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plasma rocket [Q&A]

Vinay

A student from Bhandarkar’s College asks, what are plasma rockets?

Sounds like something out of science fiction, but they are real. In 1998, NASA launched a technology proving mission called Deep Space 1 that was powered by ionized Xenon atoms.

In a rocket, propulsion is provided by expelling mass at high momentum in one direction, propelling the main body of the spacecraft, by reaction, in the opposite direction. In typical rockets, the momentum for the expelled mass is provided by heat, generated by strongly exothermic reactions, which causes solid or liquid propellants to escape at high velocity through the nozzles at the base of the rockets.

In a plasma rocket, the propellant is made up of ionized atoms. Electric fields are used to accelerate the ions to enormous speeds (~30 km/s on DS-1, so 1 mol of Xe could in principle provide a change in momentum of ~3900 kg m/s) so the momentum transfer can be quite significant. Even though the thrust is tiny at any given instant, these ion engines are highly efficient and run for long durations. They are not very powerful, but like the tortoise in the fable, they don’t stop, and eventually their speeds can match (and exceed) that of even the swifter hares.

There are more details about ion propulsion at the DS-1 FAQ page and the Dawn Spacecraft Mission webpage.