Japanese scientists are celebrating the successful deployment of their solar sail, Ikaros.
The 200-sq-m (2,100-sq-ft) membrane is attached to a small disc-shaped spacecraft that was put in orbit last month by an H-IIA rocket.
Ikaros will demonstrate the principle of using sunlight as a simple and efficient means of propulsion.
The technique has long been touted as a way of moving spacecraft around the Solar System using no chemical fuels.
The mission team will be watching to see if Ikaros produces a measurable acceleration, and how well its systems are able to steer the craft through space.
The Japan Aerospace Exploration Agency (Jaxa) said in a statement that its scientists and engineers had begun to deploy the solar sail on 3 June (JST).
On 10 June, Jaxa said, confirmation was received that the sail had expanded successfully. Some thin-film solar cells embedded in the membrane were even generating power, it added.
The principle of solar sailing is a simple one. Photons, or particles of light, falling on a highly reflective, ultra-thin (in this case, just 7.5 microns) surface will exert a pressure.
The force is tiny but continuous, and over time should produce a considerable velocity.
Solar sails will never replace conventional propulsion systems like chemical thrusters, but they do have the potential to play a much greater role in certain types of space mission.