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United Launch Alliance
United Launch Alliance has identified the basis reason behind a failure that destroyed the upper stage of its Vulcan rocket in late March. Based on the corporate’s chief executive, Tory Bruno, the Centaur V upper stage failed as a consequence of higher-than-anticipated stress near the highest of the liquid hydrogen propellant tank and barely weaker welding.
Bruno outlined the character of the failure and steps the corporate is taking to remediate it during a teleconference with space reporters on Thursday. He said United Launch Alliance is working toward flying the heavy lift Vulcan rocket on its debut mission in the course of the fourth quarter of this 12 months.
Tank failure
The Centaur V upper stage was destroyed during pressure testing at Marshall Space Flight Center in Alabama on March 29. Bruno said this was the fifteenth test in a series of 45 tests to qualify the Centaur stage for all potential mission profiles. Nonetheless, about halfway through the test the hydrogen tank began leaking, and over the course of 4 and a half minutes the leak expanded.
During this time hydrogen leaked right into a confined area of the test stand, a comparatively enclosed space. After it reached a flammable concentration and located an ignition source, the hydrogen caught fire. This seriously damaged the test stand in addition to the hydrogen tank and liquid oxygen tank—loaded with liquid nitrogen for this test.
Pretty quickly, the failure investigation team identified that the leak occurred within the forward dome, or top section, of the hydrogen tank. Analyzing pieces of the tank using “fractography,” Bruno said investigators were capable of pinpoint where the crack in the chrome steel tank originated, near the highest of the dome.
To grasp the character of the failure, Bruno said the corporate ran a high-fidelity model of the masses and stresses on the hydrogen dome on this location and located there have been unexpectedly higher loads there. Moreover, the team analyzed the strength of the welds nearby and located they weren’t as high as previously assessed.
“The 2 things together, higher loads and somewhat lower strength within the weld, are what caused the crack to start,” he said. “The opposite thing I might ask you to understand, since we’re being completely transparent here, is how we were already 15 tests in, which is considerably more testing and exposure to many more pressure cycles and much and plenty of more time with the structure sitting under pressure than would ever occur in any single flight.”
Corrective actions
To handle the failure, Bruno said the fix is comparatively straightforward. The realm near the failure will likely be strengthened with an extra ring of chrome steel and strips of metal. These corrective actions will add about 140 kg to the mass of the upper stage, which he characterised as a negligible lack of payload capability on a vehicle projected to lift 27 metric tons to low-Earth orbit.
The corporate is preparing a brand new dome with these fixes, and this Centaur V tank will undergo a handful of additional pressure tests to confirm its predicted behavior. As well as, the Centaur V upper stage that was for use on the debut flight of the Vulcan rocket—often called the Cert-1 mission, because it is the primary of two certification flights for the US Space Force—has been shipped from the launch site back to the corporate’s factory in Decatur, Alabama. It would undergo similar modifications.
Bruno said performing the ultimate qualification tests for the Centaur V anomaly and modifying the flight version of the tank are the ultimate two steps needed before Vulcan can launch. He said he was pleased with the performance of the rocket’s first stage during a recent “flight readiness firing” test, when the rocket’s BE-4 engines ignited for just a few seconds.
“We were really, really pleased with the flight readiness firing,” Bruno said. “Every thing was phenomenal. And there have been no, I’ll say, no actions required on any of the hardware, any of the procedures.”
Schedule
Bruno said he anticipates a period of 4 to 6 weeks between the completion of the qualification tests and the launch of Vulcan. This mission will carry a lunar lander for Astrobotic, in addition to two test satellites for Amazon’s Project Kuiper megaconstellation. Along with the rocket’s readiness, the Astrobotic mission launch date can even be determined by lighting conditions on the Moon for the lander, so there are only just a few acceptable launch dates per 30 days.
The second flight of Vulcan will launch the Dream Chaser spacecraft for Sierra Space. CNBC reported this week that certainly one of the 2 BE-4 engines intended to fly on this Vulcan core exploded during acceptance testing in June at Blue Origin’s facilities in West Texas. Bruno said it was fairly routine for rocket parts to fail this acceptance testing, especially within the early stages of development. He said Blue Origin understands the reason behind the issue and has additional engines under construction.
Assuming this second certification mission occurs in the course of the first quarter of 2024, United Launch Alliance and the US Space Force would wish just a few months to review data from these first two launches. After that, the Vulcan rocket can be certified for national security launches. Bruno said the corporate is targeting the second quarter of 2024 for this initial Space Force launch.
As is commonly the case in space missions, that timeline seems fairly optimistic. However it does appear as if United Launch Alliance has a transparent path toward finally launching its Vulcan rocket and getting the vehicle ready for a lengthy manifest that features each missions for the military in addition to dozens of flights for Amazon’s Kuiper constellation.