Cape Canaveral, Fla. ? Astronauts aboard space shuttle Atlantis and the international space station got to see the results of their handiwork Sunday, with the rotation of brand new radiators.

But the main event the unfolding of one of the three exterior radiators was put off until today because of a fleeting electrical problem. A sensor was apparently too sensitive, and engineers needed extra time to reset the cutoff point for a potential short circuit.

“This is new hardware,” Mission Control said, apologizing to the nine space fliers who had gathered at windows to watch the center radiator extend to its full 75 feet in length.

Instead, the astronauts observed as the folded-up radiators swung back and forth in unison on their rotating beam. The massive, elaborate air-conditioning system is part of the $390 million girder that was delivered and installed by Atlantis’ crew last week.

“It looks like it’s moving pretty fast, guys but not out of control,” shuttle astronaut Sandra Magnus told Mission Control. She was informed the radiator rotary joint was moving 45 degrees per minute; it’s designed to rotate 105 degrees in each direction.

“It’s a great sight,” Magnus said.

The extension of the middle radiator is meant as a test to make sure all the moving parts work. The system will not be activated to shed heat until next year.

Once all three are deployed, the radiating surface will be about the size of a tennis court enough area to cool the equivalent of four 2,000-square-feet homes. NASA will aim the radiators at deep space, to keep the ammonia coolant in the lines as cold as possible.

The international space station complex orbits the earth in this image from television. Astronauts took a day off Sunday before finishing their spacewalk mission today.

The three space station residents and six shuttle astronauts took time out Sunday to chat with reporters.

Shuttle astronauts Piers Sellers and David Wolf were getting ready for their third and final spacewalk, set for today. They will finish hooking up the plumbing for the girder, and attach more pressure-relief clamps to the coolant lines.

Sellers said it should be “a walk in the park but it’s not over ’til the fat lady floats.”