The upper part of the Vulcan failed due to high stress and weak welds


Grow up / United Launch Alliance’s Vulcan rocket completes a “flight ready shot.”

United Launch Alliance

United Launch Alliance has identified the cause of the failure destroyed the upper part of his Vulcan rocket at the end of March. According to the director of the company, Tory Bruno, the Centaur V upper stage failed due to higher-than-expected pressure near the top of the water hydrogen propellant tank and a little weak welding.

Bruno explained the failure and the steps the company is taking to repair it during a teleconference with Astronomy reporters on Thursday. He said United Launch Alliance is working to fly the Vulcan heavy rocket on its first mission in the fourth quarter of this year.

Tank failure

The upper part of the Centaur V was destroyed during a stress test at the Marshall Space Flight Center in Alabama on March 29. Bruno said that this was the 15th test in a series of 45 tests to qualify the Centaur part in all possible situations. However, about halfway through the test the hydrogen tank began to leak, and four and a half minutes later the leak increased.

During this time the hydrogen jumped into the closed area of ​​the test site, the closed area. When it reached the point of ignition and found an ignition source, the hydrogen ignited. This caused significant damage to the test rig and the hydrogen tank and liquid oxygen tank—filled with liquid nitrogen for measurement.

Quickly, the failure investigation team determined that the leak occurred in the front, or upper part, of the hydrogen tank. By analyzing pieces of the tank using fractography, Bruno said researchers were able to determine where the cracks in the stainless steel tank started, near the top of the dome.

To understand the type of failure, Bruno said that the company ran a reliable model of the load and pressure on the hydrogen dome at this location and found that there was an unexpectedly high load there. In addition, the team analyzed the strength of the adjacent welds and found that they were not as high as previously evaluated.

“These two factors together, high load and low welding power, are what caused the crack,” he said. “Another thing that I would ask you to appreciate, because we are doing transparency here, is how we already had 15 tests, which is a lot of testing and exposure to a lot of problems and more time and more time. The design is under pressure more than it would have been in any aircraft.”

Control actions

To deal with failure, Bruno said the fix is ​​simple. The area close to failure will be reinforced with an additional ring of stainless steel and steel cables. These maneuvers will add about 140 kg to the surface area, which he saw as a negligible loss of payload for a vehicle expected to lift 27 metric tons to low-Earth orbit.

The company is preparing a new dome with these improvements, and this Centaur V tank will also undergo a few tests to confirm the predictions. In addition, the Centaur V upper stage that was to be used for the first flight of the Vulcan rocket, known as the Cert-1 mission, since it is the first of two US Space Force verification flights – has been sent from the launch pad back to the company’s factory in Decatur, Alabama. It will be updated accordingly.

Bruno said conducting the final tests of the Centaur V in unison and changing the type of tank are the last two steps needed before the Vulcan is launched. He also said he was pleased with how the rocket performed in the first phase of the latest “ready-to-launch” test, where the BE-4 rocket’s engines fired for a few seconds.

“We had a lot of fun with the pre-flight shoot,” Bruno said. “Everything was amazing. And there was, I would say, no action required on any hardware, any method.”


Bruno said he expects a period of four to six weeks between the completion of the qualification tests and the launch of the Vulcan. The mission will carry the Astrobotic lunar probe, as well as two experimental satellites for Amazon’s Project Kuiper megaconstellation. In addition to the rocket preparation, the launch date of the Astrobotic mission will also be determined by the illumination of the Moon for the astronauts, so there are only a few days allowed each month.

The second Vulcan flight will launch Sierra Space’s Dream Chaser spacecraft. CNBC reported this week that one of the two BE-4 engines intended for flight on the Vulcan core exploded during an acceptance test in June at the Blue Origin facility in West Texas. Bruno said it was common for rockets to fail this acceptance test, especially early in development. He said Blue Origin understands the cause of the problem and has additional engines under construction.

Assuming that this second certification process takes place in the first quarter of 2024, the United Launch Alliance and the US Space Force will need several months to review the results of the first two launches. After that, the Vulcan rocket will be approved for national security. Bruno said the company is targeting the second phase of 2024 for the first Space Force launch.

As is often the case in space travel, this time looks exciting. But it seems that United Launch Alliance has a clear plan to launch its Vulcan rocket and prepare the vehicle for a long-term demonstration that includes both military missions and several flights to the Amazon Kuiper constellation.


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