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Up tp now ROSAT carries out its mission very successfully since more than seven years. During this time the first six month have been dedicated to the scan mode, followed by the pointing mode.

During the scan mode ROSAT has systematically scouted the celestial sphere for X-ray sources covering all the sky within half a year. To perform the survey motion ROSAT rotates in an orbit synchronous way, that means with one revolution per orbit, around the sun vector.

[Artist's View - ROSAT]
ROSAT - Artist's View

This rotation combined with the earth's motion around the sun (about 1° per day) gives the complete sky survey in 180 days. The main telescope field of view allows the investigation os a 2°-wide band during one orbit.

The field of view proceeds by about 4 arcmin per orbit, giving a 1° progress per day. Hence a specific source can be observed over a two days period.

[Artist's View - ROSAT Mission]
ROSAT Mission - Artist's View

A periodical reversal of the scan rotation is necessary when the sun vector crosses the orbit plane to prevent the telescopes from viewing unintentionally into the earth's atmosphere or even towards the earth itself. When the angle between sun vector and orbit plane is positive the spin vector must be directed towards the sun and vice versa. The scan reversal occurs about all 34 days.

The main objective of the pointing mode is the detailed observation of selected X-ray sources for a longer period (up to three hours). The sun aspect angle is restricted to 90° ± 15° so that at a given time a 30° band perpendicular to the sun direction can be observed.

[ROSAT Mission Phase I]
ROSAT Mission Phase I -
Survey Scan Mode

ROSAT (Röntgensatellit)
Copyright © 1998 Max-Planck-Institut für extraterrestrische Physik, 85740 Garching, Germany.
The ROSAT project is run by the German Aerospace Center (DLR) (former DARA), Bonn, by order of the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF). All rights reserved.