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Solar-System Targets
From the ISO mission planning point of view the solar-system targets differ from other astronomical targets. This is due to the fact that solar-system objects have no fixed equatorial coordinates. Therefore solar-system objects are identified by their names which link them to ephemerides used in position calculation at the moment the observation is planned. The data base of ephemerides contains all outer planets, most of their moons, major comets and selected asteroids. Appendix C lists all solar-system targets of that data base. In case a target, which is not included in Appendix C, is proposed, the observer will be requested to provide the orbital parameters for Phase 2 if the proposal has been recommended by OTAC.
Observations of solar system targets require tracking of the specific
object, i.e. a spacecraft raster. As the spacecraft raster option is
already used for tracking, there is no possibility to use the spacecraft
raster mode for observations. Therefore, observations of solar
system targets in the spacecraft raster mode are forbidden.
Additionally, in a certain direction chopping may not be feasible. In
Appendix D the full list of available AOTs and restrictions with respect
to observations of solar system objects is given. The spacecraft raster
limits the observations to objects with an apparent velocity of less
than 2 arcminh 
with respect to equatorial coordinates.
There are several additional aspects specific to solar-system targets (e.g. change of orbital parameters, eclipse of a moon around a planet, change of galactic background or stray radiation level). Therefore observers of solar-system objects are requested to be in close contact with the ISO Science Operations Team from Phase 2 on in order to guarantee optimal scientific return.
ISO Science Operations Team
Tue Aug 6 11:04:33 MET DST 1996