The very name of the T6 ion thruster sounds like something from sci-fi. But it's very real, and this little engine will be one of four that take the European Space Agency's BepiColombo spacecraft to Mercury. The device measures just 28cm in diameter and was designed for the ESA by UK-based Qinetiq. Most thrusters rely simply on a chemical reaction to create heat, which ejects propellants to cause thrust. But an ion thruster ionises the propellants, creating charged particles that can be accelerated further using an electric field.
That simple-sounding trick ejects the propellant about ten times faster than a normal chemical thruster, allowing it to use less propellant in a given time period in order to save weight. But there's a catch, as the ESA's propulsion engineer Neil Wallace explains:
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 BepiColombo spacecraft will carry the Mercury Transfer Module close to the innermost planet of our Solar System, where Europe's Mercury Planetary Orbiter and Japan's Mercury Magnetospheric Orbiter will be let loose. The whole mission will last almost seven years.