Preparations for the world's first solar-powered round-the-world flight hit a major snag Thursday when the Swiss team behind the project was forced to postpone a 24-hour test flight because of an equipment problem.

The idea was to fly the prototype aircraft all day, taking advantage of clear skies to charge the plane's batteries to full capacity, and then use the stored solar energy to fly through the night until a dawn landing.

In the end it was a cellphone-sized piece of communications equipment that kept the one-seater plane with its massive 262.5-feet (80-meters) wingspan on the ground.

"It's the first big problem that we have," said Bertrand Piccard, co-founder of the Solar Impulse team, speaking at its base in Payerne, Switzerland.

Engineers worked all night to find a solution but finally decided to postpone the effort for safety reasons, he said.

"The brain of the mission control is fed through this piece," said Piccard, a record-breaking balloonist whose father and grandfather also accomplished pioneering airborne and submarine feats.

The "piece," known as a telemetric transmitter, is meant to keep the ground team in touch with the aircraft and its pilot.

"If it doesn't work, the mission control is blind," said Piccard. "The pilot is alone and basically we just have the radio to know what Andre is doing up there."

Pilot Andre Borschberg, who would have flown the plane nonstop for 24 hours if everything had gone to plan, described the failed transmitter as "very critical."

Without it, the team risked calamity because so much of the experimental aircraft works at the limits of current technology, he said.

No new date has been set for the next attempt, but it has to happen before early August or the days won't be long enough to allow the batteries to be fully charged for the night, said Piccard.

Having achieved the first nonstop circumnavigation of the globe in a balloon, the Breitling Orbiter III, in 1999, Piccard said problems such as these were to be expected on such a pioneering mission.

"We need to go through these frustrations in order to have the success," he said. "If this project was easy, everybody else would have already done it."