India’s space agency last week launched a pair of European Space Agency satellites that will hopefully demonstrate high-precision formation flight techniques that make it possible to create “virtual satellites”.
The mission is called Proba-3 and its launch phase went so well that India’s space agency was able to show off video from its PSLV-XL rocket. The video included the mission's Passive Spring-Out Mechanism separation, state ignition and satellite separation.
The ESA welcomed the launch and promised that “After a short preparatory period the two satellites will be separated and injected into a safe relative tandem orbit.”
That’s when the real fun begins because Proba-3’s payloads – the Coronagraph and Occulter spacecraft - are designed to fly in formation with arc-second precision. Angles are measured in degrees, each of which can contain sixty minutes, and each minute has 60 seconds. These satellites are therefore required to maintain positions relative to each other that ensure their relative angles differ by tiny distances.
That precision is needed because the disk-shaped Occulter will fly between Coronagraph and the Sun. From Coronagraph, the Sun’s light won’t be visible, making it possible to observe Sol’s outermost layer, the corona.
From Earth, the corona is visible only during solar eclipses – and even then, not for very long.
If these two spacecraft can fly in the right formation, we should get more looks at the corona thanks to Coronagraph’s cameras and other instrumentation.
The duo will alternate between flying in tight formation for six hours before passively drifting to conserve fuel – demonstrating acquisition, rendezvous, proximity operations, formation flying, separation and convoy flying every orbit.
The satellites are an experiment hoped to prove the potential of future missions that see multiple spacecraft act a virtual observatory.
ESA believes successful formation flights will advance applications like Earth observation, satellite servicing, and scientific exploration. The mission will also test collision avoidance, proximity operations, and rendezvous techniques, which could inform Mars Sample Return missions and satellite de-orbiting efforts.
The ESA already has similar projects on the way, such as the planned 2035 launch of the Laser Interferometer Space Antenna (LISA), which will comprise three spacecraft flying in a triangular formation to detect gravitational waves produced by compact binary systems and mergers of supermassive black holes.
LISA is currently slated to launch aboard an Ariane 6 rocket.
While ESA missions have previously relied more on Arianespace rockets, ISRO's PSLV has proved a good option for the space agency – particularly amid recent delays with Ariane 6 and Vega-C. For Proba-3, PSLV offered both cost effectiveness and suitability for smaller payloads. ®