ESA launches double satellite mission that aims to create man-made solar eclipses

A pair of European satellites launched into orbit from India on Thursday on the first mission to create artificial solar eclipses through precise formation flying in space.

Each fake eclipse should last six hours once operations begin next year. That's considerably longer than the few minutes of totality offered by a natural eclipse here on Earth, allowing for prolonged study of the Sun's corona, or outer atmosphere.

"We are a very, happy science team here" in India, Joe Zender, the mission scientist at European Space Agency (ESA), said via email.

Billed as a tech demo, the two satellites will separate in a month or so and fly 150 m apart once reaching their destination high above Earth, lining up with the Sun so that one spacecraft casts a shadow on the other.

This will require extreme precision, within just 1 mm, equivalent to a fingernail's thickness, according to ESA.

To maintain their position, the satellites will rely on GPS, star trackers, lasers, and radio links, flying autonomously.

Each cube-shaped spacecraft is less than 1.5 m across. The shadow-casting satellite holds a disk to block the sun from the telescope on the other satellite.

This disk will mimic the Moon in a natural total solar eclipse, with the darkened satellite posing as Earth.

Studying the Sun's corona

"This has a huge scientific relevance in addition to testing high-precision formation flying," said ESA's technology and engineering director Dietmar Pilz.

Scientists need the glaring face of the Sun completely blocked in order to scrutinise the wispy crown-like corona encircling it, getting an especially good look close to the solar rim on this mission.

They're particularly interested to learn why the corona is hotter than the surface of the Sun, and also want to better understand coronal mass ejections, eruptions of billions of tons of plasma with magnetic fields out into space.

The resulting geomagnetic storms can disrupt power and communication on Earth and in orbit. Such outbursts can also produce stunning auroras in unexpected places.

With a lopsided orbit stretching from 600 km to 60,000 km away, the satellites will take nearly 20 hours to circle the world.

Six of those hours - at the farther end of certain orbits - will be spent generating an eclipse. Other orbits will be strictly for formation flying experiments, according to ESA.

2-year operation

The first eclipse results should be available in March, following checkout of both craft.

Zender said eclipses will be created at least twice a week, with six hours of totality each time for corona observations.

The frequency will depend on solar activity, he noted, and prove a boon for scientists who now must travel across the world for a mere three to five minutes of totality during the occasional eclipse.

The $210 million (€199 million) mission, dubbed Proba-3, is aiming for at least 1,000 hours of "on demand" totality during its two-year operation.

Once their job is done, both satellites will gradually drop lower until they burn up in the atmosphere, likely within five years.

Liftoff was delayed a day by a last-minute issue with the backup propulsion system of one of the satellites, crucial for precision formation flying.

ESA said engineers relied on a computer software fix.