Sail on, pushed by the wind of sunlight.

Over the past week, engineers have demonstrated how they can steer LightSail-2, a small privately financed spacecraft with a billowing silver sail. The technology could be used to propel future space probes through the solar system.

Most space missions today are propelled by engines that provide bursts of acceleration with limited amounts of fuel. The rest of the time, the spacecraft are coasting.

By contrast, with LightSail-2, particles of light from the sun bounce against the spacecraft’s 344 square feet of sails — roughly the area of a boxing ring — generate a modicum of force, the equivalent of the weight of a paper clip pushing down on your hand. But because the sun always shines, the sail offers a continuous nudge that adds up over time to faster speeds — all without needing any fuel at all.

Officials at the Planetary Society, the nonprofit organization that is running the mission, announced the achievement during a telephone news conference on Wednesday.