What problems were encountered during the dress rehearsal?
NASA first shot the SLS rocket to the launch site in mid-March. In early April, it attempted a “wet dress rehearsal” of countdown procedures, including loading more than 700,000 gallons of liquid hydrogen and liquid oxygen rocket propellants. However, technical glitches, including a hydrogen leak during three rehearsal attempts, curtailed the countdown. NASA then dropped the rocket back to the Vehicle Assembly Building to perform repairs. In June, the rocket returned to the launch site for another attempt at the wet dress rehearsal. That attempt, on June 20, encountered a different hydrogen leak, at a fuel line connector in the booster stage of the rocket. However, the propellant tanks were fully filled for the first time and the controllers were able to continue the rehearsal until the countdown ended with 29 seconds remaining. Initially, the goal was to stop the countdown in less than 10 seconds, when the engines would start for an actual launch. Despite the leak, NASA officials determined that all critical systems had been adequately tested and declared the test a success. The missile headed back to the Vehicle Assembly Building for final preparations, including the installation of the flight termination system, which would detonate the missile if something went wrong during launch and eliminate the possibility of hitting a residential area. The flight termination system’s batteries, installed Aug. 11, are normally rated to last only 20 days, but the United States Space Force division that oversees the launches from Florida granted NASA a waiver extending the period to 25 days. This allows for a release date of August 29th, as well as backup opportunities on September 2nd and 5th. NASA hopes to fix the hydrogen leak, but won’t know for sure until the Aug. 29 countdown, when the propellant line will cool to extremely low temperatures that can’t be tested in the Vehicle Assembly Building.
