When the Mercury Transfer Module of the BepiColombo mission fires its electric propulsion thrusters an ion beam is extracted. This is created through the ionization of xenon propellant, generating the charged particles that can be accelerated further using an electric field.
Together with gravity assist flybys at Earth, Venus and Mercury, the thrust from the ion beam provides the means to travel to the innermost planet.
After escaping the pull of Earth’s gravity with the Ariane 5 launcher, the spacecraft is on an orbit around the Sun. The transfer module then has to use its thrusters to brake against the mighty pull of the Sun’s gravity. It also has to tune the shape of its orbit in order to make a series of nine gravity assist flybys at the planets before finally delivering the mission’s two science spacecraft into Mercury orbit.
This image is an excerpt from a supercomputer simulation that models the flow of plasma around the spacecraft just after the high energy ion beam is switched on. An outline of the composite spacecraft with its extended solar arrays is included for reference.
The simulation tracks the particles in the beam as well as those that diffuse around the spacecraft, which are created by the interaction of the high energy beam ions with the neutral xenon atoms that also flow out of the thruster. It shows the density of the plasma flowing around the spacecraft and its evolution: red represents high density, blue is low density (see animation for detailed scale).
Although the animation is several seconds long it has been slowed down, representing a mere eight milliseconds of real time – the time necessary for the plasma to reach a steady state.
The simulation was performed to demonstrate that the plasma produced by the thruster is not damaging to the spacecraft: its materials, including solar arrays or instruments, for example, or to the electric propulsion system itself. The simulations also confirmed there are no spurious or dangerous charging events.
Inflight measurements will verify the simulation results and help improve ways in which the generated plasma, spacecraft and space environment interactions can be better modelled.
BepiColombo is a joint endeavour between ESA and JAXA. After their seven-year interplanetary journey, the two science orbiters – the Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter – will start their main mission to provide the most in-depth study of mysterious Mercury to date.
The spacecraft begin transferring to Europe’s spaceport in Kourou this week, where an intensive period of preparations will ready the mission for launch later this year.
The simulations were performed by Félicien Filleul as part of ESA’s Young Graduate Trainee programme.