A lick of paint could help a spacecraft powered by a solar sail get from Earth to Mars in just one month, seven times faster than the craft that took the rovers Spirit and Opportunity to the Red Planet.

Gregory Benford of the University of California, Irvine, and his brother James, who runs aerospace research firm Microwave Sciences in Lafayette, California, envisage beaming microwave energy up from Earth to boil off volatile molecules from a specially formulated paint applied to the sail. The recoil of the molecules as they streamed off the sail would give it a significant kick that would help the craft on its way. “It’s a different way of thinking about propulsion,” Gregory Benford says. “We leave the engine on the ground.”

Solar sails are in essence nothing more than giant mirrors. Photons of light from the sun bounce off the surface, giving the sail a gentle push. It was while developing a solar sail five years ago that the brothers stumbled upon their idea for enhancing the effect.

The pair were testing a very thin carbon-mesh sail by firing microwaves at it. To their surprise, the sail experienced a force several times stronger than they expected. They eventually worked out that the heat from the microwave beam was causing carbon monoxide gas to escape from the sail’s surface, and that the recoil from the emerging gas molecules was giving the sail an extra push.

In a forthcoming issue of the journal Acta Astronautica, the Benfords explain how a sail covered with a paint designed to emit gas when it is heated might propel a spacecraft to Mars in just a month. A rocket would take the craft to low-Earth orbit, 300 kilometres up. After the craft unfurls a solar sail 100 metres across, a transmitter on Earth would fire microwaves at it to heat it up. The Benfords calculate a one-hour burst of microwaves could accelerate the craft to 60 kilometres per second, faster than any interplanetary spacecraft to date.

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