After an aborted launch the Starliner is back in the factory for more repairs and analysis.
After years of delays, the Boeing CST-100 Starliner was finally supposed to launch its crucial uncrewed mission to the International Space Station (ISS). That launch never happened.
During a preflight test of the mission, named Orbital Flight Test-2 (OFT-2), a total of 13 propulsion system valves failed to properly open and the mission was called off. While seven of the valves were restored to working order in the following days, Boeing still does not know what caused the problem.
The valves in question are important components. In the Starliner’s propulsion system there are 24 oxidizer valves, 24 fuel valves and 16 helium valves that pressurize both sides of the system. The valves isolate thrusters from propellant tanks, and they need to be open prior to launch in order to perform abort and maneuvering commands. All the valves are the exact same design and are made of Teflon, but the problems arose only in the oxidizer valves.
According to John Vollmer, Boeing’s vice president and Starliner program manager, the most probable cause of the malfunction was permeation of dinitrogen tetroxide (NTO), an exceptionally corrosive oxidizer, through the seals of the valves in question. When NTO interacts with moisture (and there was some moisture on the “dry” side of the valves) it creates nitric acid—a substance which caused some corrosion that led to the valves sticking.
Once the nitric acid bond is broken and the valves are cycled, they get back to working order—and that’s what happened with the valves that were successfully reopened. Vollmer speculated that continued cycling could have freed the remaining valves, but they simply ran out of time in the launch window to do so. NASA and Boeing decided to send Starliner back to the factory for analysis and repair.
The valves are the same design used in Starliner’s first foray into space, as well as the launch pad abort test, and worked fine at that time. They also performed properly when tested before OST-2’s original July 30 launch date, which was delayed due to the Nauka module incident on the ISS.
The mission was to be an important milestone: it was supposed to demonstrate that the Starliner, which navigates autonomously, could launch, rendezvous with the ISS, dock and return to Earth on its own. A successful mission would have paved the way for NASA to allow a crewed test flight—and eventually use the spacecraft to ferry astronauts to space and back.
“This is another example of why the demo missions are so very important to us,” said Kathy Lueders, NASA’s Commercial Crew Program Manager. “We use these demo missions to make sure we have the system wrung out before we put our crews on these vehicles.”
This is Boeing’s second uncrewed mission attempt. The first one in 2019 also resulted in failure: while Starliner made it to space, a software malfunction prevented the vehicle from docking with the ISS and forced its early return. Ground control lost contact with Starliner a whopping 37 times during that mission, and the ensuing NASA investigation admonished Boeing for not conducting a full end-to-end test of the capsule before launch. The aerospace giant strengthened Starliner’s software with new algorithms designed to address communications failures and addressed more than 80 issues identified by an independent investigator.
The spacecraft was grounded for a year and a half to implement those fixes, but after getting the green light for a second test, has found itself back in the shop again after an aborted launch.
This latest setback is another black eye for Boeing’s aerospace program. Boeing and SpaceX were both awarded contracts to develop crewed spacecraft for NASA under the organization’s Commercial Crew initiative. While Boeing has seen one mishap after another, in the same time period SpaceX’s Crew Dragon (which was also behind schedule) has already completed three successful human spaceflight missions to the ISS and back.
Boeing and NASA are committed to making Starliner work, however. “We will get this vehicle ready as soon as possible and turn it around so that we can support NASA’s mission as quickly as possible,” said Vollmer.
Read more about the private sector spacecraft that NASA is relying on to take astronauts into space at The SpaceX Crew Dragon: This Ain’t Your Parents’ Space Shuttle.
