An innovative solar sail launched in May has been accelerated by sunlight, successfully demonstrating a new fuel-saving propulsion technique in interplanetary space, the Japanese space agency announced Friday.

A small camera jettisoned from Ikaros last month captured this image of the solar sail. Credit: JAXA

An analysis of radar tracking data showed the Ikaros spacecraft began a gradual acceleration as it unfurled its kite-like solar sail June 9, the Japan Aerospace Exploration Agency said in a statement Friday.

"The small solar power sail demonstrator Ikaros, which successfully deployed its solar sail, was confirmed to accelerate by solar sail receiving solar pressure," JAXA posted on its website. "This proved that the Ikaros has generated the biggest acceleration through photon during interplanetary flight in history."

Photons, or units of light, from the sun bombard the ultra-thin solar sail and transfer small amounts of energy to the spacecraft.

JAXA said they measured an acceleration of 1.12 millinewtons, or just one-four thousandth of a pound of force.

The 680-pound spacecraft is more than 11 million miles from Earth on a path toward Venus.

Ikaros launched May 20 along with JAXA's Akatsuki spacecraft, which will fire an engine to brake into orbit around Venus around Dec. 7. Ikaros will continue on a trajectory through the inner solar system.

JAXA says its engineers confirmed the craft's acceleration through Doppler measurements and radar tracking of the giant solar sail.

This chart shows the small acceleration of Ikaros on the line extending to the upper right. The data in the lower left of the chart shows measurements before the acceleration began. Credit: JAXA

The sail membrane is made of heat-resistant yellowish polyimide resin with a thickness of 7.5 micrometers, more than 13 times thinner than the width of a human hair. One side of the sail is coated with silver aluminum material to better reflect sunlight.

It stretches 46 feet wide on each side and 66 feet in diameter from corner to corner.

Lightweight solar cells covering the membrane are already producing electricity, another major milestone for solar sails.

Controllers next will test the sail's maneuverability by tilting the spacecraft's angle to change its orientation and test navigation methods.

Officials hope solar sails are an answer for long-duration missions, which are often limited by finite supplies of chemical propellant. Harnessing a natural resource like sunlight could propel future missions farther and faster into space.