Solar Electric Propulsion (SEP)
"What is pride? A rocket that emulates the stars."
~ 19th century English poet William Wordsworth ~
As NASA plans to extend human presence across the solar system, including the Moon and Mars, it also seeks to shorten the time required to develop and apply transformative technologies that increase the nation's capabilities in space, enable future missions and support a variety of commercial spaceflight activities.
NASA's Solar Electric Propulsion (SEP) project is developing critical technologies to enable government and commercial customers to extend the length and capabilities of ambitious new exploration and science missions. Advanced propulsion technologies such as SEP deliver the right mix of cost savings, safety and superior propulsive power to support a variety of next-generation journeys to destinations in deep space.
Energized by the electric power from on-board solar arrays, the electrically propelled system will use 10 times less propellant than a comparable, conventional chemical propulsion system, such as those used to propel the space shuttles to orbit. Yet that reduced fuel mass will deliver robust propulsion capable of boosting robotic and crewed missions well beyond low-Earth orbit: sending exploration spacecraft to distant destinations, ferrying cargo to and from points of interest, laying the groundwork for future missions or resupplying those already underway.
NASA's Glenn Research Center in Cleveland leads the Solar Electric Propulsion project for the agency and is preparing a system-level flight demonstration within the next decade.
Technologies the project is developing and demonstrating include advanced solar arrays, high-voltage power management and distribution, power processing units, high-power Hall thrusters and spaceflight diagnostics for measuring system performance.
Under the guidance of NASA's Game Changing Development Program, prior to transitioning to the Technology Demonstration Missions Program, the SEP project began developing large, flexible, radiation-resistant solar arrays that can be stowed into small, lightweight, more cost-effective packages for launch. After launch, they unfurl, capturing solar energy to provide the electrical power required to enable high-powered electric propulsion.
In the case of solar electric-propelled craft, large solar cell arrays convert sunlight to electrical power. The SEP project worked with ATK Space Systems Inc. and Deployable Space Systems Inc., both of Goleta, California, to build and test two solar array designs: one that folds out like a handheld fan (ATK MegaFlex) and another that rolls out like a window shade (DSS Mega-ROSA). Both use lightweight, durable structures and flexible blanket technology and can operate for long periods in Earth orbit or passing through the punishing Van Allen radiation belts.
With SEP technology, energy is fed into exceptionally fuel-efficient thrusters to provide gentle but nonstop thrust throughout the mission. The SEP project uses electrostatic Hall thrusters with advanced magnetic shielding -- doing away with conventional chemical propellant delivered by a traditional rocket engine.
The thruster generates and traps electrons in a magnetic field, using them to ionize the onboard propellant -- in this case, the inert gas xenon -- into an exhaust plume of plasma that accelerates the spacecraft forward. Several Hall thrusters can be combined to increase power. A system able to accelerate xenon ions to more than 65,000 mph will provide enough force over time to move cargo and perform orbital transfers.
In 2015, researchers successfully tested a new 12.5-kilowatt (kW) Hall thruster that employs magnetic shielding, enabling it to operate continuously for years -- a capacity important to deep-space exploration missions. NASA contracted in 2016 for a flight-capable SEP system, including a power processing unit, a Hall thruster and a xenon flow controller that can demonstrate the technology during spaceflight and ultimately be used on operational vehicles to achieve NASA's mission in space.
The Solar Electric Propulsion project will demonstrate key technologies necessary for robotic and human exploration-class solar electric transportation systems as well as highly efficient orbit transfer capabilities for commercial space operations and science missions. The first element of NASA's Lunar Orbital Platform-Gateway will demonstrate the use of advanced, high-power SEP to maintain the gateway's position and move it through orbits. Recently, five companies completed four-month studies into the development of the power and propulsion element.
For more information about SEP, please contact:
Michael J. Barrett, PhD
NASA's Glenn Research Center