Failed Telecommunications Satellite Drifts Out of Control
PARIS - The Astra 5A commercial telecommunications satellite is out of control after an unexplained failure Jan. 15 and is drifting eastward along the geostationary orbital arc, with ground controllers pessimistic about their ability to re-establish sufficient communications to guide it into a graveyard orbit, industry officials said Thursday.
Officials said Astra 5A used a large portion of its remaining fuel during the hours following the initial loss of attitude control Jan. 15. They described several chaotic hours during which Astra 5A's sun sensors, which help keep the spacecraft oriented toward the sun so it can recharge its batteries, failed in turn
The satellite subsequently went into an uncontrolled spin on its axis, which ground teams attempted to stop by firing its on-board motors. Most of Astra 5A's remaining on-board fuel was depleted in the attempt, and even then the situation could not be salvaged.
With its solar arrays only intermittently pointed toward the sun, the satellite's batteries were soon depleted, and controllers were unable to send commands to reorient Astra 5A, which now has left its orbital slot at 31.5 degrees east longitude and is moving eastward, officials said.
Astra 5A's owner, SES of Luxembourg, has informed owners of neighboring satellites of the event, and there is a possibility that one or more satellites will need to perform a collision-avoidance maneuver.
The first two satellites in Astra 5A's path are owned by Intelsat of Washington and Bermuda. An Intelsat official said Jan. 22 that SES had issued the necessary warnings to permit Intelsat to prepare, and that an early analysis has concluded that the Galaxy 11 satellite, at 32.8 degrees east, will not have to be moved. Analysis is ongoing on whether the Intelsat 802 spacecraft, at 32.9 degrees east, will need to perform a collision-avoidance maneuver, the Intelsat official said.
After it passes the two Intelsat satellites, Astra 5A will cross into the 33 degrees east position occupied by Paris-based Eutelsat's Eurobird 3 satellite. Two other Eutelsat satellites are located at 36 degrees and 36.1 degrees. A Eutelsat official said Jan. 22 that a preliminary assessment has concluded that the company will not need to conduct any avoidance maneuvers.
It is unusual for a healthy satellite to fail without warning, but one industry official said in this case Astra 5A was working fine one moment and then went into emergency sun-acquisition mode for no apparent reason.
One industry official said that while the satellite is not responding to commands from the ground, it is sending sufficient data to confirm that its remaining fuel is sufficient to propel it into a graveyard orbit about 300 kilometers above the geostationary arc if control can be re-established.
SES spokesman Markus Payer said Jan. 22 that the company would not comment on Astra 5A's status but that the investigation into what happened is continuing. He said it is too early to say whether the failure is a consequence of a short-duration loss of control of Astra 5A last October. SES officials at the time said the incident was due to a faulty command issued by a ground operator. Astra 5A is controlled by the Swedish Space Corp.
Astra 5A was returned to service in early November. But an industry official said bringing the satellite back on line was particularly difficult and, in hindsight, may have given a clue as to its future problem. But this official agreed with Astra that it is too early to say whether the January failure is related to the October event.
Because Astra 5A returned to nominal operations with no further problems, the investigation into the October incident was cut short.
Astra 5A is the former Sirius 2 spacecraft that was operated by SES Sirius of Sweden at 5 degrees east after its launch in November 1997. The spacecraft is a Spacebus 3000 model built by Thales Alenia Space of France and Italy, with avionics provided by Astrium Satellites of Germany. In April 2008 it was moved to SES's 31.5 degrees east location, an orbital slot that SES hopes to develop to expand its services into Central and Eastern Europe.
Thales Alenia Space issued a statement Jan. 21 saying the prime contractor is working with Swedish Space Corp. and SES "to initiate any possible safety actions." The statement said Astra 5A had a contractual in-orbit service life of 12 years. SES had expected it to operate for 15 years.
Payer said SES still expects to develop the 31.5 degree slot. The Astra 1D satellite remains in place there, but in an inclined orbit, meaning that, to save fuel, it is no longer maintained stable on its north-south axis. That limits its commercial utility.
Payer said SES has several options for replacing Astra 5A at 31.5 degrees east and will select one in the coming weeks.
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