Second SLS Hot Fire is GO at NASA Stennis

Space Coast, FL – NASA has concluded that they will go with another Space Launch System (SLS) Hot Fire Test. The first “final” Green Run Test happened on Jan. 19, 2021 at 0027 UTC (1727 EST) and was to last eight minutes. It only lasted 67.2 seconds due to an auto shutdown triggered by test parameters. These test parameters were intentionally conservative to ensure the safety of the core stage during the test.

NASA SLS hot fire test on January 19th 2021
SLS core stage during first hot fire test and NASA Stennis, near Bay St. Louis, Mississippi, USA | photo: NASA

SLS Auto Shutdown

First a few explanations on what the system is. There is a thrust vector control (TVC) system that gimbals, or pivots, each engine. There are also two actuators that generate the forces to gimbal each engine. The actuators in the TVC system are powered by Core Stage Auxiliary Power Units (CAPU). As planned, the thrust vector control systems gimbaled the engines to simulate how they move to direct thrust during the rocket’s ascent.

NASA Stennis with SLS core stage Hot Fire
Birds take flight as SLS’s RS-25s kick off the first Hot Fire test | photo: NASA

During gimballing, the hydraulic system associated with the core stage’s power unit for Engine 2, exceeded the pre-set test limits. As they were programmed to do, the flight computers automatically ended the test. The specific logic that stopped the test is unique to the ground test. Should this scenario have occurred during a flight, the rocket would have continued to fly using the remaining CAPUs to power the thrust vector control systems for the engines.

Hot Fire Test, Take 2

The Green Run team at NASA Stennis determined that a second hot fire test will be conducted. And even though the first test was to last eight (8) minutes, the second test is only slated to run for four (4) minutes. Teams have decided this will be ample time to provide significant data to verify the SLS core stage for flight.

The first wet dress rehearsal and hot fire completions:

  • transitioning to the automated launch sequence operated by the core stage flight computer and Green Run software,
  • completing the terminal countdown sequence that is like the launch countdown
  • pressuring the tanks and delivering propellant to the engines and demonstrating performance of the core stage’s main propulsion system,
  • firing the engines at 109 percent power level, and
  • operating the thrust vector control system that steers the engines.
SLS mounted at NASA Stennis
NASA SLS mounted at NASA Stennis awaiting 2nd hot fire test | photo: NASA

Currently the second Hot Fire test is targeting sometime in the week of February 21, 2021. To conclude, the SLS will take roughly a month to refit and refurbish along with it’s engines. It will then board barge Pegasus and be transported to NASA Kennedy Space Center in Florida. There it will be assembled to other parts of the SLS rocket and Orion spacecraft in being prepped for the Artemis I launch in late 2021

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