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Proba-3 becomes two: Satellites successfully separate

Last night, a crucial step in the European Space Agency's eclipse-making Proba-3 mission was completed: the two spacecraft, flying jointly since launch, have successfully separated. This leaves them ready to begin their cosmic dance in the world's first-ever precision formation-flying mission.

The two Proba-3 platforms remained attached together for six weeks following their 5 December 2024 launch on a four-stage PSLV-XL rocket from Satish Dhawan Space Center in Sriharikota, India.

The mission control team at ESA's European Space Security and Education Center in Redu, Belgium managed the initial in-orbit commissioning during this stage. The team uses four ground antennas in Australia, Chile and Spain to communicate with the spacecraft.

Last night, 14 January, at 23:00 GMT (15 January 00:00 CET), the pair successfully separated from each other while flying 60,000 km above Earth at a speed of 1 km per second.

Proba-3 mission manager Damien Galano describes the critical milestone: "The separation relied on a well-known technology, routinely used when a spacecraft separates from its launcher. The two Proba-3 spacecraft were held together by a clamp-band, which is essentially a belt tightened around two metal rings, each attached to one spacecraft. Once the clamp was released, the two satellites started slowly drifting away from each other."

Although the clamp-band technology is not new, performing this kind of separation at spacecraft level—as opposed to the spacecraft/launcher separation—is uncommon, as not many satellites are launched while attached together in this way.

"Now, the two platforms will drift up to 50 km away from each other. Over the coming week, we will determine their relative positions, then use their propulsion systems to stop this drift and bring them back into a stable, safe configuration," Damien adds.

In their most precise formation, scheduled to be achieved initially in about two months' time, the two Proba-3 spacecraft will be flying 150 m apart, the equivalent of one and a half football pitches, and will need to maintain their relative position down to a single millimeter, for up to six hours at a time. The distance will be maintained by a sophisticated set of propulsion and navigation systems working together using on-board autonomy.

The mission will demonstrate this level of precision by creating artificial solar eclipses in orbit. The Occulter satellite will cast a shadow onto the main optical instrument of the Coronagraph satellite, allowing it to study the elusive solar corona.

Multiple sensors, including a laser-based system, will ensure that the shadow of just 8 cm across created by the occulting disk will remain on the sensitive coronagraph instrument positioned 150 meters away. In this precise configuration, the two satellites will be mimicking a single, giant spacecraft.

As the next step following separation, the flight control team will now make sure all systems on both spacecraft are running smoothly in preparation for the operational phase of the mission, due to begin in March.