The European Space Agency (ESA) has announced the completion of two satellites that will mimic a total solar eclipse in space, part of a mission called Proba-3.
1. The Sun corona
During a total solar eclipse is the only time the Sun’s corona can be accurately studied, as the rest of the time the sun shines too bright and covers it. A million degrees warmer than the surface of the Sun beneath it, the corona is of interest both scientifically and practically, according to ESA. This is where solar wind and space weather form, along with violent ejections, known as coronal mass ejections, that drive space weather and solar storms, potentially impacting both satellites in orbit and terrestrial power and communications networks.
To see more of the corona, specialised telescopes on the ground and in orbit called coronagraphs can incorporate occulting disks – carefully engineered shields to cover the sun within their field of view, mimicking a solar eclipse. But their effectiveness is limited due to light diffraction and stray light spills over the edges of coronagraphs. The way to minimise this effect is to move the occulting disk much further apart from the observing coronagraph, but practical limits on the size of spacecraft have rendered that solution impractical for space until now.
2. Proba-3
ESA has completed the construction of two satellites – a Coronagraph and an Occulter, and is now testing them at a facility in Belgium. The two crafts will be deployed from India in September, the agency has announced at the Redwire Space facility in Kruibeke.
The Occulter will be orbiting 144 metres closer to the sun than the Coronagraph, thus casting a shadow over the Coronagraph, similarly to how the Moon casts a shadow on Earth during a naturally occurring solar eclipse. However, while totality only lasts a few minutes on Earth, Proba-3 will be able to recreate the same conditions for up to 6 hours at a time.
Achieving this will be extremely technical challenging however, because the tiniest bit of misalignment and it won’t work.
Dietmar Pilz, ESA Director of Technology, Engineering and Quality
“The two spacecraft will act as if they are one enormous 150-m long instrument”, said Dietmar Pilz, ESA Director of Technology, Engineering and Quality, explaining that even just a few millimetres of misalignment could compromise the mission. “The development process has been correspondingly long – undertaken by a consortium of smaller ESA Member States led by Spain and Belgium – so I am very pleased to see Proba-3 here today, being prepared for launch.”
Although the system is formed of two satellites, they will be functioning as a single rigid spacecraft due to the precise formation they are flying in. Besides the main objectives of studying the Sun’s corona, the mission will also give insight into the logistics and feasibility of precise formation flying. If successful, Proba-3 could pave the way for missions much larger than any single spacecraft, ESA says, such as giant in-orbit radio and optical interferometry arrays, while precise orbital rendezvous could make in-orbit satellite servicing possible, extending the lifetime of space infrastructure.
