Observability of the Rosetta Fly-bys at Minor Planets 3840 Mimistrobell and 2530 Shipka from Ground-Based Doppler Tracking.

Abstract

During its flight to comet Wirtanen, the Rosetta spacecraft will encounter two minor planets following the first and second Earth swing-by. The relative motion of Rosetta and the asteroids during these encounters is examined. An analytical expression for the expected Doppler signal due to the deflection of the spacecraft trajectory is derived in terms of fly-by distance, relative velocity and line-of-sight direction. Assuming an X-band Doppler measurement accuracy of 0,1mm/s, the Mimistrobell fly-by may be observed for a minimum mass of *)3 times 10 to the 15th kg, whereas the observability of the Shipka encounter requires a mass of *)1.7 times 10 to the 16th kg. Taking into account mass estimates from photometric parameters, the Mimistrobell encounter is most likely unobservable, while the Shipka fly-by might be detactable under favourable circumstances.