As the world looks forward to the next total solar eclipse, scientists are already preparing for a unique type of eclipse—an "artificial" one. Here’s what that means and why it’s capturing attention. The European Space Agency (ESA) has been working on the Proba-3 (short for 'Project for OnBoard Autonomy") mission for over 14 years. This long-term project has been carefully planned and developed, showcasing years of dedication and advanced scientific efforts. The Proba-3 mission is scheduled for launch on December 4, 2024, at 4:08 PM IST. It will take off from the Satish Dhawan Space Centre (SDSC) in Sriharikota using ISRO's PSLV-XL rocket which is equipped with additional boosters for enhanced thrust. This mission aims to study the Sun’s corona, the faint and dim outer layer of the sun’s atmosphere, by detecting its tiny, subtle features more effectively.
The Proba-3 mission includes two separate, three-axis stabilized spacecraft: the Coronagraph Spacecraft (CSC) ,Weighing 340 kgs and the Occulter Spacecraft (OSC), Weighing 200 Kgs. These spacecraft will travel close to each other in a highly elliptical orbit around Earth. At the nearest point, known as the perigee, they will be about 600 kilometers above Earth, while at the farthest point, called the apogee, they will reach up to 60,530 kilometers. The orbit will have a 59-degree inclination, meaning it is tilted at a 59-degree angle compared to Earth’s equator.
In this type of orbit, the spacecraft will take about 19.7 hours to complete one full circle around Earth.
“Proba-3 is a special mission involving two spacecraft that fly in perfect formation, maintaining a distance of just 150 meters between them in orbit. The "Occulter" is designed to block the Sun's bright disc, using a 1.4-meter-wide occulting disk aligned perpendicular to the Sun’s light, creating an artificial solar eclipse. This disk will create a shadow approximately 8 cm wide at a distance of 150 meters,” explained space expert Girish Linganna.
The second spacecraft, called the "Coronagraph", is designed to study the Sun’s corona in detail. The corona, which is the Sun’s faint outer layer, is typically visible only during a total solar eclipse. The Coronagraph Spacecraft (CSC) is equipped with a scientific telescope that has a 5 cm aperture.
“A natural solar eclipse lets scientists study the Sun’s corona for about 10 minutes, and there are usually 1-2 such eclipses each year. In contrast, Proba-3 will provide six hours of observation time, equal to the coverage of 50 natural eclipses in a year. This extended viewing will give researchers a much better understanding of the Sun’s corona than ever before,” added Linganna.
Experts point out that the Sun's corona is surprisingly over a million degrees hotter than its surface, even though it's farther from the core. This strange temperature difference has puzzled scientists for years and is still being studied.
Scientists are working hard to understand the Sun’s corona, not just to learn more about the Sun itself, but also because it’s where solar weather, like solar storms and eruptions, begins. These events, such as coronal mass ejections, can send powerful bursts of energy into space. When they reach Earth, they can disrupt satellites, mess with communication systems, and even cause power outages. Understanding the corona helps us prepare for and protect against these effects.
One of the most exciting aspects of the Proba-3 mission is its potential to transform the way we study space weather. “The Sun’s corona is the source of solar winds and coronal mass ejections, which can have significant effects on Earth’s magnetic field and the operation of satellites. Proba-3’s ability to study the Sun’s atmosphere in such detail will provide valuable insights into these phenomena and help scientists better understand space weather and its impact on Earth. This knowledge will be critical for protecting space-based infrastructure and ensuring the safety of future space missions,” remarked Srimathy Kesan, founder and CEO of Space Kidz India.
Furthermore, the mission will have important implications for the future of space exploration. The formation-flying technologies demonstrated by Proba-3 could be applied to a wide range of missions, from Earth observation satellites to interplanetary exploration. “By enabling multiple satellites to work together in close formation, Proba-3 opens the possibility of building larger, more powerful space telescopes, conducting more detailed Earth observations, and performing complex in-orbit servicing tasks, such as satellite repairs and de-orbiting. The ability to operate multiple satellites as a single cohesive unit will unlock new possibilities for both scientific research and commercial applications in space,” added Kesan.
The mission is planned to run for two years. After the mission ends, the satellites' orbit will gradually shrink because of the gravitational pull from the Sun and Moon. This will cause the satellites to naturally re-enter Earth’s atmosphere about five years after launch, following ESA's Zero Debris policy. The Proba-3 mission is backed by 13 ESA member countries.
Spain contributes the most, covering 38 percent of the funding, followed by Belgium at 34 percent. Poland and Romania each contribute around 4 percent, while Austria, Luxembourg, Switzerland, and the UK each provide about 3 percent. The mission’s total budget under ESA’s General Support Technology Programme (GSTP) is Euros 200 million which includes the launch, operations and ground stations, science payload development and operations and the procurement of two spacecraft and development of formation-flying technologies.
India's PSLV-XL rocket was selected because it can handle the weight of the Proba-3 satellites (550 kg) and place them into their highly elliptical orbit. “ESA's Vega-C rocket doesn’t have enough power for this mission, while using the Ariane-6 rocket would be too expensive for a budget-friendly technology demonstration. ESA has carried out three Proba missions to date: Proba-1 in 2001, Proba-2 in 2009, and Proba-V in 2012. Proba-1 was launched as a secondary payload aboard India’s Polar Satellite Launch Vehicle (PSLV) from the Shriharikota launch site on October 22, 2001,” said Linganna.
Proba-3 is known as ESA’s technology demonstration mission. Indian solar physicists are likely to get exclusive access to the data from the Proba-3 mission. Some Indian scientists also worked with Belgian researchers to help design the mission’s scientific objectives.
Shortly after the launch, India plans to hold a meeting with ESA’s Proba-3 team to discuss ways to use data from both Proba-3 and Aditya L1, India’s first solar mission launched in 2023, for joint research. This collaboration will give Indian scientists a chance to contribute to new discoveries about the Sun.
