PPPL physicist Fatima Ebrahimi in front of an artist’s impression of the fusion rocket (Photo credit: Elle Starkman (PPPL Office of Communications) and ITER)
A new type of rocket engine, mimicking the mechanism behind solar flares, could send people to Mars and beyond, one researcher has claimed.
Fatima Ebrahimi, a senior research physicist at Princeton Plasma Physics Laboratory (PPPL) in New Jersey, suggested the concept. The engine would apply magnetic fields to cause plasma particles to shoot out of the rear of the rocket and propel it forward. Current space-proven plasma thrusters use electrical fields to propel the particles.
The new concept would accelerate the particles through magnetic reconnection – a process found throughout the universe, including the surface of the sun – in which magnetic field lines converge, suddenly separate, and then join again, creating a lot of energy. Reconnection is also done within donut-shaped tokamak fusion devices.
“I’ve been cooking this concept for a while,” said Ebrahimi, the author of a paper that included the idea in the Journal of Plasma Physics. “I got the idea in 2017 while sitting on a deck pondering the similarities between a car’s exhaust and the high-speed exhaust particles produced by PPPL’s National Spherical Torus Experiment (NSTX). During its operation, this tokamak generates magnetic bubbles called plasmoids, which move at a speed of about 20 kilometers per second, which seemed to me very much like thrust. “
Current plasma thrusters, which use electric fields to propel the particles, can only generate a low specific impulse. However, computer simulations showed that the new plasma engine concept can generate exhaust gases at speeds of hundreds of kilometers per second, ten times faster than other engines.
That faster speed at the beginning of a spacecraft’s journey could bring the outer planets within reach of astronauts, Ebrahimi said.
“Long-distance travel takes months or years because the specific momentum of chemical rocket engines is very low, so it takes a while for the vehicle to be up to date,” she said. “But if we make engines based on magnetic reconnection, we could potentially complete long-range missions in less time.”
There are three main differences between Ebrahimi’s engine concept and other devices. The first is that changing the strength of the magnetic fields can increase or decrease the amount of thrust. Second, the new thruster creates motion by ejecting both plasma particles and plasmoids, adding power to the engine. The third difference is that, unlike electric field thrusters, the magnetic fields in Ebrahimi’s concept allow the plasma to be made up of either heavy or light atoms.
“While other thrusters require heavy gas made from atoms like xenon, you can use any type of gas you want in this concept,” she said. In some cases, scientists may prefer light gas because the smaller atoms can move faster.
Ebrahimi emphasized that her engine concept resulted directly from her research into fusion energy. “This work was inspired by previous fusion work and this is the first time plasmoids and reconnections have been proposed for space propulsion,” she said. “The next step is building a prototype.”
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