6. Results of the First Fight on ORFEUS-SPAS

  The Shuttle flight STS-51 for ORFEUS-SPAS was launched on 12 September 1993 at 11:45 GMT and landed on 22 September at 7:56 GMT. ORFEUS-SPAS was released by the Shuttle 27 hours after launch, and astronomical observations began about 8 hours later, after engineering tests of various systems on the Astro-SPAS spacecraft had been completed. Because of a failure of one of the other instruments (the echelle spectrograph in ORFEUS), the observing time allocated to IMAPS was slightly more than the pre-arranged 1/5 fraction of the total time allocated to science operations. IMAPS functioned for 20 orbits out of a total of 82. The first 6 orbits of IMAPS operations were devoted to a systematic checkout of the instrument, troubleshooting, and a determination of the offset of the instrument's optical axis relative to that of the Astro-SPAS startracker.

According to plans made in advance, the apportionment of orbits for any one instrument was distributed into a number of sessions with the gaps being filled by observations by the other instruments. The rationale for not having each instrument take a single, contiguous observing session was that people would have a chance, while other instruments were observing, to think about changes in observing strategies in response to contingencies or devise corrective actions for failures, without the pressure of losing valuable time while doing so.