FASTER, PLEASE: NASA’s longshot bet on a revolutionary rocket may be about to pay off.
The rocket engine starts with a neutral gas as a feedstock for plasma, in this case argon. The first stage of the rocket ionizes the argon and turns it into a relatively “cold” plasma. The engine then injects the plasma into the second stage, the “booster,” where it is subjected to a physics phenomenon known as ion cyclotron resonance heating. Essentially, the booster uses a radio frequency that excites the ions, swinging them back and forth.
As the ions resonate and gain more energy, they are spun up into a stream of superheated plasma. This stream then passes through a corkscrew-shaped nozzle and is accelerated out of the back of the rocket, producing a thrust.
Such an engine design offers a couple of key benefits over most existing propulsion technology. Perhaps most notably, unlike chemical rockets, the plasma rocket operates on electricity. As it flies through space, therefore, it does not need massive fuel tanks or a huge reservoir of liquid hydrogen and oxygen fuel. Instead, the rocket just needs some solar panels.
The Sun powers both the production of plasma and the booster exciting the plasma, and the extent to which it does either can be shifted. When a spacecraft needs more thrust, more power can be put into making plasma. This process uses more propellant, but it provides the thrust needed to move out of a gravity well, such as Earth orbit. Later, when the vehicle is moving quickly, more power can be shifted to the booster, providing a higher specific impulse and greater fuel economy.
“It’s like shifting gears in a car,” Chang-Díaz explained. “The engine doesn’t change. But if you want to climb a hill, you put more of your engine power into torque and less into rpm, so you climb the hill, slowly, but you’re able to climb. And when you’re going on a freeway, flat and straight, you upshift. You’re not going to go to Mars in first gear. That’s the problem. It’s why we run out of gas going to Mars with a chemical engine.”
Not needing a huge propellent tank means more cargo space for supplies, equipment, habitat, or people.