Tory Bruno, president and CEO of the United Launch Alliance, said today that the Vulcan rocket will be ready to launch by the end of the year. The root cause of a test failure of the Centaur V upper stage has been identified and fixes are underway. A launch date has not been set in part because one of the payloads is a lunar lander that can only be launched on certain days each month.
In March, ULA’s new Vulcan rocket was on track for its first launch in May. Vulcan will replace ULA’s two existing rockets, Atlas V and Delta IV, over the next several years. The final Delta IV is scheduled for next year and although there are several Atlas Vs remaining, all are already assigned to various customers so ULA is eager to get Vulcan up and running. DOD will be a major user of Vulcan and requires ULA to conduct two certification launches, Cert-1 and Cert-2, before putting their most expensive and critical satellites onboard.
The launch planned for May 4 was Cert-1, launching Astrobotic’s Peregrine lunar lander, two test satellites for Amazon’s Project Kuiper communications satellite system, and cremated remains in 150 capsules that will be sent into deep space for Celestis.
On March 29, however, a Centaur V upper stage failed during a test at NASA’s Marshall Space Flight Center. It was not the upper stage for Cert-1, but ULA had to determine what happened before committing to launch.
Today Bruno briefed reporters with comprehensive details on what happened and how ULA is responding.
The Centaur V upper stage delivers payloads to their intended destinations in Earth orbit or beyond after separating from the Vulcan first stage. There are many different trajectories it can fly and must be tested for each of them separately because the stresses on the stage vary. On March 29, this particular Centaur V test article was on its 15th test when a weld failed in the stage’s forward dome. A crack developed in the section filled with liquid hydrogen, creating a leak. Engineers detected the leak, but couldn’t shut the test down before the hydrogen found an ignition source, resulting in an explosion.
Outside of the test rig/ stand. Test article is inside (you can’t see it). Hydrogen leak. H2 accumulated inside the rig. Found an ignition source. Burned fast. Over pressure caved in our forward dome and damaged the rig. pic.twitter.com/0d0KpI1ggj
— Tory Bruno (@torybruno) April 13, 2023
Engineers traced the failure to a weld that didn’t hold at a particularly complicated load and stress site where 15 triangles of stainless steel come together at the top of the stage to form the dome. The stainless steel sheets are “thinner than a dime,” Bruno explained. ULA had switched from arc welding used for Centaur III upper stages to laser welding and as part of the investigation discovered the laser welds did not maintain their strength over time. The combination of higher loads and weaker welds caused the failure.
The solution is adding another layer of stainless steel. That process is already underway for the Centaur V that will be used for Cert-1. Tests will be conducted to qualify that upper stage for that trajectory. Other tests of the Vulcan Cert-1 rocket have been taking place in the interim, including the Flight Readiness Firing on June 7. Bruno is confident everything will be ready by the 4th quarter of this year.
One of the customers on Cert-1 is Astrobotic, which is sending its Peregrine lunar lander to the Moon’s South Pole as part of NASA’s Commercial Lunar Payload Services program. Peregrine can only be launched on certain days each month to ensure it lands during the best lighting conditions on the lunar surface. ULA and Astrobotic are working to determine what launch opportunities are available.
Additional tests will be needed to qualify Centaur V for all the other potential trajectories, which will take until the 1st quarter of next year. Then Cert-2 will fly, launching Sierra Space’s Dream Chaser cargo spacecraft a few months after Cert-1. Next will be the first launch under DOD’s National Security Space Launch or NSSL procurement in the 2nd quarter of 2024.
Adding the extra stainless steel will increase the weight of the stage by 300 pounds, which means it can launch that much less payload, but Bruno doesn’t expect that to be a problem. Vulcan can launch 60,000 pounds to low Earth orbit and there is plenty of margin for Cert-1. Production changes for future stages will reduce that to 150 pounds and even that will be ameliorated over time through a performance improvement program.
Bruno also noted that even before the test failure they had decided to go back to arc welding intead of laser welding because they didn’t achieve the efficiencies they expected, so any concerns about the weakening of welds over time will also be resolved.
Vulcan uses two BE-4 engines produced by Blue Origin. Bruno downplayed the significance of a BE-4 engine failure last month, emphasizing that it was during acceptance testing of that one engine, not qualification testing of the BE-4 design. The BE-4 design already has completed qualification tests, but every engine also undergoes acceptance testing for workmanship. Occasional failures are not unexpected and this one “won’t be the last.”
“There will be other components on the rockets that also fail acceptance testing. You know, I’m flattered by the attention we now have that a routine acceptance test was colorfully discussed on social media, but it really isn’t news.”
BE-4 engines use methane and liquid oxygen (methalox) instead of more traditional propellants. SpaceX’s Starship, Relativity Space’s Terran-1 and Landspace’s Zhuque-2 also use methalox engines. Landspace is a Chinese company. They have been in a bit of race to see which would get to orbit first. Starship, Terran-1 and Zhuque-2 each suffered failures on their first attempts, but Zhuque-2 succeeded yesterday.
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