ESA’s groundbreaking Proba-3 mission has successfully initiated its formation-flying phase, with two spacecraft now set to maintain a precise distance of 150 meters in orbit. This precision will facilitate the creation of artificial solar eclipses, providing unprecedented views of the solar corona.
On January 14, the European Space Agency (ESA) achieved a major milestone in its Proba-3 mission, designed to create artificial solar eclipses. After flying together since their launch, the mission’s two spacecraft successfully separated, marking the beginning of the world’s first precision formation-flying mission.
The two Proba-3 spacecraft were launched on December 5, 2024, aboard a four-stage PSLV-XL rocket from the Satish Dhawan Space Centre in Sriharikota, India. They remained connected for six weeks following launch as part of their initial mission phase.
Achieving Separation
During this period, the mission control team at ESA’s European Space Security and Education Centre in Redu, Belgium, oversaw initial system checks and calibrations. To communicate with the spacecraft, the team relied on four ground stations located in Australia, Chile, and Spain.
The separation took place on January 14 at 23:00 GMT (January 15 at 00:00 CET) while the spacecraft were orbiting 60,000 kilometers above Earth, traveling at a speed of 1 kilometer per second.
The Next Steps in Space
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.
Precision Formation Flying
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 onboard 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 disc 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.
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