The scientific programme for ISO consisted of more than 1000 individual proposals from nearly 600 principal investigators from the world-wide astronomical community.
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About 10% of ISO's time was used for Solar System studies, 23% for the Interstellar Medium (ISM), 29% on Stellar/Circumstellar topics, 27% for Extragalactic observations and 11% for Cosmology (see Figure 4.8).
The full list of accepted and performed proposals is given in Appendix B.
There were no restrictions on the duration nor the size of the programmes except those set by the technical constraints of the mission, e.g. sky visibility and the orbit.
The OTAC considered each proposal on its scientific merits without any, a priori, preference for programmes of any specific size.
Taking advantage of this, some ISO programmes were proposed by observers and approved by the OTAC requesting a large amount of observing time. They intended to produce homogenous data sets on large samples of sources in a variety of scientific areas.
Table 4.1 gives an overview of the largest survey programmes.
| Programme | PI |
| European Large Area ISO Survey (ELAIS) | Rowan-Robinson |
| Spectroscopy of Bright Galactic Nuclei | Genzel |
| ISOCAM Survey of the Inner Galaxy (ISOGAL) | Omont |
| ISOCAM Deep Survey Programme | Cesarsky |
| ISM of Normal Galaxies | Helou |
| Dust Debris Around Solar Mass Stars | Becklin |
| Exploring the Full Range of Quasar/AGN Properties | Wilkes |
| Structure of the FIR Background | Puget |
More details of the survey programmes can be found in `ISO Surveys of a Dusty Universe' (Lemke et al. 1999, [112]).
In order to maximise ISO's scientific return from unpredictable astronomical events some of which needed rapid reaction times, a number of small teams were also set up to define and prepare the necessary ISO observations for likely Targets of Opportunity (ToO), such as supernovae, novae, bright comets, etc.
These teams prepared generic observations in advance, stored pre-planned observation sequences in the SOC's databases, fine tuned them as needed and were responsible for publishing the data to the community as quickly as possible. Such observations were executed only in the event that the specified phenomenon actually occured and it was the responsibility of the Principal Investigator of the team to inform the SOC of the occurrence of the phenomenon. Time for any such ToO observations came from the general Open Time.
These ToO proposals were reviewed by OTAC in the same way as other observing proposals. Each selected team contained, ex officio, one or more SOC astronomers. These were either included in the original proposal or were added to selected teams. The roles of these SOC staff included co-ordination during definition, responsibility for maintaining the appropriate observations in the SOC's databases and, being the focus at the SOC, during any execution of these observations.
Table 4.2 gives a summary of the performed ToO programmes. These proposals are also contained in Appendix B under Open Time proposals.
| Programme | PI | Observed Targets |
| Observations of Novae during the ISO Mission | Barlow | Nova Cas 95, |
| Nova Aql 95 | ||
| Nova Cru 96,... | ||
| The Nature of the Superluminal Galactic | ||
| Source GRS 1915+105: ISO Monitoring of the Most | ||
| Powerful Source in the Galaxy | Castro-Tirado | GRS 1915+105 |
| The Nature of the Superluminal Galactic Source | ||
| GRS 1915+105: ISO Observations during the Oct 1997 | ||
| X-Ray and Radio Outburst | Castro-Tirado | GRS 1915+105 |
New Soft Gamma-Ray Repeater (SGR 1814 1340): |
||
| A New IR-Source? | Castro-Tirado | SGR 18141340 |
| Studies of High Mass X-ray Binary Systems: Multi- | ||
| waveband Investigations of such Systems in Outburst | Coe | 4U1145619, |
| 4U170037 |
||
| Observations of Unexpected Comets | Crovisier | P/Hale-Bopp |
| Spectroscopic Observations of Comets | Crovisier | P/Hale-Bopp |
| ISO Observations of Cygnus X-3 in Outburst: | ||
| Infrared Studies of a Flaring Microquasar | Fender | Cyg X-3 |
| Observations of New Novae in Outburst | ||
| Physics Characteristics and Contributions to the ISM | Gehrz | Nova Aql 95, |
| LMC1 1995, | ||
| Nova Oph 94, | ||
| Nova Sco 97,... | ||
| ISOPHOT Observations of a Bright Comet Coma: | ||
| Composition and Dust Production | Grün | P/Hale-Bopp |
| ISOPHOT Observations of a New Comet: | ||
| Coma Composition and Dust Production | Grün | P/Hale-Bopp |
| The Nucleus of a New Bright Comet | Lamy | P/Hale-Bopp, |
| P/Tempel-Tuttle, | ||
| P/Hartley 2 | ||
| Observations of Low-Mass X-ray Binaries | Naylor | V404 Cyg, |
| GX1+4 | ||
| Cometary Comae in the IR: | ||
| Dimensions, Structures and Composition | Peschke | P/Hale-Bopp |
| Evolution of the Circumstellar Environment during | ||
| an FU Ori or EX Lup Outburst | Prusti | FU Ori in Serpens |
| Dust Formation around R CrB Type Stars at their | ||
| Minima: Search for Fullerenes | Tanabe | LR Sco, V Cra |
| The Infrared Counterpart of GRS 1915+105: | ||
| Observations of Outbursts | Winkler | GRS 1915+105 |
ISO made new and unexpected discoveries and, in many cases, ISO itself was the only facility capable of follow-on investigations of these discoveries. Additionally, compelling new observations became apparent during ISO's in-orbit life. Thus, a small pool of `discretionary time' was kept available, outside the normal `Call-Proposal-Review' cycle, for observations that could not have been foreseen at the time of proposal submission. An average of 30 minutes of discretionary time observations per day was foreseen.
To use this discretionary time, a request had to be made to the scientific head of the Observatory, the Project Scientist. Whenever possible, the Chairman of the OTAC was consulted by the Project Scientist before any additional observations were authorised. The Project Scientist reported to the next meeting of OTAC on all discretionary time observations.
Over 150 discretionary time proposals were received during the ISO operational lifetime, 40% of them in the last four months of the mission.
Following a recommendation of the OTAC, after a meeting held on 16 September 1997 where the overall status of the ISO scientific programme was reviewed, recommendations were made concerning use of the extra-time available as a consequence of the longer lifetime of ISO.
The principal conclusions were: that the
amount of discretionary time should be significantly increased for
the rest of the mission; that an additional 
200 hours should be
made available to the previously-approved large surveys; and that some
300 hours should be devoted to observations of `general interest' which
should be placed in the public domain without the usual 12 months
proprietary period. Thus, about 20 additional proposals on
specific topics were solicited to the community;
these can be recognised in the
ISO Data Archive as the programme names all start with `ZZ'.
The parallel and serendipity modes were not available to proposers. The data from these modes needed to be taken and reduced in a systematic and completely different manner. This was done by the respective instrument consortia, in collaboration with the SOC, and the data are available now through the ISO Data Archive. Table 4.3 gives an overview of all performed parallel and serendipity programmes of ISO. The parallel data were obtained while other instruments were prime, the serendipity data were taken during slews of the satellite.
| Programme | Wavelength | No. of observations / sky coverage |
| ISOCAM Parallel | 6.0, 6.7, 14.3 m |
 40000 observations |
| ISOCAM Serendipity | 6.0, 6.7, 14.3m |
 10 to 15% sky coverage |
| ISOPHOT Serendipity | 170m |
15% sky coverage |
| LWS Parallel | 10 wavelengths: 46 to 178m |
17000 obs. 1% sky coverage |
| LWS Serendipity | 10 wavelengths: 46 to 178m |
10% sky coverage |
Most of the parallel and serendipity programmes are explained in detail in `ISO Surveys of a Dusty Universe' (Lemke et al. 1999, [112]).
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