Space Force plans solar-powered vehicles for operations near the moon

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RSA has won a Space Force-funded SBIR contract to design a spacecraft with a solar-thermal propulsion system.

WASHINGTON — A startup under contract with the US Space Force is studying the use of solar-powered vehicles for deep-space operations beyond Earth orbit.

As Space Force plans possible missions into cislunar space – the vast area between Earth and the Moon – one concern is the limits of traditional chemical propulsion. Solar thermal powered spacecraft that use water as their primary propellant could be a viable alternative, says Shawn Usman, astrophysicist and founder of startup Rhea Space Activity.

RSA has been awarded a Space Force-funded Small Business Innovation Research (SBIR) Phase 1 study contract to design a spacecraft with a solar-thermal propulsion system.

The company envisions a spacecraft that, when launched into space, will deploy an origami-like solar reflector panel. Concentrated sunlight will provide both thermal and electric propulsion using water as the propellant.

The solar reflector, shaped like a satellite dish, will also be used to collect and transmit communication signals, Usman says. The spacecraft, named Scorpius, could meet military needs for space maneuvers and other operations in the cislunar region hundreds of thousands of miles from Earth.

Rapid delivery of payloads to destinations beyond geosynchronous orbit is not efficient with chemical propulsion, he says. Electric propulsion can move large payloads, but it could take months or years to reach cislunar space.

The Defense Advanced Research Projects Agency (DARPA) in a program known as Demonstration Rocket for Agile Cislunar Operations (DRACO) is developing a nuclear-thermal propulsion system as an alternative to conventional chemical propulsion.

Beau Rideout, an aerospace engineer at RSA, says one of the issues with systems like DRACO is the safety and political challenges of working with nuclear reactors.

Rideout claims that the Scorpius vehicle promises similar capabilities to DRACO but without using radioactive material to achieve its level of high performance propulsion.

RSA’s propulsion concept is based on Howe Industries’ solar thermal propulsion system developed for small satellites. Howe Industries, based in Scottsdale, Arizona, has won contracts with NASA and DARPA for its ThermaSat engine.

Troy Howe, president of Howe Industries, says Scorpius is “a new twist on an old concept”. He notes that solar thermal propulsion has been widely studied since the 1990s but considered impractical.

Rideout claims that the RSA design would be more efficient because it uses high-thrust maneuvers instead of the old low-thrust continuous burn concept, and takes advantage of the Earth-Moon gravitational environment.

The Scorpius concept was designed based on input from the US Space Force’s Space and Missile Systems Center (SMC), Usman said. “They said they wanted a bimodal system and asked us to think about different payloads or different capacities that could be used with this propulsion system.”

“We suggested doing the communications part because we already have this huge dish which is also part of the propulsion architecture,” he says. “And so it was kind of a wacky idea that we had and SMC really liked it as a new way to do deep space communications.”

RSA’s SBIR Phase 1 contract provides $50,000 for the initial study. The company will introduce Scorpius to an audience of U.S. Air Force and Space Force officials on August 19 at a “Space Pitch Day” event hosted by SMC. The goal is to win a Phase 2 contract worth up to $1.7 million.

This funding would pay for the lab tests. If the project is successful, the Space Force could fund a Phase 3 award to fly a demonstration spacecraft and prove the concept.

A small satellite of about 100 kilograms would be used to prove the concept. The final size of the vehicle would be around 22,000 kilograms and five meters in diameter when stowed.

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