Space Shuttle Program managers and engineers met this morning to discuss options following an issue that occurred this weekend while shuttle Discovery’s aft fuel propellant tanks were being vented in preparation for fuel loading.
The Right Reaction Control System, or RRCS, fuel helium tank pressure unexpectedly decreased in unison with the RRCS fuel propellant tank when the fuel tank was vented. This indicates that at least one of the two parallel helium isolation valves is leaking or is remaining in the open position when it is expected to be closed.
Two helium system regulators, a primary and a secondary, will be tested to verify they are functioning correctly. The regulators are “downstream” of the isolation valves, and help to maintain helium pressure to the fuel tank. Knowing whether the regulators are operating correctly is a key factor for managers who must decide whether to launch with the errant condition of the isolation valves. The test is expected to occur late this week once a ground support equipment test panel has been calibrated. The helium system will be brought to flight pressure and engineers monitoring the panel will ascertain whether the regulators function properly.
Managers now are targeting Friday, March 19 to move Discovery’s payload to Launch Pad 39A starting at 12:01 a.m. EDT.
There still are a few days of contingency left in the schedule to make the targeted launch date of April 5.