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Setting sail for the Stars


Space pioneers could soon be setting sail for the stars. Martin Hickes reports.

IT might look like something out of one of the new Star Wars films, but thanks to the latest technology, space scientists have plans to set sail for the stars – quite literally.

NASA and The Planetary Society are gearing up for three pioneering missions for the revolutionary new Light-Sail craft, namely Light-Sail 1, 2 and 3, which will push the boundaries of space travel.

The new craft – if given the green light next year – will deploy a sail which will use the impact of photons from sunlight and lasers against a special gigantic space sail to accelerate the probe into orbit and possibly to the stars.

Scientists say it is a major leap forward for both a clean and cheap means of space propulsion.

Sunlight, rather than the solar wind, will power the craft, and tiny lasers could kick in when the sun's rays are too weak to propel the probe. Each method uses photons to bombard a huge solar sail, powering the craft through space.

The new solar sail project, boosted by a one-million-dollar anonymous donation, is the beginning of an innovative program that could see the launch of three separate space-sailing craft over the course of several years.

A spokesman for the Planetary Society, which is in talks with NASA over future mission plans, says:

“Solar sail propulsion is simple in concept. Light photons bounce onto a mirror-like aluminium Mylar sail. As each photon hits, its momentum is transmitted to the spacecraft.

“Photons have no mass but lots of energy, so a solar sail space probe requires no on-board fuel. The force acts continuously, meaning a solar sail can eventually reach speeds five to ten times greater than any chemical rocket.

“Russia, the U.S. and the European Space Agency all started solar sail missions and technology programs but cut them back when money got tight. Japan, we are happy to say, is now moving ahead to develop an innovative solar sail and solar-powered ion drive hybrid.

“Yet solar sail propulsion remains largely neglected. That's why the Society has long championed efforts to prove its value.

“We partnered with Cosmos Studios on the far-sighted Cosmos 1 solar sail project. But technology has advanced enormously since then. We can do more in a fraction of the size, with a fraction of the weight and at a fraction of the cost. This has led us to re-think everything…and what we've arrived at is far more advanced, and ultimately far more valuable.

“This technology also opens up many new possibilities for piggyback launching into Earth orbit, which is desperately needed since launch vehicles have been a hindrance preventing solar sail flight. We're considering several launch possibilities and will select the most reliable one that matches our schedule and final orbit choice best.”

So how does it work?

When the light from the Sun reflects off the surface of the solar sail, the energy and momentum of light particles known as "photons" are transferred to the sail.

This gives the sail a "push" that accelerates it through space.

Although the acceleration is very slight, it is also continuous, unlike rockets using chemical engines that fire until the spacecraft reaches a cruising speed, when they are turned off to conserve fuel.

A solar sail can accelerate constantly and reach very high speeds in a relatively short time.

The direction of the push is controlled by the angle of the sail with respect to the Sun, adding to or subtracting from the orbital velocity.

The great advantage of a solar sail is that it requires 'no fuel'.

A solar sail spacecraft can, in time, move the spacecraft even faster than a chemical rocket. For a round trip to another planet and back, solar sails have great advantages since they don’t need to carry fuel for the return leg.

The sails are made of aluminium-coated, reinforced Mylar about 1⁄4 the thickness of a bin liner. The sail must be as light as possible to maximize the acceleration.

The real advantage of solar sailing is that, unlike a chemical rocket that applies a lot of thrust for a very short time, sunlight hitting the sail applies thrust continuously.

In 100 days, a sail-propelled craft could reach 14,000 kilometres per hour. In just three years, a solar sail could reach over 150,000 miles per hour.

At that speed, the craft could reach Pluto in less than five years.

NASA announced this week that the Planetary Society's LightSail-1 solar sail mission is on their short list for upcoming launch opportunities. The missions selected are Cubesats destined for piggyback launches as part of NASA's CubeSat Launch Initiative.

"This is great news," said Louis Friedman, Program Director for LightSail-1. "Our spacecraft will be ready this summer, and we are hoping for the earliest launch possible."

LightSail-1 will have four triangular sails, arranged in a diamond shape resembling a giant kite.

It will be placed in an orbit over 800 kilometers above Earth, high enough to escape the drag of Earth’s uppermost atmosphere.

At that altitude the spacecraft will be subject only to the force of gravity keeping it in orbit and the pressure of sunlight on its sails increasing the orbital energy.

The Planetary Society team say solar sails can be used to boost or decrease the orbits of spacecraft, hold a spacecraft in position to monitor the Sun for solar storms, provide stable Earth observation platforms, travel between the planets within our solar system, and someday take us to worlds around other stars.


* Writers and visionaries have imagined 'clipper-ships' to the stars and planets for years.

* If the early missions are given the green light and are successful, the third Light-Sail-3 craft when launched, could be parked at a special balanced gravity point in space between the the earth and the Sun, called a Lagrange point, where is could act as a solar weather station feeding data back to earth.

Pic caption: LightSail-1 artist depiction by Rick Sternbach. Credit: The Planetary Society