Gone but not forgotten: An artist's impression of The Planetary Society's Cosmos 1 in orbit. The solar sail-equipped craft was lost during launch in 2005, but a replacement is already under development.

Credit: The Planetary Society

Under development: A four quadrant, 20-metre-across solar sail is fully deployed during testing in a space simulation chamber at NASA's Glenn Research Centre in Ohio, USA.

Credit: NASA

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Low Earth orbit

Now, NASA's smaller NanoSail-D is shooting for the immediate future, and space.

Researchers led by Edward E. Montgomery's at the Marshall Space Flight Centre and Elwood Agasid at NASA's Ames Research Centre in California are working towards deploying the sail "any day now," says Montgomery. It will travel to orbit onboard a SpaceX Falcon 1 rocket, to be launched from the island of Omelek in the Pacific Ocean.

NanoSail-D will feel two kinds of pressure: aerodynamic drag from the wispy top of Earth's atmosphere and the pressure of sunlight. Montgomery's team hopes to measure both types of pressure as the sail circles Earth.

"Our primary objective is to demonstrate successful deployment of a lightweight solar sail structure in low Earth orbit," says Montgomery.

Johnson cautions: "If – and it's a big if – they can measure the solar pressure, they will have demonstrated [it] as a primary means of orbital manoeuvring. [But] they'll have to show conclusively the effects of solar pressure, with a convincingly high signal-to-noise ratio."

Montgomery acknowledges that challenge. "The orbit available to us in this launch opportunity is so low, it may not allow us to stay in orbit long enough for solar pressure effects to accumulate to a measurable degree," he says. "We are going to have to look closely at the flight data to see if we can make that determination."

"Practical interstellar flight"

Unlike the NASA initiative, Cosmos 2 is a privately funded mission, a partnership of The Planetary Society and Carl Sagan-linked, U.S. media company, Cosmos Studios. Work has begun at the Russian Space Research Institute on some Cosmos 2 spacecraft hardware and they are also studying possible launch configurations on a reliable launch vehicle.

If successful, NanoSail-D and Cosmos 2 could profoundly affect the future of science and exploration missions. "Success would be huge for the future of space exploration," says Montgomery.

"Solar sailing is the only means known to achieve practical interstellar flight," says Friedman. "It is our hope that the first solar sail flight will spur the development of solar sail technology so that this dream can be made real."

Each effort "is a stepping stone," in the great visionary Carl Sagan's words, along "the shore of the cosmic ocean," leading us closer to sailing among the stars.