AMSAT-OSCAR 40 mission patch. Photo: AMSAT

A team of volunteer satellite engineers is working to restore contact with an amateur radio satellite that has been silent since an attempted maneuver last week.

Telemetry transmissions from the AMSAT-OSCAR 40 (AO-40) spacecraft were lost December 13 while work was in progress on a 400-newton thruster on the spacecraft. Controllers had hoped to reestablish contact with the spacecraft last Saturday, when software on the spacecraft was supposed to trigger emergency measures, but AO-40 remained silent.

Because contact with AO-40 was lost during work with the thruster, there were concerns that a catastrophic explosion destroyed the spacecraft. Those concerns eased earlier this week, however, when radar sweeps conducted by NORAD found no evidence of debris that would have been left behind by an explosion. "This should end speculation of an explosion as NORAD found only one object with a radar cross section that was consistent with a satellite the size of AO-40," said a statement issued by satellite operators Monday.

While the 400-N thruster may not have destroyed the spacecraft, past problems with the thruster suggest it may be connected to the communications problems. The thruster was scheduled to fire for the first time on Monday, December 11, in a maneuver to adjust the spacecraft's elliptical orbit. The thruster did not fire, however, because of a software problem that failed to pressurize helium tanks needed to open propellant valves.

The pressurization problem was corrected later in the day and the thruster finally fired late on the 11th. However, the engine did not shut down at the proper time, but instead continued to fire for almost three extra minutes. An investigation into why the engine did not shut down as intended was underway when contact was lost with AO-40.

AO-40, originally known as Phase 3D, is a project of AMSAT-NA, the Radio Amateur Satellite Corporation of North America, and its German counterpart, AMSAT-DL, to build the largest and most powerful amateur radio satellite ever. The spacecraft carries a number of receivers and transmitters designed to facilitate communications by amateur radio operators worldwide, as well as a cosmic ray experiment, a pair of cameras, and a GPS receiver. The spacecraft was built by an international team of volunteers and paid for with several million dollars in donations.

After years of work, as well as several years of launch delays, AO-40 made it into orbit last month as a secondary payload on the Ariane 5 booster that launched the PAS-1R communications satellite and the STRV-1C and STRV-1D British military research spacecraft. Initially placed in a geosynchronous transfer orbit, AO-40 will maneuver into a Molniya-like elliptical, inclined orbit ranging between 4,000 and 47,000 km, phased to maximize coverage over North America, Western Europe, and Japan. Those maneuvers require the use of the spacecraft's 400-N thruster as well as a separate electric propulsion system.

The volunteers working on AO-40 plan to continue their efforts to restore communications with the spacecraft. "Several options still remain to be investigated, and the control stations are still working to develop a positive sequence of events," Robin Haighton, president of AMSAT-NA, said in a report issued Monday by the American Radio Relay League.