Proba-3: Twin spacecraft will launch to create an artificial solar eclipse

The European Space Agency (ESA) is aiming to create an artificial eclipse in space with its upcoming Proba-3 mission, which will help study the sun and demonstrate extremely precise formation flying, down to just a millimetre.

Scheduled to launch on an Indian PSLV-XL rocket on 4 December, the mission comprises two spacecraft. After launch, they will be placed into a highly elliptical orbit around Earth that comes as close as 600 kilometres to the planet, but as far as 60,000 kilometres from it.

One spacecraft, called the Occulter, is equipped with a 1.4-metre-wide disc made of carbon fibre and plastic. The other spacecraft will fly about 150 metres behind the first, pointing a camera towards it. From this vantage point, the Occulter’s disc will block out the surface of the sun, just as the moon appears to cover the sun during a total solar eclipse. This will allow the imaging craft to view the solar corona, the sun’s atmosphere, in unprecedented detail.

“It will be the closest to the sun we have observed the corona in visible light,” says Damien Galano, the mission manager for Proba-3 at ESA. “This can give us some specific information about the temperature of the corona, the creation of solar wind and how the corona expands into space.”

Proba-3 will achieve this feat by flying with incredible precision. Both spacecraft are laden with sensors to track their position in space and the Occulter will use 12 nitrogen thrusters to autonomously maintain position with its partner to a single millimetre in accuracy. The thrusters can eject just 10 millinewtons of thrust, 50 times less force than a human breath.

Each artificial eclipse will last 6 hours when the spacecraft are furthest from Earth, in order to limit the destabilising effect of Earth’s gravity. More than 1000 eclipses are planned during the two-year mission. Galano says it is the first artificial eclipse experiment in space since an effort on the Apollo-Soyuz Test Project in 1975.

The experience gained from the Proba-3 mission could also have applications in spacecraft refuelling, developing large telescopes in space and more. “Up until now, we’ve only been able to do a centimetre precision or more,” says Steve Buckley, the lead engineer for Proba-3 at US company Onsemi, which developed some of the sensors for the mission. “This is 10 times better.”