After a virtually flawless launch Monday morning, the space shuttle Discovery and its seven-member crew are gearing up for their arrival at the International Space Station in the wee hours of Wednesday morning.
When the orbiter arrives, however, the crew will conduct their final approach without the benefit of the radar that the space shuttle commander usually has at his disposal to help him guide the craft.
The radar, used during the final 25 miles of the approach, relies on an antenna that failed to work properly when astronauts tried to activate it just after reaching orbit. The antenna, about three feet across, also is used to send and receive images, data, videos, and voice at high data speeds.
"The team did a significant amount of troubleshooting to try to get that system working, but so far that's been unsuccessful," acknowledged LeRoy Cain, who chairs the mission management team, during a press briefing Tuesday evening.
The shuttle crew trains for failures such as this, he continued, and has other tools at hand to help with final approach and docking.
He anticipates a smooth docking Wednesday.
The mission is expected to continue
The meat of the mission starts shortly after the shuttle docks with the station, an event currently scheduled for 3:44 a.m.
Discovery is delivering some eight tons of supplies and hardware to the International Space Station. The mission also calls for three spacewalks designed to help prepare the station for the post-shuttle era and the loss of the orbiters' considerable resupply capabilities.
But the loss of the antenna puts a crimp in the crew's ability to beam back data from their inspection of the shuttle's tiles – a procedure they perform with a laser scanner mounted on the tip of an extension to the orbiter's robotic arm.
Instead of getting quick feedback on whether the orbiter sustained any damage to its crucial thermal protection system, or whether mission managers see a need for a second, "focused" inspection if the first inspections turns up something unusual, the crew will have to wait until they've docked with the station to send the data to Houston.
Tile flew off soon after launch
Images taken from the ground during launch showed what appeared to be a tile flying off the back edge of the orbiter's tail some 42 seconds after launch.
"That is an item of interest for us," Mr. Cain said. Engineers are looking at the event to try to determine what the object was and how large it was.
If it was tile, its loss may be less worrisome than it might appear.
Cain notes that the heat-resistant tiles at that location are used to protect the surfaces from the heat of the shuttle's engines. On re-entry, the tail's trailing edge doesn't encounter the intense heating the orbiter's underside, nose, and wing leading edges must endure.
"This is going to turn out to be a non-issue for us; that's what I expect," he said.
But over the next several days, engineers will be analyzing the event to make sure that's the case.