Preparations are underway for a groundbreaking space mission that will use satellites flying in close formation to simulate solar eclipses above Earth.
The European Space Agency’s (ESA) Proba-3 mission marks its first foray into precise formation flying. It involves two spacecraft orbiting Earth with a separation accuracy of less than a millimeter—the thickness of a human fingernail.
The mission is scheduled to launch from India’s Satish Dhawan Space Centre in Sriharikota at 4:08 PM local time (10:38 AM UK time) on Wednesday. After a four-month journey, the satellites will enter a highly elliptical orbit, ranging from 370 miles to over 37,000 miles above Earth.
“This is an experimental mission to showcase a novel concept and technology,” said Damien Galano, Proba project manager at ESA. “It’s highly challenging as the flight paths of both spacecraft must be precisely controlled.”
If successful, the lead spacecraft will cast a perfectly aligned shadow onto its companion, enabling the latter to study the sun’s corona—the outermost layer of its atmosphere. Traditionally, scientists observe the corona during natural solar eclipses, which offer limited and unpredictable observation windows.
The €200m (£166m) Proba-3 mission will produce up to 50 artificial solar eclipses annually, each lasting six hours. The lead spacecraft, equipped with a 1.4-meter-wide occulter disc, will block the sun’s glare as seen from its partner. Together, the pair will function as a 150-meter-long coronagraph, offering unprecedented insights into the corona.
The mission aims to solve the enduring mystery of why the corona is vastly hotter than the sun’s surface—over 1 million°C compared to 5,500°C. Improved understanding of the corona could enhance predictions of solar weather, including coronal mass ejections and solar storms, which can disrupt satellites, power grids, and communication systems on Earth.
The Proba-3 satellites will orbit Earth every 19.7 hours for two years, spending six hours per orbit in formation. Optical sensors, flashing LEDs, and precision lasers will maintain their alignment and distance. First data from the mission is expected by March 2025.
Formation flying could revolutionize space-based observatories, allowing multiple satellites to collaborate as a single, larger instrument. This approach could enable advanced studies of climate change, solar system objects, and distant exoplanets.
Dietmar Pilz, ESA’s director of technology, highlighted the potential for such innovations. “With precise satellite formations, we could assemble larger instruments made up of several spacecraft, overcoming payload size limitations of even the most powerful rockets.”
