Physicists in France have finally solved how to optimize an advanced form of electric rocket thruster that uses a stream of plasma travelling at 72,420 km/h (45,000 mph) to push spacecraft forward, letting them to run on 100 million times less fuel than current chemical rockets. Known as a Hall thruster, these engines have been working in space since 1971, and are now regularly flown on communication satellites and spacecrafts to regulate their orbits when required. These things are remarkable, and researchers want to use them to get people to Mars, but there’s one - pretty large - problem: the present lifecycle of a Hall thruster is around 10,000 operation hours, and that’s way too much short for most space exploration operations, which need upwards of 50,000 hours.
Hall thrusters work just like ordinary ion thrusters, which discharge a stream of charged ions from an anode to a cathode (positively and negatively charged electrodes), where they become neutralized by a beam of electrons. This sources the elections to shoot one way, and the physically attached rocket to shoot another, pushing it forward. The variance with Hall thrusters is as a substitute of having a physical cathode, they chain a magnetic field and a confined electron cloud to produce a totally hollow, 'virtual' cathode. A small amount of propellant gas - normally xenon - is inserted into the thruster's channel to yield a charged ion stream, and since these ions are too heavy to be caught up in the magnetic field of the virtual cathode, they can zip through unrestrained to be neutralized. This generates a low-pressure plasma discharge, which yields thrust in the opposite direction from that of the ion flow.
Prototype hall thruster firing in a vacuum chamber. CNRS/LAPLACE and CNRS/ICARE
All of this is works fine, but the portion of the Hall thruster that comprises the anode, virtual cathode, and electron cloud is what’s creating trouble. This vessel, called the discharge channel wall, is being continually bombarded with high-energy ions, and this wears it down way too much, the whole engine will ultimately need to be recalled to have the wall restored or changed.
So researchers from the French National Centre for Scientific Research decided to eliminate the discharge channel wall completely. Lead researcher, Julien Vaudolon said "An effective approach to avoid the interaction between the plasma and the discharge channel wall is to move the ionisation and acceleration regions outside the cavity, which is an unconventional design named a Wall-Less Hall Thruster,"
Unluckily, as Esther Inglis Arkell explains at Gizmodo, their first model (on the left in the image shown above) was a complete failure. She says "The red anode should be lined up on the wall emitting xenon. Instead, it's in the magnetic field, allowing electrons to glom onto it, reducing performance. The new design (on the right) makes the small change, which allows the anode to keep clear of the field. This one seems to work."
The study has been issued in Applied Physics Letters.
Since the engine consumes a whole lot less fuel than ordinary chemical rockets, this frees up a lot of room in the spacecraft to send huge amounts of cargo, or maybe more people.