1 MINUTE COUNTDOWNS MANUAL

There was also a small grass fire near a flare stack in the vicinity of the pad used to burn off excess hydrogen. Later, loading of liquid oxygen into the SLS upper stage was halted for a time after hitting a pressure limit. NASA delayed the start of tanking of the core stage by about two hours because of a problem with a valve in a backup gaseous nitrogen line serving the pad. The hydrogen leak, which was not related to the leak seen in a previous WDR in April, was the most serious but not the only issue that came up during this test. вЂњI felt like we were in a really good configuration to continue to get into terminal count and see how the hardware performed.вЂќ Launch personnel were monitoring the vehicle closely. вЂњWe were always protected in the flight software so we knew that we had protections there,вЂќ launch director Charlie Blackwell-Thompson said on NASA TV shortly after the end of the test, when asked about the decision to proceed with the countdown despite the leak.

After lengthy deliberation, NASA managers elected to proceed with the terminal countdown from a preplanned T-10 minute hold after taking steps to mask, or hide, the warnings about the leak from computers. Efforts to stop the leak, including warming then cooling the fitting in the hopes of resealing the connection, failed. That terminal count took place about five hours later than planned because of technical issues, including a liquid hydrogen leak in a вЂњquick disconnectвЂќ fitting for a bleed line that transfers that propellant from the core stage back to the pad. However, NASA TV commentary stated that they expected to see a flag at the 29-second point in the countdown.

1 MINUTE COUNTDOWNS MANUAL

NASA originally hoped to get the countdown to a manual cutoff point of T-9.3 seconds, just before, on an actual launch, the vehicle would ignite the four RS-25 engines in its core stage.

1 minute countdowns