MOSCOW (AP) - Wrapping up the most troublesome stint in the Mir's 11-year history, two Russian cosmonauts packed for home today while flight controllers looked into a potential new problem - the possibility of a water shortage.
Vasily Tsibliyev and Alexander Lazutkin, who have been plagued by cosmic misfortune since shortly after their arrival on Mir six months ago, spent their last full day on the space station before heading back to Earth Thursday.
"Their whole mission has been like one big problem," said Olga Kozerenko, chief of the psychological support team at the Russian Mission Control center near Moscow.
She said the crew made heroic efforts to fix the numerous breakdowns, sometimes working 15 hours a day.
"Tsibliyev and Lazutkin have been over-tired, literally exhausted by all those accidents, and a weary person can make a mistake," she told the ITAR-Tass news agency.
The latest report of trouble came from NASA, which said the space station's water supply was running low, and could run out if the space shuttle Atlantis doesn't arrive there as planned in late September.
Viktor Blagov, Russia's deputy chief of Mission Control in Moscow, told The Associated Press that the Mir currently has enough drinking water to last until around Oct. 7.
A Russian cargo ship carrying water is scheduled to blast off for the space station on Oct. 1, in addition to the space shuttle launch, he said.
Normally, humidity aboard Mir is condensed and recycled into drinking water. But the crew can no longer rely on that system because the water may be contaminated by antifreeze fumes from leaks months ago in the cooling system.
Russian space officials said the outgoing Mir crew is bringing back water samples Thursday that will be checked for contamination.
Frank Culbertson, manager of NASA's shuttle-Mir program, said Tuesday that if the recycled water is found unsafe, the drinking water supplies in containers on board probably will last only until late September.
Blagov agreed, but added that Russian space officials were confident the recycled water is safe to drink. He said the water recycling system has filters that could block out far more antifreeze than what leaked.
Meanwhile, Tsibliyev and Lazutkin can only hope their run of bad luck doesn't extend to the two new crew members, Anatoly Solovyov and Pavel Vinogradov, who will man the station along with U.S. astronaut Michael Foale.
Shortly after the Russian team arrived in February, an oxygen canister burst into flames, filling the station with thick smoke.
Soon afterwards, a climate control system failed, leaking antifreeze fumes and overheating the station to an uncomfortable 86 degrees.
In the most serious accident, a cargo ship slammed into the station during a practice manual docking on June 25, depressurizing one of its modules and reducing the station to half power.
Plans to repair that damage were postponed when Tsibliyev complained of an irregular heartbeat.
Kozerenko, the psychologist, said today that Tsibliyev's condition resulted from stress and a lack of sleep.
"Tsibliyev refused to sleep until he got everything done," she said. "As a result, he tired quickly during the day and didn't feel well, but still refused to rest."
During the past few weeks, Tsibliyev has been under close medical observation and doctors said his condition has stabilized.
The outgoing crew is scheduled to depart in their Soyuz TM-25 capsule at 12:53 p.m. Moscow time (4:53 a.m. EDT) Thursday. They are to land in the former Soviet republic of Kazakstan a little over three hours later.