United Launch Alliance (ULA) says despite recent anomalies involving their Centaur V upper stage and the BE-4 engines built by Blue Origin, Vulcan should still fly this year, although behind schedule.
Vulcan is ULA’s successor to the Atlas V and Delta IV heavy-lift rocket families, both of which are scheduled to be retired. The new vehicle uses liquid natural gas and liquid oxygen in its first stage, which is powered by two BE-4 engines. The upper stage, meanwhile, uses liquid hydrogen and liquid oxygen to propel satellites to their deployment orbits.
Tory Bruno, the CEO of ULA, says all components of the company’s next-generation Vulcan rocket have been certified for flight except for the upper stage, known as Centaur V. The company currently uses an upper stage with a similar name, Centaur III, which is flown on Atlas V.
The main difference between the two is the size, in which Centaur V is nearly double the size of its predecessor.
During a propellant loading and tank pressurization test at NASA’s Marshall Space Flight Center on March 29, 2023, a test article of the Centaur V upper stage was destroyed after a hydrogen leak ignited. Until this point, the first launch was scheduled for May 4 from the Cape Canaveral Space Force Station in Florida, carrying the private Peregrine lunar lander and two prototype Amazon Kuiper satellites.
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
More recently, following testing on the launch pad, the Centaur upper stage that was attached to and ready to fly aboard the inaugural Vulcan launch has been sent back to the company’s manufacturing facility in Decatur, Alabama following the explosion.
In a teleconference on July 13, Bruno outlined what went wrong with the Centaur test in March. During the fifteenth test of the stage, he explained that a leak formed near the top of the tank dome, releasing hydrogen for four and a half minutes into an enclosed space. Bruno says it then found an ignition source, causing a large fireball.
Bruno noted the region where the crack formed is in an area near a door toward the top of the stage, noting it has a unique shape.
“We would expect to have a certain load profile across that dome, but right in that narrow region, the loads went way up because of this complicated geometry,” Bruno said.
The solution involves adding an extra stainless steel ring to help strengthen that particular area. It will, however, add an additional 136 kilogram (300 lbs) of mass to the stage.
As a result, the Centaur originally scheduled to fly on Vulcan’s third flight — currently at the factory in Alabama — will be modified with this new ring and will now launch on the rocket’s inaugural flight. The stage that was sent back from the Cape will then be retrofitted with this fix and fly in the future. Finally, the Centaur set to fly on the second flight will now be used on the test stand to complete the certification needed for Vulcan to fly by the fourth quarter of this year, Bruno said.
The welding procedure used to build Centaur V will also change. So far, these new upper stages have been built using automated laser arc welding. SpaceX’s Starship also employs this welding technique.
However, following the leak, Bruno says the welds weren’t as strong as they were expecting — in fact their effort to save time with this new build technique actually takes longer.
“These seams are 12 feet long, and the time that we were saving with the faster speed on this welder was actually more than offset by the time it has been taking to set up the panels on the fixture before the robot comes in,” Bruno explained.
Instead, the company will revert back to the method used on Centaur III called gas tungsten arc welding. Bruno says it’s a wider weld which can be more forgiving, even though it is done manually.
BE-4 Engine Anomaly
The CEO also addressed a recent explosion involving the first-stage BE-4 engines. During a test firing on June 30, Bruno confirmed one of the engines exploded at a Blue Origin testing site in West Texas.
During the 15th acceptance test procedure (ATP), the engine being tested — which had previously failed an earlier ATP
– experienced a burn-through. While conducting tests, waiting to liftoff at the pad, and during the flight, computers monitor all instrumentation to see if they exceed a “red line limit.” This limit is a set mark where if any of their vehicle constraints go over that red line number, either an abort is called on the ground or a command to shut down an engine occur mid-flight.
Bruno admitted that the red line limit was set slightly too high, resulting in an explosion while the engine was attempting to shut itself down. The threshold will be lowered on all future missions and tests.
Bruno emphasized failures like these are part of the process, claiming to have seen similar test failures on engines currently in service such as the RL-10 and RD-180.
“The two engines on flight one have passed this test, as have a dozen BE-4 rocket engines, all of which have been hot fired and in total have accumulated over 26,000 seconds of operation,” Bruno said. “We are very confident in the design and the workmanship of the assets that have passed acceptance. This is not unexpected. It won’t be the last. And there will be other components on the rocket that also fail acceptance testing.”
— Chris Bergin – NSF (@NASASpaceflight) June 8, 2023
A test of the vehicle known as the Flight Readiness Firing was completed successfully on June 7, which saw the first stage ignite and fire its two BE-4 engines at flight power for approximately seven seconds. Bruno says those are among the engines that passed their ATP.
The Path Forward
According to Bruno, the first certification flight of Vulcan will occur in either the late third or early fourth quarter of this year, but no specific date was given. Full vehicle certification is expected to be completed in the first quarter of 2024. The company expects to be able to fly military payloads later in that same year as part of the United States Space Force’s National Security Space Launch program.
(Lead image: The Cert-1 Vulcan-Centaur stack rolls out to the pad at SLC-41 on May 11. Credit: United Launch Alliance)