From ISS On-Orbit Status Report for 21/04/2011.
FE-5 Paolo Nespoli had several hours blocked out on his schedule for the late-added task of troubleshooting the WHC (Waste & Hygiene Compartment) which was declared non-functional yesterday after the "Pre-Treat Bad Quality" signal lit up 3 times in a row. Paolo's efforts were successful: the WHC is back in operation, and the crew is Go to use it. [Replacing the WHC flush tank (an EDV-SB container) last night did not help: no pre-treat solution was added to the water flow from the flush tank. Early today, Nespoli replaced the DKiV Pre-Treat Tank & Water Dispenser Assembly and hose. This R&R (Removal & Replacement) was successful, and the "Pre-Treat Bad Quality" light was cleared.]
Also on Nespoli's work schedule were outfitting activities in the PMM (Permanent Multipurpose Module) Leonardo, reconfiguring RSPs (Resupply Stowage Platforms) in bays Forward 1 & Forward 2 with K-BARs (Knee-Brace Assembly Replacements) and K-BAR capture mechanisms to allow for faster rack rotation and better access to stowage than with the replaced KBs (Knee Braces). The RSPs were then to be tied down in the PMM with LSAs (Long Strap Assemblies). [If the WHC troubleshooting (above) required replacement of the EDV-SB flush tank, these RSP reconfigurations were to be deferred to a later date.]
Working on the WORF (Window Observational Research Facility) rack in the Lab, FE-3 Ron Garan adjusted its SAM (Shutter Actuator Mechanism) to improve shutter closure after the crew had reported (on 12/04) that the Lab window shutter did not fully close when activated. [External views are being coordinated to confirm the degree of success in closing the shutter.]
TVIS Failure:
The TVIS (Treadmill with Vibration Isolation & Stabilization) is currently No Go for the crew, after failing last evening when CDR Dimitri Kondratyev reported that the TVIS gyroscope would not spin up and that it was showing an "underspeed" fault message. Dmitri power-cycled it twice (which has cleared the fault seen in the past), but this was not successful. For now, Russian crews will use the T2/COLBERT advanced treadmill as appropriate while a forward plan is coordinated with US and Russian ground teams.
Elektron Failure:
RSC-Energia reported this morning that the Elektron oxygen generator failed yesterday when reactivated after the REGUL-OS repair activities. ppO2 (oxygen partial pressure) is currently in the nominal comfort range, and work is underway to restore the electrolysis device to service. Should Elektron downtime stretch out longer, an O2 repress from ATV-2 tankage could be performed next week, after which STS-134/ULF-6 would supply oxygen, and another ATV-2 repress could be done after Endeavour's departure.
SKV2 Failure:
Energia also reported failure of the SKV2 air conditioner in the SM (Service Module). Investigation is underway.
Progress 41P Undocking:
Physical separation from DC-1 (Docking Compartment-1) will occur tomorrow morning at ~11:41 AM GMT in insolation (sunshine). Progress M-09M/41P will perform a separation burn three minutes after physical separation. The crew will see the spacecraft moving below and behind the ISS, so it should be visible from any aft or nadir window. Orbital sunset will occur at 11:46 AM GMT, after which the Progress will no longer be visible.
