Approximately every 18 months, the Moon perfectly coincides with our view of the Sun, obscuring the face of the luminary. Although a total solar eclipse lasts only a few minutes, it is an ideal opportunity for scientists to explore the outer part of the Sun’s atmosphere, known as the corona, which is usually hidden under the star’s light. The upcoming mission aims to recreate this natural event on a much more regular basis, with one spacecraft blocking the Sun for another.
The European Space Agency’s (ESA) Proba-3 satellite is preparing for launch on Wednesday at 5:38 a.m. CET. The two-satellite mission will launch from the Satish Dhawan Space Centre in Sriharikota, India, aboard a PSLV-XL rocket from the Indian Space Research Organization (ISRO). The launch will be broadcast live on ESA’s web TV, while ISRO’s broadcast will begin about 30 minutes before launch.
Why two satellites?
Although both satellites will launch together, the pair will separate approximately 18 minutes after launch to begin an extremely precise flight demonstration as part of an orbital constellation. The satellites will be placed in an extremely elliptical orbit around the Earth at a distance of 492 feet (150 meters) from each other. The satellites must maintain this distance to within one millimeter to complete the mission.
“Proba-3 is very different from the others in that our satellites will be flying at a distance of only one and a half football fields from each other during active flight in combat order. And their relative positioning will be maintained to within one millimeter for six hours at a time,” said Damien Galano, Proba-3 mission manager, in a statement.
The two spacecraft will form one giant virtual telescope, with one casting a precisely controlled shadow over the other, blocking the Sun’s light so that the other spacecraft, equipped with an optical instrument, can see the star’s corona.
The active flight of the mission will take place in the upper part of the orbit, at a distance of about 37,282 miles (60,000 kilometers) from Earth. At this distance, the Earth’s gravity will not have as much effect on the spacecraft, and less fuel will be needed to change their positions.
“Early simulations showed that we would need to make so many positioning adjustments with our engines that our fuel would quickly run out; the mission would be over in about half an hour!” said ESA’s Frederic Teston in a statement.
The spacecraft will complete one orbit around the Earth in 19 hours and 36 minutes, observing the corona during a six-hour window in each orbit. Proba-3’s elliptical orbit brings it within 372 miles (600 kilometers) of Earth, orbiting in an elongated loop to consume as little fuel as possible during maneuvers. Ideally, the mission would be located at one of the Sun-Earth Lagrange points, where the gravitational forces of the two bodies hold the object in place in orbit. But this would require a bigger budget, and according to ESA, Proba-3 is considered a low-budget mission.
Why are we studying the solar corona?
The corona is a million times fainter than the Sun. The outermost region of the Sun’s atmosphere extends millions of kilometers into space and hides the greatest mystery surrounding the star that is home to the Earth.
The sun’s corona heats up to 2 million degrees Fahrenheit (about 1 million degrees Celsius), which is about 200 times the temperature at the sun’s surface. The high temperatures of the corona are quite controversial, and astronomers are not sure how exactly the outer layers of the Sun heat up.
In addition to its mysteries, the solar corona also drives the solar wind and coronal mass ejections, two of the main components that determine space weather. Charged particles in the corona are blasted out into space and can sometimes affect satellites in orbit as well as communication systems on Earth.
What are Proba missions?
Proba missions are derived from the Latin word for “let’s try” and also stands for PRoject for OnBoard Autonomy. These low-cost, small satellite missions are designed to test new technologies and concepts in spaceflight.
So far, ESA has launched three more Proba missions, one of which is currently observing the Sun. Proba-2 was launched in 2009 and was originally supposed to spend two years in a low Earth orbit synchronous with the Sun, but has been in it for more than 15 years.
Similarly, Proba-3 has an expected lifespan of two years. The limiting factor for the mission is fuel, as the cold gas engines must make small pulses every 10 seconds during the satellites’ six-hour active phase of flight.
To demonstrate the technology, the team has high hopes for a pair of tiny spacecraft. “When I first heard about it, Proba-3 seemed like a science fiction technology,” said Andrey Zhukov, principal investigator of the main Proba-3 instrument, in a statement. “But the real design will really provide excellent scientific results.”
