A new type of rocket thruster could take humankind to Mars and beyond. The device would apply magnetic fields to cause particles of plasma — electrically charged gas also known as the fourth state of matter — to shoot out the back of a rocket and because of the conservation of momentum, propel the craft forward. Current space-proven plasma thrusters use electric fields to propel the particles.
The new concept would accelerate the particles using 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 together again, producing lots of energy. Reconnection also occurs inside doughnut-shaped fusion devices known as tokamaks.
Fusion, the power that drives the Sun and stars, combines light elements in the form of plasma — the hot, charged state of matter composed of free electrons and atomic nuclei that represents 99% of the visible universe — to generate massive amounts of energy. Scientists are seeking to replicate fusion on Earth for a virtually inexhaustible supply of power to generate electricity.
Current plasma thrusters that use electric fields to propel the particles can only produce low specific impulse, or speed. Computer simulations showed that the new plasma thruster concept can generate exhaust with velocities of hundreds of kilometers per second — ten times faster than those of other thrusters. That faster velocity at the beginning of a spacecraft's journey could bring the outer planets within reach of astronauts. Long-distance travel takes months or years because the specific impulse of chemical rocket engines is very low, so the craft takes a while to get up to speed.
There are three main differences between the new thruster 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 produces movement by ejecting both plasma particles and magnetic bubbles known as plasmoids. The plasmoids add power to the propulsion and no other thruster concept incorporates them. Third, unlike current thruster concepts that rely on electric fields, the magnetic fields in the new concept allow the plasma inside the thruster to consist of either heavy or light atoms. This flexibility enables scientists to tailor the amount of thrust for a particular mission and use any type of gas.