Approaching the end of the year on a high note, quite literally, another rocket took to the skies from the Indian soil. On December 5, 2024, the Polar Satellite Launch Vehicle (PSLVC59) of the Indian Space Research Organisation (ISRO), added another milestone to its record by successfully launching the European Space Agency’s (ESA) Proba-3 mission.

Launched from the First Launch Pad (FLP), Satish Dhawan Space Centre (SDSC-SHAR), Sriharikota, PSLV-C59/Proba-3 mission successfully achieved its launch objectives. PSLV-C59 vehicle carried Proba-3 spacecraft into a highly elliptical orbit as a dedicated commercial mission of NewSpace India Limited (NSIL), the commercial arm of ISRO. This marked a landmark moment for NSIL, the commercial arm of ISRO, as it solidified its position as a key player in global commercial satellite launches and reinforced PSLV’s reliability for complex orbital deliveries.

Proba-3 is an In-Orbit Demonstration (IOD) mission of ESA with the goal to demonstrate precise formation flying. A pair of satellites were flown together, maintaining a fixed configuration as if they were a single large rigid structure in space, to prove innovative formation flying and rendezvous technologies in space.

“PSLV-C59 has successfully soared into the skies, marking the commencement of a global mission led by NSIL, with ISRO’s technical expertise, to deploy ESA’s groundbreaking Proba-3 satellites. A proud moment celebrating the synergy of international collaboration and India’s space achievements,” ISRO said in its social media post.

ISRO Chairman S. Somanath, speaking from the control room after the successful launch, said, “The PSLV C59 Proba-3 mission is successfully accomplished. The spacecraft has been placed in the right orbit, which is a very highly elliptical orbit for almost 600 km perigees, which is the closest point to Earth, and 60,000 km at its apogee, the farthest point, and an inclination of 59 degrees has been precisely achieved by PSLV in its 61st mission.

Proba-3 lifted off on a four-stage PSLV-XL rocket from India. 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 from mission control at the European Space Security and Education Centre, ESEC, in Redu, Belgium.

THE PROBA-3 MISSION: A REVOLUTION IN FORMATION FLYING

Proba-3 is ESA’s first precision formation-flying mission and a global first in demonstrating the potential of two satellites working as one. The mission consists of two spacecraft—the Coronagraph Spacecraft (CSC) and the Occulter Spacecraft (OSC)—designed to fly in tandem 150 meters apart. Together, they form a single large virtual structure capable of producing artificial solar eclipses in orbit. This enables the CSC to observe the Sun’s faint corona, the outermost part of the solar atmosphere, in unprecedented detail. The mission addresses critical gaps in solar observation, tracking phenomena such as Coronal Mass Ejections and the acceleration of the solar wind.

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. The OSC and the CSC, align precisely to cast a shadow that blocks the Sun’s bright disk, enabling unobstructed observation of the solar corona. Without this perfect alignment, the Sun’s light would overwhelm instruments, obscuring corona studies.

Proba-3 mission manager Damien Galano adds, “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.”

The Proba-3 mission is ESA’s first precision formationflying mission and a global first in demonstrating the potential of two satellites working as one

Proba-3 will function as an orbital laboratory, demonstrating acquisition, rendezvous, proximity operations and formation flying, while validating innovative metrology sensors and control algorithms, opening up novel methods of mission control. The two satellites will adopt a fixed configuration in space, 150m apart while lined up with the Sun so that OSC blocks out the brilliant solar disk for the CSC. This will open up continuous views of the Sun’s faint corona, or surrounding atmosphere, for scientific observation. Basically, Proba-3 employs the two satellites to create artificial solar eclipses for six hours at a time. This configuration blocks the Sun’s disk to allow close-up observations of the faint solar corona, addressing a significant observational gap.

The satellites operate at a high altitude of over 60,000 km to minimise perturbing forces like Earth’s gravity and atmospheric drag, reducing the propellant needed for formation maintenance. The solar corona holds critical insights into solar weather phenomena like coronal mass ejections. Proba-3’s ability to create extended eclipses over six hours per orbit fills a crucial observational gap, offering unprecedented views of this enigmatic region, which previously required rare and brief total solar eclipses for study.

The mission’s innovative design, involving millimetric precision in formation flying, allows continuous observation of the inner corona, enabling breakthroughs in understanding solar dynamics and improving our ability to monitor and predict space weather events.

“We are honoured that ESA entrusted 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 which 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.”

Led by Sener in Spain and involving 14 ESA Member States and Canada, Proba-3 leverages ESA’s General Support Technology Programme to integrate cutting-edge technologies, supported by Airbus Defence and Space, Redwire Space, and other key European players. The mission is expected to separate the spacecraft for individual testing early next year, with operational observations commencing in four months.

This novel approach of this mission has significant implications for the future of space missions, including the possibility of deploying constellations of small satellites to create virtual telescopes or advanced sensors.

INDIAN-EUROPEAN COLLABORATION

The Proba-3 mission exemplifies international collaboration in space technology. NSIL’s partnership with ESA brought together 14 European countries and Canada, with each contributing expertise to the spacecraft’s design and operations. The mission’s success underscores India’s growing capability in commercial satellite launches and its contribution to global space science. Prior to this, ESA had even launched the Proba-1 mission as well on ISRO’s PSLV in 2001.

India’s PSLV-XL launcher was chosen since the lift required to place the combined Proba-3 satellites (550 kg) on their desired highly elliptical orbit is above the capability of ESA’s Vega-C launcher, while Ariane-6 would be too costly for a tightly-budgeted technology demonstration mission.

With Proba-3, both India and Europe have taken a significant step toward redefining what’s possible in orbit. This mission not only strengthens India’s reputation in the global launch market but also sets the stage for future innovation in precision space operations.

“The Proba-3 was important for us because this is a mission, which is looking at the heliophysics and we have a strong science group within the country who have collaboration with the scientists in ESA. We have a solar mission Aditya L1, which is working along with this satellite and we will give a fantastic science outcome in the days to come,” said the ISRO Chairman.

TECHNOLOGICAL INNOVATIONS

Proba-3 represents a confluence of cutting-edge technologies:

• Formation Flying: The mission is a testbed for advanced rendezvous and proximity operations, with positioning accuracy at millimeter levels.
• Solar Observation: The mission’s ASPIICS coronagraph, developed by Belgium’s Royal Observatory, fills observational gaps between 1.1 and 3 solar radii. This data is crucial for understanding solar phenomena that affect space weather
• Autonomous Operations: Proba-3’s onboard systems, developed by Redwire Space and GMV, allow for real-time adjustments, a step forward in autonomous satellite operation.

Proba-3 paves the way for innovative satellite missions, proving that complex scientific goals can be achieved through smaller, collaborative platforms.