NASA is loading liquid hydrogen onto its Space Launch System moon rocket at Kennedy Space Center on Thursday for an unreleased but critical test of repairing the leaky umbilical that derailed the countdown rehearsal on Feb. 2.
Operations to load liquid hydrogen into the giant fuel tank on the rocket’s main stage are believed to be already underway at Launch Complex 39B on Thursday morning. The test will determine whether new seals installed in the launch pad navel are working.
A NASA spokesperson said of the previously undisclosed test, “As part of our work to assess repairs made to the area where we observed increased hydrogen gas concentrations during the previous wet dress rehearsal, engineers are testing the new seal by running some liquid hydrogen into the interface and partially filling the core stage liquid hydrogen tank. The data will inform the timeline for our next wet dress rehearsal.”
During the Wet Dress Rehearsal, or WDR, the launch team managed a hydrogen leak from the navel at the base of the rocket by stopping and starting the process that feeds propellant into the rocket, allowing the navel seal to heat up and seal off the leak.
Liquid hydrogen is extremely difficult to handle because its tiny molecules can escape through even the smallest imperfections in the propellant system. It is also highly explosive when mixed with air.
The launch team was able to fully load the propellant tanks during the February 2 fuel test, but the countdown was aborted due to a large increase in hydrogen leakage when the fuel tanks were pressurized during the final minutes of the countdown.
The spokeswoman did not immediately provide any additional details, including the amount of hydrogen that would be loaded onto the rocket or whether the propellant tanks would be pressurized to replicate the conditions that impede WDR.
Following the Feb. 2 dress rehearsal, technicians disconnected hydrogen lines that are located on a plate that folds into a three-story high structure rising from the deck of the mobile launcher. There are two tail service masts, one for liquid hydrogen and one for liquid oxygen. Engineers removed and replaced seals on two hydrogen lines.
If all goes well with the hydrogen test on Thursday, NASA could schedule a second wet dress rehearsal as soon as next week.
