Artemis 1 Attempt ends in Scrub, Vehicle Healthy on the Pad

SLS standing on Launch complex 39b.
The Space Launch System standing ready at Launch Complex 39b.
Credit: AN Tran

Artemis I, the first uncrewed flight in NASA’s ambitious campaign to return humans to the surface of the Moon, ended in a scrub early Monday morning, after weather and other issues caused headaches for the NASA/ESA team. During the countdown on August 29th, the first launch attempt of NASA’s Space Launch System was called off due to an issue relating to engine number three (serial number 2058) during its chill down, or Kick Start Bleed Test. 

Mission Launch Director Charlie Blackwell-Thompson and her launch teams decided  to scrub the launch attempt. Even though the countdown was paused, the launch window closed as they tried to resolve the issue. On top of the engine problems, there were also propellant loading and weather issues. Earlier in the count, two unique propellant loading events raised some concern, including a potential hydrogen leak in the Tail Service Mast Umbilical. Errant sensor data occurred while chilling the RS-25 main engines. This led to a stop-start process which ate into the two hour window allotted to the SLS team. 

Unfortunately, weather during the opening and closing of the window was in the red. Ultimately teams were told to stand down and go home and rest before reconvening on August 30th to review the data and come up with a plan to resolve the issues. However, the team did face a victory in achieved the first 100% fill of the SLS vehicle, including the upper stage, on the pad—something not accomplished during Wet Dress Rehearsals earlier this year. 

That evening, NASA held a press conference to discuss the results of this data review and how the teams will be moving forward with key leadership present: agency Director Senator Bill Nelson, Associate Administrator for Exploration Systems Development Jim Free, and Artemis 1 Mission Manager Mike Sarafin. NASA  confirmed the main issue that precluded a launch on August 29th was the Kick Start Bleed test, a test in which liquid hydrogen is run through the cooling system on the four RS-25 engines’ cooling systems. Each engine is chilled down to their operational flight temperature of -420° Fahrenheit to ensure they do not catastrophically overheat or experience thermal shock. According to Sarafin, engines 1, 2, and 4 were trending towards that temperature, while engine 3 was consistently reading higher. This discrepancy was caused by a temperature sensor located in the core stage reading incorrectly, which may be related to the positioning away from the bleed line. A sensor issue caused the difficulty, rather than a fault of the coolant system or the engine itself which may have necessitated more repairs and delays. The team highlighted that many problems and unexpected issues were successfully worked through during the countdown, and that SLS and Orion were looking healthy on the pad. 

Following the review of all of this data and the plans to modify the flight protocol around the faulty sensor, NASA announced the next launch date for Artemis I as Saturday, September 3rd, in a press conference on August 31st. The 2 hour window will open at 2:17pm and close at 4:17pm, Eastern Time. Tanking is expected to begin earlier than the previous attempt to allow for more time to work through any potential issues that may crop up, however, this does result in some commodity loss in the LH2 and LOX tanks on the ground. The SLS team expects to remain within the predicted margins. This modified procedure is similar to one  used for the Green Run at Stennis Space Center, a necessary hotfiring of the first Core Stage. The Tail Service Mast Umbilical, also known as the 8-inch Quick Disconnect, was examined by way of scaffolding on the pad and cleared for an attempt on Saturday. 

Weather is currently forecast to be 60% favorable at the opening of the launch window, and improving to 80%for this attempt, with the 48hr backup window on Monday the 5th at 70% favorable. As always in Florida, this is subject to change as the official time of launch nears. However, teams did express excitement and confidence about the Saturday launch, and expressed their thanks to the teams working to resolve issues. Sunday was ruled out as a launch date due to unique aspects of the SLS flight profile, which would result in Orion being in eclipse and not generating power. The SLS team also stressed the vehicle does have tanking cycles remaining, having only used 8 of their 22 attempts at filling the vehicle. Crowds at the Cape, viewers across the world, and the SLS team are now looking forward to their second shot this coming Saturday. 

Edited by Andrea Lloyd.

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