Shuttle schedule in limbo due to Alpha robot arm

The crew of Atlantis: Seated with the isignia mission commander Steven Lindsey, right, and pilot Charles Hobaugh. Standing, from left, are mission specialists Michael Gernhardt, Janet Kavandi and James Reilly

By Richard Stenger
CNN

(CNN) -- NASA has delayed yet again a space shuttle launch as ground controllers diagnose a mysterious ailment afflicting the robot arm on the international space station.

The early June departure date for the shuttle Atlantis has been pushed back three times already and on Wednesday it was postponed further to no earlier than July 12.

Another delay could force shuttle managers to keep Atlantis on the ground until September, which would mean another NASA orbiter would visit the space station first.

The crew of the shuttle Discovery, originally set to fly in July, now expects to blast off from the Kennedy Space Center in Florida on August 5. The Discovery mission is intended to bring a new Alpha crew and return with the old one.

The current residents, Russian commander Yury Usachev and NASA astronauts Jim Voss and Susan Helms, expected to spend four months on Alpha. But Friday will mark the 100th day in space for the second Alpha crew and there is no firm return itinerary in sight.

The reason for the schedule limbo -- problems with the new robot arm on space station Alpha. Soon after arriving in April, the $600 million mobile crane was plagued with technical problems during testing, in particular a shoulder joint that seemed to have faulty computer software in its backup system.

In recent weeks, the arthritic joint went into remission and ground controllers were mystified as to why. They have pushed back shuttle launches in order to uplink software patches and do more testing to make sure the arm works properly.

Atlantis, left, and Discovery remain grounded with the shuttle launch schedule up in the air

NASA could decide Monday whether to flip-flop the Atlantis and Discovery missions, after more robot arm testing by ground controllers and the Alpha crew this week.

Installed in April, the multi-jointed Canada-built robot arm is designed to travel across the exterior of the station, mimicking the locomotion of an inchworm as it attaches to various data and power ports.

The 57-foot (15-meter) arm, larger and more sophisticated than its shuttle crane cousins, is needed to complete many big construction jobs planned for the space station, which the United States, Russia and other partners hope to complete by 2006.

The first task is to attach an airlock to Alpha that later station crews would use to stage spacewalks. Atlantis is scheduled to deliver the $164 million airlock.

Departure timing is particularly important for the Atlantis and Discovery missions. Beginning July 17, the space station will orbit Earth for about three weeks in a manner that could prove hazardous for docking orbiters.

And beginning August 18, a network of military ground stations that helps track shuttle flights will be down for scheduled maintenance for a month.

Just in case NASA changes the order of the flights, the third Alpha crew has been training to install the airlock with the robot arm, a chore that Usachev, Voss and Helms were expected to perform.