World / Science & Health

Tiny photon-powered spacecraft sails into higher Earth orbit

Reuters, AFP-JIJI

A small crowd-funded satellite promoted by TV host and science educator Bill Nye has been propelled into a higher orbit using only the force of sunlight blowing against its sail in space, a novel propulsion system developers say could “democratize” spaceflight.

The Lightsail 2 spacecraft, roughly the size of a loaf of bread, was launched into orbit in June and unfurled a tin foil-like solar sail designed to steer and push the spacecraft into a higher orbit using the momentum of photons from the sun.

“In the past four days the spacecraft has raised its apogee, or orbital high point, by about 1.7 kilometers attributable to solar sailing,” said Bruce Betts, LightSail 2 program manager.

Lightsail 2 is only the second light-powered spacecraft ever to fly, following Japan’s experimental IKAROS spacecraft, which began a voyage to Venus in 2010.

The satellite was developed by the Planetary Society, a California-based space research and education nonprofit group whose chief executive is the TV personality popularly known as Bill Nye the Science Guy.

The technology promises a virtually inexhaustible source of space propulsion as a substitute for finite supplies of rocket fuels that the current generation of spacecraft rely on to maneuver in flight.

“We are thrilled to declare mission success for Lightsail 2,” Betts said Wednesday on a call convened with reporters to reveal the spacecraft had raised its own orbit by roughly a mile, sailing under the pressure of light beams from the sun.

Flight by light, or “sailing on sunbeams,” as Nye said, could best be used for missions carrying cargo in space or on small satellites with enough room for deploying larger, and thus more powerful, solar sails.

Other applications include monitoring solar radiation that interferes with Earth-bound communications networks.

The solar sail technology could also reduce the need for expensive, cumbersome rocket propellants and slash the cost of navigating small satellites in space.

“We strongly feel that missions like Lightsail 2 will democratize space, enable more people, more organizations around the world to send spacecraft to exciting and remarkable destinations in the solar system that will lead us to answer that deep question ‘where did we all come from?’ ” Nye said.

He said he would like to see the technology applied to missions searching for life on Mars, the Jovian moon Europa and the Saturnian moon Titan.

Another application could be in maintaining a probe at a stationary point in space, such as a telescope that looks out for asteroids in the vicinity of Earth, or a satellite that needs to be fixed in a stationary orbit above the North Pole.

The idea of solar sailing was first theorized in the 1600s by Johannes Kepler, who wrote that sails and ships “could be adapted to heavenly breezes.”

LightSail 2 puts that into practice via a sail made from Mylar that unfurls to a size of 32 sq. meters. As photons bounce off the sail, they transfer their momentum, pushing the vessel along with a thrust that is tiny but unlimited. With no friction in the near-vacuum of space, the vessel will eventually achieve incredibly high speeds.

The parallels to ocean sailing don’t stop there. If it flies toward the sun, the sail orients itself edge-on, effectively turning off its thrust. When flying away from it, the sail turns broadside to the photons, getting a slight push.

LightSail 2, which is controlled autonomously via software, does not have the precision to maintain a circular orbit. Therefore as its apogee rises, its perigee, or orbital low point, decreases, exposing it to atmospheric drag that will overcome its weak thrust. LightSail 2 will orbit for about a year before falling back into Earth’s atmosphere.

The Lightsail project kicked off in the 1990s, but its first planned prototype, Cosmos 1, was destroyed during a faulty launch on a Russian rocket taking off from a submarine in 2005.

The Planetary Society got its the next prototype, Lightsail 1, into space in 2015, but technical problems kept it from climbing high enough to be steered by sunlight.

The Lightsail project grew from an idea imagined by the society’s co-founders — executive director Louis Friedman and late astronomer and author Carl Sagan — to send a solar sail craft to rendezvous with Halley’s Comet in the 1970s.

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