CAPE CANAVERAL, Fla. -- In what NASA officials characterize as a "big deal," one of four control moment gyroscopes (CMGs) used to help keep the International Space Station pointed in the correct orientation as it orbits Earth failed on Saturday.
The trouble, however, did not prevent the astronauts and cosmonauts aboard the combined shuttle and station complex from completing their planned work for the day.
Maintaining the proper attitude is key to the station's ability to keep its power-generating solar wings pointed at the sun during every orbit. Changing the station's orientation also helps control heating and cooling, and assists when spacecraft approach to dock.
The station is designed to maintain its pointing ability with only two of the four CMGs installed, so there is no danger yet of the outpost tumbling out of control, said NASA flight director Paul Hill.
But there is an increased risk to the station with one of its redundant components not working, and it could be at least six months before a replacement can be delivered.
"Big picture-wise losing a CMG is a big deal. This is a major component. But from a risk perspective right now, we're in good shape," Hill said.
A fairly common piece of space hardware, the CMGs are housed outside the complex on the Z1 truss and are designed to last 10 years in space. The unit that failed has been in space a little more than one year.Officials are not sure exactly what happened but they believe a mechanical failure of a bearing caused the unit to seize up and literally begin tearing itself apart, producing an alarming vibration that could be heard inside the station's Unity node.
"We're hearing a pretty loud, audible noise. A kind of a growling noise in the node," astronaut Carl Walz radioed Mission Control in Houston early Saturday afternoon.
Weighing more than 500 pounds (227 kilograms) and spinning normally at 6,500 rpm, the CGM packs a lot of energy in a small package. However, none of the crew or any of the cameras detected any debris escaping the CMG housing.
Additional looks with cameras on the shuttle's robot arm will be attempted and mission managers are likely to direct mission specialist Franklin Chang-Diaz to take a look when he floats outside on Sunday with French astronaut Philippe Perrin during a planned six-hour spacewalk.
Hill said he didn't know how much the unit cost.
"I'm sure the program has a price tag and I'll bet they're getting updated quotes right now," Hill said.
Designed to be replaced by spacewalking astronauts, the weight and volume of equipment needed to carry the CMG into orbit makes it difficult to find a shuttle mission that can handle the task. The cargo bays of the next two station-related shuttle missions, scheduled for August and October, are full.
A mission targeted for early 2003 might be able to accommodate the job, which officials say they are confident can be done.
"The fine details we need to go hammer out, but for the most part we know what it would take to go change this out," Hill said.
Attaching Leonardo
As flight controllers and mission managers considered the implications of the CMG failure, the 10 humans onboard Endeavour and the frontier outpost continued following their planned timeline and accomplished the major goals of the day.
Chief among those was the installation of the Italian "moving van" known as Leonardo, a module containing nearly three tons of food, equipment, supplies and two new science racks for the just-arrived Expedition Five crew.
Endeavour commander Ken Cockrell operated the shuttle's robot arm to grab hold of Leonardo and lift it from Endeavour's cargo bay, perfectly aligning it with an open berth on the Unity node on the first try and gently locking it in place by 10:28 a.m. EDT (1428 GMT).
"All in all it was a successful and by the book operation," said NASA mission commentator John Ira Petty.
As planned, it took most of the rest of the day for the crew to power up the module, pressurize its atmosphere, check for leaks and crack the hatches open.
Officials said the crewmembers were to begin unloading the module's cargo late Saturday, but the real serious unpacking was expected to take place on Sunday and conclude by Monday.
At that point the more difficult work will begin, Hill said, which is packing the module with more than two tons of trash, unneeded equipment and completed science experiments.
When completed by the end of the week, the crew hopes to have Leonardo filled to 90 percent of its total capacity.
The module will then be closed up and removed from the station's side on Friday, June 14, and returned to Endeavour's cargo bay for the trip home to Earth.
Send Cindy Up
On a much lighter note, Expedition Five commander Valery Korzun, flight engineer Sergei Treschev and Expedition Four commander Yuri Onufrienko participated in a press conference early Saturday with Russian news media in Moscow.
During the exchange a reporter asked Korzun for his comments about the possibility that *NSynch boy band member Lance Bass might fly to the station aboard a Soyuz taxi mission scheduled for launch in late October or early November.
"Well how about Cindy Crawford?" Korzun joked. "We would be very happy to see one of the supermodels."
Although Bass is not formally approved for the next space tourist seat -- in fact, no one is -- and Korzun's stay aboard ISS is scheduled to conclude before the taxi mission flies, it's not beyond the realm of possibility that Korzun and Bass could wind up in space together.
In any case, Korzun said he would look forward to receiving any space tourist at the station.
"They're very welcome here. For example, speaking about (South African tourist) Mark Shuttleworth, he is a great computer specialist and he was very helpful aboard the station. So probably somebody with certain professional qualities would be better," Korzun said.
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