Martin Kessler
Ariane injected ISO into a transfer orbit with a perigee of 500 km and an apogee of 71600 km. The operational orbit (perigee of 1000 km and apogee 70600 Km) was achieved, as planned, with three uses of the hydrazine reaction control system. A test burn of five minutes was made on 18 November as a rehearsal of the perigee raising manoeuvre, which was successfully carried out with a 111 minute burn the following day. On 24 November, after the apogee had drifted to its desired position, another burn of 39 minutes was made to lower the apogee and to attain the planned operational orbit. An estimated 50 kg of hydrazine remains on-board whereas only about 12 kg are needed for the planned ISO operations.
Approximately eight percent of the planned observations (9% in observing time) have failed due to various on-board or ground problems, with telemetry drops accounting for about half of the failures. Activities to reduce this failure rate during routine operations are on-going.
Prior to launch, it was estimated that the ISO instruments could be operated for about 16 hours per day. From preliminary tests, it seems as if at least an additional 40 minutes per day could be scientifically useful.
Kieron Leech