The temperatures measured where the oxidizer enters the vehicle at an umbilical connection were about four degrees Rankine or Fahrenheit too high. “The requirement is about 169.1 Rankine, that’s -290.57 degrees Fahrenheit, so we didn’t quite get there on Monday,” Bassler explained. “What we saw at the temperature for the interface to the Core Stage was 173 Rankine, which is -286.67 degrees Fahrenheit.”

A slow flow rate of propellant chills down the facility and vehicle lines to start the loading process, so they aren’t shocked by the sharp, several-hundred degree drop in their temperature. Normally after the chilldown phase, the loading transitions to a slow fill phase, which is at a higher flow rate, and then a fast fill phase to load the propellant tank to the top.

The concern with the warmer propellant in the early phases of loading is geysering. “The thing that the team is trying to protect in the [temperature] limits that got tripped are relative to the concern of developing a gas bubble in [a] feedline,” SLS Program Manager John Honeycutt said. “[A bubble] could end up collapsing and then you could have quite a bit of energy released when the liquid oxygen above that bubble could release and fall back down the feedline.”