Newly-launched satellite beset by major problem
BY STEPHEN CLARK
Posted: February 6, 2008
The life of an African communications satellite will be drastically shortened after a helium leak forced engineers to use much of the craft's maneuvering propellant reserves to reach its final orbit.
Originally designed to last up to 15 years, officials say the Rascom-QAF 1 communications satellite may now only operate for about two-and-a-half years.
Ground controllers at Thales Alenia Space, the satellite's prime contractor, discovered the leak a few days after the spacecraft's launch in December. Gaseous helium is used to pressurize the satellite's boost propulsion system, which is designed to raise the craft's altitude from the transfer orbit to the geosynchronous belt.
Rascom-QAF 1, based on the Thales Spacebus 4000B3 platform, was deployed in an orbit stretching from a low point of about 364 miles to a high point of 22,291 miles. Its inclination was 5.49 degrees, according to Arianespace, the launch services provider.
The leak was found during the pressurization of the propulsion system before orbit-raising activities were scheduled to begin. Thales announced the temporary suspension of normal operations on Dec. 29.
Engineers devised a plan in early January to raise the craft's altitude to a circular orbit 22,300 miles high and reduce its inclination to zero degrees, where the satellite would match Earth's rotation and hover above the equator.
During four weeks of maneuvers, controllers gradually raised Rascom-QAF 1's altitude until it finally reached its geosynchronous orbit parking spot earlier this month at 2.85 degrees east longitude.
The sequence included a single firing of spacecraft's primary propulsion system, pressurized by the small quantity of remaining helium. The satellite's smaller station-keeping thrusters fired 18 times over the next few weeks to complete the job, according to a written statement.
"It is the first time in the space industry that a company succeeded in placing a satellite in its final (geosynchronous) orbit with such a process," said Florence Pontieux, Thales spokesperson.
The use of the station-keeping thrusters exhausted much of the craft's maneuvering propellant, reducing its expected lifetime by up to 13 years.
"We are currently analyzing all data available and determining the root cause of this failure," Pontieux said.
Pontieux said such a failure has never occurred on any earlier Thales-built satellite. Other Spacebus craft already in orbit are immune from such problems because helium is only used in the apogee boost engine for orbit-raising, she said.
Once a root cause is found, engineers will investigate the problem to see if other Spacebus satellites on the ground need any changes.
Rascom-QAF 1 is the world's first pan-African satellite, designed to beam telephone, Internet and direct-to-home television services to both rural and urban Africans at affordable costs. The craft is owned by RascomStar-QAF, founded by a consortium of African and European investors, including Thales.
"Rascom-QAF 1 will contribute to bridging the digital divide within Africa and between Africa and the world," said Faraj Elamari, CEO of RascomStar-QAF, shortly after the satellite's launch.
The company had been in preliminary talks to field a second spacecraft, but it is unclear if those plans will now be accelerated. Attempts to contact RascomStar-QAF officials about the failure were unsuccessful.
Pontieux said Thales regularly communicated with RascomStar-QAF in the past few weeks, and the company agreed with the control team's work to recover the satellite.