Final preparations are under way for the launch of a British-built spacecraft that will travel five billion miles to Mercury, the planet closest to the sun.
BepiColombo is due to blast off from the European spaceport at Kourou, French Guiana, at 2.45am UK time on Saturday October 20.
The four-tonne craft will be carried into space by a heavy lift Ariane 5, the European Space Agency’s most powerful rocket.
It will then immediately begin a complex journey that will take seven years.
At its destination, BepiColumbo will deploy two orbiters, one European and the other Japanese, to circle the planet for up to two years.
Scientists hope to unravel some of Mercury’s mysteries, such as the reason for its oversized iron core, its spectacular volcanic vents, and the possible existence of water ice in shadowy parts of its blazing hot surface.
The answers they get from the £1.4 billion mission are expected to shed new light on the origins and evolution of the solar system.
The spacecraft is fitted with futurist ion plasma engines, designed and built in the UK, which emit beams of electrically charged xenon gas.
It is the first time the technology has been used on a major interplanetary mission. Smaller craft have previously employed ion thrusters to reach asteroids and the moon.
The ion drive will be used not to accelerate the spacecraft but to act as a brake as it falls into the grip of the sun’s powerful gravity.
A complex series of fly-bys past the Earth, Venus and Mercury will further reduce its velocity.
Even so, BepiColumbo will reach a top speed of 60 kilometres (37 miles) per second.
The European Space Agency’s Mercury Planet Orbiter (MPO), which will survey the planet’s surface and probe its chemistry, was built by satellite company Airbus Defence and Space in Stevenage.
Airbus also constructed the power unit carrying the orbiters, the Mercury Transfer Module (MTM), in the UK. The ion thrusters were supplied by British defence technology company QinetiQ.
One of the European orbiter’s 11 instruments, the Mercury Imaging X-ray Spectrometer (Mixs) was designed and built at the University of Leicester.
The Japanese space agency Jaxa’s Mercury Magnetosphere Orbiter (MMO) will study the planet’s internal structure and enveloping magnetic field.
A major challenge 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, spinning.
Dr Graham Turnock, chief executive of the UK Space Agency, said: “UK scientists, engineers and technicians have played a vital role in developing BepiColombo and the incredibly sophisticated set of scientific instruments on board.
“The international collaboration involved in this mission shows how our leading role in the European Space Agency is ensuring the UK thrives in the new space age, bringing real benefits to UK companies and scientists.”
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, taking photos of the surface.
Dr Jerry Bolter, project manager at Airbus Defence and Space in Stevenage, said: “The scientists describe Messenger as the hors d’oeuvre and Bepi as
the main course.”
The spacecraft was named after the late Guiseppe “Bepi” Colombo, an Italian scientist and engineer who played a leading role in the 1974 Mariner 10 mission to Mercury.
Paolo Ferri, head of missions at the European Space Operations Centre (ESOC) in Darmstadt, Germany, said: “Mercury is a planet of extremes, and getting there requires some equally extreme techniques, navigation solutions and operations expertise.”
Justin Byrne, head of science and earth exploration systems at Airbus, said: “Mercury is extremely hot and it’s an extremely difficult place to get to because of the gravity of the sun.
“You could get to Mercury in a few months, but you’d shoot straight past it. The challenge is to get to Mercury and be captured in its orbit, and to do that you have to brake, brake, brake for years and years.”
The cycling ion engines, firing two at a time, contributed about half the braking power, he said. Planetary fly-bys around the Earth, Mercury and Venus provided the rest of the energy needed to slow the spacecraft down by about 7km (4.3 miles) per second.