

NEAR.Press.Kit    9Feb96





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 1,775- pound (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 best-observed 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 second-largest 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).

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. High- resolution 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.
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 time- variation 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 aof 0.10- 0.18. 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 chondrite
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 (0.4 kilometer)
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 first-discovered
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 convex- shaped surface.

     There is no air and no evidence of water on Eros.  Daytime
temperature is about 100C (148F), while at night it plunges to -150C
(-238F). 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 anti- coincidence
shielded gamma-ray detector (Gamma-ray Spectrometer).

- First space flight of a laser incorporating an in- flight
calibration system (Laser Rangefinder).

     - First space flight using a near-infrared system with a radiometric
calibration target and an indium-gallium- arsenide 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 five-element, 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/Gamma-ray 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 field- of-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
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-of-view. 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 eight- hour 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
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).

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 X- ray 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.

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
90 from the direction of the antenna, so they can point at Eros as
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 30 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
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

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 X- band 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.

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.

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 pre-launch 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 8-foot
(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.

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.  22-24second 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-the- clock
o seven days a week in the MOC. Support will be four shifts plus a
day shift Monday through Friday. All personnel share responsib 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.html


NSSDC ASTEROID FACT SHEET

http://nssdc.gsfc.nasa.gov/planetary/factsheet/asteroidfact.html


ASTEROIDS

http://seds.lpl.arizona.edu/nines/nineplanets/asteroids.html


METEORS AND METEORITES

http://seds.lpl.arizona.edu/nineplanets/nineplanets/meteorites.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
dsavage@pao.hq.nasa.gov



The Johns Hopkins University

Applied Physics Laboratory
Laurel, MD

Luther Young
(301) 953-6268
luther.young@jhuapl.edu



Kennedy Space Center
Cape Canaveral, FL

George Diller
(407) 867-2468
george.diller-1@kmail.ksc.nasa.gov



McDonnell Douglas Aerospace
Huntington Beach, CA


Anne Toulouse
(714) 896-6211
atoulouse@apt.mdc.com

















