CAPE CANAVERAL, Fla. — NASA asked an astronaut aboard the international space station to exercise vigorously Friday, hoping the rapid movement would jostle a half-retracted solar wing that refuses to fold up properly.

German astronaut Thomas Reiter of the European Space Agency was told to do 30 seconds of robust exercise on a bungee-bar machine in an attempt to vibrate wires on the 115-foot (35-meter) solar array and prevent an unplanned, fourth spacewalk.

Reiter tried several times, but his exercise did not appear to change the solar array.

“I’m very sorry to hear that,” said Reiter, who has been at the space station since July. “I was training for it for a half year.”

Mission Control radioed back, “We’ll give you a silver medal for that.”

Earlier in the day, flight controllers jiggled the solar array 10 degrees to either side by remote control to try to relieve tension in a wire system that is preventing it from folding up like an accordion, as designed. That too did not appear to have the desired effect.

Flight controllers thought Reiter’s workout might fix the solar array problem based on previous experience. NASA officials recalled an incident in which the space agency saw an array shaking and found that the cause was astronaut Leroy Chiao working the exercise device hard.

“If you think of the station as kind of a long beam ... If you’re at one end putting a force into it, you’ll get some vibration going on,” Chiao told The Associated Press on Friday. He lived aboard the space station from October 2004 to April 2005.

The solar wing was part of an interim power system. A primary goal of space shuttle Discovery’s seven-day visit to the space station was to rewire the lab and hook a new set of solar wings onto the permanent electricity grid.

The new panels rotate with the movement of the sun to maximize the amount of solar energy produced, but in order for the new panels to spin, the old panel had to be retracted.

While it was folded far enough to give clearance to the new panels, the old one got stuck after retracting halfway. NASA had wanted it to retract fully.

NASA was considering a fourth spacewalk if Friday’s efforts failed, and the solar array could be jettisoned in a worst-case scenario.

“You’ve probably heard us use the analogy of trying to fold a map,” U.S. astronaut Michael Lopez-Alegria, a space station crew member, said during a news conference from space. “At times, when you’re folding a map, it’s helpful to poke it here and there. ... It won’t be very different from that, although we’ll be poking very gently.”

During two previous spacewalks, the Discovery crew installed a 2-ton, $11-million addition to the space station and rewired half of the orbiting space lab. A third spacewalk is scheduled for Saturday to rewire the other half.

NASA astronaut Robert Curbeam and Swedish astronaut Christer Fuglesang — who have performed both of the spacewalks — would likely conduct the fourth spacewalk, if needed. It could also be performed later by one of the space station crew members.

Discovery’s crew had their quietest day since arriving at the space station. They took time out to talk to reporters, and Fuglesang, the first Swede in space, talked to Swedish students and dignitaries, including Crown Princess Victoria.

Fuglesang, who is a former Swedish national Frisbee champion, spun one of the flying discs in the air for 20 seconds, assisted by zero gravity.

The 12 orbiting astronauts on the International Space Station were hailed by the chief on Thursday — and also got a humorous scolding for keeping their android crewmate locked up in its packing for so long.