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Way to the stars- Space sailing by sunlight not solar wind

by Sail-World Cruising on 11 Nov 2009
Ikaros - solar sail from Japan - photo by JAXA SW
Sailing through space - the possibility of space travel by sailing pushed along, not by solar wind, but by sunlight - is coming closer with not one, but two experimental flights scheduled to take place in the next year by both Japan, with the Ikaros mission, and the USA, with the Lightsail-1 mission.

Next May, The Japan Aerospace Exploration Agency (JAXA) is planning to launch an interplanetary solar sail mission called the unlikely name of Ikaros. Ikaros, (Icarus) if you remember, was the Greek mythological figure who was destroyed when he flew too close to the sun. JAXA maintains that Ikaros stands for Interplanetary Kite-craft Accelerated by Radiation Of the Sun - much less romantic.

California's Planetary Society will follow with its own demo flight by the end of 2010, called Lightsail-1.

Solar sails have been studied by all of the world's major space agencies, but flight tests have only attempted to deploy solar sails and not tried to use the structures for propulsion.

How Solar Sailing works:

A Solar Sail converts sunlight to a propulsion force by means of a large membrane while a Solar “Power” Sail gets electricity from thin film solar cells on the membrane in addition to acceleration by solar radiation.

Then, if the ion-propulsion engines with high specific impulse are driven by such solar cells, it can become a “hybrid” engine that is combined with photon acceleration to realize fuel-effective and flexible missions.

The Ikaros Mission:
JAXA is studying two missions to evaluate the performance of the solar power sails. Ikaros will be launched together with the Venus Climate Orbiter, "AKATSUKI"(PLANET-C), using an H-IIA (Japan's primary general launch vehicle). This will be the world's first solar powered sail craft employing both photon propulsion and thin film solar power generation during its interplanetary cruise.

Ikaros will be launched from the Tanegashima Space Center, based on Tanegashima Island, one of the most southerly islands in Japan, using the H-IIA. After separation from H-IIA, it will spin at up to 20 rpm( =revolution per minute ), deploying the membrane and generating solar power by means of thin film solar cells (minimum success level) within several weeks. Acceleration and navigation using the solar sail will then be demonstrated (full success level) within half a year

The sqaure Ikaros sail, with a diagonal diameter of 66 feet, is covered with thin film solar cells to generate electricity. The spacecraft will spin up to about 20 rpm for stability during its mission.

Japan has led solar sail research in recent years. A small reflector was deployed from a suborbital sounding rocket in 2004 and a larger sail failed to open completely during an orbital test in 2006.

The Lightsail-1 Mission - helped by an anonymous donation:
The Planetary Society's mission LightSail-1 will come five years after its Cosmos 1 solar sail failed to reach orbit on a Russian submarine-launched Volna rocket.

"We're back!" said Louis Friedman, Executive Director of The Planetary Society. “With an even more ambitious solar sail program than our last venture."

The new solar sail project, boosted by a one-million-dollar anonymous donation, was unveiled at an event on Capitol Hill in Washington, D.C on the 75th anniversary of the birth of Planetary Society co-founder Carl Sagan, a long-time advocate of solar sailing.

LightSail is an innovative program that will launch three separate spacecraft over the course of several years, beginning with LightSail-1, which will demonstrate that sunlight alone can propel a spacecraft in Earth orbit. LightSails 2 and 3, more ambitious still, will reach farther into space.

“We are going to merge the ultra-light technology of nanosats with the ultra-large technology of solar sails in an audacious new program,” said Friedman.

Taking advantage of the technological advances in micro- and nano-spacecraft over the past five years, The Planetary Society will build LightSail-1 with three Cubesat spacecraft. One Cubesat will form the central electronics and control module, and two additional Cubesats will house the solar sail module. Cameras, additional sensors, and a control system will be added to the basic Cubesat electronics bus.

"To get sunlight to push us through space, we need a large sail attached to a small spacecraft. Lightsail-1 fits into a volume of just three liters before the sails unfurl to fly on light. It's elegant," exclaimed Planetary Society Vice President Bill Nye the Science Guy.

LightSail seeks to create and prove solar sail technologies that in a few years can

* monitor the Sun for solar storms,
* provide stable Earth observation platforms, and
* explore our solar system without carrying heavy propellants.

Sailing on light pressure (from lasers rather than sunlight) is also the only known technology that might carry out practical interstellar flight, helping pave our way to the stars.

"Sailing on light is a pathway to the stars, but on that path are also some very important scientific and engineering applications that help us understand and protect our own planet and explore other worlds," remarked Planetary Society President Jim Bell.

Reflected light pressure, not the solar wind, propels solar sails. The push of photons against a mirror-bright surface can continuously change orbital energy and spacecraft velocity. LightSail-1 will have four triangular sails, arranged in a diamond shape resembling a giant kite. Constructed of 32 square meters of mylar, LightSail-1 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.

Lightsail-2 will demonstrate a longer duration flight to higher Earth orbits. LightSail-3 will go to the Sun-Earth Libration Point, L1, where solar sails could be permanently placed as solar weather stations, monitoring the geomagnetic storms from the Sun that potentially endanger electrical grids and satellite systems around Earth.

The Planetary Society’s attempt in 2005 to launch the world's first solar sail, Cosmos 1, was scuttled when its launch vehicle, a Russian Volna rocket, failed to reach Earth orbit. But the organization’s membership never lost faith in the goal to sail on wings of light, and now, thanks to their continued support – including the million dollar private (and anonymous) donation – the new LightSail project will begin.

Sagan’s widow and collaborator, Ann Druyan – whose Cosmos Studios was the Society’s partner and principal sponsor of Cosmos 1 – serves as Chief Advisor to the current project.

The last words are by Ann and Carl Druyan: ‘We have lingered too long on the shores of the cosmic ocean. It’s time to set sail for the stars.’

About the Planetary Society:
The Planetary Society has inspired millions of people to explore other worlds and seek other life. Today, its international membership makes the non-governmental Planetary Society the largest space interest group in the world. Carl Sagan, Bruce Murray and Louis Friedman founded The Planetary Society in 1980. For more complete information go to their!WEBSITE.

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