Space exploration missions and electric propulsion

Various space exploration missions are possible only thanks to the technology advancements and electric propulsion. These missions would not be possible with chemical propulsion due to a high amount of propellant that would be required for a satellite to travel in space for several years.

© ESA/ATG medialab

Space exploration mission: BepiColombo

BepiColombo is a joint European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA) mission to Mercury, the least explored rocky planet in the inner Solar System.

The mission consists of two jointly launched spacecraft – ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (MMO) – carried by the ESA-built Mercury Transfer Module (MTM).

The mission will carry out a comprehensive study of Mercury, including characterization of its magnetic field, magnetosphere, interior and surface structure.

Launch and cruising of BepiColombo

The spacecraft was launched by Ariane 5 on 20 October 2018. It is scheduled to arrive at Mercury on 5 December 2025. The journey from Earth to Mercury will therefore take just over 7 years. BepiColombo is expected to begin scientific operations in February 2026.

BepiColombo thrusters

BepiColombo is equipped with both chemical and ion thrusters. The chemical thrusters will perform critical manoeuvres such as orbit insertion and trajectory correction. The 4 ion thrusters will enable the spacecraft to make the long journey to Mercury, make trajectory corrections and small adjustments to the spacecraft’s orbit around Mercury, and carry out its scientific mission with precision and efficiency. The ion thrusters use xenon gas as a propellant and produce a very small but continuous thrust, allowing the spacecraft’s trajectory to be precisely controlled over long periods of time (operating ion thrusters typically consume 1-7 kW of power, have exhaust velocities of 20-50 km/s (=2000-5000 s), thrusts of 25-250 mN, and propulsion efficiencies of 65-80%). This type of mission would not be possible with chemical propulsion alone.

Gridded ion engines and space exploration

The main advantage of gridded ion thrusters is their ability to provide precise and efficient control of the spacecraft’s trajectory over long periods of time. The basic operation of a gridded ion thruster involves:

  1. The use of a propellant, typically a gas such as xenon, which is introduced into a chamber with a grid system on one side.
  2. A high frequency alternating electromagnetic field maintains a plasma discharge.
  3. By carefully selecting the voltages applied to the grid system, ions can then be extracted from the plasma to generate thrust.

Gridded ion engines have already been used in missions such as SMART-1 (ESA) to study the Moon. It used a gridded ion engine as its primary propulsion system, allowing it to reach the Moon using only 82 kilograms of xenon propellant. It was also used in NASA’s Dawn mission to study Vesta and Ceres, which was notable for its record-breaking use of gridded ion thrusters.

GIESEPP MP gridded ion thruster

The GIESEPP MP project, co-funded by the European Union, is developing the first plug-and-play gridded electric propulsion platform for ion engines on the market. Its main advantage is efficiency, mass saving and the possibility to use it for Ariane Group ion engines with the option of alternative engines for a medium power application.

The project is expected to reach Technology Readiness Level 6/7 with partial qualification to enable flight readiness, optimize industrialization, increase GIE systems production capacity and significantly reduce recurrent costs.