Second Ground Station

The orbit originally adopted for ISO had a period of 12 hours and two ground stations were needed in order to track the spacecraft for up to 22 hours per day. The orbit was later changed to one with a period of 24 hours so as to spend more time outside the Earth's trapped radiation belts, which reduce the sensitivity of the IR detectors. To offset partially the increased cost of launching into the higher orbit, it was agreed that ESA would only fund one ground station, limiting communications to 12-14 hours per 24 hour orbit. It was, however, recognised that additional scientific return could be gained by adding a second ground station and operating ISO for longer each day. Arrangements are now practically in place with the Institute of Space and Astronautical Science (ISAS), Japan and with NASA, USA for the provision of a second ground station and associated facilities. In return, ISAS and NASA will each receive 30 minutes per day of guaranteed observing time. These agreements will mean that it will be possible to operate ISO scientifically for about 16 hours per day. ISAS and NASA have allocated their guaranteed observing time to selected ``Key Projects'' to be conducted by their astronomical communities as an extension of the original ISO Central Programme.