Two NASA astronauts will not return from the International Space Station (ISS) for four days, the latest in a series of delays that have marred the Starliner program for years.
NASA and Boeing have postponed the Starliner spacecraft’s undocking for a second time, now targeting June 26 to return the Crew Flight Test mission from the ISS. “We want to give our teams a little more time to look at the data, do some analysis and make sure they’re really ready to go home,” Steve Stich, manager of NASA’s Commercial Crew Program, said during a press conference on Tuesday.
from Boeing Starliner capsule launched atop United Launch Alliance’s Atlas V rocket on June 5, carrying NASA astronauts Butch Wilmore and Suni Williams. The spacecraft had a tricky docking at the orbiting space station, which was characterized by a number of technical problems.
Five of the spacecraft’s thrusters failed during the approach, and four were subsequently recovered. “The rendezvous put some more demands on the propulsion system,” Stich said. “In other words, it fired the thrusters a little more often, and it fired them in succession a little more often, and that caused a little bit of extra heating.”
Starliner also developed five helium leaks, one of which was identified before launch. The technical teams now believe that the leaks may be related to the activity of the thrusters. Stich assured reporters that in the past nine days since Starliner docked with the ISS, leak rates have decreased.
Helium is used in the spacecraft’s thrust systems to allow the thrusters to fire without being flammable or toxic. “We need about seven hours of helium, and we have about 70 hours of margin to achieve the deorbit burn,” he said. Easy math tells us this is 10%.
Because it is parked outside the ISS, Starliner teams on the ground are conducting tests on the vehicle and collecting data before giving the green light to return the astronauts to Earth. “We want to understand how the thrusters will perform during the deorbit burn,” Stich said.
Engineers are also evaluating an RCS oxidation isolation valve in the service module that has not closed properly. An RCS, or Reaction Control System, uses thrusters for attitude control and steering, while the oxidizer isolation valve controls the flow of oxidant, which is essential for burning fuel in the thrusters.
Despite all these issues, Stich said the Starliner teams “now feel really comfortable with their return.”
The Crewed Flight Test is part of NASA’s Commercial Crew Program and is intended to transport crew and cargo to and from the International Space Station (ISS) under a $4.3 billion contract with the space agency. NASA’s other commercial partner, SpaceX, has launched eight crews to the space station so far, while Boeing’s Starliner suffered several delays and technical problems along the way.
Boeing launched two unmanned flights to the ISS, which also suffered from a number of problems. This is the first time the vehicle has carried a crew to orbit. “This is a test flight and we’re going to learn some things,” Mark Nappi, vice president and program manager of the Commercial Crew Program at Boeing, said during the news conference. “So here we are, we’ve learned that our helium system is not performing as designed, even though it is controllable. It’s still not performing as we designed it, so we need to figure that out.”
NASA’s Stich reiterated that the Starliner teams also discovered that the vehicle’s service module is “a very complicated module.” “We did a series of tests [on the ground]…and now we are trying to get to know this vehicle in a different way,” he added. “Maybe we could have done different tests on site to characterize some of that in advance.”
Both NASA and Boeing officials have confirmed that the Starliner spacecraft is safe to return astronauts as of today, but teams have decided to keep it on the ISS where they can conduct more tests on the vehicle in orbit . Starliner can remain docked with the ISS for up to 45 days during its current mission.
Starliner’s journey home is expected to take about six hours, and the spacecraft will land in the Utah desert.
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