In January 1994 Clementine I was launched to map the moon and to perform a close flyby (100 km) of the near Earth asteroid Geographos. This mission was sponsored by the Ballistic Missile Defense Organization (BMDO). Clementine I successfully mapped 100% of the lunar surface but due to an on-board software bug, the spacecraft lost its attitude control fuel during the transfer phase from the lunar orbit to the Geographos transfer trajectory and thus was unable to carry out the asteroid flyby.
In the summer of 1995, the Clementine program office, now at the USAF/Phillips Laboratory (USAF/PL) made the decision for a follow-on Clementine II mission to multiple asteroids to complete the original Clementine I goals and to extend those goals. The primary mission of Clementine II is to perform a close, fast flyby of multiple near Earth asteroids, to launch science probes which will impact the asteroids, and to image the actual impact. The objectives of the mission are to perform a cost effective and stressing space test demonstration and flight qualification of lightweight spacecraft and sensor technologies; to test autonomous navigation and terminal optical navigation techniques for encounter of cold bodies; and to demonstrate the feasibility for quick-reaction observation of near-Earth objects. The Naval Research Laboratory (NRL) which designed, built and integrated the Clementine I spacecraft will perform the same role for Clementine II. The Lawrence Livermore National Laboratories (LLNL) will design and build the science probes with the help of USAF/PL and will also build the suite of sensor instruments. The spacecraft will be operated from the NRL control center used for Clementine I known as the ''Batcave''. The mission will continue the ''faster, better, cheaper'' philosophy of the Clementine I mission.
The nominal mission design of Clementine II will involve a transfer from an initial low Earth parking orbit in May of 1998 into phasing loops similar to the profile of Clementine I to gradually increase the energy of the orbit and to increase the launch window for the mission while remaining within the DV constraints of the onboard system. The first asteroid encounter of 1987 OA will occur in August of 1998 and the second encounter of 1989 UR will occur just four months later in December of 1998. An Earth gravity assist in early May of 1999 will be used for the third encounter of 1991 JX at the end of May. The flyby altitude for the three asteroids is currently designed for 50 km and an impactor probe will be released at each encounter. The probes are fully autonomous micro-spacecraft of about 21 kg weight with guidance, navigation, and control capabilities. The probes will have a DV capability of approximately 100 m/sec and will perform the impact autonomously once released from the mother ship. The entire mission duration is therefore approximately 400 days and launch is to occur approximately 26 months from the end of the preliminary study completed in February of 1996. A science team composed of government, industry, and university members similar to that of Clementine I, will be responsible for the analysis and dissemination of the science data gathered on this mission.
The paper will present the details of the trajectory design, the mission concept, and the terminal navigation.