Lunar and Planetary Science XXX 1129.pdf PHYSICAL PROPERTIES OF SOME SPACECRAFT MISSION TARGETS. A. Doressoundi- ram and P. Weissman, Jet Propulsion Laboratory, MS 183-601, 4800 Oak Grove Drive, Pasadena, CA 91109. Introduction: We present results from last time to observe this cometary nucleus while photometric observations of asteroids and com- it is far enough from the Sun to be inactive, and ets which are targets of upcoming spacecraft prior to the freezing of the spacecraft design in missions. early 2000. From our data, we will derive esti- Asteroids and comets are direct descendents mates of the nucleus radius, axial ratio, and ro- of the planetesimals which formed in the solar tation period. These are required to aid in the nebula 4.5 Gyrs ago. These objects are the rem- design of the lander subsystems and in planning nants of the primordial processes which charac- spacecraft trajectories and observational se- terized the origin and evolution of the Solar quences at the comet. Also we will determine System, immediately after the collapse of the the broad-band colors of the nucleus, which will protoplanetary nebula and before the formation give rough compositional information on the of the planets. Comets appear to have experi- nature of its surface. enced a very low level of compositional evolu- tion since then, and many asteroids, although 140 Siwa and 4979 Otawara: 140 Siwa they experienced an intense collisional evolution and 4979 Otawara are the two asteroidal targets that altered their shape, size and surface mor- of the International Rosetta mission phology, seem to have undergone relatively (ESA/NASA) to be launched in January 2003. modest geological and thermal evolution. The mission will rendezvous with comet Therefore, small bodies, more than any other, 46P/Wirtanen, orbiting around it, making obser- preserve materials which witnessed the conden- vations as it journeys towards the Sun, and sation and the early phases of the formation of landing a package of instruments on its surface. the Solar System. On its eight-year journey to the comet, the A number of spacecraft missions to comets spacecraft will pass close to the two asteroids. and asteroids are now either on their way, under 140 Siwa is a 110 km diameter asteroid and development, or in the proposal and planning belongs to the primitive C class [1]. A tentative stages. These include NEAR, Deep Space 1, period of 18.5 hours has been determined [2]. Stardust, Contour, Muses C, Deep Space 4 and We are conducting further observations so that Rosetta. Knowledge about the physical parame- the period can be defined uniquely, as well as ters of the target bodies is required for both op- learning more about the asteroid’s shape and timization of the mission scenarios and refine- pole orientation. ment of the designs of the spacecraft and their Nothing is known at present about 4979 payloads. Otawara, which we are also observing. We will derive the rotation period for this asteroid, as 9P/Tempel 1 : Comet P/Tempel 1 is the tar- well as estimate its size, shape and spectral type. get of the NASA/CNES Deep Space 4/Champollion mission, which will be launched References: in April, 2003. DS-4/Champollion will rendez- [1] Barucci M. A. et al. (1998) Plan. Spa. vous with P/Tempel 1 in early 2006 and will de- Sci. 46, 75-82. [2] Lagerkvist C.-I. et al. (1992) ploy a lander to the surface. We are now ana- Astron. Astrophys. Suppl. Ser., 95, 461-470. lyzing Tempel 1 data obtained during the fall/winter of 1998 and have observations planned for the winter/spring of 1999. This is the.