Discovery and its crew -- which includes six U.S. astronauts and a Japanese mission specialist -- remain scheduled to dock at the international outpost about 1:45 p.m. Eastern Daylight Time (17:45 GMT) Friday.

Under normal circumstances, the dish-shaped Ku-band antenna would be used to feed the astronauts precise data on the shuttles distance to the station and the speed at which it is closing in on the outpost.

The antenna failure, however, will force the astronauts to rely on shuttle star trackers, cargo bay sensors and hand-held radar guns like those used by the highway patrol to ease their way up to the station.

"Its simply a matter of performing the rendezvous with the alternate rendezvous tools," said NASA flight commentator Kyle Herring.

The apparent loss of the antenna, however, will prevent the astronauts from beaming back live television coverage of their bid to mount a new shuttle docking port and the first piece of the stations girder-like metal backbone atop the 13-story outpost.

TV coverage of four spacewalks to wire up the new additions also is out of the question unless engineers on the ground can figure out how to fix the antenna.

"Right now, I would not bet that were going to get real-time TV back," Shaw said. "But there are some pretty clever folks that are going to be working on this for us."

If the antenna cant be fixed, the astronauts will send back sequential still video snapshots by way of a smaller, less capable S-band antenna.

Deployed late Wednesday after Discoverys launch from Kennedy Space Center (KSC), the antenna at first was working just fine, beaming back TV pictures as the shuttle began a two-day chase to catch up with the station.

The antenna, however, failed in the midst of a television downlink Thursday, sending back a signal that looked a lot like a snowy TV channel.

"The signature is puzzling because (the antenna) just quit," Shaw said. "We saw the test pattern, but it was really, really garbled -- like you didnt have a TV station tuned in all the way. Thats how I would characterize it."

Engineers will continue to troubleshoot the problem overnight in an attempt to get the antenna working once again.

Discoverys astronauts, meanwhile, soldiered through their first full day in space, gearing up for a six-day flurry of construction work that will begin in earnest Saturday.

The crew tested a trio of $12 million spacesuits and had to replace a burned-out bulb in a helmet light. Two jet backpacks that will be tested during the mission also were checked out along with the shuttles 50-foot (15-meter) robot arm.

Japanese astronaut Koichi Wakata will use the Canadian-built construction crane to pluck the new station parts from shuttle cargo bay cradles and then mount them atop the outpost.

Hell also use the arm to hoist crew mates to various work sites around the station during four consecutive days of spacewalking construction work now scheduled to begin Sunday.

All tolled, Discovery and its crew will spend a week docked at the outpost. The astronauts then will depart the station October 20 and head for a 2:10 p.m. EDT (18:10 GMT) October 22 landing at KSC.