid's surface composition and physical properties. Asteroids, along with comets and meteorites, are thought to include debris left over from the earliest days of planetary formation 4.6 billion years ago. The mission will help answer important questions about the formation and evolution of the planets in our solar system. NEAR will be the first launch in the Discovery Program for small-scale planetary missions with rapid, lower-cost development cycles and focused science objectives. The mission is managed by The Johns Hopkins University Applied Physics Laboratory (JHU/APL) for NASA's Office of Space Science, Washington, DC. "We're very excited that we will soon be on our way to exploring Eros. Asteroids may well be a key to understanding early solar system evolution just as a fossil can reveal information about events that happened long ago on Earth," said Dr. Wesley T. Huntress, Jr., Associate Administrator for NASA's Office of Space Science, Washington, D.C. "NEAR is an historic mission in another respect because it's the first launch under NASA's new philosophy of designing and building `cheaper, better, faster' missions. The team at Johns Hopkins APL deserves a lot of credit for turning this concept into reality." Discovery Program guidelines put a cost ceiling of $150

million (FY92 dollars) on spacecraft development to launch plus 30 days, with a maximum three-year development cycle. JHU/APL developed NEAR in 27 months for less than $112 million (FY92 dollars). As the first non-NASA space center to conduct a NASA planetary mission, JHU/APL will direct NEAR from an operations center on its campus in Laurel, MD. "We have created a new paradigm for planetary missions in which one can design to cost, without increasing risk, and still maximize the science capability, all in record time," said Dr. Stamatios M. Krimigis, head of the JHU/APL Space Department. "This is a terrific beginning for the Discovery Program." SPACECRAFT AND INSTRUMENT PAYLOAD The NEAR spacecraft is designed to emphasize simplicity, reliability, and lower cost, with redundant critical subsystems, fixed instruments, and a fixed 5-feet (1.5-meter) diameter high-gain antenna. Four solar panels producing 1,800 watts at 1 AU (93 million miles/150 million kilometers) are the only deployable system on the 1,775pound (805-kilogram) spacecraft. The instrument payload includes an X-ray/gamma ray spectrometer, near-infrared spectrograph, laser rangefinder, magnetometer, radio science experiment, and multi-spectral imager fitted with a CCD (Charge Coupled Device) imaging detector capable of photographing details on Eros' surface as small as 3 feet (1 meter) in diameter. Several of the instruments are derived from designs developed by JHU/APL for Department of Defense spacecraft, an example of dual-use technology transferred to the civilian sector. LAUNCH AND CRUISE TO 433 EROS The NEAR mission's 16-day launch window opens on Feb. 16 at 3:53 p.m. EST and extends through March 2. Daily launch opportunity is approximately one minute. NEAR will be launched on a three-stage Delta II-7925 expendable launch vehicle from Pad 17-B at Cape Canaveral Air Station, FL. After approximately 13 minutes in an Earth parking orbit, NEAR will be injected into its initial mission

trajectory with a four-minute burn by the solid-fueled Delta third stage. Until the spacecraft exits Earth's shadow 37 minutes after launch, it is dependent on battery power. The solar panels, deployed 22 minutes after launch, provide power for the remainder of the mission, making NEAR the first spacecraft to operate solely on solar power beyond the orbit of Mars. NEAR will follow a so-called "Delta VEGA" trajectory to provide the extra energy needed to accomplish the rendezvous with Eros, which orbits the Sun at an angle of 10.8 degrees to the ecliptic. "Delta V" (​V) stands for change in velocity; "EGA" is an abbreviation for Earth Gravity Assist. Several milestone events occur during NEAR's 35-month cruise to the asteroid. On June 27, 1997, at 2.2 AU (205 million miles/330 million kilometers) from Earth, an opportunity exists for the spacecraft to pass within 750 miles (1,200 kilometers) of the asteroid 253 Mathilde. This flyby -- representing the first close-up look at a C-type (carbonaceous) asteroid -- is a secondary mission objective dependent on nominal launch and early cruise. The Mathilde opportunity is lost if NEAR's launch is delayed beyond February 26. A week later, on approximately July 3, 1997, a Deep Space Maneuver with the hydrazine/nitrogen tetroxide-fueled main thruster will brake the spacecraft by 625 miles/hour (279 meters/sec), sending NEAR back towards Earth for the mission-critical gravity assist. Scheduled for Jan. 22, 1998, the Earth swingby will bend the spacecraft trajectory into the orbital plane of Eros and reduce the aphelion distance by 0.4 AU (37 million miles/60 million kilometers). NEAR's ground track will take it over Europe and the Hawaiian Islands at an altitude of 297 miles (478 kilometers). RENDEZVOUS AT EROS The 25-mile (40-kilometer) long Eros is the bestobserved of the "near-Earth" asteroids (NEAs), which orbit within 1.3 AU (120 million miles/195 million kilometers) of the Sun and sometimes cross Earth's path. Unlike the more abundant "main belt" asteroids which orbit the Sun in a vast

torus between Mars and Jupiter, NEAs are thought to be dead comets or fragments from main belt asteroid collisions. Approximately 250 NEAs are known, and scientists estimate there are at least 1,000 with diameters of 0.6 mile (1 kilometer) or more. 433 Eros -- the first discovered (1898) and secondlargest of the NEAs -- is one of the "S-type" (silicaceous) asteroids that dominate the inner main asteroid belt. It has passed as close as 14 million miles to Earth but poses no impact threat to our planet. NEAR will arrive in the Eros vicinity in early 1999. Beginning on Jan. 9, 1999, a sequence of rendezvous maneuvers with the main thruster will slow NEAR by 2,123 miles/hour (949 meters/sec) to achieve a relative velocity between the spacecraft and Eros of just 11 miles/hour (5 meters/sec). The spacecraft makes its initial closest approach on the asteroid's Sunlit side at approximately 310 miles (500 kilometers) altitude on Feb. 6, 1999. During that close flyby, NEAR will obtain preliminary estimates of physical parameters for rendezvous navigation purposes. The spacecraft will then be maneuvered into orbit around the asteroid, using its small hydrazine-fueled thrusters. Mission controllers will direct NEAR into an initial high orbit of approximately 125 by 250 miles (200 by 400 kilometers), then gradually circularize the orbit and tighten its radius as parameters are determined with increasing precision. Regular station-keeping will be required to maintain nominally circular orbits around the potato-shaped asteroid, which has dimensions estimated from ground observations at 25 by 9 by 9 miles (40 by 14 by 14 kilometers). Because of the complex orbital dynamics involved, NEAR must travel in a retrograde orbit relative to the asteroid's spin. The spacecraft orbital plane will be carefully controlled so the fixed solar panels are always pointed within 30 degrees of the Sun. NEAR's fixed, co-aligned instruments are aimed at Eros' surface by slowly rolling the spacecraft into pointing position.

SCIENCE OPERATIONS The NEAR science phase at Eros will begin on approximately March 15, 1999. For the next 10 months, the spacecraft will operate in a range of orbits with radii as small as 22 miles (35 kilometers), corresponding to altitudes as low as 9 miles (15 kilometers) above the asteroid surface. These lowest orbits -- scheduled for approximately 120 days of the rendezvous -- will provide the prime opportunities for close-in gamma-ray and X-ray measurements. Many of the mission's observations will be performed in a 31-mile (50-kilometer) radius orbit. NEAR may provide clues to such long-standing scientific mysteries as the nature of planetesimals, the origin of meteorites, and the relationship between asteroids, meteorites and comets. By the mission's official end on Dec. 31, 1999, NEAR will provide the first comprehensive picture of the physical geology, composition, and geophysics of an asteroid. Highresolution imagery will yield detailed maps of craters, grooves, and other landforms. Other analyses will offer insights into the thickness and distribution of regolith (the debris layer that forms on airless solar system bodies) and the history of impacts as recorded in the crater population. Spectroscopic analysis will provide maps of mineralogy at 1,000-foot (300-meter) resolution and elemental composition at 2.5-mile (4-kilometer) resolution. The radio science and magnetometer experiments will yield information on the strength and character of the magnetic field, and on global density and density distribution. The NEAR Science Data Center (SDC) will be located at JHU/APL. The SDC will maintain the entire NEAR data set online, and data from all instruments will be accessible by every member of the NEAR Science Team. Data, including images, will be released over the Internet as soon as they are validated. The NEAR project is managed for NASA by JHU/APL, Laurel, Md. Program Manager is Elizabeth E. Beyer, NASA Headquarters; Program Scientist is John F. Kerridge, NASA

Headquarters; Project Manager is Thomas B. Coughlin, JHU/APL; and Project Scientist is Andrew F. Cheng, JHU/APl. Navigation support for the mission is provided by the Jet Propulsion Laboratory through the Deep Space Network (DSN). Major spacecraft subsystems were provided by companies including Gencorp Aerojet, Spectrolab Inc., Motorola Inc., Delco Electronics Corp., Honeywell Inc., Eagle-Picher Industries, Hughes Aircraft Co., Ithaco Inc., SEAKR Engineering, and Ball Corp. The Delta II booster is produced and managed by McDonnell Douglas Corp. 2.0 NEAR Science Objectives In 1986, the NEAR Science Working Group identified the following reasons to explore near-Earth asteroids: · Except for the Moon, NEAs are Earth's nearest and most accessible neighbors. · Asteroids, comets, and meteorites preserve records of processes and conditions in the early solar system, but relationships among these bodies are unclear. · NEAs may preserve clues to the nature of planetesimals from which the terrestrial planets formed. · Impacts of large near-Earth objects have significantly influenced the evolution of Earth's atmosphere and biosphere. · NEAs are logical sites to develop the techniques of human deep-space exploration. Overall science goals of the NEAR mission can be summarized as follows: · To characterize the physical and geological properties of a near-Earth asteroid and to infer its elemental and mineralogical composition. · To clarify relationships between asteroids, comets, and meteorites. · To further understanding of processes and conditions during the formation and early evolution of the planets. Primary measurement objectives at Eros are:

· To determine the gross physical properties of the asteroid, including size, shape, configuration, volume, mass, density, and spin state. · To measure surface composition, elemental abundances, and mineralogy. · To investigate surface morphology through comprehensive imaging under a variety of lighting conditions. Secondary measurement objectives at Eros are: · To determine regolith properties/texture by imaging to sub-meter scales. · To measure interactions with the solar wind and search for possible intrinsic magnetism. · To search for evidence of current activity as indicated by dust or gas in the vicinity of the asteroid. · To investigate the internal mass distribution through measurements of the asteroid's gravity field and the timevariation of its spin state. 3.0 Asteroids and Meteorites A year-long asteroid encounter is an exciting prospect for scientists whose appetites were whetted in October 1991 by the Galileo spacecraft's flyby of the asteroid 951 Gaspra at a distance of 1,000 miles (1,600 kilometers). In August 1993, Galileo passed within 1,500 miles (2,400 kilometers) of another asteroid, 243 Ida. Later analysis of the Ida images revealed a small moon, Dactyl, approximately 1 mile, or 1.6 kilometers, in diameter. Asteroids are metallic, rocky bodies without atmospheres that orbit the Sun but are too small to be classified as planets. Known as "minor planets," tens of thousands of asteroids congregate in the so-called main asteroid belt: a vast, doughnut-shaped ring located between the orbits of Mars and Jupiter from approximately 2 to 4 AU (186 million to 370 million miles/300 million to 600 million kilometers). Gaspra and Ida are main belt asteroids. Asteroids are thought to be primordial material prevented by Jupiter's strong gravity from accreting into a planet-sized body when the solar system was born 4.6 billion

years ago. It is estimated that the total mass of all asteroids would comprise a body approximately 930 miles (1,500 kilometers) in diameter -- less than half the size of the Moon. Known asteroids range in size from the largest -Ceres, the first discovered asteroid in 1801 -- at about 600 miles (1,000 kilometers) in diameter down to the size of pebbles. Sixteen asteroids have diameters of 150 miles (240 kilometers) or greater. The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to complete a full circuit of the Sun. Our understanding of asteroids has been derived from three main sources: Earth-based remote sensing, data from the Galileo flybys, and laboratory analysis of meteorites. Asteroids are classified into different types according to their albedo, composition derived from spectral features in their reflected sunlight, and inferred similarities to known meteorite types. Albedo refers to an object's measure of reflectivity, or intrinsic brightness. A white, perfectly reflecting surface has an albedo of 1.0; a black, perfectly absorbing surface has an albedo of 0.0. The majority of asteroids fall into the following three categories: C-type (carbonaceous): Includes more than 75 percent of known asteroids. Very dark with an albedo of 0.03-0.09. Composition is thought to be similar to the Sun, depleted in hydrogen, helium, and other volatiles. C-type asteroids inhabit the main belt's outer regions. · S-type (silicaceous): Accounts for about 17 percent of known asteroids. Relatively bright with an albedo of 0.10-0.22. Composition is metallic iron mixed with iron- and magnesium-silicates. S-type asteroids dominate the inner asteroid belt. · M-type (metallic): Includes many of the rest of the known asteroids. Relatively bright with an albedo of 0.100.18. Composition is apparently dominated by metallic iron. M-type asteroids inhabit the main belt's middle region.

The relationship between asteroids and meteorites remains a puzzle. The most common meteorites, known as ordinary chondrites, are composed of small grains of rock and appear to be relatively unchanged since the solar system formed. Stony-iron meteorites, on the other hand, appear to be remnants of larger bodies that were once melted so that the heavier metals and lighter rocks separated into different layers. A long-standing scientific debate exists over whether the most common asteroids -- the S-types -- are the source of ordinary chondrites. Spectral evidence so far suggests that the S-type asteroids may be geochemically processed bodies akin to the stony-irons. If S-types are unrelated to ordinary chondrites, then another parent source must be found. If the two are related, then scientists need an explanation for why they aren't spectrally similar. 4.0 Near-Earth Asteroids Asteroids with orbits that bring them within 1.3 AU (121 million miles/195 million kilometers) of the Sun are known as Earth-approaching or near-Earth asteroids (NEAs). It is believed that most NEAs are fragments jarred from the main belt by a combination of asteroid collisions and the gravitational influence of Jupiter. Some NEAs may be the nuclei of dead, short-period comets. The NEA population appears to be representative of most or all asteroid types found in the main belt. NEAs are grouped into three categories, named for famous members of each: 1221 Amor, 1862 Apollo, and 2062 Aten. Amors: Asteroids which cross Mars' orbit but do not quite reach the orbit of Earth. Eros -- target of the NEAR mission -- is a typical Amor. Apollos: Asteroids which cross Earth's orbit with a period greater than 1 year. Geographos represents the Apollos. Atens: Asteroids which cross Earth's orbit with a period less than 1 year. Ra-Shalom is a typical Aten.

NEAs are a dynamically young population whose orbits evolve on 100-million-year time scales because of collisions and gravitational interactions with the Sun and the terrestrial planets. Approximately 250 NEAs have been found to date, probably only a few percent of their total population. The largest presently known is 1036 Ganymed, with an approximate diameter of 25.5 miles (41 kilometers). Estimates suggest at least a thousand NEAs may be large enough -- 0.6 mile (1 kilometer) or more in diameter -- to threaten Earth. Many bodies have struck Earth and the Moon in the past, and one widely accepted theory blames the impact 65 million years ago of an asteroid or comet at least 6 miles (10 kilometers) in diameter for mass extinctions among many lifeforms, including the dinosaurs. Other theories suggest that the chemical building blocks of life and much of Earth's water arrived on asteroids or comets that bombarded the planet in its youth. On June 30, 1908, a small asteroid 330 feet (100 meters) in diameter exploded over the remote region of Tunguska in Siberia, devastating more than half a million acres of forest. One of the most recent close calls occurred on March 23, 1989, when an asteroid 0.25-mile (0.4kilometer) wide came within 400,000 miles (640,000 kilometers) of Earth. Surprised scientists estimated that Earth and the asteroid -- weighing 50 million tons and traveling at 46,000 miles/hour (74,000 kilometers/hour) -had passed the same point in space just six hours apart. 5.0 433 Eros The target of the NEAR mission is 433 Eros, the firstdiscovered near-Earth asteroid and the second-largest. Eros also is one of the most elongated asteroids, a potato-shaped body with estimated dimensions of 25.3 by 9.1 by 8.8 miles (40.5 by 14.5 by 14.1 kilometers). Its size qualifies Eros as one of only three NEAs with diameters above 6 miles (10 kilometers). Eros was discovered on Aug. 13, 1898, by Gustav Witt, director of the Urania Observatory in Berlin, and independently observed on the same date by Auguste H.P.

Charlois in Nice, France. In a break with tradition at the time, the asteroid was given a male name: Eros, the Greek god of love and son of Mercury and Venus. As a member of the NEA group known as the Amors, Eros has an orbit which crosses Mars' path but doesn't intersect that of Earth. The asteroid follows a slightly elliptical trajectory, circling the Sun in 1.76 years at an inclination of 10.8 degrees to the ecliptic. Perihelion distance is 1.13 AU (105 million miles/169 million kilometers); aphelion is 1.78 AU (165 million miles/266 million kilometers). Eros' average distance from the Sun is 1.46 AU (135 million miles/218 million kilometers). The closest approach of Eros to Earth in the 20th century was on January 23, 1975, at approximately 0.15 AU (14 million miles/22 million kilometers). Previous close approaches occurred in 1901 at 0.32 AU (30 million miles/48 million kilometers) and in 1931 at 0.17 AU (16 million miles/26 million kilometers). Because of its repeated close encounters with Earth, Eros has been an important object historically for refining the mass of the Earth-moon system and the value of the astronomical unit. More than a century of ground-based study -- including a world-wide observation campaign during the 1975 close approach -- has made Eros the best-observed of the NEAs. Astronomers assign the asteroid a rotation period of 5.27 hours. Geometric albedo is 0.16. Thermal studies indicate a regolith, and radar suggests a rough surface. Eros is known to be compositionally varied: one side appears to have a higher pyroxene content and a facet-like surface, while the opposite side displays higher olivine content and a convexshaped surface. There is no air and no evidence of water on Eros. Daytime temperature is about 100šC (148šF), while at night it plunges to -150šC (-238šF). Gravity on Eros is very weak but sufficient to hold a spacecraft in orbit. A 100-pound (45-kilogram) object on Earth would weigh about an ounce on Eros, and a rock thrown from the asteroid's surface at 22 miles/hour (10 meters/sec) would escape into space. Eros is one of the S-type asteroids, the most common type in the inner asteroid belt and the subject of debate

over their relationship to meteorites. Galileo's flyby observations of Gaspra and Ida (both of which are S-types) did not provide the answer, largely because remotely sensed spectral data cannot accurately determine the relative abundances of key elements. This is a major goal of the NEAR mission to Eros. 6.0 253 Mathilde Asteroid 253 Mathilde was discovered on Nov. 12, 1885, by Johann Palisa in Vienna, Austria. The name was suggested by V.A. Lebeuf, a staff member of the Paris Observatory who first computed an orbit for the new asteroid. The name is thought to honor the wife of astronomer Moritz Loewy, then the vice director of the Paris Observatory. Although Mathilde's existence has been known for more than a century, it wasn't until 1995 that observations with ground-based telescopes first identified the asteroid as a C-type. The 1995 observations also revealed an unusually long rotation period: 418 hours, or approximately 17 days. Orbital period is 4.30 years. Perihelion is 1.94 AU (180 million miles/290 million kilometers). Mathilde's inclination is 6.7 degrees. Geometric albedo is 0.036. Data obtained by the Infrared Astronomy Satellite has established Mathilde's diameter at approximately 38 miles (61 kilometers). This is substantially larger than the diameters of either Gaspra (10 miles/16 kilometers) or Ida (20 miles/33 kilometers), which would make Mathilde the largest asteroid to be visited by a spacecraft. The proposed NEAR encounter with 253 Mathilde would produce the first close-up images of a C-class asteroid. Preliminary plans call for a closest approach distance of 750 miles (1,200 kilometers) on June 27, 1997. NEAR Science Team The NEAR Project Science Group is co-chaired by John F. Kerridge, NEAR Program Scientist, NASA Headquarters, and Andrew F. Cheng, NEAR Project Scientist, The Johns Hopkins University Applied Physics Laboratory. Members of the NEAR Science Team are:

Multispectral Imager/Near Infrared Spectrograph: Joseph Veverka (Team Leader), Cornell University, Ithaca, NY; James F. Bell III, Cornell University, Ithaca, NY; Clark R. Chapman, Southwest Research Institute, San Antonio, TX; Michael C. Malin, Malin Space Science Systems, Inc., San Diego, CA; Lucy-Ann A. McFadden, University of Maryland, College Park, MD; Mark S. Robinson, United States Geological Survey, Flagstaff, AZ; Peter C. Thomas, Cornell University, Ithaca, NY; Scott L. Murchie (Instrument Scientist), The Johns Hopkins University Applied Physics Laboratory, Laurel, MD X-Ray/Gamma-Ray Spectrometer: Jacob I. Trombka (Team Leader), NASA/Goddard Space Flight Center, Greenbelt, MD; William V. Boynton, University of Arizona, Tucson, AZ; Johannes Bruckner, Max Planck Institut fur Chemie, Mainz, Germany; Steven W. Squyres, Cornell University, Ithaca, NY; Ralph L. McNutt, Jr. (Instrument Scientist), The Johns Hopkins University Applied Physics Laboratory, Laurel, MD Magnetometer: Mario H. Acuna (Team Leader), NASA/Goddard Space Flight Center, Greenbelt, MD; Christopher T. Russell, University of California, Los Angeles, CA; Lawrence J. Zanetti (Instrument Scientist), The Johns Hopkins University Applied Physics Laboratory, Laurel, MD NEAR Laser Rangefinder: Maria T. Zuber (Team Leader), Massachusetts Institute of Technology, Cambridge, MA, and NASA/Goddard Space Flight Center, Greenbelt, MD; Andrew F. Cheng (Instrument Scientist), The Johns Hopkins University Applied Physics Laboratory, Laurel, MD Radio Science: Donald K. Yeomans (Team Leader), NASA/Jet Propulsion Laboratory, Pasadena, CA; Jean-Pierre Barriot, Centre National D'Etudes Spatiales, Toulouse, France; Alexander S. Konopoliv, NASA/Jet Propulsion Laboratory, Pasadena, CA

8.0 Instruments The NEAR science instruments were developed as a "facility" instrument payload, in contrast to the traditional principal investigator system. The payload was chosen by an independently selected NEAR Science Definition Team. After instrument development was underway, the NEAR Science Team was chosen in 1994 by NASA through an announcement of opportunity. Science Team Leaders for the individual instruments work closely with the facility-class Instrument Scientists and Lead Engineers at JHU/APL. Despite the lower cost and rapid development schedule of the NEAR spacecraft, the instrument designs incorporate many technical innovations. They include: · First space flight of a silicon solid state detector viewing the Sun and measuring the solar input X-ray spectrum at high resolution (X-ray Spectrometer). · First space flight of a bismuth germanate anticoincidence shielded gamma-ray detector (Gamma-ray Spectrometer). · First space flight of a laser incorporating an inflight calibration system (Laser Rangefinder). · First space flight using a near-infrared system with a radiometric calibration target and an indium-galliumarsenide focal plane array that does not require cooling with liquid nitrogen (Near-Infrared Spectrograph). 8.1 Multispectral Imager (MSI) MSI is a high-resolution, visible-light camera that will determine the overall size, shape, and spin characteristics of Eros and map the morphology and mineralogy of surface features. The imager also will be used for optical navigation at Eros and to search for satellites. Images taken during approach, flyby, and orbit of Eros can detect surface features as small as 10 feet (3 meters). Adapted by JHU/APL from a military remote sensing

system, MSI is a 537 by 244 pixel CCD camera with fiveelement, radiation-hard refractive optics. The instrument covers the spectral range from 0.4 to 1.1 microns. It has an eight-position filter wheel with filters chosen to optimize sensitivity to minerals expected to occur on Eros. MSI has a field of view of 2.25 degrees by 2.9 degrees and a pixel resolution that corresponds to 31 by 53 feet (9.5 by 16.1 meters) from 62 miles (100 kilometers). The instrument has a maximum framing rate of 1 per second with images digitized to 12 bits. It has a dedicated digital processing unit with an image buffer, autoexposure capability, and onboard image compression. MSI Science Team Leader Joseph Veverka, Cornell University MSI Instrument Scientist Scott L. Murchie, JHU/APL MSI Lead Engineer S. Edward Hawkins III, JHU/APL NEAR Payload Manager Robert E. Gold, JHU/APL MSI Development JHU/APL

8.2 Near-Infrared Spectrograph (NIS) NIS will measure the spectrum of Sunlight reflected from Eros in the near-infrared range from 0.8 to 2.7 microns, in 64 channels. NIS data will provide the main evidence for the distribution and abundance of surface minerals like olivine and pyroxine. Together with the measurements of elemental composition from the X-ray/Gammaray Spectrometer (XGRS) and color imagery from MSI, NIS will provide a link between asteroids and meteorites and clarify the processes by which asteroids formed and evolved. NIS -- also adapted from a military remote sensing instrument -- is a grating spectrometer that disperses light from the slit field-of-view across a pair of passively cooled, one-dimensional array detectors. One detector is a germanium array covering the lower wavelengths from 0.8 to 1.5 microns; the other is an indium-gallium-arsenide array

covering 1.3 to 2.7 microns. The NIS slit field-of-view is 0.38 degree by 0.76 degree in the narrow position and 0.76 degree by 0.76 degree in the wide position. At 62 miles (100 kilometers) from the asteroid, these positions correspond to 0.4 to 0.8 mile (0.65 to 1.3 kilometers) and 0.8 miles x 0.8 mile (1.3 by 1.3 kilometers). A scan mirror slews the fieldof-view over a 140-degree range. Mirror scanning combined with spacecraft motion will be used to build up hyperspectral images. NIS also carries a diffuse gold calibration target that can reflect Sunlight into the spectrograph and provide in-flight spectral calibration.

NIS Science Team Leader Joseph Veverka, Cornell University NIS Instrument Scientist Scott L. Murchie, JHU/APL NIS Lead Engineer Jeffery W. Warren, JHU/APL NEAR Payload Manager Robert E. Gold, JHU/APL NIS Development JHU/APL, Sensor Systems Group Inc., Sensors Unlimited

8.3 X-Ray/Gamma Ray Spectrometer (XGRS) The XGRS will measure and map abundances of several dozen key elements at the surface and near-surface of Eros. X-rays from the Sun striking the asteroid can produce significant count rates of fluorescence X-rays from low atomic number surface elements such as magnesium, aluminum, and silicon. The elements sulfur, calcium, titanium, and iron are also present in asteroids, but count rates are lower and data take longer to accumulate. Similarly, cosmic ray protons (and energetic particles associated with solar flares) can interact with the asteroid surface to produce gamma rays characteristic of the nuclear energy levels of a given element. Gamma rays also can be spontaneously emitted by naturally occurring radioactive elements such as potassium, uranium, and thorium.

The XGRS consists of two state-of-the-art sensors: an X-ray spectrometer and a gamma-ray spectrometer. X-Ray Spectrometer (XRS) XRS is an X-ray resonance fluorescence spectrometer that detects the characteristic line emissions excited by solar X-rays from major elements in the asteroid surface. XRS covers the energy range from 1 to 10 KeV using three gas proportional counters. The balanced, differential filter technique is used to separate the closely spaced magnesium, aluminum, and silicon lines below 2 KeV. The gas proportional counters directly resolve higher energy line emissions from calcium and iron. A mechanical collimator gives XRS a 5 degree field-of-view to map the chemical composition at spatial resolutions as low as 1.2 miles (2 kilometers). XRS includes a separate solar monitor system to measure continuously the incident spectrum of solar X-rays. In-flight calibration capability also is provided. Gamma-Ray Spectrometer (GRS) GRS detects characteristic gamma rays in the 0.3 to 10 MeV range emitted from specific elements in the asteroid surface. GRS uses a body-mounted, passively cooled sodium iodine detector, enveloped by an active bismuth germanate anti-coincidence shield to provide a 45 degree field-ofview. Abundances of several important elements -- such as potassium, silicon, and iron --will be measured in four quadrants of the asteroid. XGRS Science Team Leader Jacob I. Trombka, NASA/Goddard Space Flight Center XGRS Instrument Scientist Ralph L. McNutt, Jr., JHU/APL XGRS Lead Engineer John O. Goldsten, JHU/APL NEAR Payload Manager Robert E. Gold, JHU/APL XGRS Development JHU/APL, Goddard, Metorex, EMR Photoelectric

8.4 NEAR Laser Rangefinder (NLR)

NLR will determine the distance from the spacecraft to the asteroid by precisely measuring the delay time between firing of a laser pulse and its return reflection from the surface. NLR uses a neodymium-doped yttrium-aluminum-garnet solid state laser and a compact reflecting telescope. It sends a small portion of each emitted laser pulse through an optical fiber of known length and into the receiver, providing a continuous in-flight calibration of the timing circuit. The ranging data will be used to construct a global shape model and a global topographic map of Eros with horizontal resolution of about 1,000 feet (300 meters). NLR also will measure detailed topographic profiles of surface features on Eros with a best spatial resolution of about 20 feet (6 meters). The profiles will complement the study of surface morphology from imaging. NLR Science Team Leader Maria T. Zuber, MIT and NASA/Goddard Space Flight Center NLR Instrument Scientist Andrew F. Cheng, JHU/APL NLR Lead Engineer: Timothy D. Cole, JHU/APL NEAR Payload Manager Robert E. Gold, JHU/APL NLR Development JHU/APL, McDonnell Douglas Corp. 8.5 Magnetometer (MAG) MAG is a 3-axis fluxgate sensor mounted on a tripod bracket above the high-gain antenna, a location chosen for minimum exposure to spacecraft-generated magnetic fields. Magnetometer electronics are located on the top deck. This instrument will measure the strength of Eros' magnetic field to within 45 nanoTeslas. Data from the Galileo flybys of the asteroids Gaspra and Ida suggests that both of these bodies are magnetic, but the results are inconclusive. Discovery of an intrinsic magnetic field at Eros would be the first definitive

detection of magnetism at an asteroid and would have important implications for its thermal and geologic history. MAG Science Team Leader Mario H. Acuna, NASA/Goddard Space Flight Center MAG Instrument Scientist Lawrence J. Zanetti, JHU/APL MAG Lead Engineer David A. Lohr, JHU/APL NEAR Payload Manager Robert E. Gold, JHU/APL MAG Development Goddard, JHU/APL 8.6 Radio Science Experiment (RS) RS will use the NEAR telemetry system to determine the gravity field of the asteroid. RS will measure the two-way Doppler shift in radio transmissions between the spacecraft and Earth to an accuracy of 0.025 inch/sec (0.1 mm/sec). These measurements will determine line-of-sight velocity variations in the spacecraft motion, which will be analyzed for the effect of the asteroid's gravity field on spacecraft accelerations. Combined with data from other NEAR instruments, this information will allow highly accurate modeling of Eros' density and large-scale density variations. RS Science Team Leader Donald K. Yeomans, NASA/Jet Propulsion Laboratory NEAR Payload Manager Robert E. Gold, JHU/APL RS Development: Motorola 9.0 Mission Profile: Launch Phase NEAR's 16-day launch window opens on Feb. 16, 1996, at 3:53 p.m. EST, with a daily launch opportunity of approximately one minute. A Mathilde flyby is possible only for the first 11 days of the window. The post-launch ​V requirement increases rapidly by 9 to 14 miles/hour (4 to 5 meters/sec) per day during this period, so it is highly desirable for NEAR to launch as early as possible. During

the last five days of the launch window, the Mathilde flyby is no longer a possibility. After close of the window on March 2, 1996, another equally favorable rendezvous opportunity with Eros will not be available for seven years. The Delta II parking orbit has an altitude of 100 miles (183 kilometers) and an inclination of 28.74 degrees. The launch azimuth is fixed at 95 degrees. The coast period in the parking orbit is relatively short (13 minutes), allowing solar power to be used starting one hour after launch. The injection burn, accomplished mainly be the third stage solid motor, is entirely inside Earth's shadow. Approximately 22 minutes after launch, the spacecraft separates from the third stage. A yo-yo despin mechanism simultaneously releases the solar panels from their stowed launch position and despins the spacecraft from a maximum of 69 rpm to a nominal rate of 0 rpm. Once the solar panels are released, spring-loaded hinges deploy them to the on-orbit configuration. From launch until this time, the spacecraft is battery-powered. Because weight constraints limited the size of the battery, only those components considered mission critical during this phase are powered. At third stage separation, responsibility for attitude control passes from the Delta to the spacecraft's guidance and control subsystem. 10.0 Mission Profile: Cruise Phase During the first few weeks of cruise, a series of component functional tests check the health of the spacecraft. Also during this time, low-level burns are performed to calibrate the propulsion system and to correct for any trajectory errors. After this checkout period the spacecraft maintains minimal activity. Due both to limited electrical power beyond 2 AU (186 million miles/300 million kilometers) and a desire not to thermally stress the solar panels during cruise, spacecraft operations Sunward of 1.5 AU (140 million miles/225 million kilometers) and outward of 2 AU are intentionally limited. All of the instruments are off. The telemetry subsystem periodically samples low-level housekeeping and navigation data and stores the information

on the solid state recorder. Heaters are used to maintain the temperature of the inactive systems. The spacecraft maintains this hibernation mode except during ground station contacts. Conducted during four-hour passes, three times per week, the ground contacts permit the mission operations team to analyze current spacecraft health, upload the next week's series of command sequences, and dump recorded telemetry. NEAR will maintain this routine until preparations begin for two critical mission events -- the Mathilde flyby and the Deep-Space Maneuver -- in the June/July 1997 timeframe. In support of the increased activity, the DSN will provide continuous coverage from its 34-meter network from June 20 to July 10, 1997. NEAR will require 21 eighthour passes per week from these antennas instead of the normal cruise coverage. A third major event during cruise -the Earth swingby -- is scheduled for January 1998. As part of preparations for the flybys, the multispectral imager periodically points at the target and an image is transmitted to Earth. This optical navigation (OpNav) data is combined with ground tracking information to calculate a flyby trajectory. The trajectory calculation is refined throughout the flyby approach as more ground data is taken and more images are returned. Prior to the flyby, a time-tagged command sequence is uploaded to the spacecraft defining a time-ordered sequence of command to be executed during the flyby. These commands include an open-loop pointing trajectory and instrument data capture sequences. 10.1 Mathilde Flyby NEAR's flyby of the 38-mile (61-kilometer) diameter asteroid 253 Mathilde is tentatively scheduled for June 27, 1997, at a distance from Earth of 2.2 AU (205 million miles/330 million kilometers). For planning purposes, a closest approach distance of 750 miles (1,200 kilometers) has been specified. Although the approach phase angle is almost 140 degrees, NEAR's imaging system should be able to obtain useful optical navigation images beginning about three days before the encounter. OpNav sequences are scheduled at four-hour

intervals with each sequence consisting of four pictures. Flyby speed is estimated at 22,150 miles/hour (9.9 kilometers/sec). The primary science instrument will be the camera, but measurements of magnetic fields and mass also will be made. The whole illuminated portion of the asteroid will be imaged in color at about 0.6-mile (1-kilometer) resolution, with the best monochrome views at some 660 to 980 feet (200 to 300 meters) resolution. As the spacecraft recedes from Mathilde, a thorough search for satellites will be conducted. 10.2 Deep Space Maneuver The Deep Space Maneuver (DSM) will be executed about one week after the Mathilde flyby, on July 3, 1997. The DSM represents the first of two major burns during the NEAR mission of the 100-pound (450-Newton) bi-propellant thruster. This maneuver is necessary to lower the perihelion distance of NEAR's trajectory, from 0.99 AU to 0.95 AU (92 million miles/148 million kilometers to 88 million miles/142 million kilometers). The DSM will be conducted in two segments to minimize the possibility of an overburn situation. The first segment, DSM-1, will provide 90 percent of the required ​V of 279 m/sec and must be performed with the high gain antenna in operation to monitor critical engineering data. Accelerometer measurements of DSM-1 will then be used to update DSM-2, which will supply the remaining 10 percent of the ​V. 10.3 Earth Swingby The next critical phase of NEAR's flight profile occurs on January 22, 1998, when the spacecraft passes by the Earth at an altitude of 297 miles (478 kilometers). This maneuver alters NEAR's heliocentric trajectory, changing the inclination from 0.5 to 10.2 degrees and reducing the aphelion distance from 2.17 to 1.77 AU (200 million miles to 165 million miles/325 million kilometers to 265 million kilometers). Consequently, NEAR's post-swingby trajectory

virtually matches the inclination and aphelion distance of Eros' orbit, which significantly reduces the magnitude of the rendezvous maneuver. An interesting aspect of the Earth flyby is that the post-swingby trajectory remains over the Earth's south polar region for a considerable time. This may provide an opportunity for NEAR to obtain some unique images of the Antarctic continent. Also, because of its extreme southerly declination, the spacecraft can be viewed continuously from the DSN Canberra station for 71 days following the Earth flyby. The first visibility from the Goldstone and Madrid stations will not occur until 110 and 120 days, respectively, after the flyby. 11.0 Mission Profile: Asteroid Approach First detection of Eros by the multispectral imager is anticipated in Fall 1998, approximately 200 days prior to closest approach. Following this early observation, clusters of images will be obtained weekly for optical navigation and for initial shape and rotation determination. Beginning on Jan. 9, 1999, a series of four rendezvous maneuvers with the main thruster -- spaced seven days apart -- will slow NEAR by 2,123 miles/hour (949 meters/sec) to achieve a relative velocity between the spacecraft and Eros of 11 miles/hour (5 meters/sec). The rendezvous burn sequence is targeted to put NEAR into an initial slow flyby trajectory, with closest approach to Eros scheduled for Feb. 6, 1999. NEAR will fly by the asteroid on its Sunward side at a distance of about 300 miles (500 kilometers). This first pass is expected to provide improved estimates of Eros' physical parameters, which are critical for navigation. Goals include a mass determination to within 1 percent accuracy, identification of several hundred surface landmarks, and a vastly improved estimates of Eros' spin vector. As the spacecraft is maneuvered closer to the asteroid, estimates of mass, moments of inertia, gravity harmonics, spin state, and landmark locations will be determined with increasing precision. A search will be conducted for

satellites and debris around Eros, which should pick up any bodies bigger than about 17 feet (5 meters). By comparison, Ida's satellite Dactyl is 2,300 feet (700 meters) in radius. Since the orbit plane during rendezvous will be near the Eros terminator, most of the observations obtained during the NEAR mission will be made at large phase angles (Sun-asteroid-spacecraft angle). These angles are favorable for imaging but not for infrared spectral mapping. Since phase angles during the initial flyby are relatively low, scientists anticipate more than 30 hours of observations that are not accessible within the nominal rendezvous geometry. This will provide an important opportunity to obtain global infrared spectral maps under optimal lighting conditions. 12.0 Eros Rendezvous/Science Operations Two days after closest approach, the NEAR spacecraft will be maneuvered into an initial orbit around Eros, with a maximum radius of approximately 600 miles (1,000 kilometers). By Feb. 21, 1999, mission planners will have gradually circularized the orbit to a radius of 125 miles by 125 miles (200 kilometers by 200 kilometers) and will begin tightening the radius to as small as 22 miles (35 kilometers). Since the mass and density of Eros are presently unknown, and shape and rotation pole estimates are uncertain, it is not possible to plan a detailed "tour" of Eros far in advance. Tight orbital plane restrictions are required to maintain instrument fields of view of the asteroid, communications antenna coverage of the Earth, and solar illumination of the solar panels. Mission simulations performed to date have supported safe operations in nominal rendezvous orbit at a few body radii. Detailed mission operations and science sequences cannot be developed until shortly (perhaps weeks) prior to actual execution. NEAR will remain in orbit around Eros for more than 10 months. This long-duration rendezvous orbit provides the opportunity for the NEAR instruments to determine the physical and geological properties of Eros and to measure its elemental and mineralogical composition. Many of these

measurements require lengthy observation times at close range and cannot be made in flybys. The spacecraft will spend at least 120 days in 22 mile by 22 mile (35 kilometer by 35 kilometer) orbit around Eros, during which time the highest priority science will be measurement of elemental composition, although every instrument will be in operation. Much of the remaining time in orbit around Eros will be spent at semi-major axes of 31 miles (50 kilometers) or less. All instruments will be operating during these periods, but imaging and spectral mapping will have increased priority. When NEAR first enters rendezvous with Eros, the south pole of the asteroid points almost directly toward the Sun. This means that much of the northern hemisphere of Eros remains in the nightside over the entire rotation period. The multispectral imager, near-infrared spectrograph, and Xray spectrometer are able to observe only the sunlit portions of Eros; the gamma-ray spectrometer, magnetometer, and laser rangefinder are independent of sunlight. In order to make the full set of measurements over the entire surface -- and in particular to be able to image all of Eros at highest resolution -- NEAR must wait until the season changes as Eros moves in its orbit around the Sun. By about eight months after the rendezvous begins, all of Eros has become illuminated by the Sun. The irregular shape of Eros requires that NEAR remain in retrograde orbit relative to the asteroid spin. Prograde orbits tend to be unstable in the sense that the spacecraft would typically be ejected from orbit or caused to impact the surface. An orbital plane flip maneuver at approximately mid-mission is required to maintain a retrograde orbit. When data are to be downlinked, the spacecraft will be slewed if necessary to point the high-gain antenna at Earth. The instruments face 90š from the direction of the antenna, so they can point at Eros as the spacecraft rolls in its orbit. All or any combination of the instruments can operate simultaneously, taking data and storing data on the solid state recorders. The spacecraft also can take data and downlink data simultaneously, although the instruments can be pointed at the asteroid for only a small portion of the downlink periods.

Navigation constraints at Eros are designed to permit the spacecraft to orbit as low as possible for as long as possible to accomplish scientific objectives. They include: · Spacecraft orbit should be safe and stable for a timespan of weeks. · Normally there should be no less than seven days between propulsive maneuvers. · Total rendezvous ​V expenditure should be less than 224 miles/hour (100 meters/sec). · Sun pointing angle must be limited to less than 30š because of power and payload pointing constraints resulting from the fixed mounting of the solar arrays and instruments. 13.0 Spacecraft Description NEAR is a planetary spacecraft with a design lifetime of four years and the capability to operate at distances of 2.2 AU (205 million miles/330 million kilometers) from the Sun. Simplicity and low cost were the main drivers in developing the spacecraft. Simplicity was achieved by requiring that three major components -- instruments, solar panels, and high-gain antenna -- be fixed and body mounted. Although this requirement somewhat increases the complexity of spacecraft operations, it was an important factor in overall cost. The NEAR system is designed to be highly fault tolerant. Fully redundant subsystems include the complete telecommunication system except for the high-gain and medium-gain antennas, the solid-state recorders, the command and telemetry processors, the 1553 data buses, the attitude interface unit and the flight computers for guidance and control, and power subsystem electronics. Additional fault tolerance is provided by use of redundant components: NEAR has two inertial measurement units, five Sun sensors, and 11 small thrusters. Many technical innovations were achieved in spacecraft design:

· First solar-powered spacecraft to fly beyond the orbit of Mars. · First use of hemispherical resonant gyros for attitude measurement. · First use of rate 1/6 convolutional decoding. · First use of high-power solid-state X-band power amplifiers. · First use of RTX 2010 FORTH microprocessors. 13.1 Mechanical Subsystem The spacecraft structure is an eight-sided box made of 18.3 square feet (1.7 meter square) aluminum honeycomb panels connected to forward and aft aluminum honeycomb decks. The NEAR spacecraft launch mass, including propellant, is 1,775 pounds (805 kilograms) maximum. Dry mass is 1,058 pounds (480 kilograms). NEAR is designed with two independent structures: the spacecraft structure and the propulsion system structure, which are coupled at the aft deck. While this design exacted a small penalty in weight, it allowed independent design and test capability for the propulsion subsystem to expedite spacecraft development. Mounted on the outside of the forward deck is the Xband high-gain antenna, the four solar panels, and the X-ray solar monitor system. Most electronics are mounted on the inside of the forward and aft decks, and all but one of the science instruments are fixed in position on the outside of the aft deck. The magnetometer is mounted on the high gain antenna feed. A star camera points out to the side of the spacecraft away from the instruments so that a star-filled view is available during asteroid operations. The interior of the spacecraft contains the propulsion module. 13.2 Propulsion Subsystem The NEAR propulsion subsystem, supplied by Gencorp Aerojet, contains the fuel and oxidizer tanks, 11 monopropellant thrusters, a bipropellant main thruster, and a helium pressurization system. The location of the tanks

was selected to maintain the spacecraft's center of mass along the thrust vector of the main thruster throughout the mission as the bipropellant is depleted. The total ​V capability is approximately 3,240 miles/hour (1,450 meters/sec). The monopropellant system is composed of four 5-pound (21-Newton) large fine velocity control thrusters and seven 1-pound (3.5-Newton) small fine velocity control thrusters, all fueled by pure hydrazine. The specific impulses of the monopropellant thrusters range from 206 to 234 seconds. They are arranged in six thruster modules mounted to the forward and aft decks and are located so that the loss of any one thruster does not affect performance. The 21N thrusters, which point in the same direction as the main thruster, are used for thrust vector control during the bipropellant burns. The 3.5N thrusters are used for momentum dumping and orbit maintenance around the asteroid. A minimum ​V increment of 0.02 miles/hour (10 mm/sec) is achievable in all directions. The bipropellant thruster, or large velocity adjustment thruster, burns a mixture of hydrazine and nitrogen tetroxide (NTO) to produce a maximum 100 pounds (450 Newtons) of thrust, with a specific impulse of 313 seconds. The large thruster will accomplish the major velocity changes of the NEAR mission: at the deep space maneuver in July 1997 and during the series of rendezvous approach maneuvers at Eros arrival in early 1999. The propulsion system carries 461 pounds (209 kilograms) of hydrazine and 240 pounds (109 kilograms) of NTO oxidizer in two oxidizer and three fuel tanks. The 14.5 gallon (55.1 liter) oxidizer tanks are located along the launch vehicle spin axis equidistant from the spacecraft center-of-mass. The 24.0 gallon (91.0 liter) fuel tanks are arranged 120 degrees apart in the main thruster plane. 13.3 Power Subsystem The power system comprises four 6 feet by 4 feet (1.8 meter by 1.2 meter) gallium arsenide solar panels, a super nickel cadmium (NiCad) battery, and power system electronics. The solar array, produced by Spectrolab Inc.,

provides 400 watts of power at NEAR's maximum solar distance of 2.2 AU (205 million miles/330 million kilometers) and 1800 watts at 1 AU (93 million miles/150 million kilometers). The power provided by the solar array is a function of the spacecraft-Sun distance and the incident solar angle, which must remain 30 degrees or less during the rendezvous at Eros. The solar power system is divided into 20 strings, so failure of any one would lead to only a 5 percent reduction of available power. The battery, produced by Hughes Aircraft Co., is a 9 amp-hour, 22-cell super NiCad battery with cells fabricated by Eagle-Picher Industries. Battery capacity provides power to the spacecraft prior to array deployment and solar power availability. Thereafter, the battery is recharged and remains on-line to provide bus voltage regulation, and to serve as a backup source of power in the event of momentary load increases or brief solar power deficits. 13.4 Guidance and Control Subsystem The guidance and control subsystem is composed of a suite of sensors for attitude determination, actuators for attitude corrections, and processors to provide continuous, closed-loop attitude control. The sensor suite comprises five digital solar attitude detectors, a star tracker, and an inertial measurement unit (IMU). The IMU contains hemispherical resonator gyros for rate determination and accelerometers for measuring ​V. The actuator complement contains four reaction wheels plus the 11 small, monopropellant thrusters and the large bipropellant thruster. All normal attitude control is achieved using the reaction wheels alone. Any three of the reaction wheels provide complete 3-axis control, so a single reaction wheel failure results in no loss in functionality. The thrusters are used to dump excess angular momentum from the reaction wheels, accomplish rapid slew maneuvers when needed, and perform propulsive maneuvers. Attitude control is to 0.1 degree, line-of-sight

pointing stability is within 50 microradians over 1 second, and post-processing attitude knowledge is to 50 microradians. 13.5 Telecommunication Subsystem The telecommunication subsystem is an X-band system capable of simultaneously transmitting telemetry data, receiving spacecraft commands, and providing doppler and ranging tracking. In addition to the 5-feet (1.5-meter) high-gain antenna, there are two low-gain antennas, and a medium-gain antenna with a fan-shaped radiation pattern. The world-wide stations of NASA's DSN provide contact with the spacecraft after launch. Eight discrete downlink data rates are supported. In operation with the DSN 111-feet (34-meter) high-efficiency and beamguide antennas, the rates are 9.9 bps (emergency mode), 39.4 bps, 1.1 kbps, 2.9 kbps, 4.4 kbps, and 8.8 kbps. During critical operations, the DSN 230-feet (70-meter) antennas can provide downlink rates of 17.6 and 26.5 kbps. The downlink hardware, developed by JHU/APL, uses a solid state power amplifier with an output level of 5 watts. The normal uplink data rate is 125 bps, while emergency mode uplink is 7.8 bps. 13.6 Command and Data Handling Subsystem The command and data handling subsystem is composed of four major segments: two redundant command and telemetry processors, two redundant solid state recorders, a power switching unit to control spacecraft relays, and an interface to two redundant 1553 standard data buses for communicating with other processor-controlled subsystems. The functions provided are command management, telemetry management, and autonomous operations. The solid state recorders, provided by SEAKR Engineering, are constructed from 16 Mbit IBM Luna-C DRAMs. One recorder has 0.67 Gbits of storage; the other has 1.1 Gbits capacity because it contains an additional memory board which is designated as the flight spare to replace either of the other memory boards in a ground test failure.

14.0 NEAR Spacecraft Processing The NEAR spacecraft arrived at Cape Canaveral aboard a C-5 military aircraft on Dec. 7, 1995. It was taken to NASA Spacecraft Hangar AE on Cape Canaveral Air Station for prelaunch checkout activities which began on Dec. 11. This work included propulsion system and electrical system testing. On Jan. 4, 1996, spacecraft functional testing began which included checkout of each of the spacecraft's four instruments. Tests with the tracking stations of the DSN also were performed. On Jan. 25, NEAR was transported from Hangar AE to the Spacecraft Encapsulation and Assembly Facility on NASA's Kennedy Space Center. There the spacecraft was fueled with its control propellants on Jan. 26-27. The solar arrays were attached and batteries installed on Jan. 29. A spin balance procedure and weighing of the spacecraft occurred during the period Jan. 30-Feb. 2. NEAR was mated to the solid propellant upper stage on Feb. 5. The NEAR/third stage combination was scheduled to be transported to Pad B at Launch Complex 17 for mating to the vehicle's second stage on Feb. 8, and the Delta nose fairing installed around the spacecraft on Feb. 13. 15.0 Delta II Launch Vehicle The Medium Expendable Launch Vehicle Service utilizes the Delta Launch System of the McDonnell Douglas Corp. Delta boosters can be launched from either the Eastern Range at Cape Canaveral Air Station, FL, or the Western Range at Vandenberg Air Force Base, CA. The NEAR spacecraft will be launched from Cape Canaveral on a Delta II-7925 with an 8foot (2.4-meter) fairing. The Delta II 7900 series is a three-stage rocket consisting of five major assemblies: the first stage (which includes the main engine and solid rocket motors); interstage; second stage: third (or upper) stage; and payload fairing. The rocket is 125.2 feet (38.2 meters) tall and 8 feet (2.4 meters) in diameter.

The RS-27A main engine operates on a mixture of RP-1 fuel (kerosene) and liquid oxygen. The main engine nozzle is hydraulically gimbaled for pitch and yaw control. Roll control is supplied by two vernier engines. The RS-27A has a liftoff thrust of 207,000 pounds. Each of the nine strap-on graphite epoxy motors has a sea-level thrust of 97,070 pounds. Six of the solid motors are ignited at liftoff, combining with the main engine for a total liftoff thrust of 641,018 pounds. The remaining three solids are ignited at altitude during the first-stage burn. The second stage uses an Aerojet AJ10-118K engine burning Aerozine-50 fuel and nitrogen tetroxide as the oxidizer. The second stage engine is hydraulically gimbaled for pitch and yaw control. A nitrogen gas system provides roll-control during powered flight and pitch, yaw, and roll control during coast periods. The engine is ignited at altitude and has a vacuum-rated thrust level of 9,645 pounds. The third stage uses a spin-stabilized Thiokol Star 48B solid rocket motor. The fairing, attached to the forward face of the third stage, protects NEAR from aerodynamic heating during the boost flight. The first-stage main engine is produced by the Rocketdyne Division of Rockwell International in Canoga Park, CA; the second-stage engine is built by GenCorp Aerojet of Sacramento, CA; the solid rocket motors are from Alliant Techsystems of Magna, UT; the second-stage guidance computer is provided by Delco Systems of Goleta, CA; and the Star-48 motor for the third stage is from Thiokol Corp. of Ogden, UT. 16.0 Launch Vehicle Processing Erection of Delta 232 -- a Delta II expendable vehicle built by McDonnell Douglas -- began its preparation on Pad 17-B with the erection of the first stage on Jan. 19. The solid rocket boosters were erected in sets of three on Jan. 22-24. The second stage was hoisted atop the first stage on Jan. 25, and the fairing was hoisted for installation in the pad clean room Jan. 26.

The Delta began electrical qualification testing on Jan. 29. The vehicle was partially loaded with liquid oxygen in a first stage leak check on Feb. 3. A Simulated Flight Test -- an electrical test to verify the in-flight events which the vehicle normally performs -- was scheduled for Feb. 5. This was planned to be followed by a Flight Program Verification, a test of the actual flight events and associated flight software to occur on the NEAR mission. Loading of the second stage with its complement of storable propellants --an activity which normally occurs before the countdown begins -- was scheduled to occur on Feb. 14, two days before launch. Loading of the first stage with liquid oxygen and RP-1 is performed in the terminal countdown sequence which begins approximately three hours before launch.

17.0 Mission Operations System The fundamental objective of Mission Operations is to operate the spacecraft safely and efficiently to acquire the science data required for mission success. The NEAR Mission Operations System consists of the Mission Operations Ground Segment, the Mission Operations Team, and the operational processes and procedures that are executed by the team to plan, control, and assess NEAR spacecraft operations. The NEAR Ground System includes the JHU/APL-located Mission Operations Center; the Integration and Test Operations Segment (ITOGS); the Science Data Center, also at JHU/APL; the various team facilities; and the DSN operated by the Network Operations Control Center at the Jet Propulsion Laboratory. After supporting launch operations, the ITOGS returns to the MOC as a fully redundant hot backup for both command and telemetry processing. The world-wide stations of the DSN provide contact with the spacecraft after launch. Command, telemetry, and other data and voice access to the DSN is via NASCOM circuits that interface with the MOC. The non-DSN components of the ground system are connected by an Ethernet-based distributed network, called NEARnet. This common communications link permits a great deal of flexibility and control in providing

access to realtime and archived telemetry, science products, command histories, telemetry, and command dictionaries. At launch, the Mission Operations Team will total seven, all of whom will share responsibilities and functions. They are augmented by three support personnel for system maintenance and post-launch tuning, and one manager. At rendezvous, the team expands to 27 to cover around-theclock operation seven days a week in the MOC. Support will be four shifts plus a day shift Monday through Friday. All personnel share responsibilities and functions. Throughout the NEAR mission, Mission Operations interacts with all major NEAR teams, including the Mission Design Team, Navigation Team, Spacecraft Engineering Team, Science Team, DSN, and the Science Data Center. 18.0 Data Analysis/Archiving All data from the NEAR spacecraft are forwarded to the SDC for processing, distribution, and archiving. The SDC, located at JHU/APL, is the central repository for all science data as well as for mission products such as asteroid models, images, and maps. The SDC will be developed during the cruise phase of the mission. The SDC maintains an archive of telemetry, instrument and command histories as well as ephemeris and attitude data. The SDC also will create and maintain a database to facilitate access to science data based on criteria such as pointing, illumination, and states of other instruments. The NEAR Science Team will release data as soon as validated, with no proprietary period. All mission data sets will be accessible on-line by every member of the Science Team from the SDC. NEAR data also will be archived with the Planetary Data System. 19.0 Discovery Program The Discovery Program -- NASA's innovative approach to "faster, better, cheaper" planetary missions -- marks its inaugural launch with the NEAR Mission. Mars Pathfinder, the first-selected of the two original Discovery missions, is

scheduled for liftoff in December 1996. Formally initiated in NASA's FY94 budget within the Solar System Exploration Division, the Discovery Program grew out of NASA discussions with the science community to design a planetary exploration program that balances science return and mission cost in an era of declining space budgets. Discovery represents a significant departure from previous NASA planetary programs in terms of total mission cost, development time, management approach, and scope of science objectives. Among Discovery Program goals and criteria are: · LOWER COST: Design and development (Phase C/D) to launch plus 30 days is limited to $150 million, and mission operations/data analysis (Phase E) is limited to $35 million (both in FY92 dollars). Total mission cost includes preliminary analysis (Phase A), definition (Phase B), and launch services. NASA-provided launch vehicles for Discovery missions must be medium (Delta II) class or smaller. · RAPID DEVELOPMENT TIME: In order to meet the Discovery Program goal of launches every 12 to 18 months, there are tight constraints on mission development and definition times. Phase A/B is limited to 18 months or less. Phase C/D is limited to 36 months or less from start through launch plus 30 days. · STREAMLINED MANAGEMENT APPROACH: Teaming is encouraged among industry, educational/non-profit institutions, and government partners. NASA field centers are welcome as team members, as are non-U.S. individuals and organizations. Competitively selected teams have mission responsibility and authority, with a large degree of freedom in accomplishing objectives. NASA oversight and reporting requirements will focus on the essentials for mission success and agreed-upon science return. · NEW TECHNOLOGY/TECHNOLOGY TRANSFER: The Discovery selection process recognizes the inclusion of new technology to achieve performance enhancements and total mission cost reductions. The teaming of industry, university, and government is meant to foster technology transfer occurring in parallel with technology development.

· PUBLIC AWARENESS AND EDUCATION: Activities are encouraged to enhance the level of understanding and awareness of solar system exploration by the public. Such activities may include information programs to inform the public by the media or other means, and educational activities coordinated with schools and science centers. FUTURE DISCOVERY MISSIONS The third Discovery mission -- a moon orbiter called Lunar Prospector -- was selected by NASA in February 1995 and is scheduled for launch in June 1997. Stardust, the fourth mission, was selected in November 1995. Launch is planned for February 1999 on a flight to gather samples of cometary and interstellar dust for return to Earth. 20. NEAR on the NET JHU/APL NEAR HOMEPAGE http://sd-www.jhuapl.edu/NEAR/ NSSDC NEAR HOMEPAGE http://nssdc.gsfc.nasa.gov/planetary/near.html JET PROPULSION LABORATORY NEAR HOMEPAGE http://128.149.63.253/calendar/near.html NASA HQ DISCOVERY PROGRAM http://www.hq.nasa.gov/office/discovery/welcome.html NSSDC ASTEROID HOMEPAGE http://nssdc.gsfc.nasa.gov/planetary/planets/asteroidpage.ht ml NSSDC ASTEROID FACT SHEET http://nssdc.gsfc.nasa.gov/planetary/factsheet/asteroidfact. html

ASTEROIDS http://seds.lpl.arizona.edu/nineplanets/nineplanets/asteroid s.html METEORS AND METEORITES http://seds.lpl.arizona.edu/nineplanets/nineplanets/meteorit es.html ABCs OF NEAR EARTH OBJECTS http://wea.mankato.mn.us/tps/neoabc.html ENCOUNTER WITH EROS: THE NEAR MISSION http://128.149.63.253/calendar/near1.html NASA/AMES ASTEROID AND COMET IMPACT HAZARDS http://ccf.arc.nasa.gov/sst/ 21.0 PUBLIC AFFAIRS CONTACTS NASA Headquarters Washington, DC Donald Savage (202) 358-1727 [email protected]

The Johns Hopkins University Applied Physics Laboratory Laurel, MD Luther Young (301) 953-6268 [email protected]

Kennedy Space Center Cape Canaveral, FL George Diller (407) 867-2468 [email protected]

McDonnell Douglas Aerospace Huntington Beach, CA Anne Toulouse (714) 896-6211 [email protected]