Editing Infrared Space Observatory (section)

== Launch and operations ==

After a very successful development and integration phase ISO was finally launched into orbit on 17 November 1995, on board an Ariane-44P launch vehicle. Performance of the launch vehicle was very good with the apogee only 43&nbsp;km lower than expected. [[European Space Operations Centre|ESA's Space Operations Centre]] in [[Darmstadt]] in Germany had full control over ISO in the first four days of flight. After early commissioning primary control over ISO was handed over to the Spacecraft Control Centre (SCC) at [[Villanueva de la Cañada]] in Spain ([[European Space Astronomy Centre|VILSPA]]) for the remainder of the mission.
In the first three weeks after launch the [[orbit]] was [[Fine-tuning (physics)|fine-tuned]] and all satellite systems were activated and tested. Cool-down of the cryostat proved to be more efficient than previously calculated, so the anticipated mission length was extended to 24 months. Between 21 and 26 November all four science instruments were switched on and thoroughly checked out. Between 9 December 1995 and 3 February 1996 the 'Performance Verification Phase' took place, dedicated to commissioning all instruments and fixing problems. Routine observations started from 4 February 1996, and lasted until the last helium coolant depleted on 8 April 1998.

The perigee of ISO's orbit lay well inside the [[Van Allen radiation belt]], forcing the science instruments to be shut down for seven hours during each pass through the radiation belt. Thus, 17 hours in each orbit remained for scientific observation. A typical 24-hour orbit of ISO can be broken down into six phases:
* [[Orbital pass|Acquisition-of-Signal]] (AOS) by the primary [[Mission Control Center]] VILSPA in Spain and activation of the satellite.
* Science operations during the VILSPA window, starting four hours after perigee, and lasting for up to nine hours.
* Handover of operations to the secondary [[Mission Control Center|mission control center]] at [[Goldstone Deep Space Communications Complex|Goldstone]] at apogee. During this 15 minute periode the science instruments could not be operated.
* Science operations during the Goldstone window, lasting up to eight hours.
* De-activation of the instruments upon approach of the Van Allen radiation belt and Loss-of-Signal (LOS) at Goldstone.
* Perigee passage.

Contrary to IRAS, no science data was recorded on-board ISO for later transmission to the ground. All data, both science data and housekeeping data were transmitted to the ground in real-time. The perigee point of ISO's orbit was below the [[radio horizon]] of the mission control centers at both VILSPA and Goldstone, thus forcing the science instruments to be switched off at perigee.