CHENNAI: The Indian Space Research Orgaisation (ISRO) has successfully launched the European Space Agency’s (ESA) Proba-3 mission. The launch occurred as scheduled on Thursday from the Satish Dhawan Space Centre, Sriharikota, using the highly reliable PSLV-XL rocket. This was the world's first precision formation-flying mission.
The PSLV-XL (Polar Satellite Launch Vehicle-XL) executed the launch flawlessly, transporting the Proba-3 twin-satellite system into its intended highly elliptical orbit approximately 18 minutes after liftoff.
Proba-3 is a unique mission consisting of two spacecraft designed to fly in precise formation within millimetres. This cutting-edge capability will enable the mission’s primary scientific objective of creating artificial solar eclipses in space to study the Sun’s faint corona, the outermost layer of its atmosphere. By blocking the Sun’s fiery disk, Proba-3’s “Occulter” spacecraft will cast a shadow onto its companion “Coronagraph” spacecraft, allowing uninterrupted observation of the corona—an environment that is a million times fainter than the Sun itself.
“By lining up with the Sun, one spacecraft will cast a precisely controlled shadow onto another, to cover the Sun’s brilliant disc entirely, so that the million-times-fainter solar corona will become visible for sustained observation,” explained Damien Galano, Proba-3’s mission manager. “This will either work or it won’t. That is the challenge we have set ourselves.”
The twin satellites will be separated by 150 meters in orbit, and their precise alignment will allow continuous solar observation for up to six hours during each 19-hour orbit. The system’s accuracy—down to a single millimetre—is unparalleled and represents a breakthrough in satellite formation flying.
Proba-3 is not only a scientific mission but also a demonstration of next-generation space technologies. The mission incorporates a variety of advanced systems to achieve its precise formation flying. These include star trackers, GPS receivers, inter-satellite radio links, optical cameras, LEDs, and laser-based sensors.
“Following a comparable approach to terrestrial driverless cars, no single positioning system is sufficient by itself to achieve the necessary precision,” said ESA systems engineer Raphael Rougeot and added the mission combines a suite of absolute and relative positioning technologies.
During active formation flying, one spacecraft, the “Coronagraph,” will act as the leader, equipped with a hydrazine propulsion system. The “Occulter” spacecraft will follow, using cold gas thrusters to maintain its position. This coordination allows the pair to perform complex maneuvers such as resizing their separation distance and retargeting their orientation, mimicking the functionality of a single large spacecraft.The ability to create solar eclipses on demand will enable unprecedented solar studies. Proba-3’s instruments can observe closer to the Sun’s edge than any previous Earth- or space-based observatory, down to just 1.1 solar radii. Such observations are crucial for understanding the dynamics of the solar corona and its influence on space weather, which can have significant impacts on Earth’s technological infrastructure.
The mission also carries additional scientific payloads, including the Digital Absolute Radiometer (DARA), which will measure the Sun’s total energy output, known as total solar irradiance. This data is essential for understanding the energy input driving Earth’s climate.
“It is essential to keep track of total solar irradiance because it is the dominant energy input to the surface of the Earth,” said Wolfgang Finsterle, DARA’s Principal Investigator at the Physical Meteorological Observatory Davos. “Even the tiniest variations are hugely significant.”
Proba-3’s successful launch marks the first ESA mission to fly aboard an ISRO launcher since the Proba-1 mission in 2001. It is expected to operate for two years, with its fuel likely being the limiting factor. The mission will continue to test innovative formation flying techniques, which have broader applications for future multi-satellite missions. Following its operational life, the spacecraft will re-enter Earth’s atmosphere and burn up, ensuring no long-term orbital debris.
