PARIS — Intelsat has regained control of its runaway Galaxy 15 telecommunications satellite, which stopped responding to commands in April and had been drifting around the Earth along the principal orbital highway, and is guiding it to a test location to determine whether it can be returned to commercial service, Intelsat officials said.
What Intelsat and the satellite’s manufacturer, Orbital Sciences Corp., had predicted would occur did in fact occur, if several months later than expected: Galaxy 15’s ability to remain oriented toward the Earth gradually deteriorated; its solar arrays then lost contact with the sun, leading to the draining of its batteries and full system shutdown.
A full reset maneuver followed. Commands from the ground to return the satellite to sun-pointing orientation worked as designed, and as expected, Galaxy 15 was brought back to controlled status.
Dianne J. VanBeber, Intelsat’s vice president for investor relations and communications, said Jan. 7 that Galaxy 15 is being guided along the geostationary arc 36,000 kilometers above the equator at a speed of 0.3 degrees per day and will be subjected to several weeks of testing once it reaches 93 degrees west. The satellite is expected to arrive at that location around Jan. 15.
VanBeber said a board of inquiry that has been studying what happened to the satellite is expected to deliver its conclusions by the end of January. Already, Dulles, Va.-based Orbital Sciences and its current satellite customers have modified in-orbit satellites of a similar design, and retrofitted satellites under construction, to reduce the likelihood of a similar situation.
The special drama of Galaxy 15 was not in its size or financial value to Intelsat, but rather the fact that its telecommunications payload remained stuck in the “on” position, looking for signals to rebound back to Earth, as the satellite drifted from one occupied orbital slot to another. It passed through the orbital slots of about 15 satellites owned by operators including SES of Luxembourg, Telesat of Canada and Mexico’s Satmex.
The risk of a collision between Galaxy 15 and one of the satellites whose neighborhood it drifted into was never considered high as satellite operators know where their assets are and can move them to a corner of their orbital stations while waiting for Galaxy 15 to move out of the area.
But preventing signal interference, especially to C-band satellites in whose territory the C-band-equipped Galaxy 15 was moving, was a challenge. Washington- and Luxembourg-based Intelsat and the first competitor affected by Galaxy 15, SES, devised a strategy that permitted SES customers to continue sending signals, in part through the use of an Intelsat-owned ground antenna, to the SES spacecraft without drawing the attention of Galaxy 15.
Intelsat and Orbital had hoped Galaxy 15 would lose its Earth-pointing ability sometime in August. Instead, the satellite retained its orientation — demonstrating exceptional and, in this case, unwanted, resilience — until Dec. 17, when it lost its lock on Earth and its batteries started to drain, according to Tobias Nassif, Intelsat vice president for satellite operations and engineering.
That ended the interference problem. On Dec. 23, the full discharge was completed, ending an eight-and-a-half month ordeal.
Nassif said Intelsat remains confident that Galaxy 15 will be brought back to normal commercial service without any increased risk of returning to rogue status. He said Intelsat and Orbital have tested the reset maneuver on the ground since April and have concluded that switching on the satellite will not trigger a repeat of a loss of control. Launched in October 2005 on a planned 15-year mission, the satellite has enough on-board fuel remaining that Intelsat and Orbital Sciences will try to recover its full functions.
There are more than 100 retired or defective satellites performing a slow seesaw drift in geostationary orbit. These dead satellites are nuisances, but operators of active satellites know where they are and how to avoid them when they enter the orbital neighborhood of an active spacecraft.