IKAROS spacecraft to unfurl solar sail, head to Venus

Japan will launch a spacecraft that will use a solar sail to attempt a trip to Venus and beyond later this week.

The IKAROS spacecraft will be the first to attempt interplanetary travel using only solar power. It is among a package of satellites originally scheduled for launch in Japan on Tuesday but postponed until at least Friday due to thunder clouds. Also to be launched is a satellite named AKATSUKI designed to orbit Venus and study its climate.

But it is IKAROS (an acronym from "Interplanetary Kite-Craft Accelerated by Radiation Of the Sun") that is grabbing the attention of the global scientific community with its hybrid solar sail technology, not least because its relatively low $16 million price tag carries the prospect of a boom for space exploration.

After it separates from the launch rocket, centrifugal force will open IKAROS' wafer-thin sail, which Japan's JAXA space agency expects will propel the craft to Venus.

The craft will use energy from the sun in two different way. Photonic radiation will bounce off the 14 meter (46 foot) solar sail, pushing the craft forwards like a yacht sailing into the wind. In addition, thin-film solar panels on the 0.0075 millimeter thick sail should power an ion-propulsion engine, making IKAROS a hybrid spacecraft.

The idea of solar sails has been around for almost a century and the European Space Agency, Russia and the US have all tried to master the technology.

“One of the main differences between IKAROS and the two solar-powered craft the US launched previously is that they were earth-orbiting satellites. Whereas this is the first time interplanetary travel has been attempted with solar technology,” explains Yuichi Tsuda, one of the scientists working on the project. “And the two US missions failed.”

Six-month trip to Venus

IKAROS is expected to take six months to reach Venus, and the team is hoping it will go on communicating for up to a year as it goes past the planet and continues its journey.

“Solar sailing has been the 'ace in the hole' of space travel. And now the technology seems to have been developed very well by this project,” says Kazuto Suzuki, an expert on space policy who has previously worked for JAXA and as a government adviser on the subject.

The IKAROS, which weighs 675 pounds, cost about a tenth of a conventional spacecraft, according to the project’s Dr. Tsuda.

“The budget was very limited from the start, so we used components from other projects, including aborted launches and failed projects, to keep costs down,” Tsuda said. “And we developed the solar cells and other materials by ourselves... The fact that we’re piggybacking on another satellite’s rocket also means we don’t have to pay any launch fees either."

Space exploration on a down-to-earth budget

The mission is being run under the auspices of the Institute of Space and Astronautical Science (ISAS), an organization that was merged into JAXA when the Japanese space program was restructured to save money.

“ISAS has always been very focused on the mission rather than pure science, and has been used to working under very tight budgets. The whole field of solar sailing and the ion engines has been developed under ISAS,” says Dr. Suzuki.

The ISAS scientists are “the real heroes of Japan’s space program” who have “an international reputation for lean, well thought-out, innovative, and sometimes daring missions that have unique and important scientific value,” according to Paul Kallender-Umezu, a long-time observer of Japan’s space development, and author of an upcoming book on the subject, “In Defense of Japan.”

Kallender-Umezu calls any space mission “very, very risky.” But he says that if it does work, “it will be a classic example of ISAS's daring and innovative planetary exploration program, which each decade since the 1970s has opened new vistas of knowledge and insights about our solar system and universe.”

Solar panels in space?

The super-thin sail on IKAROS is unlikely to be damaged by impact from space debris, according to Tsuda.

“We have designed it to withstand impact from the many tiny particles that will hit it, and we think it’s very unlikely to hit anything larger. Even if a section of it is damaged, it can still function,” says Dr Tsuda.

Some of the mission’s ultra-lightweight solar technology may also be applicable back on terra firma, and could contribute to research into building solar panels in space that could beam energy back to earth, according to Tsuda.

One thing the scientists behind the mission insist won’t happen is a repeat of the mistakes of Icarus of Greek mythology, who crashed after his wings melted when he flew too close to the sun.

This story was updated at 3:12 a.m. on Tuesday, May 18.

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