Trevor Mahlmann
After three attempts to complete a critical fuel test of the Space Launch System rocket, NASA has decided to take a break.
On Saturday evening, the space agency announced plans to roll the large SLS rocket from the launch pad at the Kennedy Space Center to the Vehicle Assembly Building in the coming days. This marks a notable step backwards for the program, which since April 1 has attempted to complete a “wet dress rehearsal” test, which involves fueling the rocket and launching it within 10 seconds of launch.
The decision comes after three attempts in the past two weeks. Any attempt at refueling was scuttled by one or more technical problems with the rocket, mobile launch tower, or ground systems that deliver propellants and gases. In the most recent attempt, on Thursday, April 14, NASA managed to load 49 percent of the liquid oxygen fuel tank in the core and 5 percent of the liquid hydrogen tank.
While this represents progress, it didn’t include the most dynamic part of the test, where the rocket is fully fueled and pressurized; and it, the ground systems and computer systems are placed in a terminal countdown when each variable is closely monitored. NASA had hoped to complete this wet dress rehearsal to work out the kinks in the complicated launch system so that, when the rocket rolls out for its actual launch later this year, the countdown will be fairly smooth.
NASA said its contractors, as well as its agency, will use the coming weeks to address issues that surfaced during tank testing as the SLS rocket returns to the large Vehicle Assembly Building. For example, supplier of gaseous nitrogen systems Air Liquide will upgrade its capacities. NASA will also replace a faulty check valve on the rocket’s top stage, as well as repair a leak in the mobile launch tower’s “tail service mast umbilical,” a 10-foot-tall structure that supplies propellant and power lines to the rocket on the pillow.
The space agency’s announcement did not contain any information about the ramifications of the schedule. It seems likely that it will take about a week to prepare and roll the SLS rocket back to the Vehicle Assembly Building. Work on the rocket at that location is likely to take at least most of May.
NASA will then have to make some difficult decisions. It could choose to roll the rocket and its mobile launch tower a second time to the pad and try again to complete the wet dress rehearsal. Then, following normal procedure, NASA would roll the rocket back to its assembly building to arm the “flight safety system,” before rolling to the launch pad a third time for takeoff. It seems that the first launch of the SLS rocket in such a scenario would be August, but a trap launch is more likely.
Another option NASA could pursue is to roll out, complete a wet-dress test on the trail and, if successful, go ahead and launch in a few days. In such a scenario, NASA could launch the SLS rocket in June or July. However, this would be risky due to the flight safety system.
During a conference call on Friday, Artemis Launch Director Charlie Blackwell-Thompson confirmed that there is a 20-day timeline once the flight safety system is armed. (This is a safety mechanism used by all orbital rockets that destroys the booster if it goes off course.) After the system is activated, it takes about a week to make final preparations in the Vehicle Assembly Building and a week to to roll to the launch pad and make preparations there. That would leave just one week for a tank test, raw material recycling and maybe one or two launch attempts before the 20-day deadline closes.
In other words, this means that the wet-clothes test must be nearly flawless and the launch attempt must also be flawless. It would also mean that summer weather in Florida — when there are numerous thunderstorms and other bad conditions — should cooperate.
Finally, NASA engineers have to weigh up a myriad of other factors, such as rocket wear, the side-mounted boosters exposed outside, as well as seemingly countless lifetime considerations with the hardware. For example, agency officials are closely monitoring the health of the fuel in the solid rocket boosters, which were stacked about 16 months ago, among others.
Still, NASA seems confident it will get through this painful teething process for the SLS rocket: a program now 11 years old, in which NASA has invested more than $30 billion in the rocket and ground systems now being tested.
“I have no doubt that we will complete this test campaign, and we will listen to the hardware, and the data will lead us to the next step,” Blackwell-Thompson said Friday. “And we will take the right steps, and we will launch this vehicle. I don’t know exactly what that date is, but I have no doubt that we will complete the test campaign and we will be ready to fly.”
