Testing Day

There is a slim chance that NASA will be forced to announce a postponement in Atlantis' launch to space station Alpha as early as today.

A recently discovered problem with one of seven joints on the station's Canadian robot arm prompted the need for programmers to write a new set of software to work around what is believed to be a hardware failure on the $600 million Canadarm2.

The software patch was to be uploaded to the station's computers on Sunday and tested aboard the outpost today, said NASA spokesman James Hartsfield.

If the test fails for some reason, it's possible officials will decide to delay this week's launch in order to give them time for additional troubleshooting. The duration of the delay would greatly depend on if there is a need to train Atlantis' astronauts in new procedures for using the station arm to install the S0 truss, mission commander Mike Bloomfield told SPACE.com.

Future assembly missions rely so heavily on the Canadarm2 that officials decided to permanently fix the problem by replacing the suspect wrist roll joint with a spare. The assignment went to the next shuttle crew, whose mission aboard Endeavour was delayed nearly four weeks to May 31 to allow time to load the hardware aboard and train the crew for the added spacewalk.

As a result of the delay, the current Expedition Four crew of Yuri Onufrienko, Dan Bursch and Carl Walz will get to spend an extra month in space. For Bursch and Walz, the bonus time means they will break Shannon Lucid's 188-day record for the longest spaceflight by an American, set by her in 1996 thanks to delays in her shuttle ride home from the Russian space station Mir.

Those trailblazing shuttle missions to Mir were considered to be Phase One of the space station program by NASA.

Phase Two began with the 1997 launch from Kazakhstan of the Russian Zarya space tug, followed quickly by the launch of the U.S. Unity node from Florida. Two years passed before Russia was able to launch the Zvezda service module, and then a month later the Expedition One crew lifted off in a Soyuz spacecraft to dock with the fledgling outpost.

Phase Two of the assembly effort ended last July when Atlantis carried the Quest airlock up to the station, which by then had grown to a complex 17 stories in length and weighed some 300,000 pounds (136,000 kilograms).

Nine months have passed and officials say they are anxious to continue building out the station through 2003, increasing the amount of electrical power available to the outpost so that additional science modules contributed by NASA's European and Japanese partners can be deployed.

"Sometimes we think we're about done, but we really have a lot of work left to do in the next two years to get to the point where we're ready to deploy the international partners," said NASA station chief Tommy Holloway.

To kick off Phase Three the space agency is launching what is arguably one of the most complex pieces of hardware ever built, a truss section that when fully operational will be the place from which all electrical power and cooling capability for the U.S. side of the station will be managed.

"S0 is more than just a truss element that some people may generally think of as just a girder or a piece of structure," said Ben Sellari, the launch package manager for this mission. "It has a lot of functionality as well."

In addition to providing the distribution of power and cooling, the S0 truss -- which measures 44.2 feet (13.5 meters) long and 14.5 (4.4 meters) feet wide -- includes:

• Four computers for managing the flow of electricity and fluids through the entire length of the completed truss. Two of the computers will manage the activity of the nine other truss segments still to be installed, while the other two computers handle the S0 truss.

• A set of four Global Positioning System antennas and two gyroscopes for determining the station's position in space and changing its orientation, a capability that will complement and back up what the Russians already are able to do with the station.

• Mechanical, electrical and fluid umbilical lines that must be attached to the Destiny module and other station parts during the four spacewalks planned while Atlantis is docked.

• The rail upon which the Canadarm2's Mobile Transporter can be moved along the entire length of the completed truss at a blazing top speed of one inch per second.

Fully installing the truss is the principal goal of STS-110 crew, which includes three rookies: pilot Stephen Frick and mission specialists Lee Morin and Rex Walheim.

But if any problem threatens to end the shutle mission early, at minimum NASA officials say they would like to get the truss mechanically attached to Destiny in at least three spots, while also hooking up power from the station to warm the truss' electronics.

Once the truss is lifted from the cargo bay by Atlantis astronaut Ellen Ochoa, who will be operating the station's Canadarm2, power of some kind must be connected to the truss by spacewalkers within about a day, or the truss' electronics will be damaged.

Two spacewalking teams will share duties in installing the hardware. Astronauts Walheim and Steven Smith will handle the first and third spacewalks, while Ross and Morin will be on duty for the second and fourth spacewalks.

Of note is that, according to spacewalk managers in Houston, Ross and Morin will become the first pair of spacewalking grandfathers ever, and have earned the nickname the "silver team," from fellow astronaut Smith.

Dina Barclay, the lead spacewalk manager for this mission, said the two are fully trained and physically ready for the arduous tasks ahead.

"The only time it even comes up is when these proud grandpas bring out their photos," she said.

The second shuttle mission of the year is scheduled to end April 15 with a midday landing back in Florida.