ISO was launched at 01:20 UTC on November 17, 1995 from Kourou (French Guiana) using an Ariane 44P (with 4 solid strap on boosters) launch vehicle on Flight V-80.
The trajectory was nominal and, after successful re-orientation of the composite Ariane 3rd stage/ISO, separation was reported by Arianespace at 01:40 UTC.
First orbit determination from Flight Dynamics revealed that the initial transfer orbit was very accurate and the dispersion of all elements much less than the standard deviation.
The apogee height was 71577 km, about 43 km lower than the expected
apogee of 71620 km. The perigee height of 500 km and the inclination of
5.25
were as expected. The orbital period was 1 min. 15 sec.
larger than expected.
A detailed summary of the events that took place during the 4 days of duration of this Phase (revolutions 0 to 3) can be found in the ISO Launch and Early Orbit Phase & Satellite Commissioning Phase Report, [87]
With the successfully performed handover of operations from ESOC/OCC to VILSPA/SCC, LEOP terminated and the Satellite Commissioning Phase (SCP) started. The SCP was carried out jointly by the ISO Spacecraft Control Centre (SCC) and the Science Operations Centre (SOC), under the overall responsibility of the ISO Project from November 21, 1995 (revolution number 4) to December 9, 1995 (revolution number 21) inclusive.
The objectives of the SCP were the following:
The first step of the SCP was to continue with spacecraft check-out and subsystems performance verification, as initiated during LEOP, to reach the mission orbit, and to eject the cryostat cover.
The second step of the SCP was to complete the overall check-out of the ISO payload, i.e. the scientific instruments. To validate the instrument activation and de-activation sequences, and initiate the study of the in-flight performance of each instrument, in order for the space segment to be ready to execute the Performance Verification (PV) phase and the Routine Phase (RP). In the process of executing the SCP, the overall integrated Ground Segment (SCC, SOC, Ground Stations, and communications network) was also validated.
In addition, all the nominal modes of the Service Module subsystems were successfully verified, including AOCS units and functions, OBDH (On-Board Data Handling), RF (Radio Frequency), power conditioning and thermal control performance.
Similar to the Service Module subsystems, all nominal modes of the payload
module were also successfully verified. There was no indication that the
telescope was defocussed or suffering from aberrations. The performance
of the four scientific instruments was nominal with respect to
functionality of the hardware and software. The cool-down phase of the
cryostat was determined to be well in line with the thermal model and the
helium flow rate was found well within limits anticipating a lifetime
of 24 
2 months, compared with the baseline of 18 months.
PHT was the first of ISO's four scientific instruments to be switched on at 09:56 UTC on November 21, 1995 (revolution 4). PHT-specific tasks during SCP comprised, among other activities, wheel commissioning, general instrument behaviour check-out, detector curing and determination of the PHT focal plane geometry offsets to measure the precise location of the instrument apertures with respect to the Quadrant Star Sensor (QSS) boresight. PHT was used as prime instrument in revolutions 4 to 9, 12, 13, 17 and 21.
CAM was switched on at 08:41 UTC on November 24, 1995 (revolution 7). Soon while instrument check-up was in progress, column 24 was reported missing in the Long Wavelength (LW) array. confirming the results obtained during testing on ground. Appart from the general instrument behaviour check-out, other CAM-specific tasks during SCP included detector transient measurements and determination of the CAM focal plane geometry offsets. CAM was used as prime instrument in revolutions 7, 8, 11, 13 to 16 and 21, and in parallel mode in revolutions 12 to 14 and 18 to 20.
LWS was switched on at 08:42 UTC on November 25, 1995 (revolution 8). LWS-specific tasks during SCP comprised, among oher activities, general instrument behaviour check-out, detector curing and determination of the LWS focal plane geometry offsets. LWS was used as prime instrument in revolutions 8, 11 to 14 and 21.
SWS was the last of ISO's four scientific instruments to be switched on. The initial switch on of SWS took place at 08:08 UTC on November 26, 1995 (revolution 9). As for the other ISO instruments, SWS-specific tasks during SCP included general instrument behaviour check-out, detector performance evaluation, detector curing, Fabry-Pérot parallelisation and determination of the focal plane geometry offsets. SWS was used as prime instrument in revolutions 9, 11 to 14 and 17 to 21.
Furthermore, the following general activities were performed: uplink time jitter buffer test, solar system object tracking, four instrument automatic activation and de-activation sequences validation, ground station `modulation index' investigations and the verification of the overall observatory functionality.
During the course of the SCP several (minor) deviations from the flight operations plan were required in response to unexpected or unplanned events. But in general, no major problems occurred. All anomalies could be closed and the ISO observatory was declared ready to support the PV Phase.
A full description of the events that took place during this phase and of the few minor anomalies detected is given in the above mentioned ISO Launch and Early Orbit Phase & Satellite Commissioning Phase Report, [87].
After a successfully completed SCP, the Scientific Performance Verification Phase started on revolution 22 (December 9, 1995) and ended on revolution 78 (February 3, 1996).
The objectives of this phase were the following:
It was anticipated that, contrary to the Routine Phase, re-planning of revolutions on short notice would be necessary. In order to allow quick re-planning it was decided to operate only one instrument per revolution.
With the exception of an anomaly in the scanning of the LWS long-wavelength Fabry-Pérot interferometer, the instruments appeared to operate functionally as expected from ground-based testing.
High energy particle impacts (glitches) adversely affected the sensitivity of the two spectrometers. Preliminary analyses showed sensitivity losses of up to around a factor of 4, depending on detector type; however, this loss was later reduced by optimised operating conditions and improved data processing.
The sensitivities of CAM and PHT appeared to be close to their pre-launch expectations, although, an additional set of procedures was needed for some detectors once per day to remove effects induced by high energy particle impacts.
From an operational point of view the PV phase consisted of two parts, the core PV part and the so-called Observatory Verification part. The core PV part covered revolutions 22 to 77, thus 56 revolutions, with a mid-term review held at VILSPA on January 12, 1996 to summarise the current status of instrument performance and to release some of the AOTs for use during the first weeks of the Routine Phase. The Observatory Verification part consisted of one revolution only, revolution 78, and marked the transition to the Routine Phase. This was the first time when all four instruments were activated and operated on the same revolution with the same operational SOC hardware and software used for the Routine Phase. The purpose of this revolution was to verify that ISO and the Ground System could successfully execute and generate a schedule as planned with the Mission Planning system in its nominal mode, and to commission and calibrate the PHT serendipity and the CAM parallel modes. At the end of the PV Phase 16 observing modes (AOTs), 80% of total, had been released for use by observers.
The ISO Routine Phase comprised the period between revolution 79 (February 4, 1996) and revolution 875 (April 8, 1998).
During this phase the SCC was responsible for all spacecraft operations. This included:
The SCC was also responsible for the safety of the scientific instruments.
On the other hand, the SOC was responsible for the scientific aspects of the ISO mission and in particular for all activities related to the four instruments. This included the following tasks:
A general description of the satellite and instruments performance and of the main events occured during this Routine Phase is given in Chapter 5. More specific information on individual instruments performance can be found in the corresponding instrument specific volumes (II to VI) of the ISO Handbook.
At 07:00 UTC on April 8, 1998 (revolution 875) ISO's telescope started to
warm up, which was the sign that ISO had exhausted the superfluid helium.
Observations ceased at 23:07 UTC when the temperature of the instruments
had risen above 
269C (4.2 K). Observations from revolutions
875 and later have to be
taken with care because of the higher temperatures of the detectors.
However, a few of the detectors in the Short Wavelength Spectrometer (SWS),
could still be used after exhaustion of the liquid helium.
Some 150 extra hours were used to measure nearly 300 stars at
wavelengths between 2.4 and 4 microns (see Vandenbussche et al.
2002, [158]),
interspersed between technology tests, where various software and hardware
systems were subjected to detailed analysis under non-standard conditions.
Some of the main activities during this Technology Test Phase were testing the operation of the star trackers at low altitudes, i.e. in the radiation belts, use of the on-board redundant units that were not needed during the routine operations due to the superb performance of the satellite, and evaluation of the software intended to overcome multiple gyro failures.
The ISO satellite was switched off on May 16 at 12:00 h UTC, thereby bringing to a close the highly successful in-orbit operations.
