The European Space Agency's Proba-3 mission blasted off on a Indian rocket from a launchpad on the island of Sriharikota at around 4:04 pm (1034 GMT), an online broadcast showed.
Around 20 minutes later, the spacecraft separated from the rocket, which marked a successful launch and was met with applause by mission control in India, according to the ESA broadcast.
The mission's aim is to find out more about the Sun's corona, the outermost part of its atmosphere, which is not visible on Earth except during a total solar eclipse when the Moon blocks out the light.
The half-ton spacecraft, which has been deployed into Earth's orbit, holds two satellites that will separate from each other early next year.
They will then line up around 150 metres (500 feet) apart, so that one casts its shadow on the other.
In tandem, and without guidance from the ground, the solar-powered satellites will embark on an extremely elliptical 19-hour orbit, swinging out towards the Sun around 60,000 kilometres (37,000 miles) from Earth.
- No need for moon shadow -
One satellite has a 1.4-metre (five-foot) shield that will play the role of the Moon in blocking the Sun's light.
The other satellite will then be able to observe and measure the Sun's corona from the shadow.
While total eclipses on Earth last just minutes and only occur around 60 times a century, it is hoped that Proba-3 will manage to secure 10 to 12 hours of observations a week over two years, the ESA has said.
To achieve this feat, the two satellites will need to fly in formation at a level of precision never before seen in such a mission, according to the ESA.
"The two satellites need to achieve positioning accuracy down to the thickness of the average fingernail while positioned one and a half football pitches apart," ESA's Proba-3 project manager Damien Galano said in a statement.
The Sun's corona, which is several million kilometres thick, still remains little understood. Invisible to the naked eye and telescopes, it is normally hidden by the bright light coming from the Sun.
The biggest mystery is why the corona is so much hotter than the Sun's surface. It can clock in at up to two million degrees Celsius, while the Sun's surface is normally around 6,000C.
- Improving solar weather forecasts -
The corona is also where solar weather comes from, so another question Proba-3 will probe is why solar winds reach such tremendous speeds.
There are also coronal mass ejections, which are giant explosions of plasma and magnetic fields that can damage satellites and can cause other problems when they reach Earth.
Proba-3 project scientist Joe Zender told a press conference that better understanding the physics behind the corona "can improve our models -- and subsequently improve our forecasts for satellites and the impact on Earth" these solar storms will have.
The ESA hopes that future space missions or even commercial satellites will benefit from the high level of precision and delicate manoeuvres carried out by the 200-million-euro ($210-million) Proba-3 mission.
The Indian Space Research Organisation hailed the "proud moment" for India's space efforts in a post on X.
The ESA determined that the PSLV-C59 rocket was the "most economical solution" to launch Proba-3 into its specific orbit, said Dietmar Pilz, the space agency's director of technology, engineering and quality.
The ESA has struggled to launch its missions into space since Russia pulled out its rockets in 2022 over the war in Ukraine.
The Proba-3 launch had originally been planned for Wednesday, but was postponed by one day due to a technical issue, according to the ESA.
Another ESA mission was scheduled to launch later on Thursday after two days of delays.
The Earth-observing Sentinel-1C satellite was now expected to launch on Europe's lightweight Vega-C rocket at 1720 GMT from the European spaceport in Kourou, French Guiana.
It will be Vega-C's first launch since an engine failure in December 2022 resulted in the loss of two satellites.
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