A scheme for target tracking and pointing during small celestial body encounters

A scheme has been developed and simulated for closed-loop tracking and pointing space-borne science instruments at small celestial bodies such as comets and asteroids during high-velocity encounters. To overcome ephemeris uncertainties for these bodies, the scheme involves sequential estimation of flyby model parameters. The design consists of a two-axis gimbaled platform mounted on a three-axis stabilized spacecraft. A platformmounted optical tracker provides target direction measurements, while precision microstep actuators enable high-rate platform slewing. For comet missions which involve dust particle impact disturbances, a dual-mode attitude control scheme is presented for minimizing transient response time.