On December 5, the Indian Space Research Organization (ISRO) successfully launched the European Space Agency’s (ESA) Proba-3 mission. This innovative satellite system aims to create long-duration artificial solar eclipses, allowing scientists to explore the Sun’s corona in unprecedented detail.

Two satellites to study the corona

ESA has spent the past decade developing Proba-3. The system consists of two coordinated satellites: a coronagraph and an occulter. The coronagraph is an instrument designed to capture detailed images of the Sun’s faint outer atmosphere (the corona) while the occulter essentially acts as a “shield” that positions itself directly in front of the Sun to block its bright surface, creating an artificial solar eclipse and enabling the coronagraph to get a clear view of the corona without interference from the Sun’s glare.

Together, these satellites will provide new insights into the Sun’s corona and coronal mass ejections — powerful solar eruptions that can disrupt communications, navigation systems, and power grids on Earth.

The artificial eclipses created by the Proba-3 mission will not be visible from Earth. These eclipses occur in space between the two satellites, which will separate to around 150 meters away from each other.

Proba-3’s satellites must maintain formation with extreme precision — within a few millimeters. Remarkably, this will be achieved autonomously, without ground guidance. The two satellites effectively create a virtual giant observatory, capable of generating extended artificial eclipses.

Proba-3’s journey after the launch 

“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,” Andrei Zhukov, the Principal Investigator for Proba-3 coronagraph, said.

Proba-3 was launched aboard ISRO’s superstar rocket, the Polar Satellite Launch Vehicle (PSLV-XL) from the Satish Dhawan Space Center in Sriharikota, India. About 18 minutes after the successful launch, the twin satellite system separated from PSLV. 

The rocket has placed them in a highly elliptical orbit, where the satellite duo will maintain a maximum distance of 37,612 miles (60,530 kilometers) and a minimum distance of 373 miles (600 km) from Earth. Currently, the satellites are attached but will separate from each other in a month. 

A solar eclipse occurs when something blocks the Sun’s bright surface (photosphere), allowing scientists to study the Sun’s faint outer atmosphere, the corona in detail. However, while natural solar eclipses last for a few minutes, with Proba-3, scientists could study the corona for hours without interference from the Sun’s excessive brightness. That’s where the artificial solar eclipse comes in.

“Compared to a total eclipse [on Earth], each one of which lasts just a few minutes and occurs only around 60 times a century, Proba-3 will be able to study the corona for six hours in every 19hr 36min orbit, a factor of a hundred improvement in uninterrupted study time,” the ESA team said in a statement.

“As a world first, its two satellites — the Coronagraph spacecraft and the Occulter spacecraft — will maintain formation to a few millimeters and arc second precision at distances of around 150 meters for six hours at a time. In effect, the pair will be forming a virtual giant satellite. And this will be achieved autonomously, without relying on guidance from the ground,” the ESA team added.

Solving solar mysteries on a budget

One of the enduring solar puzzles is why the Sun’s corona, which reaches temperatures of over one million degrees Celsius (~1.8 million °F), is vastly hotter than the Sun’s surface at 5,500°C (~10,000°F). Proba-3’s extended observations could help solve this mystery and improve our understanding of space weather.

ESA achieved this groundbreaking mission for $210 million, significantly less than traditional solar missions, which can cost between $400 million and several billion dollars. By partnering with ISRO and using the cost-effective PSLV rocket, ESA combined reliability and affordability.

To realize Proba-3, ESA spent nearly $210 million. Generally, launching small and medium satellites to study the Sun costs somewhere between $400 million to billions of dollars. For instance, during the making and launch of the solar orbiter, ESA expended over half a billion (that was just ESA’s contribution, the total cost was ~$1.5 billion). 

However, this time ESA adopted several strategies to reduce its mission cost. For instance, they could have chosen SpaceX’s Falcon 9, but they opted for ISRO’s PSLV due to its significantly lower cost and impressive mission success rate of over 97 percent, making it one of the most reliable and economical options for satellite launches.

If successful, Proba-3 could pave the way for more budget-friendly, high-impact space missions in the future.