Preparations are nearing completion for an extraordinary space mission that will use satellites flying in perfect synchronization to simulate solar eclipses high above Earth. Known as the Proba-3 mission, this endeavor marks the European Space Agency’s (ESA) first attempt at precise formation flying in orbit. Two spacecraft will orbit the Earth with a precision margin of less than a millimeter, akin to the thickness of a fingernail.
The mission is set to launch from India’s Satish Dhawan Space Centre in Sriharikota on Wednesday at 4:08 PM local time (10:38 AM UK time). After a four-month journey, the satellites will enter an elongated orbit ranging from 370 miles to over 37,000 miles from Earth.
“This is a groundbreaking experiment to showcase a new concept and technology,” said Damien Galano, ESA’s Proba project manager. “The challenge lies in the meticulous control needed to maintain the two spacecraft’s exact flight paths.”
If successful, the satellites will align perfectly with the sun, enabling the lead spacecraft to cast a precise shadow onto its partner. This alignment will allow instruments on the second spacecraft to study the sun's corona, the outermost layer of its atmosphere.
Historically, scientists have relied on natural solar eclipses, when the moon blocks the sun, to observe the corona. However, these fleeting opportunities often require global travel and are limited by unpredictable weather.
The €200m (£166m) Proba-3 mission aims to revolutionize solar corona research by producing 50 artificial eclipses annually, each lasting six hours. The lead satellite will carry a 1.4-meter-wide occulter disc, which, when combined with its partner satellite, forms a 150-meter-long instrument called a coronagraph.
This mission is expected to unravel mysteries surrounding the corona, including why it is vastly hotter than the sun's surface—temperatures in the corona can exceed 1 million degrees Celsius, compared to 5,500 degrees on the sun’s surface. Better understanding of the corona could improve predictions of solar weather, such as coronal mass ejections and solar storms, which can disrupt satellites, power grids, and communication systems on Earth.
For the next two years, the Proba-3 spacecraft will complete an orbit every 19.7 hours. During six hours of each orbit, the satellites will utilize optical sensors, LEDs, and a precision laser system to maintain their exact alignment and distance. The first images from the mission are anticipated in March 2025.
ESA scientists also plan to test maneuvers for future missions, such as repairing malfunctioning satellites or removing space debris. Formation flying could pave the way for advanced space-based observatories and instruments, where multiple satellites collaborate in precise configurations.
“With precise formation flying, we could build larger instruments composed of multiple satellites,” said Dietmar Pilz, ESA’s director of technology. Such instruments could explore climate change, study objects within the solar system, and examine exoplanets around distant stars.
Despite advancements in rocket technology and payload capacity, Pilz noted, “There will always be a limit to what a single spacecraft can achieve. This mission shows a new path forward.”