CAPE CANAVERAL, Fla. — Astronauts ran into trouble Saturday while setting up the International Space Station's newest room, Tranquility: A critical insulating cover does not fit.

The fabric cover is supposed to go between Tranquility and its observation deck, but the metal bars are not locking down because of interference from a hand rail or some other structure at the hatch.

Flight director Bob Dempsey said engineers are trying to figure out how to proceed.

Until this snag, everything had been going smoothly in NASA's final major construction job at the space station.

The cover is needed to protect Tranquility's seals and docking mechanisms from the cold. This port will be exposed, temporarily, when the domed lookout is moved to its permanent location on the other side of Tranquility.

Dempsey said the astronauts may be asked to remove the interfering pieces or, possibly, do away with the cover entirely and proceed with the original relocation plan. Once the lookout is moved, a docking adapter will take its place so the port would not be exposed for too long, provided nothing else went wrong.

Another option may be to hold off on moving the observation deck until a properly fitting cover can be flown on another shuttle flight.