CAPE CANAVERAL—United Launch Alliance (ULA) has resolved a ground support system problem that scotched a June 1 launch attempt of Boeing’s CST-100 Starliner spacecraft aboard an Atlas V rocket, with liftoff now targeted for 10:52 a.m. EDT June 5.
ULA has launched Starliner spacecraft twice previously, but the upcoming mission will be the first with crew onboard for both Boeing and for ULA, which is a joint venture of Lockheed Martin and Boeing. The Crew Flight Test (CFT) is needed to certify Starliner for International Space Station (ISS) crew rotation missions for NASA.
With an instantaneous launch window, ULA on June 1 had no time to troubleshoot a problem with the triple-redundant ground launch sequencer (GLS) system, which triggered a scrub 3 min. 50 sec. before liftoff. ULA later found a faulty ground power unit and replaced the power chassis with a spare.
“A full failure analysis of the power unit will be performed to better understand root cause,” NASA wrote in a mission update on June 2. “ULA has completed functional checkouts of the new chassis and the cards, and all hardware is performing normally.”
ULA CEO Tory Bruno noted that a satellite mission would still require three redundant GLS to enter terminal count, but two things would have been different. “One, we almost never have an instantaneous launch window when we are not launching people,” Bruno told reporters after the June 1 scrub. “This is a very unique and special trajectory that protects the safety of the crew,” by providing continuous abort capability from the pad through orbit insertion.
Second, with a more generous launch window, ULA would have had time to study the problem during the countdown. “Knowing that there was no crew present, we may have arrived at a conclusion that it was worth proceeding with dual-redundancy versus triple. It depends on what we would have been able to assess during that time,” Bruno said. “However, with crew present, that was an unacceptable condition. We were not going to make that decision in a few seconds, which is really all we had.”
ULA also scrubbed Starliner’s first launch attempt on May 6 due to another operational requirement for crewed flights. That countdown was halted about two hours before liftoff due to an oscillating pressure regulation valve in the liquid oxygen tank on the rocket’s Centaur upper stage.
“Our philosophy is we don't change the fueled state of the vehicle when the crew is present,” Bruno said after the May 6 scrub. “You can do otherwise—and other people do—but that's our philosophy, so we built our flight rules, our procedures and our decision points around that.”
For satellite missions ULA typically would cycle a buzzing valve, which usually resolves the problem.”But that changes the state of the fueled Centaur and we don't do that when people are present,” Bruno said.
ULA ended up replacing the valve. In the interim, Boeing also assessed a slight helium leak that was traced to a thruster in Starliner’s service module. While the leak is not a concern for flight, follow-on analysis revealed a design issue that could render moot one of Starliner’s backup deorbit burn protocols. NASA and Boeing devised a new standby plan, clearing the way for the second launch attempt on June 1.
ULA will make a third attempt on June 5 to launch the Starliner spacecraft, carrying NASA astronauts Barry “Butch” Wilmore and Sunita Williams for a shakedown mission to the ISS. Following an eight- to 14-day CFT, Boeing is looking to complete certification and join SpaceX in ferrying crews to and from the ISS beginning next year.
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2024-06-03 09:44:34Z
CBMiW2h0dHBzOi8vYXZpYXRpb253ZWVrLmNvbS9kZWZlbnNlLXNwYWNlL3NwYWNlL2JvZWluZy1zdGFybGluZXItY3Jldy1mbGlnaHQtdGVzdC1yZXNldC1qdW5lLTXSAQA
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