Japanese Craft Sail Off to Venus

Akatsuki spacecraft at Venus
Japan's Akatsuki spacecraft is intended to operate for at least two years after it begins orbiting Venus in December 2010.

Japanese Craft Sail Off to Venus

The Americans have done it. So have the Soviets and the Europeans. Now the Japanese are giving it a go.

"It" is putting a spacecraft in orbit around Venus.

The journey of Akatsuki, Japan's latest interplanetary probe, began on May 21st at 6:58 a.m. local time (21:58 Universal Time the previous evening) when a powerful H-IIA rocket soared into an overcast sky from a launch pad on Tanegashima Island. Officials from the Japan Aerospace Exploration Agency (JAXA) report, albeit briefly, that so far everything is going smoothly. The spacecraft has already relayed a few test images of a crescent Earth taken from 150,000 miles (250,000 km) away.

Akatsuki means "dawn" or "daybreak," which is where you'll find Venus in early December when the spacecraft reaches its destination. Depending on the source, this spacecraft is also known as "Planet C" (its designation prior to launch) and "Venus Climate Orbiter" — take your pick.


Crescent Earth from Akatsuki
Hours after its launch on May 21, 2010, the Venus-bound Akatsuki spacecraft recorded the receding crescent Earth at near-infrared (left) and ultraviolet wavelengths.

This craft is all about understanding the Venusian atmosphere. Scientists want to know why the dense airmass is "superrotating," that is, circling completely around in just 4 or 5 days when the planet itself takes 100 times longer. How does its opaque blanket of clouds form? Are volcanoes actively spewing sulfur dioxide (SO2) into the air? Does lightning — long suspected but as yet unproven — really occur, and if so where and when?

A few weeks after settling into a polar orbit that'll range from 200 to 50,000 miles (300 to 80,000 km) above the planet, the boxy, half-ton craft will get to work. Five instruments will take images: one recording ultraviolet wavelengths (to study SO2), two for near-infrared work (ground and lower atmosphere), one looking deep in the infrared (night-side studies of winds and cloud motion), and one keyed to selected visible-light bands for detecting lightning flashes and airglow. A sixth "instrument," an ultrastable radio transmitter, will permit mission scientists to map temperatures as its signal passes through the upper atmosphere.


IKAROS, Japan's solar sail
Measuring 46 feet (14 m) square, IKAROS is a "solar sail" designed to navigate through interplanetary space using the pressure of sunlight for propulsion.

Tagging along with Akatsuki is a secondary payload called IKAROS, a cutesy acronym derived from Interplanetary Kite-craft Accelerated by Radiation Of the Sun. This "solar sail," a giant sheet of thin polymer membrane about 46 feet (14 m) square, will be unfurled in a few weeks, and engineers hope to use it to demonstrate how future spacecraft might glide through the inner solar system powered by nothing more than solar radiation pressure.

Louis Friedman, executive director of the Planetary Society, has championed the potential of solar sailing for decades. In fact, the organization hopes to once again launch its LightSail craft next year. Click here to get Friedman's take on IKAROS and LightSail.

But wait — there's more! The H-IIA also lofted four other small satellites built by Japanese universities. Three of these will remain in orbit around Earth; the fourth, initially called UNITEC 1 but renamed Shin-en ("abyss"), is a test of computer durability that's coasting toward Venus as well.