Section M 2.9.
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Clementine Mission Notes

From the National Space Science Data Center.

The Clementine Spacecraft

The Clementine spacecraft was built at the U.S. Naval Research Laboratory in Washington, DC and carried sensors, attitude control systems and software designed and built by the Lawrence Livermore National Laboratory (LLNL). The USAF supplied advanced lightweight composite structures and the launch vehicle, a Titan II B refurbished ICBM. Several other organizations were involved, especially NASA with communications support, through the Jet Propulsion Laboratory's (JPL) Deep Space Network, and orbit determination and operations support from both the Goddard Space Flight Center and JPL. Supporting these laboratories were scores of industrial contractors, both large and small.

The spacecraft consists of an octagonal prism about 2 meters high. A 110-pound thruster for delta-V maneuvers is on one end of the prism and a high-grain fixed dish antenna is on the other end. The spacecraft propulsion system consists of a nonpropellant hydrazine system for attitude control and a biptopellant nitrogen tetraoxide and monomenthyl hydrazine system for the maneuvers in space. The bipropellant system had a total capability of about 1.9 km/s with about 550 m/s required for lunar insertion and 540 m/s for lunar departure. The power system consisted of a gimbled, single axis, GaAs/Ge solar array providing a total spacecraft power of 360 watts at 30 Vdc, with a special power of 240 w/kg, based on lightweight construction. Two arrays of the rotating solar panels protrude from oposite sides; by rolling the spacecraft and rotating the panels, full solar illumination of the panels would be achieved. The solar array was used to charge a 15 A-h, 47-w hr/kg, Nihau common pressure vessel battery. The total mass of the spacecraft in the launch configuration was 1690 kg, with most of the weight in the solar rocket motor required for translunar insertion. The spacecraft dry mass is about 227 kg, with a roughly equal mass for liquid fuel. This weight was achieved by incorporating many of the lightweight technologies developed through the research and development activities of the Strategic Defense Initiative (SDI).

The spacecraft data processing was performed by 3 computing systems. A MIL-STD-1750A computer with a capacity of 1.7 million instructions per second was used for save mode, attitude control system, and housekeeping operations. A reduced instruction set computer (RISC) 32-bit processor with 18 million instructions per second was used for image processing and autonomous operations. The Clementine mission represents the first long duration flight of a 32-bit RISC processor. Also incorporated is a state-of-the-art image compression system provided by French Space Agency CNES. A data handling unit with its own microcontroller sequenced the cameras, operated the image compression system, and directed the data flow. During imaging operations, the data were stored in a 3 kg, 2 Gbit dynamic solid state data recorder and later transferred to the ground stations using a 128 kb/downlink. The spacecraft was commanded from the ground using a 1 kb/s uplink from the NASA Deep Space Network and DoD stations. Demonstration of autonomous navigation including autonomous orbit determination was a major goal of the Clementine mission. Autonomous operations were conducted in lunar orbit.

Clementine was launched on January 25, 1994, from Vandenburg Air Force Base aboard a Titan IIG rocket. After two Earth fly-bys, lunar insertion was achieved on February 19th. Lunar mapping took place over approximately 2 months in two systematic mapping passes over the Moon. After successfully completing the Lunar mapping phase of the mission, Clementine suffered an on-board malfunction at 9:39 AM EST, Saturday, May 7, 1994. The result of the malfunction prevented Clementine from performing the planned close fly-by of the near-Earth asteroid Geographos scheduled for August 1994. Preliminary analysis traced the cause of the malfunction to the on-board computer which controls most of the satellite's systems, including the attitude control thrusters. The computer activated several thrusters during a 20 minute telemetry interruption with the ground station, thus depleting all the fuel in the Attitude Control System (ACS) tanks. With the depletion of the ACS tanks, the spacecraft was left spinning at 80 revolutions per minute with no remaining fuel to despin the spacecraft.

Clementine Spacecraft Sensors

The main instrumentation on Clementine consists of four cameras, one with a laser-ranging system. The cameras include an ultraviolet-visual (UVVIS) camera, a long-wavelength infrared (LWIR) camera, the laser-ranger (LIDAR) high-resolution (HIRES) camera, and a near-infrared (NIR) camera. The spacecraft also has two star tracker cameras (A-STAR, B-STAR), used mainly for attittude determination, but they also serve as wide-field cameras for various scientific and operational purposes. The sensor package has a mass of 8 kg and represents the state-of-the-art at the inclination of the Clementine program. The sensors are all located on one side, 90 degrees away from the solar panels. Clementine has 12 small attitude control jets that were used to orient the spacecraft to point the cameras toward desired targets. The attitude control system includes the two star tracker cameras and two lightweight inertial measurement units, based on a ring laser gyro and an interferometric fiber optic gyro. During initial deployment at low-earth-orbit, the full size spacecraft was 3-axis stabilized. The spacecraft was 3-axis stabilized in lunar orbit via reaction wheels, with precision of 0.05 Deg. control and 0.03 in knowledge.


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