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Boeing’s Starliner will soon undergo a “hot fire” test in orbit, as NASA and the company continue to investigate the cause of lubrication failures and helium leaks in space.
Starliner will conduct the test-fire of its 28-thruster reaction control system (RCS) on Saturday (July 27) or Sunday (July 28) at the International Space Station (ISS), NASA and Boeing announced in a press conference today. 25 July). However, only 27 of the RCS thrusters will be used, as one was previously deemed unusable for the flight home.
Commands will be carried out from the ground, although NASA astronauts Butch Wilmore and Suni Williams – the astronauts flying the current Starliner mission, called Crew Flight Test (CFT) – will likely be involved, due to their interest as former US Navy test pilots. .
“We’re going to put all those thrusters on a few pulses, but to make sure before we disassemble that the whole system functions the way it was expected and the way it did the last time we checked it,” Steve Stich, NASA manager. Commercial Crew Program, reporters said in a live-streamed press conference.
“We will also have the opportunity to look at the helium system,” he said. “It’s been six weeks since we last checked that helium system; that was the 15th of June. So we’ll pressurize a manifold, and then we’ll fire up the thrusters, and then we’ll have a chance to look at the helium leak. rates and verify that the system is stable.”
CFT was initially shown to last about 10 days after launch on June 5, but faced lubrication problems and helium leaks before it safely touched down with the ISS the next day. So the mission was extended indefinitely while the engineers fixed the problem.
Related: When will Starliner come home? Boeing and NASA don’t know yet
After ground tests at the White Sands Test Facility in New Mexico in early July, engineers now have more insight into what happened during the difficult spell.
For example, Aerojet Rocketdyne’s MR-104J test thruster like the ones aboard Starliner, which had been in storage for three years before the recent ground work, suffered “major degradation” in its valve system from nitrogen dioxide vapor ; propellant flow was restricted due to a bulging in a seal, Stich said. Engineers also found Teflon stuck in a down filter, suggesting corrosion in a seal due to “bubble” under high temperatures.
The behavior of the Starliner RCS thrusters in orbit appears to match what is observed on the ground, Stich noted. The type of thruster, he told Space.com during the press conference, “is inherited” from other spaceflight programs by Aerojet (L3Harris company), but it was modified for the Starliner service module, in which the RCS thrusters and propulsion system are located.
“I think what we’re starting to understand much better on this mission – and we wouldn’t have understood this by staying on the ground and doing more analysis and testing – is we understand the effects integrated between how the guidance, navigation and control. system [and] the flight control system during rendezvous is commanding the thrusters to fire,” Stich said.
A “househouse” insulates around each RCS thruster group and protects the thrusters from the cold temperatures of space. (There are four doghouses on the service module in total.) What CFT has shown is that several RCS thruster pulses in a short time, on top of firing the orbital maneuvering and attitude control (OMAC) system, cause RCS thruster temperature. to increase more than expected.
Related: ‘I’m sure we’ll figure things out’: NASA astronauts fly to launch site for 1st crewed Boeing Starliner mission to ISS (photos)
Stich said that perhaps the problem could be addressed not by a design change, but by changing the ways in which the thrusters are used in flight (as they are fired so often). Discussions are taking place at the most senior levels of the agency, he stressed; NASA plans an agency-level review of CFT as soon as next week, and the agency’s Aerospace Safety Advisory Panel will also be invited, he said.
Aerojet Rocketdyne is working closely with Boeing during the mission, added Boeing Commercial Crew Program Manager Mark Nappi. Discussions are underway on how to tackle the issue. New seals could be inserted, for example. As for the thrusters, Boeing may ask future crews to fly a different profile to the ISS or “put a different thermal shield inside the doghouse,” Nappi said today.
Test missions like CFT usually face the unexpected, and Starliner has always been rated to leave the ISS in an emergency. CFT astronauts Wilmore and Williams participated in a troubleshooting orbit in June before being returned to ISS maintenance duties for what is now a (and counting) 50-day mission.
NASA also extended CFT’s initial limit in space for the past 45 days, saying that the battery’s performance (which originally indicated the limit) was doing better than expected in orbit. In today’s briefing, Stich said the mission is now officially rated for 90 days, or until September 3 (although the landing time is not yet confirmed.)
Understanding the root causes of the thruster and helium issues in the RCS, which controls in-orbit maneuvers, is important for future Starliner missions. After CFT, the Starliner-1 mission with at least three astronauts is supposed to spend six months on the ISS no earlier than 2025.
Starliner is one of two private US spacecraft to send astronauts to the ISS, along with SpaceX’s Crew Dragon. Crew Dragon, flight crews since May 2020, is based on SpaceX’s cargo Dragon that has been in space several times since 2012. Starliner, as a new spacecraft, faced development challenges after its first space flight.
The initial ISS Starliner launch without astronauts, in December 2019, never reached its destination due to computer problems that kept the spacecraft in the wrong orbit. The follow-up uncrewed mission reached its destination, but that was in May 2022, after the outbreak of the COVID-19 Pandemic and dozens of solutions implemented. (Dock 2022 also had smudge issues, which NASA thought had addressed CFT.)
CFT was delayed in 2023 when flammable tape was discovered in the Starliner wiring, and engineers discovered that the parachutes could carry less load than expected. For months, the mission seemed set for a May 6 launch date. Just an hour before liftoff, the astronauts were pulled from the spacecraft after a valve vibrated in the United Launch Alliance (ULA) Atlas V rocket.
Related: ‘It’s so complicated:’ Boeing Starliner crews diagnosing helium leak before astronaut launch
Starliner remained on the ground for a month when ULA replaced the valve, and after a small helium leak was discovered in one RCS thruster. Extensive on-the-ground testing and modeling found no problems for CFT, but the analysis revealed a vulnerability: Under certain circumstances, if enough RCS trucks failed in nearby doghouses, one re-entry option could be compromised. After engineering and simulator work, NASA and Boeing confirmed a new reentry method that requires fewer RCS launchers to fire simultaneously.
CFT was launched on June 5, but has so far faced another late countdown scrub due to a ground equipment fault affecting Atlas V. In addition to problems with the Á, there NASA and Boeing have emphasized that Starliner’s stay in space was uneventful and the spacecraft. functioning well. And as former US Navy test pilots, Williams and Wilmore have experience in long deployments and development programs.
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Starliner and SpaceX received billions of dollars to transport astronauts under a contract with NASA’s Commercial Crew Program in 2014. After a test astronaut flight launched in May 2020, SpaceX has now sent 11 crews to the ISS: eight on behalf of NASA, and three shorter ones for Axiom Space.
SpaceX’s missions are currently grounded due to a problem with the second stage of the Falcon 9 rocket that surfaced during the launch of the Starlink satellite earlier this month. The Falcon 9 completed a static fire last night, but the Federal Aviation Administration (FAA) has not yet responded to SpaceX’s request to fly missions under a public safety decision; SpaceX insists that there was no risk to the public during the launch, as only the second stage of the rocket (in space) was affected.
Currently, SpaceX is expected to launch two ISS missions in August, pending FAA approval and NASA’s independent review: Northrop Grumman’s Cygnus cargo spacecraft, and four Crew-9 astronauts aboard Crew Dragon.
