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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