from the if-at-first-you-don't-succeed-... dept.
NASA has been preparing for a wet dress rehearsal for the Artemis I rocket, but have hit several issues causing delays, the most recent being a faulty helium gas check valve. They have now announced that a modified wet dress rehearsal will start with a call to stations on April 12. This rehearsal proceeds through as an actual launch activity that scrubs at the T-10 second point. The modified test will focus on filling the core stage with cryogenic propellant, but with minimal propellant operations on the interim cryogenic propulsion stage (ICPS). Following the test, the rocket will be returned to the Vehicle Assembly Building to replace the helium check valve as well as to assess the launch procedures.
NASA is streaming live video of the rocket and spacecraft on the Kennedy Newsroom YouTube channel.
After three attempts to complete a critical fueling test of the Space Launch System rocket, NASA has decided to take a break.
On Saturday night the space agency announced plans to roll the large SLS rocket from the launch pad at Kennedy Space Center to the Vehicle Assembly Building in the coming days. This marks a notable step back for the program, which has tried since April 1 to complete a "wet dress rehearsal" test, during which the rocket is fueled and brought to within 10 seconds of launch.
The decision comes after three tries during the last two weeks. Each fueling attempt was scuttled by one or more technical issues with the rocket, its mobile launch tower, or ground systems that supply propellants and gases. During the most recent attempt, on Thursday April 14, NASA succeeded in loading 49 percent of the core-stage liquid oxygen fuel tank and 5 percent of the liquid hydrogen tank.
While this represents progress, it did not include the most dynamic portion of the test, during which the rocket is fully fueled and pressurized; and it, the ground systems, and computer systems are put into a terminal countdown when every variable is closely monitored. NASA had hoped to complete this wet dress rehearsal test to work out the kinks in the complicated launch system so that, when the rocket is rolled out later this year for its actual launch, the countdown will proceed fairly smoothly.
Also at Spaceflight Now.
NASA encountered a couple of issues while conducting the Artemis 1 "wet dress rehearsal," but it still checked off a major milestone by the time the test had ended. The agency was able to fully fuel all the Space Launch System's propellant tanks for the first time and was able to proceed to terminal launch countdown. [...]
This attempt wasn't flawless either: NASA had to put fueling on hold a couple of times since the rehearsal started on Saturday. Fueling was first put on hold on early Monday morning due to an issue with the rocket's backup supply of gaseous nitrogen. The team was able to repair the valve for the gaseous nitrogen line, however, and fueling recommenced a couple of hours later. As CNN notes, though, a few issues popped up just as the team was finishing up the fueling process on Monday afternoon. They discovered a hydrogen leak and had to find options to seal it after their first solution didn't work. Plus, the flare stack, which burns excess liquid hydrogen from the rocket, caused a small fire in the grassy area around the launch site.
In the end, the launch controllers came up with a plan to mask data associated with the leak so as not trigger a hold by the launch computer. That wouldn't fly in a real launch scenario, but they wanted to get as far into the countdown as possible to gather the data they need. They were successfully able to resume the 10-minute final launch countdown after an extended hold and got to T-29 seconds before they had to end the test completely. [...]
Regardless, they successfully performed several critical operations needed for launch during the test, including handing over control from the ground launch sequencer to the automated launch sequencer controlled by the rocket's flight software.