Shuttle Discovery Closing in on Space Station

Space shuttle Discovery is closing in on the International Space Station without a working main antenna dish, but NASA said its seven-astronaut crew should have no problems docking at the orbiting laboratory early Wednesday.

Discovery is due to arrive at the space station at 3:44 a.m. EDT (0744 GMT) to begin nine docked days delivering fresh supplies, new science equipment and spare parts to the nearly complete orbiting laboratory.

Since Discovery?s main antenna dish ? which pulls double duty as a docking radar ? is broken, the astronauts will have to rely on star trackers and other tools to keep track of their position as they pull up to the hulking, 800,000-pound (362,873-kg) space station. It?s a scenario the shuttle astronauts are trained for, but one that hasn?t happened in flight in a decade.

?It?s just a great day to be in space and we?re really looking forward to joining up with the International Space Station today,? Dutton said.

Discovery?s astronauts are working an overnight shift during their 13-day mission. They launched into orbit early Monday.

Broken space antenna

Discovery?s failed antenna, which relays Ku-band signals to Mission Control, has forced the shuttle astronauts to work without the ability to beam television signals to Earth or receive large files, e-mail and transfer any large amounts of data.

On Tuesday, the astronauts had to store 40 gigabytes of data recorded from a standard inspection of Discovery?s heat shield so it can be beamed to Earth tomorrow from computers onboard the space station.

During tonight?s docking, the antenna is also expected to be out of commission as a radar ranging tool that is typically used update astronauts on their shuttle?s precise position as it nears the station. The glitch has occurred on at least two other shuttle missions in the past, most recently in 2000 on NASA?s STS-92 mission ? one of the early space station construction flights.

?We have real flight experience with this,? NASA?s space shuttle program manager LeRoy Cain told reporters late Tuesday.?It?s part of the crew?s normal training template to train this event.?

Discovery?s crew has hand-held laser ranging devices, rendezvous sensors and a trajectory control system in addition to the star trackers and non-functioning antenna for docking assistance, he said.

Back flip in orbit

Before Discovery docks at the space station, shuttle commander Alan Poindexter will fly the 100-ton spacecraft through an orbital back flip so astronauts inside the space station can snap high-resolution photos of the shuttle?s tile-covered underbelly.

Those photos will be beamed to Mission Control for analysis to help engineers determine the health of Discovery?s heat shield. Like the Tuesday inspection by Discovery?s crew, the station photos are a safety measure instituted after the 2003 Columbia disaster to make sure a shuttle?s heat shield is intact and safe for the return through Earth?s atmosphere.

Cain said NASA cameras did spot what appeared to be a heat-resistant tile falling from Discovery?s tail during its launch into space on Monday.

Video of the shuttle?s ascent show an object appearing to fall from the left side of the tail-mounted speed brake about 42 seconds after liftoff. Discovery was zooming spaceward at Mach 1 at the time.

?Preliminarily, I don?t believe this will be any impact for us,? Cain said, adding that engineers will complete a full analysis anyway. "This is going to turn out to be a non issue for us, is what I expect."

Discovery?s seven-astronaut crew are flying NASA?s fourth-to-last shuttle mission before the fleet is due to be retired in the fall.

When the shuttle arrives at the space station, its seven astronauts will temporarily boost the station?s population up to 13 people ? tying the all-time record for largest group in space.

There are three women aboard Discovery and one living on the space station to make four in all. When the shuttle docks, it will be the first time that many will be together in orbit at the same time.

Discovery and the space station also have one Japanese astronaut on each of their crews, marking the first time Japan has had two astronauts in space, and together, simultaneously as well

• Images - Shuttle Discovery's Stunning Pre-dawn Launch
• Spotting Spaceships From Earth
• New Space Record! 4 Women in Orbit at the Same Time

SPACE.com is providing complete coverage of Discovery's STS-131 mission to the International Space Station with Managing Editor Tariq Malik and Staff Writer Clara Moskowitz based in New York. Click here for shuttle mission updates and a link to NASA TV.