ESA has announced that one of the two satellites of the Galileo constellation launched on August 22, 2014 and ended up in the wrong orbit will be moved in the course of this month. A problem of the Fregat last stage of the rocket caused the insertion of the two satellites in an orbit very different from the planned one. If the corrective maneuvers will be satisfactory, they’ll be repeated for the other Galileo satellite in the same situation.

The analysis of the orbit of the two Galileo satellites, the European alternative to GPS, started a few hours after reaching orbit, didn’t leave many alternatives to ESA engineers. They were supposed to be nearly circular orbit at an altitude of 23,222 km, instead they’re elongated between 13,713 and 25,900 kilometers. Even the relative angle to the equator is different from the planned one.

The two satellites are in good health but their orbit causes some technical problems. Being elongated, it brings them into the Van Allen belts, where the level of radiation is much higher and this increases their wear. When their orbit brings them to the lowest point, the Earth appears so big as to render their sensors useless. The consequence is that they must rely only on their gyroscopes making the measurement of their position not precise enough.

Satellites have a limited amount of fuel, useful for making small orbit adjustments. Providing them with more fuel would increase costs a lot, also because it would make them larger and heavier so the cost of the launch would be higher and a more powerful rocket immediately increases the cost of millions.

The result is that the Galileo satellites don’t have enough fuel to move the planned orbit but this was clear almost from the moment the problem was discovered. It took a long time to implement a plan to recover the satellites because they have to be moved in an orbit useful and accessible with the available fuel.

The standard orbit of the Galileo satellites leads them to fly over the same area once every 10 days. If the corrective maneuvers have the desired success, the two satellites launched in August will fly over the same area once every 20 days. In this way, they can be kept synchronized with the rest of the constellation.

Over the course of two weeks, one of the two satellites will carry out 15 corrective maneuvers. Subsequently, test phase will start to verify that it works correctly and can do the job for which it was built. They cost a lot of money so being bale to use them would be a great result!

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