Amos-5 now a ‘zombie’ satellite
November 30, 2015
By Chris Forrester
Israel’s Amos-5 satellite went dark on November 21st with its owner Spacecom confirming last week that it could not communicate with the spacecraft. Spacecom said that it had attempted to re-connect with the satellite, at its 17 degrees East orbital location. Ground observation, via powerful telescopes, confirmed that the satellite was still at its nominal position.
The satellite was launched in December 2011, so was barely one-third into its operating life of some 15 years.
All satellites come – sooner or later – to an end-of-life. The normal situation is that the dying satellite maintains some on-board fuel so that ground engineers can use these final fuel supplies to boost it out of its normal geostationary orbit of 35,786 kms (22,236 miles) above the Equator. This final firing of the satellite’s thrusters is designed to lift the craft at least another 300 kms higher, and thus well out of the way of its orbiting neighbours.
Indeed, since 2002 it has been a formal requirement that geostationary satellites are lifted into a so-called ‘graveyard’ orbit.
But these rules cannot now be applied to Amos-5 which is slowly drifting as an uncontrollable “zombie” satellite. The problem is further compounded by the fact that the satellite will come extremely close to a number of near neighbours as its drifts away from 17 degrees East.
A similar situation occurred back in April 2010 when an Intelsat-owned craft (Galaxy-15) went wrong and would not listen to controls from its ground technicians. However, the Galaxy-15 was a true ‘zombie’ in that it continued transmitting. As it drifted from its official home of 133 degrees West it collected signals uplinked from the Earth and powerfully beamed them back to the ground.
As the drift continued it moved perilously close to a number of other satellites, including SES-owned AMC-11, each of which were deliberately moved out of the way. At one point it was said that the Zombie had come within 5 kms of AMC-11, which is significantly too close.
However, this particular story had a happy ending. By December 2010 the Galaxy-11’s on-board batteries had exhausted themselves and so the satellite – as they engineers had hoped – went into a safety mode, and had switched itself off, and in simple terms had re-booted its systems.
The technology worked, and the satellite again started ‘listening’ to its ground bosses. It was the perfect Christmas present, not just for Intelsat’s talented team but for the other worried and hard working engineers who could now start sleeping at night. Following in-orbit testing by October 2012 the errant satellite was back working at its proper home, of 133 degrees West.
Unfortunately, this solution is not likely for Amos-5. If, as it seems, the satellite is completely dead it will just continue to drift. And as it drifts through the Clarke Belt (named after Arthur C Clarke) the satellites in its path will just have to get out of its way – and use up precious fuel in the process.
But science – and physics – does provide an eventual solution. As the satellite drifts through space it will eventually reach a Lagrangian or Libration Point, where the gravitational pull of a large obit (ie the Earth) is counter-balanced by a powerful, but lower gravitational pull (ie the Moon). And while the satellite will suffer some movement it is out of harm’s way and the craft will stay indefinitely.