Artist's conception of a Galileo satellite in orbit

Stranded Galileo satellites handed over to operator

The European Space Agency (Esa) has handed over the control of two Galileo satellites injected into a wrong orbit to the constellation’s control centre which has yet to figure out what to do with them.

Engineers at Esa’s Space Operations Centre (ESOC) in Darmstadt, Germany, were in charge of the launch and early orbit phase (LEOP), a critical period during which controllers have to establish contact with the satellites after their separation from the rocket and navigate them into the final orbit as well as turn on all the instruments aboard.

Usually lasting about a week, in the case of the two Galileo satellites, the LEOP phase extended to over a month as the Darmstadt experts faced unexpected complications due to a rocket malfunction which left the two spacecraft stranded in an incorrect orbit.

“After launch, we quickly discovered that one of each satellite’s pair of solar wings had not deployed correctly,” said Liviu Stefanov, Esa’s Spacecraft Operations Manager.

“At the same time, difficulties in receiving radio signals – indicated by unusually low power and instability – alerted us to the fact that the orbits could be incorrect. Basically, the ground stations were pointing to where we expected the satellites to be, and they weren’t there, so we weren’t getting good signals.”

Instead of a circular orbit at the altitude of about 23,500km, the faulty Fregat upper stage of the Soyuz launcher that lifted the two spacecraft from Europe’s cosmodrome in Kourou, inserted the satellites into an elliptical orbit with the farthest point at about 25,000km and the nearest only 13,000km away from Earth.

Due to the significant difference between the lowest point of the ellipse and the required altitude, it was clear raising the orbit using the satellites’ on-board fuel won’t be an option.

Morever, the inclination of the orbit towards the equator was different from the one required.

The Esa team, working around the clock in close cooperation with Galileo project engineers and the satellite builder, managed to deploy the satellites’ solar panels and established proper contact.

“Each satellite had to be manoeuvred separately into an orientation where the undeployed panel was facing the Sun because we realised that one cause was linked to the low temperature of the release mechanism,” said Flight Operations Director Hervé Côme.

“It all required developing, validating and rehearsing new flight operation procedures ‘on the fly’.”

Esa handed control of the two spacecraft to the Galileo control centre in Oberpfaffenhofen at the end of last month, saying they were in excellent condition.

It has not yet been said whether there will be any use of the two spacecraft, the first two Full Operating Capability satellites of the Galileo constellation to have been launched, for the originally intended purposes.

Galileo is a joint venture between the European Union and Esa to create Europe’s own global navigation satellite system. Unlike US GPS, Galileo will serve entirely civilian purposes and offer improved precision. The project has been marred by organisational problems, delays and budget overruns since its inception.

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