Two European satellites launch on mission to blot out the Sun—for science

Two spacecraft developed by the European Space Agency launched on top of an Indian rocket Thursday, kicking off a mission to test novel formation flying technologies and observe a rarely-seen slice of the Sun’s ethereal corona.

ESA’s Proba-3 mission is purely experimental. The satellites are loaded with sophisticated sensors and ranging instruments to allow the two spacecraft to orbit the Earth in lockstep with one another. Proba-3 will attempt to achieve millimeter-scale precision, several orders of magnitude better than the requirements for a spacecraft closing in for docking at the International Space Station.

“In a nutshell, it’s an experiment in space to demonstrate a new concept, a new technology that is technically challenging,” said Damien Galano, Proba-3’s project manager.

The two Proba-3 satellites launched from India at 5:34 am EST (10:34 UTC) Thursday, riding a Polar Satellite Launch Vehicle (PSLV). The PSLV released Proba-3 into a stretched-out orbit with a low point approximately 356 miles (573 kilometers), a high point of 37,632 miles (60,563 kilometers), and an inclination of 59 degrees to the equator.

After initial checkouts, the two Proba-3 satellites, each smaller than a compact car, will separate from one another to begin their tech demo experiments early next year. The larger of the two satellites, known as the Coronagraph spacecraft, carries a suite of science instruments to image the Sun’s corona, or outer atmosphere. The smaller spacecraft, named Occulter, hosts navigation sensors and low-impulse thrusters to help it maneuver into position less than 500 feet (150 meters) from its Coronagraph companion.

From the point of view of the Coronagraph spacecraft, this is just the right distance for a 4.6-foot (1.4-meter) disk mounted to Proba-3’s Occulter spacecraft to obscure the surface of the Sun. The occultation will block the Sun’s blinding glare, and cast a shadow just 3 inches (8 centimeters) onto the Coronagraph satellite, revealing the wispy, super-heated gases that make up the solar corona.