Solar Electric Propulsion Could Slash the Price of Manned Missions

A schematic with all Aerojet satellite that feature SEP systems. Image Credit: Aerojet

It’s not news that propulsion methods have the potential to radically affect spaceflight. Classic chemical propellants like the liquid oxygen/refined kerosene combination that powered the Saturn V are heavy and hard to store on long-duration deep space missions. Nuclear propellants offer more power from smaller stores. But better still are propulsion systems that utilize the Sun’s energy. Earlier this week, Aerojet announced that after a concept study mission, the company’s Solar Electric Propulsion system could cut future manned deep space mission costs by more than half. 

Solar electric propulsion systems (SEPs) use energy from the Sun to propel a spacecraft by taking advantage of naturally occurring magnetism and electricity. As sunlight hits solar arrays, the energy generated is used to heat, ionize, and accelerate a propellant using a combination of electric and magnetic fields and positively charges atoms inside a chamber. Magnetism pulls those charged atoms towards the back of the chamber where they are pushed out by magnetic repulsion. This is the same kind of repulsion you feel if you try to hold the same poles of two magnets together – they’ll repel each other, and if they’re big enough the repulsion can be quite powerful. This steady stream of atoms propelled out of the spacecraft has the effect of pushing the spacecraft forward.

Different propellants can be used either for a rocket’s main engine or the smaller thrusters designed to fire only in space. In Aerojet’s case, it deals primarily with electric thrusters include arcjets, hall thrusters, and gridded ion thrusters. These types can achieve velocities between 3 and 10 times those of traditional chemical propelled thrusters. This translates to a dramatic reduction in propellant mass required to send a mission further into deep space.

Aerojet’s recent concept study, a self-funded one done under a collaborative Space Act Agreement, proved the value SEPs could have on future missions. The study looked at two possible missions.

The first evaluated the delivery of a small habitat to L2 – one of the Lagrange points where a satellite can achieve a steady solar orbit thanks to the gravity of larger nearby objects. The small habitat in the study was the type capable of supporting extended human stays as part of early SLS/Orion missions.

A map of Lagrange points in Earth’s orbit. L2 is beyond the orbit of the Moon. Image Credit: NASA

The second mission Aerojet evaluated was the logistics of delivering cargo to that L2 habitat over a 5 year period; the type of long duration mission needed to enable sustained operations in the habitat.

For both of these mission concepts, SEP technology reduced the total cost by about 50 percent for cargo delivery. Though delivery times were on the longer side ranging from months to a year and a half, the overall idea is to pre-position cargo and logistics using efficient solar electric propulsion and then send the crew on a fast SLS/Orion mission once the habitat is ready.

“Our team has constructed an approach that leverages the benefits of SEP to improve affordability and reduce risk for NASA Human Exploration,” said Aerojet Vice President of Space and Launch Systems Julie Van Kleeck. “Using a SEP tug for cargo delivery, combined with NASA’s Space Launch System and the Orion crew module, provides an affordable path for deep space exploration.”

The consequences of viable SEP technology are significant. SEP designs integrated with flight proven technology could ultimately allow Aerojet to provide a low-risk and affordable approach to NASA Exploration cargo missions. It could also be a stepping stone to next-generation higher power SEP transportation vehicles. But for now, Aerojet is only providing data and mission analysis to support NASA’s internal trade studies. There aren’t any concrete plans for these mission in place for the time being.

This isn’t the first time Aerojet has explored SEP systems; the company has been an industry leader in this field since the 1980s. It has flown more than 500 electric thruster systems to date and has SEP systems on over 200 active satellites. Aerojet SEP systems were used on the DoD AEHF spacecraft, enabling all to be launched on smaller and less expensive rockets; in the last 15 years Aerojet SEPs have reduced costs on over 100 missions. A SEP system actually saved the mission on an early satellite after the chemical propulsion system ran into problems.

Aerojet has been a major space and defense contractor specializing in space propulsion since its inception in 1942, leading the way in development of the technology and products that have helped further man’s exploration of space. If the company’s recent study gains traction and becomes the power source for future missions, it could be very exciting for the future of spaceflight, particularly in our current budgetary climate where space activities are concerned.

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