European scientists are preparing to launch a space mission designed to create total solar eclipses on demand.
The robotic spacecraft Proba-3 will be launched by the European Space Agency (Esa) in a few weeks in a mission that will involve several satellites flying around the Earth in close formation. They will be linked by lasers and light sensors, with one probe blocking the view of the sun as seen from the other craft. The effect will be to create solar eclipses that will last for several hours.
The observation of these eclipses will revolutionize the study of the sun and understanding how it can cause disruption to power lines, GPS satellites and other terrestrial technologies, says Esa. The agency believes the mission will also act as a pathfinder for other formation spaceflights that could transform studies of gravitational waves, exoplanets and black holes.
“This is an extraordinarily promising technology,” said solar physicist Francisco Diego of University College London. “It is also highly technically challenging. Getting it right won’t be easy, but it will be very rewarding.”
The mission, which took more than 10 years to plan, involves developing a series of complex sensors that will keep the two satellites locked in close proximity to each other with an accuracy of less than a millimeter as they orbit 150 meters apart around the Earth flies. In effect, the two probes will act as a single 150 m long observatory.
“When the two satellites are in exactly the right orbit, one will release a disk that will exactly cover the sun as seen from the second satellite and thus create eclipses that will last up to six hours a day,” Proba-3’s project manager , Damien Galano, joined the Observer.
On Earth, total solar eclipses occur when the moon passes before the sun, blocking out its blinding glare and leaving its fiery atmosphere – the corona – open for study by astronomers.
“Unfortunately, total solar eclipses occur on Earth every two years or so on average, and scientists often have to travel long distances and be at the mercy of the weather to study them – while observations can last only a few minutes,” added Diego . “It doesn’t offer much time to make detailed observations.” Likewise, appliances – mentioned coronagraphs – which simulate eclipses and which are fitted to telescopes, cannot observe the sun’s inner corona in detail.”
Scientists are particularly keen to study the sun’s inner corona because of its temperature. The sun’s surface is about 6,000 C, while the temperature of its corona is about 1 million degrees. “It’s a paradox,” said Andrei Zhukov, principal investigator for the corona experiment to be flown on Proba-3. “You would expect it to get colder as it goes further away from the sun, but that is not the case.”
By allowing scientists to create solar eclipses that last for hours, Proba-3 should generate the data that will solve this mystery. “We will be able to study the inner corona extensively and in detail and generate information that will explain why it is so hot while the sun’s surface underneath is relatively cool. This should give us a handle on understanding how the sun affects space weather,” added Diego.
This point was supported by Zhukov: “The sun is the source of disturbances in space weather, which can affect GPS navigation, power transmission and other technology. We need to understand how it does that.”
Improved understanding of the Sun’s corona will also be crucial in future space missions. Sometimes an event known as a coronal mass ejection occurs when the sun throws a large plume of plasma into space. When it hits Earth’s upper atmosphere, it produces auroras and can sometimes disrupt power transmission.
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“In general, we are protected by the atmosphere and the Van Allen radiation belts that surrounds the earth,” said Diego. “In deep space, however, there is no such protection against this radiation, and if we want to send men and women to the moon and Mars, we want to be able to understand and predict how the sun’s corona will take action and thus prevent our astronauts from being injured.”
However, Proba-3 should do more than revolutionize solar physics. As a trailblazer for the technology of flying probes in the making, it could form the core of a whole new approach to robotic spaceflight – using a few small satellites to mimic the operations of a single giant spacecraft, says astronomers.
“The techniques developed to operate Proba-3 can be exploited for many other astronomical missions, including groups of satellites that can study black holes, exoplanets, gravitational waves and many other phenomena,” Galano added. “This whole approach to spaceflight has a great deal of promise.”
