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A solar-powered Hall-effect thruster is being tested under vacuum conditions at NASA. Credit: NASA
Since the beginning of the space program, people have been captivated by large and powerful rockets, such as POTit is Saturn The V rocket that sent Apollo to the lunar surface, or the Space Launch System that will produce millions of pounds of thrust while sending the Artemis astronauts back to the Moon.
But what if the most powerful propulsion system in NASA’s toolbox produces less than a pound of thrust while reaching speeds of up to 200,000 mph? What if it costs less, carries more, and uses less fuel?
This radical system is electric propulsion in space. It can reduce the amount of fuel or propellant required by up to 90% compared to chemical propulsion systems, saving millions in launch costs and providing greater mission flexibility.
Newton’s third law in space
Chemical propulsion uses a fuel and an oxidant, converting the energy stored in the chemical bonds of the propellants, to produce a short and powerful thrust, or what we see as fire. It is loud and exciting, but not that efficient.
An electric propulsion system uses energy collected by solar panels (solar electric propulsion) or a nuclear reactor (nuclear electric propulsion) to generate thrust, eliminating many of the needs and limitations of storing propellants on board.
That power is then converted and used to ionize, or positively charge, inert gas propellants like Xenon and Krypton (no, it’s not from Superman’s home planet). A combination of electric and magnetic fields (Hall effect thruster) or an electrostatic field (gridded ions) accelerates the ions and pushes them out of the thruster that propels the spacecraft at tremendous speeds over time. And instead of fire, its escape is a bright blue-green trail, like something straight out of science fiction.
A simple illustration of how electric propulsion systems work. Credit: NASA / ATS Lisa Liuzzo
Drag race vs. road trip
A chemical spacecraft is a superior fuel dragster as it leaves Earth’s orbit toward its destination. The initial burst is pretty powerful, but it can actually only go in the direction you’re pointing when you step on the gas. The spacecraft fires like a bullet, but once its fuel supply is depleted, there is little ability to accelerate, slow down, or change direction. Therefore, the mission is locked into specific launch windows and orbital departure time periods, and you can only make minimal corrections along the way.
An electrically powered spacecraft, once in space, sets off for a cross-country trip, limited only by the gas in the tank. The initial thrust is quite low, but it can continue to accelerate for months or even years, and it can also slow down and change direction.
NASA’s Dawn mission is a perfect example. After launch, it sped towards Vesta in the asteroid belt. Due to the spacecraft’s small solar panels, it took more than five years to get there, but as it got closer, the spacecraft turned 180 degrees, burned off its thrusters to slow down, and orbited for a year. When he finished, he fired again and traveled to Ceres, where it still orbits today. This would not be possible with chemically powered spacecraft.
Systems like Dawn’s are widely used in NASA and the commercial sector, generally operating in the 1-10 kilowatt (kW) range. But as we prepare to use electric propulsion in more complex science and technology missions and human missions for the first time, we will need more power.
An illustration of the PPE-HALO in lunar orbit. Credit: NASA
More power to the people!
The Power Propulsion Element (PPE) for Gateway will demonstrate advanced high power solar electric propulsion around the Moon. It is a 60kW-class spacecraft, 50 of which can be dedicated to propulsion, making it about four times more powerful than current electric-powered spacecraft. We do this not by building one big booster, but by combining several in a string with giant solar panels.
This advanced system will allow our orbital platform to support lunar exploration for 15 years given its high fuel economy, and its ability to move while in orbit will allow explorers to land virtually anywhere on the Moon’s surface.
While a fundamental piece of our Artemis lunar exploration plans, the PPE will also help drive U.S. commercial investments in higher-powered electric propulsion systems, such as those that could be used to reach Mars.
Illustration of a Mars transit habitat and a nuclear propulsion system that could one day take astronauts to Mars. Credit: NASA
Next stop, Mars
Future transfer vehicles to Mars will need around 400kW-2 megawatts of power to successfully transport our astronauts or cargo to and from the Red Planet. We are still exploring vehicle and propulsion concepts for Mars, including a combination of nuclear electric and chemical propulsion and other emerging options such as nuclear thermal propulsion.
No matter how we get to the Moon and eventually Mars, one thing is for sure … the future of space exploration is exciting, you could even say it is electrifying.
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