Chuck Taylor is principal investigator of in-space propulsion and space power generation within the Game Changing Development Program. He is responsible for a portfolio of technologies, including large-scale solar electric propulsion systems.

NASA Tech Briefs: What is solar electric propulsion (SEP)?

Chuck Taylor: Solar Electric Propulsion is a form of spacecraft propulsion used in space. It relies on the acceleration of ions using electricity generated by solar arrays instead of the chemical energy stored in the propellant itself. It is attractive because by using the Sun’s energy in the process we can bring considerably less propellant mass into orbit; this reduces our launch mass and cost. An SEP system is usually considered to consist of the large arrays that generate electric power, the power processing units or PPUs that convert this power, and the thruster which uses the electric power to ionize the inert propellant and accelerate it out of the spacecraft to generate thrust.

NTB: What is currently being done with the system?

Taylor: We have two vendors working right now on producing advanced lightweight solar arrays that are autonomously deployable, that can give us something on the order of 50 kilowatts of prime power. We’re also defining our requirements for the thruster. That’s the system that is going to take that electrical power and basically work on xenon gas to provide us with propulsion. We have to develop what’s called a power processing unit, which basically changes the voltage coming off the solar array and gives the thruster the power it needs. We have to develop a thruster that will work at the right power levels, and we have to develop large xenon tanks in order to carry enough fuel with us for what is anticipated to be a 4-5 year mission to get an asteroid and bring it home.

NTB: What are your biggest technical challenges?

Taylor: Beyond just the solar cell, you have the technology of how that solar cell is put into a panel or a blanket, and then how that panel and blanket is deployed on an array. We’re working on lightweight structures to improve upon the present systems: less mass, better structural integrity, and— probably the most important thing when we go to these very large arrays — the autonomous nature of the deployment. With the arrays we’re developing today, we’re trying to get as much power as we have on station, but get it in a form factor where it’s stowed for launch and deployed autonomously.

You’re orbiting the Earth very quickly. You’re moving away from the Earth toward other objects, and you have to make sure that you have this system pointed at the Sun throughout the spacecraft’s movement. In order to do that, you have to have the strength and stiffness within these systems, and at the same time, have the ability originally to stow them in a very small volume.

NTB: What role will large-scale electric propulsion systems play in future missions?

Taylor: Solar electric propulsion actually runs the gamut, [starting with] very small thrusters that are actually working today on orbit for attitude control and orbit adjustment of communication satellites, both for commercial satellites and military and intelligence capabilities. We hope to expand the horizons of the capability by adding larger solar arrays, creating more power, and giving thrusters the requisite power to actually do both asteroid retrieval, and one day maybe satisfying the requirements for a Mars mission.

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