JOIN USHopes to set sail on sunlight
It has long been the dream of rocket scientists to inch nearer to the sun. Kenneth Chang meets some individuals with innovative ideas who are close to making this dream come true
The Planetary Society, a non-profit that promotes space exploration, has announced that it would send the first of two small spacecraft testing the technology of solar sails into orbit this May, tagging along with other small satellites on an Atlas V rocket. “We strongly believe this could be a big part of the future of interplanetary missions,” said William Sanford Nye, the chief executive of the organisation. “It will ultimately take a lot of missions a long, long way.”
When photons - particles of light - bounce off a shiny surface, they impart a tiny bit of momentum, an effect that comes directly from the equations of electromagnetism published by physicist James Clerk Maxwell in the 1860s. In his 1865 novel, From the Earth to the Moon, Jules Verne appears to have been the first to realise that this force could be harnessed for travel through the solar system. The bombardment of sunlight over a large area can gradually but continuously accelerate a spacecraft.
On launching, the Planetary Society’s craft, LightSail, is about the size of a loaf of bread - 4 inches by 4 inches by 1 foot. In orbit, the spacecraft will undergo a month of testing before it extends four 13-foot-long booms and unfurls four triangular pieces of Mylar, less than 1/5,000th of an inch thick, to form a square sail that spans almost 345 square feet.
The May flight is to check that the sail deployment and other systems work as designed. But at the altitude that LightSail will be flying - the Planetary Society cannot say how high, because the Atlas V’s main payload is a military satellite - the drag of air hitting the sail will be greater than the pressure of light, and the spacecraft will drop out of orbit and burn up in a few days.
Next year, a second LightSail is to be lofted higher, to an altitude of 450 miles, by a Falcon Heavy rocket from Space Exploration Technologies Corp., or SpaceX. That flight is to be the first to demonstrate controlled solar sailing while in orbit around Earth. “The idea ultimately is to be able to tack like a sailboat on each orbit,” said Nye, better known as Bill Nye the Science Guy. Both LightSails were built for less than $4 million, financed entirely by private citizens, Nye said.
NASA considered solar sails in the 1970s for a mission to meet up with Halley’s comet in 1986. That spacecraft would have been huge. The initial design called for a square sail roughly half a mile on a side - an area of almost 7 million square feet - to be deployed from NASA’s space shuttle. That was swapped for a design the engineers had more confidence in - a dozen rectangular sails, each 25 feet wide and more than 4 miles long, arrayed like helicopter blades that spun slowly to generate enough centrifugal force to keep the sails stretched out.
Ultimately, the immense sails were regarded as too risky a technological jump. “It was very audacious for its time,” said Louis D. Friedman, who was the engineer at NASA’s Jet Propulsion Laboratory leading the project. Because of delays and cost overruns with the space shuttle program, NASA ended up canceling the Halley’s comet mission, and sails fell out of favour at the space agency. “There was a visceral negative reaction to solar sailing,” Friedman said.
A decade ago, the Planetary Society collaborated with Russian scientists on a solar sail spacecraft called Cosmos 1, raising $4 million from members. “I said, now we have a chance to realistically do something,” said Friedman, who left NASA in 1980 and helped found the Planetary Society, serving as its executive director.
Cosmos 1 launched in June 2005 from a Russian nuclear submarine. But the rocket failed, and Cosmos 1 was lost before the sail could be tested. Instead of attempting to build another Cosmos 1, the society turned to something smaller - LightSail - taking advantage of a new generation of cheaper, miniaturized satellites known as CubeSats. “This is a more accessible, easier-to-build gizmo,” Nye said. “You don’t need a whole space agency.”