A ground-breaking Solar Electric Propulsion System (SEPS) developed and manufactured by an industrial consortium led by British company QinetiQ, will provide the engine power behind the BepiColombo mission to Mercury, scheduled to launch on 20 October. 


Following its launch aboard Ariane 5 from Europe’s spaceport in French Guiana, four QinetiQ T6 Gridded Ion Thrusters will propel the Mercury Composite Spacecraft along with gravity assists (Earth, Venus and Mercury) from Earth’s orbit to Mercury.


During early planning the European Space Agency (ESA) determined that BepiColombo would require electric propulsion, a first for a mission visiting one of the Solar System’s inner planets. Following QinetiQ’s successful development of the T5 ion thruster for ESA’s GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite, which orbited Earth for 4 years, ESA selected the larger T6 thruster for BepiColombo. QinetiQ was tasked with the manufacture and qualification of a SEPS, based around the T6.


Powered by solar energy, the T6 is super-efficient, enabling the spacecraft to reach maximum velocity with minimal fuel consumption. This decreases the propellant mass needed on board by between 10 and 20 times compared to a typical chemical rocket, which is key to maximising the science payload within the constraints of the launch vehicle.


QinetiQ designed the SEPS to enable ESA to address key challenges, including those presented by the Sun’s enormous gravitational pull. The system will provide the low thrust required for the spacecraft to continuously ‘brake’ against this pull during its seven-year journey to Mercury. The thrusters are capable of withstanding the high vibration and shock levels that will be experienced during launch/separation, as well as extreme temperatures during the cruise phases ranging from around -135c to 175c. 


Peter Randall, Systems Engineer Electric Propulsion, from QinetiQ says: “It’s a source of great pride that QinetiQ is playing such a pivotal role in this voyage to investigate the secrets of Mercury. The use of solar electric propulsion has provided ESA with an extremely efficient and robust engine system, and our rigorous testing of the T6 ion thrusters we’ve delivered will ensure it achieves its mission objectives. QinetiQ has more than 50 years’ experience of researching and testing electric propulsion thrusters – and this couldn’t have resulted in a more thrilling ESA cornerstone science project.”


UK Space Agency Chief Executive, Dr Graham Turnock, 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.”


QinetiQ’s Steve Clark, Electric Propulsion Engineering Lead said, “Thrusters are a key enabling technology for the BepiColombo mission, which is set to fascinate and inspire millions of people around the globe. This is a fantastic example of how British expertise and innovation have the potential to support European space exploration, and make significant contributions to discoveries of worldwide importance.”




Notes for Editors:


The technology

The QinetiQ T6 ion engines are 22cm diameter, 4.5kW Kaufman-type ion thrusters, powered by solar energy from the spacecraft which they’ll use to accelerate Xenon gas to an exhaust velocity exceeding 50Km/s. This high propellant velocity allows the thruster to give a very high specific impulse (akin to miles per gallon for a car); around 10 times higher than traditional chemical rockets. In testing, the engine demonstrated it was capable of providing up to 145 mN of thrust at a specific impulse of around 4,000 seconds. These incredible exhaust speeds are key to the thruster’s performance, allowing the craft to achieve large changes in velocity for minimal fuel consumption.


The thrusters will be vital for future interplanetary travel as although the speed of the emerging plasma is extremely fast (equivalent of 90,000mph), the force it produces is small – but can be maintained with high efficiency over a long period of time.


Other advantages of using gridded ion engine electric propulsion systems include:

·         Reduced mass of the launch vehicle, resulting in lower launch cost

·         Increased payload capacity

·         Fine control of thrust levels, compared to the typical on/off setting of chemical rockets

·         Increased mission duration

·         Accurate thrust vectoring capability over the mission duration

·         Minimal spacecraft interactions, e.g. solar array contamination.


Only two thrusters are operated at one time; four thrusters provide redundancy in line with the customer’s requirements. 


QinetiQ also designed, built and qualified the Solar Electric Propulsion Harness (SEPH) and Solar Electric Propulsion Pipework (SEPP) forming part of the  SEPS, and worked closely with other partners who provided the power processing units (PPU) that will take the power from the solar cells to the thrusters, and the flow control units (FCU) which supply Xenon from the propellant tanks and regulates the Xenon flow to the thrusters.


The mission

BepiColombo is a joint mission between ESA and the Japan Aerospace Exploration Agency (JAXA), executed under ESA’s leadership. The objective is to better understand the structure and evolution of Mercury, which is the least explored of all terrestrial planets due to its close proximity to the Sun. The spacecraft will arrive in late 2025, when it will gather data during a one-year nominal mission, with a possible one-year extension. 


The mission comprises two spacecraft: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). The Airbus-built Mercury Transfer Module (MTM) will carry the orbiters to Mercury using a combination of solar electric propulsion and gravity assist flybys. The spacecraft will make one flyby of Earth, two at Venus, and six at Mercury.


The mission is named after the Italian mathematician and engineer Giuseppe (Bepi) Colombo (1920–84).


About QinetiQ

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