PARIS - A Russian telecommunications satellite in geostationary orbit failed March 29 following what its builder says was a "sudden external impact" of undetermined origin. The satellite, Express-AM11, is being moved into a graveyard orbit before on-board temperatures render it uncontrollable, the Russian Satellite Communications Co. (RSCC) announced March 30.

RSCC's Express-AM11 telecommunications spacecraft, launched in April 2004, is stationed at 96.5 degrees east longitude. The satellite, built by prime contractor NPO PM of Krasnoyarsk, Russia, with the electronics payload provided by Alcatel Alenia Space of France and Italy, carries 26 C-band and four Ku-band transponders. It was designed to operate for 12 years.

RSCC said communications traffic that has Russian government priority has been transferred to other RSCC spacecraft located at 80 degrees, 103 degrees and 140 degrees east longitude. The company said most commercial traffic also has been transferred to other spacecraft.

The failure occurred suddenly at 3:41 a.m. Moscow time March 29, RSCC said in its statement.

"According to the preliminary finding of NPO PM ... the telemetry information shows that due to a sudden external impact, an instantaneous depressurization of the thermal control system fluid circuit happened, followed by a sudden outburst of the heat-carrying agent. This resulted in ... spacecraft orientation loss and rotation."

One industry official said an external agent such as a micro-meteorite could have caused a sudden rupture of the satellite's thermal-control piping, which in a severe case could result in a loss of spacecraft control. But this official also said NPO PM could conclude that an external factor was the cause in the absence of any other explanation, and the absence of earlier signs of trouble on the spacecraft. While this conclusion would be reasonable, this official said it would not eliminate the possibility that a soldered thermal-control circuit broke for other reasons.

RSCC spokeswoman Elena Polischuk said March 30 that the rupture of the thermal-control lines means the satellite's temperatures cannot be controlled, and that it must be moved soon to avoid becoming a menace to the geostationary arc at 36,000 kilometers in altitude. RSCC ground teams currently have the satellite under control, Polischuk said.

"In order to prevent fatal consequences associated with space garbage formation ... which would result in the impossibility of using this orbital slot in future ... measures aimed at removing Express-AM11 from 96.5 degrees east into a disposal orbit have been taken," RSCC said.