ISO, an infrared astronomical observatory in space, was launched by Ariane
on 17 November 1995. With its instrument complement of an imaging
photopolarimeter (called ISOPHOT), a camera (ISOCAM), a long wavelength
spectrometer (LWS) and a short wavelength spectrometer (SWS), ISO offers
astronomers a unique opportunity to make a wide variety of high-sensitivity
imaging, spectroscopic, photometric and polarimetric observations in the
wavelength range from 2.5 to 240 
m using a cryogenically-cooled
telescope with a primary mirror diameter of 60cm. Current estimates of
ISO's lifetime--limited by its supply of liquid helium--indicate that it
will be operational until around December 1997.
The majority of ISO's observing time is being made available to the astronomical community by the traditional route of Calls for Observing Proposals, followed by peer review. These Calls are, in principle, open only to proposers in ESA member states, the USA and Japan. This time is referred to as ``Open Time''. A pre-launch Call for Observing Proposals was issued in 1994 and the successful proposals are currently being executed by ISO. This Supplemental Call solicits proposals to be carried out in the period from December 1996 to the end of the mission. Although completely new proposals are not excluded, priority will be given to proposals aimed at continuing, completing and extending existing ISO observing programmes, see section 4.3.1 for further details.
Responses to this Call must consist of a so-called Phase 1 proposal. After peer review by the ISO Observing Time Allocation Committee (OTAC), successful proposers will have to enter full details of their observations (Phase 2) into an ISO data base.
The following schedule has been established for the Supplemental Call:
| Issue of Call 5 August 1996 | 5 August 1996 |
| Phase 1 Proposals (electronic version) due by | 07.00 GMT, 7 October 1996 |
| Phase 1 Proposals (paper version) due by | 12.00 GMT, 9 October 1996 |
| OTAC review complete by | late November 1996 |
| Start of Phase 2 data entry | end November 1996 |
| End of Phase 2 data entry | ~end January 1996 |
Note that as soon as Phase 2 data entry of a successful proposal is complete, the observations will be made available for scheduling. Thus, execution of observations resulting from Supplemental Call proposals could start as early as December 1996.