Today, a pair of spacecraft were launched together from India, and they can potentially change the nature of future space missions. ESA’s twin Proba-3 platforms will perform precise formation flying down to a single millimetre, as if they were one single giant spacecraft. To demonstrate their degree of control, the pair will produce artificial solar eclipses in orbit, giving prolonged views of the sun’s ghostly surrounding atmosphere, the corona. 

Fourteen ESA Member States, including Canada, came together on this mission, set to demonstrate game-changing European technology in the areas of autonomous operations and precision manoeuvring by delivering never-before-seen scientific results. 

Proba-3 lifted off on a four-stage PSLV-XL rocket from Satish Dhawan Space Centre in Sriharikota, India, on Thursday, 5 December, at 11:34 CET (10:34 GMT, 16:04 local time). Stacked together, the two satellites separated from their upper stage about 18 minutes after launch. 

The pair will remain attached together while initial commissioning takes place, overseen by mission control at the European Space Security and Education Centre, ESEC, in Redu, Belgium. 

Dietmar Pilz, ESA Director of Technology, Engineering, and Quality notes, “Proba-3 has been many years in the making, supported through ESA’s General Support Technology Programme fostering novel technologies for space. It is an exciting feeling to see this challenging enterprise enter orbit.” 

Proba-3 mission manager Damien Galano adds, “Today’s liftoff has been something all of us in ESA’s Proba-3 team and our industrial and scientific partners have been looking forward to for a long time. I’m grateful to ISRO for this picture-perfect ascent to orbit. Now the hard work really begins, because to achieve Proba-3’s mission goals, the two satellites need to achieve positioning accuracy down to the thickness of the average fingernail while positioned one and a half football pitches apart.” 

“We are honored that ESA entrusted NewSpace India Limited, NSIL, with its Proba-3 mission, and we are extremely satisfied to have delivered the satellites precisely into their designated orbit,” remarked Radhakrishnan Durairaj, Chairman and Managing Director of NSIL. “This is an extremely ambitious mission, with an ambitious orbit to go with it: the satellites have been placed into a highly elliptical orbit that extends more than 60,500 km from the surface of Earth. Reaching this orbit required the most powerful PSLV-XL variant of our launcher, equipped with additional propellant in its six solid rocket boosters.” 

Up around the top of their orbits, the Proba-3 Occulter spacecraft will cast a precisely controlled shadow onto the Coronagraph spacecraft around 150 m away to produce solar eclipses on demand for six hours at a time. 

“There was simply no other way of reaching the optical performance Proba-3 requires than by having its occulting disc fly on a separate, carefully controlled spacecraft,” explains ESA’s Proba-3 mission scientist Joe Zender. “Any closer and unwanted stray light would spill over the edges of the disc, limiting our close-up views of the sun’s surrounding corona.” 

“Despite its faintness, the solar corona is an important element of our Solar System, larger in expanse than the Sun itself, and the source of space weather and the solar wind,” explains Andrei Zhukov of the Royal Observatory of Belgium, Principal Investigator for Proba-3’s ASPIICS (Association of Spacecraft for Polarimetry and Imaging Investigation of the Corona of the Sun) coronagraph. 

“At the moment we can image the Sun in extreme ultraviolet to image the solar disc and the low corona, while using Earth- and space-based coronagraphs to monitor the high corona. That leaves a significant observing gap, from about three solar radii down to 1.1 solar radii, that Proba-3 will be able to fill. This will make it possible, for example, to follow the evolution of the colossal solar explosions called Coronal Mass Ejections as they rise from the solar surface and the outward acceleration of the solar wind.” 

ESA Director General Josef Aschbacher commented, “Proba-3’s coronal observations will take place as part of a larger in-orbit demonstration of precise formation flying. The best way to prove this new European technology works as intended is to produce novel scientific data that nobody has ever seen before. 

“It is not practical today to fly a single 150-m long spacecraft in orbit, but if Proba-3 can indeed achieve an equivalent performance using two small spacecraft, the mission will open up new ways of working in space for the future. Imagine multiple small platforms working together as one to form far-seeing virtual telescopes or arrays.” 

If Proba-3’s initial commissioning phase goes to plan then the spacecraft pair will be separated early in the new year to begin their individual check-outs. The operational phase of the mission, including the first observations of the corona through active formation flying, should begin in about four months. 

Proba-3 was led for ESA by Sener in Spain, overseeing a consortium of 14 ESA Member States and Canada Defence and Space in Spain manufacturing the spacecraft and Redwire Space in Belgium responsible for the spacecraft avionics, assembly and operations. CSL in Belgium produced Proba-3’s ASPIICS coronagraph Spacebel in Belgium developed the onboard and ground segment software with GMV being responsible for the formation flying system and flight dynamics.