As space-shuttle officials prepare the "Welcome Home" sign for astronaut Shannon Lucid, who has set records during her time aboard Russia's Mir space station, they are keeping a wary eye on the orbiter that will bring her back.
Shortly after the shuttle Atlantis arched skyward yesterday morning, one of three devices vital to controlling the shuttle during launch and landing failed.
Known as auxiliary power units (APUs), the 88-pound turbines power the pumps that keep fluid in the craft's hydraulic systems pressurized. The hydraulic systems control the wing flaps, rudder, and landing gear critical to landing the shuttle. They also steer the nozzles for Atlantis's three huge main engines, a function vital to achieving a desired orbit.
Flight controllers saw indications prior to launch that one of the APUs might have a problem, but the sensor signals were sporadic, according to Pam Alloway, a spokeswoman at the Johnson Space Center in Houston. So the launch went ahead. The balky APU shut down about the time Atlantis shut off its main engines as it reached orbit.
Although Atlantis's two remaining auxiliary power units work, "any time you lose redundancy, it's a concern," she says. In principle, the shuttle can land successfully with only one APU operating, according to shuttle designer Rockwell International.
Initially, mission planners considered speeding up the timetable to bring Atlantis and its crew home sooner. But after calculating the extra amount of fuel the orbiter would burn to accomplish a quicker docking with Mir, planners opted to stick to the original schedule. The timetable calls for the Atlantis crew to dock with Mir tomorrow at 10:17 p.m. Central Daylight Time.
Once Atlantis is linked to Russia's orbiting lab, the shuttle crew will begin transferring more than 2 tons of supplies to their colleagues and, in turn, loading more than a ton of research samples and hardware bound for Russia and the European Space Agency, as well as for the US.
They also will return with Dr. Lucid, who has spent the past six months conducting research aboard Mir and is eager to get back to husband and family. Although she has noted how much she enjoyed her time on orbit, several weeks ago she told her replacement, John Blaha, that he could rest assured that she "would not be on the wrong side of the hatch" when it closes for the return. Mr. Blaha, a retired Air Force colonel, is set to remain aboard Mir to conduct research until January, when his next American replacement is scheduled to arrive.
IF mission planners allow Atlantis to remain on orbit until its scheduled Sept. 26 landing at Kennedy Space Center in Florida, Lucid will have spent 188 days in space. Even if the mission ends early, she will have logged more hours in space than any US astronaut and more than any female astronaut in the world - and she will have inaugurated a permanent US presence in space when she and Blaha trade places.
Her endurance record is due in no small part to technical glitches and bad weather. Atlantis originally was scheduled to retrieve her in early August. But problems cropped up with troublesome solid-rocket boosters. Technicians discovered evidence that hot gases were burning into the joints between booster sections - a problem that led to the Challenger disaster in 1986.
After engineers pinpointed the source of the trouble - a new sealant used on the joints - they switched back to the old sealant. This meant replacing the boosters already mated to Atlantis.
The mission was further delayed by two hurricanes and a scheduling conflict with an unmanned launch at the Kennedy Space Center. The delays added 48 days to Lucid's tenure on Mir.
Atlantis's trip is the fourth of nine shuttle-Mir missions planned between 1996 and 1998. NASA planners intend to use the results of research done on the missions to help in the design and evolution of the international space station, which the US space agency hopes to have up and running by 2002.