Vulcan Repairs Are Already Underway For A Launch This Year
Earlier this year an explosive upper stage test of the Centaur V caused some concerns with a separate Vulcan test article preparing for a maiden flight. While initially, the thought was that this mishap wouldn’t affect the launch schedule, an investigation found a weakness in the stage’s design. This meant ULA needed to de-stack the Vulcan preparing to launch and ship the upper stage back to the factory for repairs.
While this happened quite recently, ULA is making good progress and has already begun upgrades on the stage. Tory Bruno has confirmed that he is very confident Vulcan will be ready to lift off this year in quarter 4. He also gave more insight into exactly how they are strengthing the stage and how this will impact the payload capacity, schedule, etc.
For a while now Vulcan has been running into delays for all sorts of reasons continuing to push back its madien flight. ULA is now trying everything in their power to get this rocket off the ground. Here I will go more in-depth into the upper stage’s progress, what they still need to complete, the chances of a launch this year, and more.
Centaur V Upgrades
Back in March, images and eventually video were released of a Centaur V test article exploding on the test stand. While this hardware was separate from the Vulcan test article preparing for flight, it brought up concerns about the different Centaur V upper stage stacked on Vulcan. At first, ULA thought that the anomaly was unique and wouldn’t effect Vulcan flight, however they still launched an investigation to figure out exactly what happened.
The investigation found that the leak originated in the forward dome of the tank, which is made of very thin stainless steel, near a door at the top of the structure. A very detailed finite element model of that part of the tank revealed a “stress riser,” or intensification of loads, because of the complicated geometry around that part of the dome. That had been missed in earlier, coarser analysis of the tank. To add on to this, the Centaur 5 uses a new laser welding technology, rather than arcwelding on earlier Centaurs, for seams in the tank dome. The strength of the laser welds is less than what had been expected from earlier tests.
“The two things together — higher loads, somewhat lower strength in the welds — are what caused the crack to begin,” Bruno said. The amount of testing of that specific Centaur may have also contributed to the crack, he added. To correct the problem, ULA will add a layer of stainless steel around the door on the top of the dome and strips along the welds extending about 60 centimeters from it. “It’s not a very sophisticated or high-tech or high-risk action,” he said. “We simply need it to be just a little bit thicker.”
A few days ago on the 27th, Tory Bruno tweeted saying, “Rocketship is doing great. CV is marching through the factory. The reinforced forward dome is built and getting ready to go on top of the rest of the tank. Here’s a pic, since I know you’ll ask. (The doublers are on the inside). This included an image of the forward dome in the factory. Doublers is another sheet of stainless steel that is laid on top of a local area and welded down. It’s important to point out that the company is already incorporating these changes in a Centaur that was originally going to be used on the third Vulcan mission. That will instead be used for the inaugural Vulcan launch, Cert-1, while the Centaur that had already been shipped to Cape Canaveral and tested for that launch will be returned to ULA’s Decatur, Alabama, factory for modifications.
The additional material will add about 300lbs (135kg) of mass to the Centaur initially, but that increase will be cut in half on later ones. That will reduce the payload performance by the same amount, but Bruno said none of the upcoming Vulcan missions would be affected by that change given the requirements of those missions and vehicle margins.
Closer to when this news originally came out, Tory Bruno said, “In terms of schedule, that means that we expect to fly in the fourth quarter of this year,”. On this first mission, Vulcan is carrying multiple payloads for a few different customers. For example, ULA is working with the primary customer of Cert-1, Astrobotic, to identify the windows in the fourth quarter that would be available for launching that company’s Peregrine lunar lander. ULA previously said only a few days were available each month for launching Peregrine. Just earlier today Bruno confirmed that they still are targeting the fourth quarter and are very confident they can launch this year. This is an ambitious goal that could easily get pushed back to early next year, however, a launch late this year is possible.
Vulcan Overview
The upper stage of Vulcan, also known as the Centaur V, is an upgraded variant of the Centaur III, the first high energy upper stage. The Centaur III variant is currently used on the Atlas V. Previous plans called for the Centaur V to be eventually upgraded with Integrated Vehicle Fluids technology to become the Advanced Cryogenic Evolved Stage (ACES), but this was subsequently canceled. It relies on two RL10C engines to power its second stage. Logging an impressive record of nearly 400 successful flights and nearly 700 firings in space, RL10 engines, manufactured by Aerojet Rocketdyne, harness the power of high-energy liquid hydrogen. The RL10 boasts a precision control system and restart capability to accurately place payloads into orbit.
Focusing on the dome which experienced a few issues, normally ULA uses friction stir welding when they can. Friction stir welding is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material. Heat is generated by friction between the rotating tool and the workpiece material, which leads to a softened region near the FSW tool. While the tool is traversed along the joint line, it mechanically intermixes the two pieces of metal, and forges the hot and softened metal by the mechanical pressure, which is applied by the tool, much like joining clay, or dough.
In this case, however, the dome is stainless steel which is too tough to do friction stir welding on. They use resistance welding for most of the welds. Tory Bruno confirmed this in a quote saying, “Too thin for FSW (0.045” at thickest). Currently using laser welding for seams. Resistance welding for features like brackets and doublers. As partially mentioned prior, this somewhat unique method relative to the rest of the rocket was one of the company’s reasons for it being weaker.
As for the rest of the rocket, it looks to be in good shape and ready to fly. While there was the BE-4 test stand incident, both Blue Origin and ULA are very confident this will have little to no effect on Vulcan’s maiden flight.
The two BE-4 engines already underwent extensive acceptance testing at Blue Origin before delivery to the ULA factory for installation into the Vulcan rocket. FRF verified engine operations while coupled together with Vulcan to demonstrate engine start, throttle up, steady-state firing, and shutdown. The entire sequence lasted approximately 6 seconds. This milestone gave them the opportunity to observe critical elements of Vulcan as a complete rocket in the launch environment. It provided a rigorous performance check of the vehicle, pad systems, and the launch control team. The objectives included assessing the integrity and function of the main propulsion system, propellant feed systems, and engines. “FRF is really about confirming the operational readiness of the integrated system: launch vehicle, ground systems, facilities, and the associated software. In addition, we will demonstrate the ability to successfully execute the engine start sequence and validate our hot-fire abort response procedures,” said Dillon Rice, ULA’s Vulcan launch conductor.
Engineers studied temperatures, pressures, and other parameters while controllers monitored vital signs from Vulcan and send commands to the rocket and pad systems from the launch control center at the Advanced Spaceflight Operations Center (ASOC). The countdown matched normal launch day timelines and activities except the Certification-1 (Cert-1) mission payloads were not aboard nor involved. These different metrics combined with the test itself is why Tory Bruno and Blue Origin are not worried about the BE-4 engine explosion at the test stand.
At its core, Vulcan Centaur is a two-stage-to-orbit, heavy-lift launch vehicle that’s been under development since 2014. It is principally designed to meet launch demands for the U.S. government’s National Security Space Launch (NSSL) program for use by the United States Space Force and U.S. intelligence agencies for national security satellite launches. It will replace both of ULA’s existing launchers (Atlas V and Delta IV Heavy) in this role, as these launchers are retiring. Vulcan Centaur will also be used for commercial launches, including an order for 38 launches from Kuiper Systems. This busy future among other reasons is why this maiden flight is so important. Not to mention, with other companies relying on ULA such as Sierra Space with Dream Chaser, the sooner this rocket launches the better.
Conclusion
ULA is already working on the Centaur V dome to reinforce and prepare it for Vulcan’s maiden flight. While not ideal, its good that the company found the issue and is now working to repair it in time for a launch in the fourth quarter of this year. We will have to wait and see how it progresses and the impact it has on the space industry.