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Earth Occultation


ROSAT was placed into a circular low earth orbit with an initial altitude of 580 km (see Table 7.1 gif for the nominal orbit parameters). As seen from ROSAT, Earth subtends a cone with an opening half angle of tex2html_wrap_inline2240 ; most targets will therefore be occulted for part of the orbit and observations will have to be broken into smaller segments which will be interleaved with observations of other targets. Hence the resulting data stream for a particular target will in general show large data gaps.


Altitude 580 km
Inclination tex2html_wrap_inline2242
Orbital period 96 minutes
Precession period 66 days
Table 7.1:   ROSAT Orbit Parameters

No earth blockage occurs for targets in directions perpendicular to the instantaneous orbit plane (which changes due to precession); they are located in a so-called continuous viewing zone. Attempts will be made to schedule targets in continuous viewing zones whenever feasible since such targets can be observed with essentially no loss in viewing time other than losses due to the radiation belts and SAA.

Michael Arida
Tue Jun 11 16:18:41 EDT 1996