European space agency will use four larger ion thrusters

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The European Space Agency has a flagship mission to Mercury powered by ion drives. BepiColombo will provide the best understanding of Mercury to date. It consists of two individual orbiters: the Mercury Planetary Orbiter (MPO) to map the planet, and the Mercury Magnetospheric Orbiter (MMO) to investigate its magnetosphere.

BepiColombo mission is based on two spacecraft:

  • a Mercury Planetary Orbiter (MPO); and
  • a Mercury Magnetospheric Orbiter (MMO)

BepiColombo Mercury Transfer Module

Among several investigations, BepiColombo will make a complete map of Mercury at different wavelengths. It will chart the planet’s mineralogy and elemental composition, determine whether the interior of the planet is molten or not, and investigate the extent and origin of Mercury’s magnetic field.

Only NASA’s Mariner 10 and Messenger have visited Mercury so far. Mariner 10 provided the first-ever close-up images of the planet when it flew past three times in 1974-1975. En route to its final destination in orbit around Mercury in 18 March 2011, Messenger flew past the planet 3 times (14 January 2008, 6 October 2008, and 29 September 2009), providing new data and images. Once BepiColombo arrives in late 2024, it will help reveal information on the composition and history of Mercury. It should discover more about the formation and the history of the inner planets in general, including Earth.

The eerie blue exhaust trail of an ion thruster during a test firing. A quartet of these highly efficient T6 thrusters is being installed on ESA’s BepiColombo spacecraft to Mercury at ESA’s ESTEC Test Centre in Noordwijk, the Netherlands.

The Mercury Transfer Module will carry Europe’s Mercury Planetary Orbiter and Japan’s Mercury Magnetospheric Orbiter together to Sun’s innermost planet over the course of 6.5 years.

T6 Ion Thruster Firing

“BepiColombo would not be possible in its current form without these T6 thrusters,” explains ESA propulsion engineer Neil Wallace.

The twin ‘QinetiQ T6’ ion thrusters operate at maximum combined throttle of 290 mN

The Mercury Planetary Orbiter will have a mass of 1,150 kilograms (2,540 lb) and will have its sides covered with solar cells providing 150 Watts at perihelion.

“Standard chemical thrusters face a fundamental upper limit on performance, set by the amount of energy in the chemical reaction that heats the ejected propellant producing the thrust.

“Ion thrusters can reach much higher exhaust speeds, typically an order of magnitude greater, because the propellant is first ionised and then accelerated using electrical energy generated by the solar panels. The higher velocity means less propellant is required.

“The down side is that the thrust levels are much lower and therefore the spacecraft acceleration is also low – meaning the thrusters have to be operating for long periods.

“However, in space there is nothing to slow us down, so over prolonged periods of thrusting the craft’s velocity is increased dramatically. Assuming the same mass of propellant, the T6 thrusters can accelerate BepiColombo to a speed 15 times greater than a conventional chemical thruster.”

The 22 cm-diameter T6 was designed for ESA by QinetiQ in the UK, whose expertise in electric propulsion stretches back to the 1960s.

It is an scaled-up version of the 10 cm T5 gridded ion thruster, which played a crucial role in ESA’s GOCE gravity-mapping mission by continuously compensating for vestigial atmospheric drag along its extremely-low orbit.