Spaceflight Now STS-108

Station command handed over; shuttle glitch studied
Posted: December 13, 2001

Departing space station commander Frank Culbertson formally turned over the lab complex to Expedition 4 commander Yury Onufrienko and his two American crewmates today. Unfortunately for Culbertson, who asked to have the ceremony delayed until today to give him time to prepare remarks, no one on Earth was able to listen in because of an ill-timed television dropout.

After comments by his two Expedition 3 crewmates, Culbertson was beginning his part of the ceremony - the change-of-command part - when one NASA tracking satellite handed the signal off to another. When it returned a few moments later, Culbertson was concluding "... to Expedition 4, the ship is now your responsibility. Thank you very much guys. It's a pleasure."

As the incoming and outgoing station crews traded handshakes and hugs, Culbertson radioed "Houston, was there enough TV?"

Inexplicably, astronaut Stan Love in mission control replied, "We're going to call it good, Frank, thank you very much."

Culbertson's two Russian crewmates - Vladimir Dezhurov and Mikhail Tyurin - were able to make a few comments before the signal was lost.

"I hope the station is not worse than we saw when we came here," Tyurin joked in English. "At least all the computers are working, the treadmill is running, the station is flying, our great, our unbelievable program continues.

"I wish the new crew as much success as possible," he said. "I wish them to be patient enough, because they will have some troubles, they will have some difficulties. But I hope they are prepared and they are trained well enough. I believe they will have enough support from ground and they will be able to successfully accomplish their mission. So good luck guys, the best wishes to you."

The official change of command occurred Monday when the Expedition 4 crew transferred their Russian pressure suits and custom-fitted Soyuz seatliners aboard the station. Today's ceremony was more symbolic than anything else, a more formal event to mark the transition from one crew to another.

Meanwhile, engineers are troubleshooting an apparent glitch with one of the shuttle Endeavour's three inertial measurement units. The IMUs provide critical data to the shuttle's flight computers on the orbiter's position and orientation in space. Under NASA flight rules, the failure of a single IMU has no impact on a mission and officials say Endeavour's flight will not be affected even if the unit in question is, in fact, declared a failure. But if a second unit should fail, the crew would be forced to land as soon as possible.

Last night, a gyroscope in one of the IMUs began a slow drift out of its normal orientation. Endeavour's flight computers immediately "deselected" the unit and sounded an alarm, waking commander Dominic Gorie, to let the crew know about the problem. Within 45 minutes or so, the unit began operating normally again but it remains locked out of the shuttle's navigation system pending the results of an ongoing engineering review.

Again, this is not considered a serious issue at this point and as long as the shuttle's other two IMUs continue operating normally, Endeavour's mission will not be affected.

Some readers may recall that an IMU failure aboard Atlantis in November 1991 (STS-44) prompted flight controllers to declare a "minimum-duration mission" and shorten the shuttle's flight. Endeavour lead flight director Wayne Hale said today the flight rules have been updated since then based on years of additional in-flight experience with the latest generation of IMUs. The units have proven to be so reliable a single failure is no longer considered a mission critical event.

The astronauts spent most of the day packing equipment and trash into the Raffaello cargo module for return to Earth. They also attempted to transfer high-pressure oxygen from the shuttle to the space station's airlock tanks, but a kinked hose forced them to forego the exercise.

An earlier test to transfer nitrogen from the shuttle to the station airlock tanks also came up short. In that case, engineers ultimately figured out what was wrong and corrected it, but by that point normal nitrogen use had lowered pressure on the shuttle side to the point where the transfer was no longer feasible.