U.S. scientists are developing a solar thermal propulsion rocket

At Johns Hopkins University's Applied Physics Laboratory (APL), a group of scientists is developing a rocket powered by thermal propulsion from the sun.

Inside the lab is a shipping container-like setup with thousands of LED lights lining one wall, a central metal trellis extending down, and a thick black curtain partially obscuring the equipment. This is the lab's solar simulator, simulating the intensity of the sun's glow.

Opposite the solar simulator is a plate with small tubes meandering beneath it, and liquid helium passes through the tubes wound under the plate and absorbs heat from the LEDs until it is eventually released through small nozzles. This is the research team's prototype for a rocket propelled by the sun's heat.

"This shows that solar thermal propulsion isn't just a fantasy, it actually works," said Jason Benkoski, who led the research team for what NASA calls the Interstellar Probe program.

According to Benkowski's calculations, such an engine would be about three times more efficient than the best conventional chemical engines available today. "From a physics standpoint, it's hard for me to imagine anything that can beat solar thermal propulsion in efficiency," Benkowski said.

Unlike conventional engines mounted on the rocket's tail, the solar thermal engine the researchers are working on will be integrated with the spacecraft's shroud. The sturdy flat case is made of black carbon foam. The key difference is the meandering pipes hidden beneath the surface. If such an interstellar probe were to get close to the sun and push hydrogen into its shield's vasculature, the hydrogen would expand and explode from a nozzle at the end of the tube, causing the heat shield to generate thrust.

It's a decades-old sci-fi concept, and if it actually succeeds, humanity could get the cheapest flight ticket for interstellar space travel.