The First Launch of The Space Launch System Has Been Scrubbed
Rocket launches are extremely complex and difficult processes that deal with hundreds of different components attempting to work together perfectly. This especially is the case for the first ever launch of a specific launch vehicle. However, NASA has learned over many years of operation that it is best to ensure everything is ready rather than rush the result.
Unfortunately, earlier today NASA scrubbed the first launch attempt of the Space Launch System rocket. After running through the standard launch operations and more, the agency eventually decided that today was not going to work and are now rescheduling to try and launch the rocket. The main reason for the scrub was a few different problems that arose during the countdown.
The agency is confident that these are easy fixes and the next attempt will not be long from now. It’s important to point out that the success of this launch will have a lasting impact on the future of Artemis and there is very little room for error. Here I will go more in-depth into the events leading up to the scrub, what went wrong, what’s next, and more.
What Exactly Happened?
Late last night many of the launch operations began. Specifically, overnight engineers evaluated data from lightning strikes to the lightning protection system at Launch Pad 39B that occurred on the 27th. They confirmed the strikes were of low magnitude and had no impacts to Space Launch System, Orion, or ground systems. In addition, Meteorologists with the U.S. Space Force predicted an 80% chance of favorable weather conditions at the beginning of the two-hour launch window that opened at 8:33 a.m. EDT Aug. 29, with a 60% change of favorable weather conditions toward the later part of the window. The primary weather concern for the two-hour launch window was still scattered rain showers. In terms of the rocket itself, overnight teams also powered up the Space Launch System rocket’s core stage, charged Orion and core stage batteries, and conducted final preparations on the umbilicals. A pre-launch walk down was also completed at the launch pad that morning.
Later last night, the Space Launch System rocket’s interim cryogenic propulsion stage, or (ICPS), was powered up, the NASA test director also gave the “go” for booster power up, and all non-essential personnel left the launch pad area in preparation for propellant loading operations. At 10:53 p.m. EDT, or L-9 hours, 40 minutes, the launch team reached a planned two hour, 30-minute built-in hold. During this time, the mission management team reviewed the status of operations, received a weather briefing, and made a “go” or “no-go” decision to proceed with tanking operations. Tanking milestones include filling the rocket’s core stage with several hundred thousand gallons of liquid oxygen and liquid hydrogen. This will occur over a series of different propellant loading milestones to fill and replenish the tanks.
Finally, only around 30 minutes until this morning at 11:30 pm, the Artemis I Mission Management Team gave the “go” to proceed toward tanking operations. During tanking operations, teams will fuel the Space Launch System (SLS) rocket with liquid oxygen (LOX) and liquid hydrogen (LH2), beginning with the rocket’s core stage and then the interim cryogenic propulsion stage. Tanking begins with chilling down the LOX lines for the core stage. The process for the chill down, or cooling, uses the propellant lines to load the rocket’s core stage LOX in preparation for tanking. The LOX tank holds 196,000 gallons of liquid oxygen, cooled to minus 297 degrees Fahrenheit. In sequential fashion, LOX and LH2 will flow into the rocket’s core stage tank and be topped off and replenished as some of the cryogenic propellant boils off. The process involves slowly filling the core stage with propellant to thermally condition the tank until temperature and pressure are stable before beginning fast fill operations, which is when the tank is filled at a quicker pump speed. As the super cold liquid oxygen fills the core stage tank, some venting may be visible.
This finally brings us to today the 29th, the official day the Space Launch System was set to take off. At around 1 am this morning, the launch team was ready to begin loading propellant into the rocket, but they held out due to a small weather cell that was producing lighting. Weather criteria for tanking stipulate that the probability of lightning must not exceed 20% in the first hour of tanking. However, only around 10 minutes after this hold, Artemis Launch Director Charlie Blackwell-Thompson gave the “go” to officially begin loading propellants into the Space Launch System rocket. The launch weather officer then reported there are no indication of lightning within five nautical miles of Launch Pad 39B. Next, at 2:30 am, after chilling the lines for liquid oxygen (LOX) and beginning with slow fill of the Space Launch System (SLS) rocket’s core stage, the team then transitioned to LOX fast fill. Teams also completed chill down of the liquid hydrogen (LH2) lines and started LH2 slow fill.
This brings us to the first problem that arose during this test attempt. At around 3:40 am engineers discovered a core stage liquid hydrogen leak in the mating interface. Specifically, during the transition from slow fill of liquid hydrogen into the Space Launch System rocket’s core stage to fast fill operations, launch controllers saw a spike in the amount of hydrogen that is allowed to leak into the purge can, a housing covering the tail service mast umbilical’s quick disconnect, or mating interface with the rocket. Engineers started reverse flow of liquid hydrogen into the core stage and began troubleshooting. The agency pointed out that although a similar issue was identified in an earlier wet dress rehearsal, it may not necessarily be the same cause. 40 minutes later teams continued to troubleshoot the liquid hydrogen leak at the mating interface with the core stage. After manually chilling down the liquid hydrogen as part of troubleshooting efforts, they were in fast fill operations.
Despite the complication, NASA continued to work on the issue and prepare for a possible launch. Around 5 am, as teams continued to fuel the Space Launch System rocket’s core stage with liquid oxygen (LOX) and liquid hydrogen (LH2), teams were given a go to begin propellant loading operations for the rocket’s interim cryogenic propulsion stage, or (ICPS). The ICPS is the upper stage of the rocket responsible for giving the Orion spacecraft the big push it needs to head toward the Moon. The core stage LOX tank was more than 80% filled, and the core stage LH2 tank was more than 61% filled. Although the LH2 tank is larger than the LOX tank, LOX is denser than LH2 and takes longer to load. At this point in time, teams continued to work toward the two-hour launch window that opened at 8:33 a.m. EDT, from Launch Pad 39B. 30 minutes had passed and the Space Launch System’s core stage liquid oxygen and liquid hydrogen tanks were fully fueled and both were being replenished. During replenish, the propellant that naturally boils off is replaced to ensure the tanks are at full capacity for launch. A “go” had been given for liquid oxygen loading into the interim cryogenic propulsion stage.
However, another issue arose around 6:30 am with one of the rocket’s main engines. While liquid oxygen loading into the interim cryogenic propulsion stage was ongoing and core stage tanks continued to be replenished with propellants, engineers began troubleshooting an issue conditioning one of the RS-25 engines (engine 3) on the bottom of the core stage. Launch controllers condition the engines by increasing pressure on the core stage tanks to bleed some of the cryogenic propellant to the engines to get them to the proper temperature range to start them. Engine 3 is not properly being conditioned through the bleed process, and engineers were troubleshooting. Teams also assessed what appears to be a crack in the thermal protection system material on one of the flanges on the core stage. The flanges are connection joints that function like a seam on a shirt, are affixed at the top and bottom of the intertank so the two tanks can be attached to it. Only a few hours later, teams were in a hold with the countdown at T-40 minutes while engineers evaluated why the bleed test to condition the engines was not successful. Engineers also looked at options to gather as much data as possible. Finally, the launch director halted today’s Artemis I launch attempt at approximately 8:34 a.m. EDT. The Space Launch System rocket and Orion spacecraft remain in a safe and stable configuration. Launch controllers were continuing to evaluate why a bleed test to get the RS-25 engines on the bottom of the core stage to the proper temperature range for liftoff was not successful, and ran out of time in the two-hour launch window. Engineers are continuing to gather additional data. As of right now, the backup launch dates are September 2nd and 5th. Until then NASA will work on some of the issues that arose and try to be ready in only a few days.
Conclusion
After a lot of preparation and work, the first launch attempt of the Space Launch System was scrubbed earlier today. While not ideal, the agency is working to fix the issues and has backup launch opportunities not long from now. We will have to wait and see how it progresses and the impact it has on the space industry.