In a world first, ESA aims to launch a satellite project in 2017 where two spacecraft can move as one single object, achieving sub-millimetre precision, with a launch vehicle from India emerging as a possible choice.
The new European Space Agency (ESA) mission includes two satellites weighing approximately 340 kg and 200 kg to be launched in 2017.
Several launchers are being evaluated, including one from India and another from the US - and they will travel jointly attached together until they separate in a highly-eccentric orbit, The Scientific Information and News Service (SINC) in Spain reported.
Their nearest point, the perigee, will only be 600 km from Earth. Every time they pass through this zone they will be in free flight, but under well controlled trajectories.
"Proba-3 will be the first mission in which two spacecraft will fly through space as a single unit, pointing at selectable directions, and with sub-millimetre precision, in other words, relative position accuracy to within less than one millimetre," Salvador Llorente, director of the project in SENER, the first Spanish company to lead an ESA mission, said.
There have been very few formation satellite missions up to now, such as the Swedish Prisma project, and only in the near Earth environment and with a level of precision of tens of centimetres.
The operations associated with precise formation flight will take place on the most distant section of the orbit, the apogee, over 60,000 km away, as here the gravitational disturbances are minimised and do not complicate or make the manoeuvres too costly.
The formation technology will be tested and the planned tests will be conducted in this region of the orbit.
One of the relevant experiments including scientific application of Proba-3 will be blocking out the Sun with one of the craft in such a way that the other, 150 metre away, can examine the Sun's corona in unprecedented detail.
The first satellite, the blocker, will create an artificial solar eclipse in order to facilitate its companion satellite, the coronograh, in gathering the data.
A similar technique was already tried in 1975 on the Apollo-Soyuz mission.
"In any case, the primary objective of this mission is to validate the precision formation flight technology, and to be able to position both craft between 20 and 250 metres apart, yet always working together as if they formed a rigid structure," Llorente said.
Rendezvous tests, orbital approach manoeuvres between spacecraft in highly elliptical orbit, will also be performed and could be applied to missions to Mars.
