NASA’s Space Launch System Continues To Face Problems During Wet Dress Rehearsal
The Space Launch System or SLS is NASA’s next-generation launch vehicle meant to return humans to the Moon and beyond. However, the massive rocket along with some of the ground systems have been experiencing different problems when attempting the wet dress rehearsal. This has continued to push back the completion of the test along with future plans for the launch vehicle.
Just yesterday NASA began the third wet dress rehearsal test after multiple attempts over the past few weeks. What was initially planned as a two to three-day test, is now surpassing two weeks since the initial attempt at the beginning of the Month. Yesterday the test was concluded after multiple different issues including a leak on the tail service mast umbilical.
Before the Space Launch System can launch for the first time this summer, the wet dress rehearsal must be completed. While the recent tests have not exactly gone to plan, they at least have provided the agency and teams working on the rocket a lot of practice and experience prior to the real deal. Here I will go more in-depth into the recent test and what exactly is going on with SLS and the various ground systems.
Recent Test Attempt
This third wet dress rehearsal attempt began yesterday morning. Specifically, at around 8 AM, NASA tweeted saying, “Artemis Launch Director, Charlie Blackwell-Thompson has given the “go to proceed” with cryo tanking for Artemis I wet dress rehearsal. GN2 issue has been resolved and the rocket has been switched to nitrogen. Teams are discussing when to resume the countdown clock.” This tanking process begins with chilling down the liquid oxygen lines for the core stage. In sequential fashion, liquid oxygen (LOX) and liquid hydrogen (LH2) will flow into the rocket’s core stage tank and be topped off and replenished as some of the cryogenic propellant boils off. At the same time, NASA conducts leak checks to ensure propellant loading is proceeding as expected. However, only minimal cryogenic operations were being conducted on the interim cryogenic propulsion stage because of an issue with a helium check valve found several days ago which cannot be fixed at the launch pad. Here teams worked to chill down the lines used to load propellant into the upper stage but not flow any actual propellant to the stage. The process for the chill down, or cooling, uses the propellant lines to load the Space Launch System rocket’s core stage liquid oxygen in preparation for tanking. The liquid oxygen tank holds 196,000 gallons of liquid oxygen, cooled to minus 297 degrees Fahrenheit. Venting from the super-cold propellant may be visible during this time. Here, liquid oxygen is intended to flow into the rocket. During this process, teams will fill the tank slowly at first and then will begin filling it more quickly. As the super cold liquid oxygen fills the core stage tank, some venting may be visible. However, this did not go exactly to plan yesterday.
Only a few hours after starting the test, NASA tweeted again saying, “As teams began the liquid oxygen (LOX) slow fill, a temperature limit was exceeded. Teams believe they understand the issue and are working a solution that will allow operations to resume. These are all important aspects of test conditions in complex environments.” Specifically, liquid oxygen loading into the core stage was automatically halted near the beginning of slow fill operations when temperature readings on the propellant showed it was warmer than intended. The rocket was put in a safe configuration while teams troubleshot and determined a path forward. Engineers believed they understood the issue and began working on a solution that would ideally allow operations to continue. Teams saw a similar issue during the wet dress rehearsal attempt on April 4, but at a slightly different point in propellant loading operations. The slow fill 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 you fill the tank at a quicker pump speed.
After troubleshooting the issue with the temperature of liquid oxygen during the early stages of propellant loading into the rocket’s core stage, launch controllers then resumed operations. Teams performed chill down operations again before liquid oxygen began flowing into the tank and adjusted pump speeds as necessary during flow to help ensure temperatures remain below limits. They also opened valves to bleed off any warm liquid oxygen. Earlier in the count, teams began slow fill operations for liquid oxygen, but were automatically halted when temperature readings on the propellant showed it was warmer than intended. The liquid oxygen is an extremely cold, or cryogenic, propellant that is maintained at minus 297 degrees Fahrenheit and must be kept at super cold temperatures. As the super cold liquid oxygen fills the core stage main propulsion system, some venting may be visible. Teams have now progressed to fast fill for core stage liquid oxygen and slow fill for liquid hydrogen.
Unfortunately, not long after the agency ran into another complication. NASA tweeted mentioning, “During the transition from slow fill to fast fill a surge in pressure prompted an automatic stop to the flow of LH2. Teams are currently reviewing a forward plan to get back into LH2 flow. Safety parameters like this ensure the rocket remains in a safe configuration.” Specifically, after fast fill on LH2 began, a surge in pressure automatically stopped the flow of liquid hydrogen. Teams began working to troubleshoot this issue and ensure the rocket is in a safe configuration. In the meantime, liquid oxygen flow was paused on the core stage to ensure the tanking operations for LOX and LH2 remained synchronized. After fast fill resumes for liquid hydrogen to the core stage, teams will load minimal cryogenic propellants on the interim cryogenic propulsion stage. Because of an issue with a helium check valve found several days ago, teams worked to chill down the lines used to load propellant into the upper stage, but not flow any actual propellant to the stage. After these events, the clock continued to count down, and the team worked to resume testing. Sure enough, not long after, NASA and the teams working at the site resumed testing of SLS and the ground systems. However, following the theme of previous attempts, this test would only continue for a short period of time before another problem arose.
Not long after NASA tweeted saying, “During an attempt to transition to fast fill for core stage hydrogen a leak was identified in the tail service mast umbilical. Teams have paused LH2 and the rocket is currently in a safe configuration.” While loading liquid hydrogen (LH2) on the rocket’s core stage earlier this afternoon, engineers detected a leak on the tail service mast, which is located at the base of the mobile launcher and connects to the core stage. This was followed by the final tweet regarding this third test attempt mentioning, “Today’s “wet dress rehearsal” activities for #Artemis I have been scrubbed due to the hydrogen leak mentioned in the previous post. This is why we test.” They reported that teams concluded yesterday’s wet dress rehearsal test at approximately 5:10 p.m. EDT after observing a liquid hydrogen (LH2) leak on the tail service mast umbilical. The leak was discovered during liquid hydrogen loading operations and prevented the team from completing the test. Before ending the test, teams also met test objectives for the interim cryogenic propulsion stage by chilling down the lines used to load propellant into the upper stage. They did not flow any propellant to the stage because of an issue with a helium check valve identified several days ago. When teams paused propellant loading, the rocket’s core stage liquid oxygen tank was about 49% filled and the liquid hydrogen tank had been loaded to about 5% capacity prior to the hydrogen leak. From here teams worked to drain propellant from the rocket. They will inspect the umbilical connection, review data, and establish a go-forward plan to address the hydrogen leak. Unfortunately for the agency, this marks the third wet dress rehearsal attempt for the Space Launch System and ground systems at the launch site. What was intended to be a multiple-day test is now surpassing two weeks after continued complications. While the recent results are not ideal, they provide the teams at NASA with a lot of valuable experience and help ensure that nothing like this happens on actual launch days.
Conclusion
Since the start of April, NASA has been working to complete the SLS wet dress rehearsal. What is intended to be a somewhat straightforward and quick test has become the opposite. Just yesterday the agency tried for the third time but was forced to scrub after the third issue presented itself during the test. As of right now, the agency is working to fix the different problems and set up another test date. We will have to wait and see how it progresses and the impact it has on the space industry.