On 22 May 2007 at about 0050 UTC, the spin-stabilised Meteosat-8 weather satellite experienced an orbit change that was not the result of a commanded manoeuvre.
Initially detected by the image processing system as a change of satellite state, the orbit change event included a decrease in spin rate, a change in attitude, some nutation, a temperature change on thrusters and fuel lines, and a small drop in solar array power.
After intensive investigations with the support of Thales Alenia Space and ESA/ESTEC, it seems that damage has been sustained in the area of one of the radial thruster pairs. The hypothesis that Meteosat-8 has suffered a collision with an object crossing the geostationary orbit and/or lost some mass remains the most likely one. Collision with either a micro-meteorite or a particle of space debris appears a possible cause of this damage, according to EUMETSAT. Less likely is loss of mass from the spacecraft, as no further spacecraft anomalies have been revealed by testing so far.
Investigations have revealed that the unified propulsion sub-system, the thermal control sub-system and to a lesser extent the electrical power sub-system have been affected by this incident. In particular, one of the nominal thrusters used for East-West station keeping manoeuvres seems affected, possibly damaged. The redundant thruster for the same function has been tested and seems to be performing well.
The external surface of the satellite has been damaged and some internal parts of the satellite are now exposed both to cold space and Sun illumination as the satellite spins. This has caused a new thermal equilibrium to be reached inside the satellite, which means that a new thermal configuration will be required to minimise the impact on the satellite and to allow safe operation during eclipse. The imaging system appears not to have been affected by the incident.
As the redundant branch of thrusters can be safely used, and as a new thermal configuration can be developed, there should be no impact on Meteosat-8's ability to serve as the in-orbit backup satellite, and to provide the Rapid Scanning service, EUMETSAT said. However, a level of redundancy has been lost which could have a longer-term impact on Meteosat-8's availability.
The satellite, built by a European consortium led by Thales Alenia Space and launched 2002, was originally expected to stay operational until 2009.
The satellite went into safe mode on 23 September 2006, 1407 UTC. Investigations conducted by Eumetsat with the support of ESA and industry concluded that all telemetry analysed from the event was consistent with a transient caused by a Single Event Upset as being the cause of the safe mode. This type of event has been observed several times on both MSG satellites in orbit and is attributed to a particular circuit (LM139) sensitive to protons and heavy ions in solar and cosmic radiation.
Following the safe mode, all operational services were configured for the backup satellite, Meteosat-9 (MSG-2). Meteosat-8 returned to nominal operations on 10 October 2006.
MSG-1 commissioning got under way on 25 September 2002. Just before switching on the imaging mission (SEVIRI) on 17 October 2002, a Solid State Power Amplifier (SSPA-C) failed. It was to be used to re-brodcast data that had been processed by the Eumetsat control centre.
Operational conditions of the satellite were nominal but the failure led to an automatic payload switch-off. All attempts to restart the SSPA failed and commissioning was suspended. A new satellite configuration was applied, and commissioning activities resumed on 26 November 2002.
In order to disseminate MSG-1 data, engineers extended EUMETCast, a multicast distribution system using commercial communications satellites. Files are distributed using the DVB (Digital Video Broadcast) standard in the Ku-band for Europe via Eutelsat Hot Bird 6 at 13 degrees East, and in the C-band for Africa via Eutelsat Atlantic Bird 3 at 5 degrees West.
MSG-1 was declared operational at the end of January 2004 and renamed Meteosat 8.