There's no air to breathe, it's 400 degrees Celsius and you are six long years away from home. Welcome to Mercury, the smallest and perhaps most mysterious planet in the Solar System. The European Space Agency (ESA) is aiming to increase our knowledge of the Sun's closest neighbor by launching its BepiColombo spacecraft to the planet Mercury in 2014. One of the key challenges faced by the mission is not just getting there, but also how to apply the brakes against the Sun’s gravitational pull when you do... and that's where QinetiQ's solar-electric ion propulsion system comes in. The company has just announced a £23m contract with EADS Astrium for the supply of its system for the BepiColombo mission.
The Ion drive
Despite it's StarTrek connotations, the use of ion drives has been investigated since the late 1950s. They work by ionizing gas (i.e. giving it an electrical charge) and passing them through an electrical grid to produce thrust. The result is a system that's about ten times more efficient in terms of thrust per kilo of propellant used than chemical thrusters and because they only require a small amount of electrical energy, they can be run for long periods of time using solar power.
QinetiQ's solar-electric propulsion system comprises four T6 ion thrusters which use the inert gas xenon as their propellant. The system is already in use aboard the Gravity field and steady-state Ocean Circulation Explorer (GOCE) which launched in March 2009 to study the Earth's gravitational field from orbit.
Despite their efficiency, ion engines are low-thrust devices, so they are not suitable for launching a rocket through the Earth's atmosphere, but in the vacuum of space they can be used to change the trajectory of a spacecraft in order to take advantage of other forces like the gravitational pull of planets. On the mission to Mercury, these "planetary gravity-assist manoeuvres" will see BepiColombo swing by Venus, Earth and Mercury.
“This has been an extremely exciting year for the Space team at QinetiQ, with the first in-orbit qualification of our smaller T5 ion engines on the GOCE spacecraft and now the confirmation of our world-class T6 engine solution for BepiColombo representing QinetiQ's largest space-related contract to date,” said Graham Love, QinetiQ CEO. "Electric propulsion will make deep space missions possible for the first time and offers significant efficiencies to enhance future communication satellite operations."
Exploration of MercuryBepiColombo is Europe's first mission to Mercury and follows in the footsteps of NASA's Mariner 10 (1974-75) and MESSENGER (due to reach orbit around Mercury in 2011 after a fly-by in January 2008).
BepiColombo consists of two separate orbiters - one for mapping and a second to study the planet's magnetosphere. It is due to arrive in 2019 and will gather information on the Planet's composition and history, in the process shedding light on the formation of other inner planets including our own.
"Mercury is the planet closest to the Sun, making it hard to get to, so an advanced electric propulsion system is an essential part of meeting the technical challenge," said Prof. David Southwood, ESA’s Director of Science and Robotic Exploration. "However the goal of the mission is very important – Mercury has regularly confounded planetary scientists with its exceptional properties and that makes it a grand scientific challenge."
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