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Solar sail spreads its wings

An image sent back from the Ikaros spacecraft shows a portion of its solar sail being unfurled.
An image sent back from the Ikaros spacecraft shows a portion of its solar sail being unfurled.

Japan's space agency stretched out its Ikaros solar sail today, but it remains to be seen whether the experimental craft's paper-thin panels are capable of catching a "wave" of solar radiation and putting the sci-fi-flavored propulsion method to its first interplanetary test.

Ikaros was launched on May 20 atop an H-2A rocket from Japan's Tanegashima Space Center, along with a Venus orbiter known as Akatsuki. The solar-sail spacecraft's name pays tribute to Icarus, the young man from Greek myth who flew too close to the sun on wings of wax, but it's also an acronym standing for "Interplanetary Kite-craft Accelerated by Radiation Of the Sun."

After separating from Akatsuki, Ikaros began unfolding four panels that, when fully unfurled, should look like a square kite measuring 66 feet (20 meters) along its diagonal. Pictures sent back by a camera mounted on the spacecraft's hub show the extension of four booms holding the panels, plus the unfurling of sail material. This is the "primary deployment" of the sail. During the secondary stage of deployment, the sail is stretched out to its full extent.

Centauri Dreams passes along hints that the secondary deployment has finished up as well, 4.6 million miles (7.5 million kilometers) from Earth, and says the day's developments qualify as "good news for the sail." But the crucial part of the experiment still lies ahead: Can Ikaros propel itself using the sun's power?


An artist's conception shows Ikaros in its fully unfurled configuration.

The craft is designed to be pushed by the pressure of the sun's photons on the thin panels, which are covered with photoelectric cells to generate electricity. If the experiment works, future solar sails might be equipped with electric-powered ion engines as a second propulsion method.

So far, solar sails have provided propulsion only in science-fiction tales. In the "Star Wars" saga, for example, Count Dooku uses a solar-sail sloop to slip stealthily between scenes. Solar sails also make appearances in the Arthur C. Clarke short story "Sunjammer," last year's mega-movie "Avatar" and other fictional locales.

The nonprofit Planetary Society tried to do solar sailing for real with its Cosmos 1 spacecraft in 2005, but the project was doomed by the failure of its Russian submarine-based launch vehicle. That setback didn't deter the society. Now it's planning to launch a series of LightSail spacecraft starting next year, and so it's watching the Ikaros test with more than usual interest. Louis Friedman, executive director of the Planetary Society, told Wired Science that Ikaros' success would represent a "milestone."

Another milestone for the Japanese space effort is coming up on Sunday, when the Hayabusa probe is due to drop a sample return capsule into Australia's Woomera Test Range. The probe visited the asteroid Itokawa five years ago, and the capsule may (or may not) contain pieces of the asteroid itself. Hayabusa suffered numerous glitches on the way back, but the latest word is that the capsule is on track for a successful re-entry.

More on Ikaros and Hayabusa:

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