The first Boeing Starliner astronauts are back at the launch site.
NASA Crew Flight Test (CFT) astronauts Butch Wilmore and Suni Williams arrived at NASA’s Kennedy Space Center in Florida on Tuesday (May 28) ahead of the expected launch of the Boeing Starliner on Saturday (June 1).
NASA will conduct a flight readiness check on the delta today (May 29) to review the launch, officials said; this is a little more detailed than the standard review to address the Starliner’s technical problems resulting from the helium leak.
Assuming the mission passes inspection and schedules, the CFT will lift off from the nearby Cape Canaveral Space Force Station as early as 12:25 p.m. EDT (1625 GMT), and you can watch the historic launch here on Space.com via NASA TV. . NASA will provide an update to reporters on Friday (May 31) at 1:00 p.m. EDT (1700 GMT), which you can also watch live here.
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This is not the first time a crew has flown to KSC on NASA T-38 training jets to attempt a launch; they first arrived on April 25 for a May 6 launch, but that effort was foiled just two hours before takeoff.
As the composite Starliner and United Launch Alliance Atlas V rocket underwent troubleshooting, the crew — still in quarantine — returned to NASA’s Johnson Space Center in Houston for several weeks to continue training and wait for a firmer launch date.
The Starliner CFT has had a long journey to the launch pad. NASA awarded billion-dollar contracts to both SpaceX and Boeing in 2014 to send astronauts to the International Space Station by 2017. Both vehicles have been delayed in that goal due to technical and financial issues.
SpaceX, borrowing from its cargo Dragon design that has flown to the ISS since 2012, completed its first crewed test in 2020. SpaceX has since completed 11 additional missions to the ISS. Starliner, a brand new spaceship, took longer.
The first Starliner mission to the ISS in 2019 without astronauts got stuck in the wrong orbit due to software glitches and failed to reach its destination. The follow-up mission in 2022 made it safely after dozens of repairs and delays due to the pandemic.
Related: 2 Astronaut Taxis: Why NASA Wants Both Boeing Starliner and SpaceX’s Dragon
The CFT encountered another delay in 2023 after the parachutes were found to be able to carry less load than expected and flammable tape was found on the wiring. NASA and Starliner officials emphasized that the mission is developmental — meaning that not only does safety take priority over any timing concerns, which is true of all missions, but that course corrections will be needed as the design matures.
Both CFT astronauts are also former US Navy test pilots, so they have been involved in the development of other aerospace projects over the decades.
All appeared on track for the May 6 launch attempt, but late in the countdown, a “buzzing” valve was discovered aboard the Atlas V, meaning the oxygen relief valve was opening and closing rapidly. The problem prompted ULA, Boeing and NASA to clean up the mission. Hours of troubleshooting resulted in the decision to tow the rocket back to its facility at Cape Canaveral for a valve replacement.
That valve replacement was on schedule by May 12, but a small helium leak in an Aerojet Rocketdyne nozzle aboard the Starliner—discovered after cleaning—then underwent a detailed inspection. Team officials told reporters at a briefing last week that they learned a few things in the process.
The leak does not pose an immediate risk to launch because helium is an inert gas; Both the Crew Dragon and the shuttle launched safely with helium leaks, they noted. The question is how this leak would affect the Response Control System (RCS); that’s a set of 28 small engines aboard the Starliner for modest orbital maneuvers.
The leak is in an area about the size of a button in the Starliner spacecraft, less than 10 sheets of paper thick, in a rubber gasket between two metal parts of the flange. The leak is roughly 50 psi to 70 psi depending on the pressure around it, but this (apparently) high velocity is relative to the small space, NASA and Boeing pointed out in the briefing.
It was not safe to open this location with the Starliner stacked on top of the Atlas V, but extensive computer analysis showed that the leak appeared to be stable. The team made pressure changes in this area as well to simulate changes in spaceflight, and were pleased with the performance they saw.
Additionally, the other 27 jets have no leaks at all, creating a large buffer should more leaks occur, NASA’s Steve Stich, program manager for the agency’s Commercial Crew Program, pointed out in a May 24 call.
He added that engineers, however, discovered a “design vulnerability” while troubleshooting the helium. Simply put, Starliner has three certified modes for returning astronauts to Earth: one mode using RCS thrusters and two modes using Orbital Maneuvering and Attitude Control (OMAC) thrusters; OMAC modes require two or four of these nozzles, depending on the situation.
The RCS re-entry mode requires eight thrusters in adjacent “doghouses”: There are four such assemblies around the Starliner. But in the rare circumstance of a helium leak, all the nozzles in the adjacent kennels can fail at the same time, meaning that the RCS will no longer be available to back up the OMAC. So the team created and simulated with CFT astronauts a new reentry mode that would require only four RCS thrusters at once. Among other things, Delta’s Airworthiness Review will confirm the certification of this new re-entry technique.