ESA Mission tests precision formation flying - aces test

The European Space Agency today announced the results of a test of the precision flying ability of two satellites in their Proba-3 mission.  The test was conducted on May 8th. 

The European Space Agency's (ESA) Proba-3 mission, consisting of two spacecraft called the Occulter and the Coronagraph, flew in perfect formation at a distance of 150 meters (492 feet) from each other with millimeter precision, the agency announced in a May 8 statement.

The pair autonomously maintained their relative position for several hours thanks to a series of sensors, including the Fine Lateral and Longitudinal Sensor (FLLS) laser instrument, a shadow position sensor, and camera-based systems, in combination with onboard software and small cold gas thrusters.

Proba-3 project manager, Damien Galano, said , "we are talking about millimetric accuracy in range, and sub-millimetric in the lateral position," in the ESA statement.  

The Proba-3 mission consists of two satellites, the Occulter and Coronagraph using the Occulter to block the sun, mimicking a total solar eclipse.  That allows the Coronagraph to study the sun in a state only occasionally seen from Earth during total solar eclipses - except Proba-3's Coronagraph can observe the sun for up to six hours at a time.

Diagram of Europe's two Proba-3 formation-flying satellites in action. (Image credit: ESA-F. Zonno)

But the breakthrough in demonstrating such exquisite levels of formation flying may well have bigger implications for future science and space applications beyond studying the sun. The precision formation technology could be used for enhancing Earth observation, docking spacecraft, using an occulter and observatory to search for exoplanets, and space-based gravitational wave detection.

When I first heard of this mission, I assumed  it was launched on an Ariane 6 or some other ESA launch vehicle.  Instead, it was launched by an Indian PSLV rocket in December.  Proba-3 is in a rather eccentric orbit, with a perigee of 600 km and apogee of 60,000 km (both numbers approximate but close) or 373 to 37,300 miles.  A reason for the 100:1 difference in nearest to farthest (to Earth) points in the orbit, is that the effects of Earth's gravitational pull are smaller out at apogee, meaning formation flying can be maintained with less use of propellant.

It's probably worth pointing out that the pair isn't ready to "do science" now.  The remaining challenge is to get all of the payloads checked out and ready to set up the first man-made solar eclipse.