Commander Yury Onufrienko and Flight Engineers Carl Walz and Dan Bursch continued packing experiments and other gear in anticipation of the arrival of the Space Shuttle Endeavour, their ride home, early next month. Shuttle managers Thursday cleared Endeavour for launch on mission STS-111 May 30, which would lead to a docking with the station on June 1.
With Onufrienko's assistance, Russian flight controllers repaired the Elektron system on the station, one of several methods available to replenish oxygen aboard the spacecraft. The Elektron splits water into hydrogen, which is disposed of, and oxygen, which is released into the cabin, as part of onboard recycling. The unit had been functioning only intermittently for the past two weeks and Russian flight controllers and the crew made several troubleshooting attempts. The problem eventually was traced to an errant sensor which was bypassed with a software adjustment provided by the Russian Mission Control Center.
There was no shortage of oxygen in the cabin air aboard the station throughout the Elektron troubleshooting procedures. While the Elektron was not operating properly, the crew supplemented the cabin air's oxygen by using several Solid Fuel Oxygen Generator cartridges, chemical canisters that release oxygen when heated. Even without the Elektron in operation, the station has oxygen supplies aboard -- in the solid fuel canisters and in U.S. oxygen tanks -- to last in excess of three months. Oxygen reserves also are replenished each time a shuttle or Progress supply craft visits the station.
In the Destiny laboratory, the crew wrapped up work this week with an experiment that grew the first zeolite crystals, a key element of refining processes used in the petrochemical industry on Earth, in a Destiny Laboratory furnace. The experiment had been delivered last month aboard the shuttle Atlantis and the completed crystals will be returned to scientists on the ground by Endeavour. In addition, work continued on the Biomass Production System, a plant growth experiment, with the crew regularly preserving Brassica plant samples and checking the growth chambers' status.
The crew spent several hours this week reviewing the plans for joint work with the astronauts that will arrive aboard Endeavour during STS-111 and the handover of station responsibilities to the upcoming Expedition 5 crew. In addition to exchanging station crews, STS-111 will deliver a Canadian-contributed Mobile Base System that will enable the station's Canadarm2 to move up and down the station's truss railway, delivered on a shuttle flight last month. Endeavour's crew also will replace a faulty wrist roll joint on the Canadarm2, preparing the arm and railway for use in missions later this year and in 2003 that will add more segments of truss to the station.
Meanwhile, station managers are investigating the need to add a safeguard mechanism to some of the fluid umbilical connections that will be used as the truss is assembled during missions later this year and early in 2003. The mechanism is designed to prevent a slight possibility of the umbilical connections, called quick disconnects, jamming over time. The mechanisms will ensure that the umbilicals may always be disconnected as needed for future assembly or maintenance operations. The new mechanisms will be installed during upcoming shuttle missions and station increments. Over this period, the installation may add one spacewalk above what is currently planned.