WASHINGTON — NASA and Boeing are planning no earlier than May 2022 for the rescheduled second uncrewed test flight of the CST-100 Starliner spacecraft after deciding to change service modules for that mission.
Under the revised plan, the service module that had been built for the Crew Flight Test (CFT) mission, the flight of that vehicle to carry people, will instead be used for the Orbital Flight Test (OFT) 2 mission. The CFT mission will instead use the service module for the first operational mission, called Starliner-1.
That approach could allow the OFT-2 mission to launch in the spring. Boeing will work United Launch Alliance, whose Atlas 5 will launch the spacecraft, and the Eastern Range to consider a launch opportunity in May. That date will depend on both the readiness of the spacecraft and the schedule of other vehicles visiting the International Space Station.
“Our objective was to get back to flight safely and as soon as possible. With this objective in mind, we set out on parallel paths: remediating valves to preserve the option of utilizing the existing service module (SM2), while also working to accelerate the build of the next service module (SM4),” John Vollmer, vice president and program manager for Boeing’s commercial crew program, said in a Dec. 13 statement. “Based on the results to date we’ve decided to fly SM4 next and continue longer-term tests with SM2 hardware, on the vehicle and in offline facilities.”
Boeing scrubbed an August launch of the OFT-2 mission when valves in the propulsion system of service module failed to open. The investigation has focused on nitrogen tetroxide oxidizer that permeated Teflon seals in the valves and reacted with moisture on the other side. That created nitric acid that corroded the seals and caused them to remain shut.
However, the exact nature of the problem — not seen on the original OFT mission in December 2019 — and how to fix it remain unclear. “Ongoing investigation efforts continue to validate the most probable cause to be related to oxidizer and moisture interactions,” NASA said in the statement, but didn’t elaborate on topics like the source of the moisture and how to resolve the problem.
NASA and Boeing said they were making “preventative remediation efforts” to the new service module for the OFT-2 mission. Engineers also tested the module to confirm it was in good condition before moving ahead with plans to swap out the service modules.
Steve Stich, NASA commercial crew program manager, said in the statement that the agency and Boeing have been working together to investigate the problem, including tests at NASA facilities. “Because of the combined work, we have a much better understanding of the contributors that led to the valve issues, and ways to prevent it from happening in the future,” he said. “Boeing remains diligent and driven by the data during its decision making, which is key to ensuring the Starliner system is ready when we fly our test missions in 2022.”
While that comment suggested NASA and Boeing still play to fly the CFT mission before the end of 2022, that schedule will be challenging even if OFT-2 flies in May 2022. For example, more than a year elapsed between SpaceX’s two Crew Dragon test flights, the uncrewed Demo-1 mission in March 2019 and the crewed Demo-2 launch in May 2020. In the statement, NASA said only that potential launch dates for CFT are under review.