Maps
Webmail
Home > Research > Low-temperature plasmas > Application areas > Plasmas for space propulsion
Plasmas for space propulsion
Towards new thrusters…
To propel a spacecraft, a space vehicle or a rocket works on the same basic principle, namely to create a propulsive force (the trust) by accelerating and excelling mass. Chemical rockets achieve a large thrust by expelling a lot of mass very quickly, and can overcome earth’s gravitation and escape into space. However, this method is very fuel or propellant consuming and therefore very expensive for a long interplanetary mission, or for keeping satellites in a desired orbit.
In this respect electric propulsion is promising and has become more and more popular in recent years. The exhaust velocity of electric propulsion systems can reach up to 20 km/s and the propellant burden is 1/10th of what is used in chemical rockets. This means 1/10th reduction in the propellant burden compared to chemical rockets. The thrust achieved by electric propulsion systems is relatively low (so they can not be used to leave earth) but they provide a large velocity change needed for long interplanetary missions.
The electric propulsion systems already used in space, are gridded thrusters (also called ion engines) and Hall thrusters (also called closed drift thrusters). Briefly, the thrust is provided by extracting and accelerating positive ions from a high density plasma. In several thrusters as in Hall thrusters, the ion beam is neutralized by electrons from a hollow cathode downstream of the acceleration stage. This neutralisation is needed to avoid a built up of negative charge on the space vessel that will counteract the accelerating field.
Electric Propulsion at LPP
At LPP, experimental, theoretical and simulation work has been carried out on electric propulsion since 2007. Work on a grid thruster (called Neptune) with an original RF acceleration system (2 patents from Ecole Polytechnique), inspired engraving plasmas, gave rise to the creation of the start-up ThrustMe in 2016.
Currently, work on electric propulsion at the LPP is carried out within the framework of two projects:
PEGASES (Plasma Propulsion with Electronegative GASES) thruster
The PEGASES electronegative plasma thruster (patented by Ecole Polytechnique in early 2007) belongs to the family of electrostatic thrusters. The major innovation is to use both positive and negative ions for thrust. To achieve this, a high-density electronegative plasma is generated (a plasma consisting of both positive ions, negative ions and electrons). A magnetic field is used to separate the electrons, so that an electron-free zone is obtained at the periphery of the plasma. This electron-free region is called an ion-ion plasma where only positive ions and negative ions are present. Thrust is achieved by extracting and then accelerating positive and negative ions from that particular region.
The first PEGASES prototype was started up in a small vacuum chamber at the end of 2007 at LPP. The experimental, theoretical and simulation work carried out at LPP made it possible (see list of publications at the bottom of the page):
– To better understand and optimize the filtering of electrons by the magnetic field,
– to study instabilities, anomalous transport, and the cooling of electrons observed experimentally
– to evaluate the performance of iodine as a fuel of the future in space propulsion
Hall thrusters
The work carried out at LPP on Hall thrusters began in 2014 as part of a CIFRE thesis with Safran and continued as part of the POSEIDON industrial ANR chair (2016-2022) supported by the LPP laboratory. The industrial partner of the chair is Safran Spacecraft Propulsion. CERFACS and ICARE (PIVOINE test bench) participated in this project. As part of the POSEIDON chair, 9 PhD theses (including 3 CIFRE) were supported, 21 articles published in international peer-reviewed journals (such as Plasma Sources Science and Technology and Physics of Plasmas...) including 2 publications on two international benchmarks, a first in the community of magnetized plasmas for electric propulsion (see list of publications at the bottom of the page). The work carried out was also presented at major international conferences in the field of low-temperature plasmas and electric propulsion, including 8 invited international conferences.
Major scientific results have been obtained on plasma instabilities and their impact on the abnormal transport of electrons in a Hall effect thruster and plasma/wall interactions. From an experimental point of view, the objectives were achieved with the manufacture of a new thruster prototype. Tests on this thruster have enabled significant progress by experimentally identifying a high-efficiency engine configuration.
In November 2023, the COMHET joint laboratory was inaugurated by CNRS, Ecole Polytechnique and Safran Spacecraft Propulsion.
The work will be carried out around three axes linked to the physical characteristics of Hall thrusters and the scientific and technological barriers specific to them:
- Focus area 1 – Study of alternative propellants.
- Focus area 2 – Digital simulation.
- Focus area 3 – Smart diagnostics.
The objective will be to increase and make the performance of the thrusters more reliable, particularly in terms of stability and compatibility, by developing innovative technological bricks in order to meet the issues and challenges of tomorrow’s satellite thrusters. To this end, the COMHET team will explore the use of a new propellant such as iodine to replace the more expensive xenon, as well as the use of numerical simulations and the development of non-intrusive to reduce the duration and number of vacuum chamber tests.
Publication list on electric propulsion at LPP since 2009
