Historical First: Solar Sail Deployed in Orbit for the First Time

JAXA’s IKAROS spacecraft, the first-ever solar sail deployed in orbit, shown en route towards Venus (June 2010).  Image credit: JAXA.

The Space Review is reporting that the Japanese Space Agency JAXA recently made history with a huge milestone reached in the science of spacecraft propulsion.  On May 21, JAXA launched its IKAROS craft, which moves by sailing on solar winds, toward Venus.  The craft was launched with the Venus Climate Orbiter, AKATSUKI (which means 'dawn' or 'daybreak'). JAXA: "This is the world's first solar powered sail craft employing both photon propulsion and thin film solar power generation during its interplanetary cruise."  JAXA's homepage for IKAROS ((Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is here and the info leaflet is here.

Space Review explains briefly how the technology works: "solar sailing is an in-space propulsion technology that has been studied for decades that involves harnessing the momentum of photons streaming out from the Sun by deploying large mirrored surfaces (“solar sails”) from spacecraft. As solar photons are reflected by the mirrors, they exchange momentum with the spacecraft, producing thrust. The pressure due to sunlight is not large—less than 10 micronewtons of force (1/3000 the weight of a penny) for each square meter of sail area. However, as it does not consume propellants the way that rockets do, this means that a solar sail can thrust for long periods of time—months and even years—and so can eventually build up much larger velocity changes than are achievable with rocket-based propulsion. This can enable solar system exploration missions that would otherwise require prohibitive amounts of propellant if using chemical rocket propulsion, such as multiple-asteroid rendezvous missions, near-Sun Solar polar science missions, and solar system escape missions. The ability to thrust continuously can also enable spacecraft to “hover” in locations where spacecraft cannot otherwise loiter."

In order to drum up public interest in the AKATSUKI project, JAXA held a campaign up until January of this year wherein they solicited messages from the public which the spacecraft will deliver to Venus: "we invite people to send us messages that will be printed in fine letters on an aluminum plate and placed aboard the Venus Climate Orbiter AKATSUKI. We will accept messages both from Japan and overseas so that we can bind the feelings and thoughts of everybody in the world into one, and inject it into the orbit of Venus."  Of course, the idea of us sending messages into space is not new; see my blog post on that here.

What would you say to the Bright Star Venus if you had a chance? The Birth of Venus, by Sandro Botticelli c. 1485–1486.

The promise is further laden with Greek symbolism derived from ancient astronomy and mythology: "Venus is well known by the Japanese as the first star, and has been called the 'morning bright star' or 'evening bright star' since ancient times. In the West, its shining beauty is explained in its name 'Venus', the Goddess of beauty. Venus comes closest to the Earth, and the dimensions of the two planets are very similar, hence they are often called 'sister planets.' However, it is imagined that there are no oceans on Venus because it is located a little closer to the Sun. As its atmosphere mostly consists of carbon dioxide, which causes the greenhouse effect, Venus has become a tropical heat planet unlike the Earth. Although Venus has little rotation, its surface is surrounded by strong east winds called a 'super rotation,' which is one of the biggest wonders of meteorology."

Image credit: JAXA.

JAXA has further plans to launch similar research vehicles toward Jupiter and the Trojan asteroids in the late 2010s. Great that everyone seems to be picking up on the mythological character of Icarus these days, isn't it?

Update: NASA has a late August report on solar sails here.