The SRB volcanic anomaly is still under investigation

MILAN – The loss of a solid rocket booster nozzle on the Vulcan Centaur’s second flight had little impact on the launch itself, but the incident’s impact on the Space Force’s certification of the vehicle remains uncertain.

During the Cert-2 launch on October 4, the nozzle of one of the two SRBs attached to Vulcan’s core stage detached about 35 seconds after launch. The incident, described as an “observation” by the United Launch Alliance, appeared to have a temporary impact on the vehicle, but it continued its ascent, with the timing of subsequent events lagging the published time frame by up to 20 seconds.

In a talk at the International Astronautical Congress here Oct. 14, ULA executive director Tory Bruno said the incident resulted in only a small loss of performance. “The net effect of that was less than 2% of the booster’s total momentum,” he said, as the engine continued to fire, but with reduced efficiency due to the missing nozzle.

The nozzle did not affect the engine itself or endanger the entire vehicle, he added. “There just wasn’t as much thrust coming out as we would have liked.”

The core stage compensated for the loss of power from the SRB, including control by the BE-4 engines to compensate for the asymmetric thrust between the two SRBs. “That was less than the liquid fuel reserves in the core stage,” he said. “Volcano is a beast.”

This was evident in the vehicle’s final performance and the accuracy of its orbital injection. Bruno said engineers are still analyzing the flight’s data and comparing it to previous ULA launches, “but I’m pretty sure this is our most accurate injection yet.”

The cause of the nozzle pop-off was still under investigation, he said, explaining that nothing of the sort had been observed in 35 firings of the GEM 63 engines and several of the larger GEM 36XL engines used on Vulcan.

Any changes to the nozzle, he said, should be easy to make on the 35 GEM 63XL engines in storage for future Vulcan launches because the nozzle section is bolted on. “Having experienced this type of anomaly more than once in my career, I’m pretty confident that we’ll get to the bottom of this pretty quickly and move on.”

“We still had a very, very successful mission,” he concluded, “probably one of the most successful missions we’ve ever flown.”

What is less certain is how the anomaly will affect the U.S. Space Force’s plans to certify Vulcan Centaur. The Cert-2 mission was the second of two Vulcan launches required to obtain the certification required for national security launches. Prior to Cert-2, ULA hoped to receive this certification in time to conduct the first two such launches before the end of the year.

When asked about this after his presentation, Bruno declined to speculate about any changes to the certification timeline. That process, he said, is in the hands of the Space Force, which has not publicly commented on a timeline for certification.

“This is something we will be working on with our Space Force customer,” he said, whose personnel are embedded with ULA teams reviewing launch data. “I hope this helps them complete their part of the certification.”

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