This pair of satellites is going to create an artificial solar eclipse

Proba-3 spacecraft aligned above Earth ESA - P. Carril

Early tomorrow morning will see the launch of an unusual European space mission, Proba-3, which will take off from Satish Dhawan Space Centre in Sriharikota, India. The launch is scheduled for around 5:30 a.m ET on Wednesday, December 4, and will see a pair of spacecraft launch into orbit which will execute a highly precise maneuver to create an “artificial solar eclipse.”

The launch of the mission will be covered by India’s space agency, the Indian Space Research Organisation, and will also be available to stream on the European Space Agency (ESA)’s Web TV. You can watch using the link below, with coverage staring just after 5 a.m. ET (15:30 local time):

The pair of spacecraft are designed to study the sun’s corona, or the region immediately around the sun’s surface, but that comes with one big challenge: the sun is so bright that it blots out any details of the corona around it. To deal with this, one of the Proba-3 spacecraft will act as a coronagraph, meaning its job is to fly slightly in front of the other and blot out the light from the brightest part of the sun. Then the other spacecraft can take readings of the corona without the glare of the sun by using the shadow from its partner.

“ESA has flown formation flying missions before, but the distances involved have been measured in the tens of kilometers or more,” explained Damien Galano, Proba-3 mission manager. “Proba-3 is very different because our satellites will be flying just one and a half football fields away from each other during active formation flying. And their relative positions will be maintained precisely to just a single millimeter for six hours at a time.”

This method of blocking out the sun means that only certain orbits will work though. Many missions sit in low-Earth orbit, where objects like the International Space Station or the Hubble Space Telescope reside, but that wouldn’t work for Proba-3 because the strong pull of Earth’s gravity and fluctations in the atmosphere would upset the delicate positioning of the pair. Another option would be in a complex orbit around the sun called one of the Sun-Earth Lagrange Points, such as where the James Webb Space Telescope orbits, but this was too far away and too expensive for a small mission.

Instead, the pair will end up in an oval-shaped orbit, moving from just 370 miles altitude at its nearest to 37,000 miles at its furthest over each orbit of 19 hours and 36 minutes.  The spacecraft will line themselves up autonomously when they are in a good position to observe the sun, using positioning technologies like GPS, optical cameras, a laser link, and shadow position sensors to automatically move into the correct positions.

Though the spacecraft will collect science data, the main aim of the mission is to test out this new method for observing the sun. The pair will try a variety of formations over their two-year lifespan to test out different ways to observe the sun.