A British-built spacecraft fitted with Star Trek-style “impulse engines” is on its way to Mercury, the planet closest to the sun.
BepiColombo was blasted into space from the European space port at Kourou, French Guiana, at about 2.45am UK time on Saturday.
It was carried on top of an Ariane 5, the European Space Agency’s (ESA’s) most powerful rocket.
After a tense countdown in French the rocket rose slowly above a ball of orange flame and thundered into the sky before disappearing into cloud.
Now begins a complex journey for the spacecraft that will take seven years and cross five billion miles (8.5 kilometres) of space.
Following the “escape trajectory” launch, BepiColombo will swing past the Earth in a wide curve before first heading for Venus.
In 2025 it will place two probes, one European the other Japanese, in orbit around Mercury, the least explored world in the solar system.
Speaking after the launch, Professor Gunther Hasinger, ESA’s director of science, said: “This is truly breathtaking. We have today written history.
“We have sent the most complex stack of spacecraft that ever have been conceived into space, and to a very long journey to an environment which is truly out of the Earth; truly out of this world.”
The Mercury Transfer Module (MTM), carrying the orbiters, was built in Stevenage by the Defence and Space division of aerospace company Airbus.
Key elements of ESAs Mercury Planet Orbiter were also assembled by Airbus in the UK.
Scientists hope the £1.4 billion mission will unravel some of Mercury’s many mysteries, such as the reason for its oversized iron core, its spectacular volcanic vents, and tantalising hints of water ice in shadowy parts of the scorching hot planet.
The answers they get will shed new light on the origins and evolution of the solar system.
A key feature of BepiColombo is that it is the first interplanetary mission to employ advanced electric ion propulsion technology.
Four Star Trek-style “impulse engines”, two firing at a time, will emit beams of electrically charged, or “ionised”, xenon gas.
They will be used not to accelerate the craft but to act as a brake against the sun’s enormous gravity.
A series of fly-bys past the Earth, Venus, and Mercury will also help to reduce BepiColombo’s velocity by 7km per second.
At top speed after launch, the spacecraft will be moving at 60km (37 miles) per second.
One of the biggest challenges for mission planners was ensuring the spacecraft could withstand searing temperatures of more than 350C so close to the sun.
Protective measures include a heat shield, novel ceramic and titanium insulation, ammonia-filled “heat pipes”, and in the case of the Japanese orbiter, “roast-on-a-spit” spinning.
A suite of 11 instruments on the MPO will map the surface of Mercury and probe its chemical composition for up to two years.
Meanwhile, the Japanese space agency Jaxa’s Mercury Magnetospheric Orbiter’s five instruments will focus on the planet’s unusual lopsided magnetic field.
One of BepiColombo’s main instruments, the Mercury Imaging X-ray Spectrometer (Mixs), was designed and built at the University of Leicester.
The ion thrusters were supplied by the UK defence technology company QinetiQ.
Only two spacecraft have previously visited Mercury. Nasa’s Mariner 10 flew past the planet three times in 1974-75 and the American space agency’s Messenger probe orbited Mercury from 2011 to 2015.
BepiColombo was named after the late Giuseppe “Bepi” Colombo, an Italian scientist and engineer who played a leading role in the 1974 Mariner 10 mission.