ULA is examining debris recovered from Vulcan rocket’s shattered booster nozzle - Ars Technica

"I’m pretty confident... that we’ll get to the bottom of this pretty quickly and move on.”

When the exhaust nozzle on one of the Vulcan rocket's strap-on boosters failed shortly after liftoff earlier this month, it scattered debris across the beachfront landscape just east of the launch pad on Florida's Space Coast.

United Launch Alliance, the company that builds and launches the Vulcan rocket, is investigating the cause of the booster anomaly before resuming Vulcan flights. Despite the nozzle failure, the rocket continued its climb and ended up reaching its planned trajectory heading into deep space.

The nozzle fell off one of Vulcan's two solid rocket boosters around 37 seconds after taking off from Cape Canaveral Space Force Station on October 4. There were some indications of a problem with the booster a few seconds earlier, as tracking cameras observed hot exhaust escaping just above the bell-shaped nozzle, which is bolted to the bottom of the booster casing.

A shower of sparks and debris fell away from the Vulcan rocket when the nozzle failed. Julie Arnold, a ULA spokesperson, confirmed to Ars that the company has retrieved some of the debris.

"We recovered some small pieces of the GEM 63XL SRB nozzle that were liberated in the vicinity of the launch pad," Arnold said. "The team is inspecting the hardware to aid in the investigation."

The solid rocket booster, or Graphite Epoxy Motor (GEM), was built by Northrop Grumman. It's a larger version of the booster used on ULA's Atlas V rocket, which Vulcan will replace. After the nozzle failure, the damaged booster continued to burn as the Vulcan rocket continued on its flight downrange over the Atlantic Ocean, albeit at a lower thrust level and with less efficiency.

Northrop Grumman's Graphite Epoxy Motors have a reliable track record. The GEM 63XL variant used on the Vulcan rocket is derived from smaller boosters that flew on the Atlas V, Delta IV, Delta III, and Delta II rockets. The last failure of such a booster, a GEM 40 motor, was in January 1997, when a booster casing ruptured and led to the explosion of a Delta II rocket just 13 seconds after liftoff.

The October 4 launch was the second test flight of the Vulcan rocket, following a nearly flawless debut launch in January. ULA launched the second Vulcan test flight without a payload after determining Sierra Space's Dream Chaser spaceplane, originally assigned to fly on the second Vulcan rocket, would not be ready for launch this year.

Instead, ULA placed a dummy payload on top of the Vulcan rocket in order to launch the test flight as soon as possible. The US Space Force is eager to certify Vulcan to launch military satellites, but the military requires two successful test flights for certification.

Tory Bruno, ULA's CEO, said earlier this week that the Vulcan rocket's two BE-4 core stage engines, made by Blue Origin, compensated for the malfunctioning booster. After losing the nozzle, the 20-story-tall Vulcan rocket briefly tilted a few degrees to the side due to asymmetrical thrust, before the main engines steered the vehicle back on course.

"We just did not have as much thrust coming out of there as we would like to have," Bruno said in a presentation at the International Astronautical Congress in Milan, according to Space News.

The rocket's core stage and Centaur upper stage made up for the shortfall in thrust from the strap-on booster by firing their engines up to 20 seconds longer. Ultimately, the rocket accurately hit its targeted trajectory at the end of the mission.

"Vulcan is a beast," Bruno said.

While the rocket's recovery from the booster malfunction was remarkable, it's not clear Vulcan could have still reached its target orbit if the problem occurred on an operational flight with a military satellite heavier than the dummy payload carried on the test flight earlier this month.

Bruno said the cause of the booster anomaly is still under investigation. The company has 35 of the GEM 63XL solid rocket boosters in storage for future Vulcan missions. Each Vulcan flight can use up to six of the strap-on boosters for additional thrust, depending on mission requirements.

"I’m pretty confident, having experienced this type of anomaly more than once in my career, that we’ll get to the bottom of this pretty quickly and move on," Bruno said. "We still had a very, very successful mission, probably one of the most successful missions we’ve flown."

ULA and the Space Force hoped to launch the first two operational flights of the Vulcan rocket before the end of this year. The first, designated USSF-106, will carry an experimental navigation satellite into orbit for the Air Force Research Laboratory. The next mission, named USSF-87, will deploy two Space Force satellites to surveil other spacecraft in geosynchronous orbit.