Clementine was a spacecraft designed to make charged particle
measurements, do imaging on a variety of frequencies, and perform
laser altimetry on the Moon and near Earth asteroid 620
Graphos. It was also to test the spaceworthyness of its sensors and
hardware. Clementine was a joint project of NASA and the Strategic
Defense Initiative Organization.
Mission History
Clementine was launched from Vandenberg Air Force base on January 25
1994 at 16:34 UTC aboard a Titan II-G rocket. The craft attained
lunar orbit on February 19 1994 after two Earth flybys, the first on
February 5 and the second on February 15. It then began its mission
with a elliptical polar orbit with a perilune of about 400 km at 28
degrees S latitude that took five hours to complete. It remained in
this orbit for a month, when on March 26 is was rotated to a new orbit
of 29 degrees N latitude.
The spacecraft exited lunar orbit on May 5. On May 7, after the
first of two Earth transfer orbits, a computer malfunction caused one
of Clementine's attitude control thrusters to fire continuously for 11 minutes, until
all of its fuel had been exhausted. The errant thruster put
Clementine into an 80 RPM spin, which made certain that the second
part of its mission, the 620 Graphos flyby, would yield no useful
results. Clementine was instead put into a geocentric orbit in the Van Allen radiation belts to study the effect of
radiation exposure on the spacecraft instruments.
Clementine died a slow death in the Van Allen belts, and in June
1994, power levels on the craft dropped to a point where transmitted
telemetry became unintelligible.
Hardware
The spacecraft was octagonal in shape, 1.88 meters high and 1.14
meters across. It carried two gimbal mounted GaAs/Ge solar panels,
which recharged a 15 amp-hour, 47 w hr/Hg Ni-H common pressure vessel
battery. Sensors were all mounted together on one of the eight sides,
perpendicular to the solar panels, and were protected in flight by a
single sensor cover. A high-gain fixed antenna was mounted on one end
of the craft, and the 489 N thruster was located on the opposite
end.
Propulsion was provided by a bipropellent system for maneuvers and
a hydrazine system for attitude control. The bipropellent system used
nitrogen trioxide and monomethyl hydrazine, and had a total capacity
of approximately 1900 m/s. 550 m/s of that capacity was required for
lunar insertion and 540 m/s was required for lunar departure.
Attitude control was provided by two inertial measurement units, two
star tracker cameras, and 12 attitude control thrusters. While in
lunar orbit, the craft was three axis stabilized by reaction wheels.
Clementine carried seven instruments, a UV/Visible camera, a near
infrared camera, a long wavelength infrared camera, a high resolution
camera, two star tracker cameras, a laser altimeter, and a charged
particle telescope. Clementine also carried an S-band transmitter,
which was used for communications, tracking, and a gravimetry
experiment.
Onboard data processing was performed by two computers. The first,
a MIL-STD-1750A computer operating at 1.7 million instructions per
seconds provided savemode, attitude control, and housekeeping
operations. The second, a RISC 32-bit processor operating at 18
million instructions per second, was used for image processing, image
compression (courtesy of the French Space Agency CNES), and
autonomous operations. Data was save on a 2 Gbit dynamic solid state
recorder.
The Clementine spacecraft used a lunar transfer booster called the
Clementine Interstage Adapter Satellite to get it from the Earth to
the Moon.
Clementine carries NSSDC (National Space Science Data Center)
Master Catalog ID 1994-004A. The information here was obtained in part
from http://nssdc.gsfc.nasa.gov/.