ARTEMIS II; ROLL BACK

 By Wes Oleszewski- Aero-News Network Spaceflight Analyst

America’s new Moon rocket will be headed “back to the barn” for some unscheduled maintenance. Following its second “Wet Dress Rehearsal” (WDR) on Thursday, February 19, during which all the launch vehicle’s tanks were filled and pressurized. Everything seemed to go well and the WDR was completed. The tanks were then drained, but when technicians attempted to cycle helium in the Interim Cryogenic Propulsion Stage (ICPS) they were unable to do so. Trouble shooting and recycling did not clear the problem. The only way for them to access that part of the launch vehicle is to roll the entire stack back into the Vehicle Assembly Building (VAB). So, it was decided on Saturday, February 21, to delay the Moon launch, scheduled for early March, and roll the Space Launch System (SLS) vehicle from Launch Complex 39B back into the VAB. That process took place on Wednesday, February 25.

Helium, although thought of as the lighter than air gas that makes kid’s balloons fly, is critical for starting and restarting liquid fueled rocket engines in space. It has been used in that function since the early 1960s and was used on ever Apollo lunar mission. Because it is inert, it is used for purging tanks and lines as well as pressurizing propellant tanks. Being inert, it will not react with any residual propellants. In the case of the SLS vehicle’s ICPS, the helium is stored in a series of small round tanks at the base of the stage. Since the ICPS is mostly enclosed within the upper fairings of the booster, once the SLS was rolled out of the VAB there was no way for technicians to physically reach the stage’s plumbing when the fault showed up.

Rollbacks of launch vehicles to the VAB for issues have taken place before. In the first week of January 1972, a helium pressure test ruptured a Teflon bladder in one of the Apollo 16 command module’s reaction control system fuel tanks. On January 7th NASA announced that the problem would require a rollback to the VAB which would delay the launch for at least a month. Exactly 20 days after that announcement a fully flight-rated Saturn V was rolled back to the VAB for the first time.

Repair of the fuel tank required that the command module had to be trucked to the MSO building, de-mated from the stack, and opened to separate the heat shield from the upper command module and permit access to the fuel tank. 

Decades later the Space Shuttle was rolled back to the VAB 19 times in that program’s history. Weather caused five roll-backs and twice roll-backs were due to hail damage. There were also two roll-backs due to hydrogen leaks. The rest were caused by assorted issues with the orbiter, payloads and external tank problems. Also, Artemis I was rolled back to the VAB on April 26, 2022, for an ICPS helium check valve issue. After repairs the vehicle was returned to LC-39B. However, on July 2, the Artemis I vehicle was rolled back to the VAB once again to fix a hydrogen leak on the SLS quick disconnect. Following that the Artemis I was successfully launched on November 16, 2022 having rolled back twice.

Currently there is a lot of social media finger pointing and mis-information directed toward the Artemis II because of recent delays and this roll-back. First there was the delay of the first WDR. It’s been said that it was due to the cold conditions and then implied a similarity to the Challenger accident. In fact, the cold had nothing at all to do with that delay. NASA had placed a forecast wind limitation of 37.5 knots on the WDR due to safety concerns for the closeout crew. The forecast was for winds over 40 knots, yet it actually went higher than 50 knots. Later the hydrogen leak caused the WDR to be scrubbed. This was not an issue with the launch vehicle. Rather it was a ground service equipment issue- and was cured at the pad. Thus, this helium issue is the first and only glitch with the Artemis II, SLS vehicle itself. 

After Artemis I, and a very similar issue, NASA thought they had cured the problem with the helium check valve. Now they will roll-back the SLS and find out if or not that is the case.