PARIS - TheAstra 5A commercial telecommunications satellite is out of control after anunexplained failure Jan. 15 and is drifting eastward along the geostationaryorbital arc, with ground controllers pessimistic about their ability tore-establish sufficient communications to guide it into a graveyard orbit,industry officials said Thursday.
Officialssaid Astra 5A used a large portion of its remaining fuel during the hoursfollowing the initialloss of attitude control Jan. 15. They described several chaotic hoursduring which Astra 5A's sun sensors, which help keep the spacecraft orientedtoward the sun so it can recharge its batteries, failed in turn
Thesatellite subsequently went into an uncontrolled spin on its axis, which groundteams attempted to stop by firing its on-board motors. Most of Astra 5A'sremaining on-board fuel was depleted in the attempt, and even then the situationcould not be salvaged.
With itssolar arrays only intermittently pointed toward the sun, the satellite's batterieswere soon depleted, and controllers were unable to send commands to reorientAstra 5A, which now has left its orbital slot at 31.5 degrees east longitudeand is moving eastward, officials said.
Astra 5A'sowner, SES of Luxembourg, has informed owners of neighboring satellites of theevent, and there is a possibility that one or more satellites will need toperform a collision-avoidance maneuver.
The firsttwo satellites in Astra 5A's path are owned by Intelsat of Washington andBermuda. An Intelsat official said Jan. 22 that SES had issued the necessarywarnings to permit Intelsat to prepare, and that an early analysis hasconcluded that the Galaxy 11 satellite, at 32.8 degrees east, will not have tobe moved. Analysis is ongoing on whether the Intelsat 802 spacecraft, at 32.9degrees east, will need to perform a collision-avoidance maneuver, the Intelsatofficial said.
After itpasses the two Intelsat satellites, Astra 5A will cross into the 33 degreeseast position occupied by Paris-based Eutelsat's Eurobird 3 satellite. Twoother Eutelsat satellites are located at 36 degrees and 36.1 degrees. AEutelsat official said Jan. 22 that a preliminary assessment has concluded thatthe company will not need to conduct any avoidance maneuvers.
It is unusualfor a healthy satellite to failwithout warning, but one industry official said in this case Astra 5A wasworking fine one moment and then went into emergency sun-acquisition mode forno apparent reason.
Oneindustry official said that while the satellite is not responding to commandsfrom the ground, it is sending sufficient data to confirm that its remainingfuel is sufficient to propel it into a graveyard orbit about 300 kilometersabove the geostationary arc if control can be re-established.
SESspokesman Markus Payer said Jan. 22 that the company would not comment on Astra5A's status but that the investigation into what happened is continuing. Hesaid it is too early to say whether the failure is a consequence of ashort-duration loss of control of Astra 5A last October. SES officials at thetime said the incident was due to a faulty command issued by a ground operator.Astra 5A is controlled by the Swedish Space Corp.
Astra 5Awas returned to service in early November. But an industry official saidbringing the satellite back on line was particularly difficult and, inhindsight, may have given a clue as to its future problem. But this official agreedwith Astra that it is too early to say whether the January failure is relatedto the October event.
BecauseAstra 5A returned to nominal operations with no further problems, theinvestigation into the October incident was cut short.
Astra 5A isthe formerSirius 2 spacecraft that was operated by SES Sirius of Sweden at 5 degreeseast after its launch in November 1997. The spacecraft is a Spacebus 3000 modelbuilt by Thales Alenia Space of France and Italy, with avionics provided byAstrium Satellites of Germany. In April 2008 it was moved to SES's 31.5 degreeseast location, an orbital slot that SES hopes to develop to expand its servicesinto Central and Eastern Europe.
ThalesAlenia Space issued a statement Jan. 21 saying the prime contractor is workingwith Swedish Space Corp. and SES "to initiate any possible safetyactions." The statement said Astra 5A had a contractual in-orbit servicelife of 12 years. SES had expected it to operate for 15 years.
Payer saidSES still expects to develop the 31.5 degree slot. The Astra 1D satelliteremains 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 itscommercial utility.
Payer saidSES has several options for replacing Astra 5A at 31.5 degrees east and willselect one in the coming weeks.
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