Ready for another try at launching on a test flight to the International Space Station, Boeing rolled a repaired Starliner crew capsule to United Launch Alliance’s seaside rocket hangar at Cape Canaveral Wednesday to prepare for a liftoff scheduled for May 19.
The test flight will not carry astronauts, but could set the stage for the first Starliner crew mission to the space station late this year or in early 2023, NASA and Boeing officials said in a press conference Tuesday.
The upcoming mission, known as Orbital Flight Test 2, is set for liftoff May 19 at 6:54 pm EDT (2254 GMT) aboard a United Launch Alliance Atlas 5 rocket. The Starliner spacecraft, carrying a mannequin and about 500 pounds of supplies, is scheduled to link up with the space station the next day to begin several days of cargo transfers and checkouts while docked at the complex.
Then the spacecraft will depart the station and jettison its expendable propulsion module. The crew module section, designed for reuse, will target a landing under parachutes at White Sands Space Harbor in New Mexico. Undocking and landing are scheduled for May 25, assuming the mission takes off May 19.
Boeing and ULA transferred the spacecraft to the Atlas 5 rocket’s Vertical Integration Facility on Wednesday, a few hours later than planned due to a hydraulic leak on the capsule’s transporter. The convoy, which included security and support personnel, briefly stopped near the Vehicle Assembly Building at Kennedy after a protective cover blew off the Starliner’s window.
A Boeing spokesperson said the cover is intended to be removed before launch, and its absence was not an issue for the spacecraft to continue to the Atlas 5 hangar. Once in position, a crane hoisted the spacecraft on top of the Atlas 5 rocket, which was assembled inside the VIF last month.
ULA and Boeing will run the Atlas 5 and Starliner spacecraft through integrated checkouts over the next two weeks. The 172-foot-tall (52-meter) rocket will roll to the launch pad May 18, the day before liftoff.
Developed in a public-private partnership, the Starliner spacecraft will give NASA a second human-rated capsule capable of ferrying astronauts to and from the space station, alongside SpaceX’s Dragon spaceship, which launched with a crew for the first time in May 2020.
“It’s very important for commercial crew to have our second transportation system up and operational to continue our assured access to the ISS, and also to grow our low Earth orbit economy,” said Steve Stich, NASA’s commercial crew program manager.
But the program has encountered a series of delays and setbacks, including an orbital test flight in December 2019 that ended prematurely due to a software programming error. The software glitch, associated with the spacecraft’s on-board timer, prevented the Starliner from docking at the space station as planned, and the capsule made a safe landing in New Mexico.
The Starliner spacecraft also ran into problems with its communications system on the two-day demonstration mission in 2019. Boeing engineers had to solve a second software problem detected in flight, which could have caused the spacecraft’s service module to collide with the crew module after the two elements separated just prior to re-entry.
Engineers completed an in-depth review of the Starliner’s software code, and added more extensive tests of the software programming before trying another test flight last year, called OFT-2.
The spacecraft was rolled to the launch pad last August at Cape Canaveral atop its Atlas 5 rocket, but tests revealed 13 stuck isolation valves in the Starliner propulsion system.
Boeing and NASA, which manages the Starliner commercial crew contract, agreed to remove the Starliner from the Atlas 5 rocket and postpone the mission to investigate the valve problem. Officials said Tuesday that testing showed corrosion inside the valves — caused by a chemical reaction between moisture, nitrogen tetroxide propellant, and the valves’ aluminum — caused the components to stick housing inside the plumbing on the spacecraft’s service module.
Nitrogen tetroxide, or NTO, is a toxic liquid used as an oxidizer on the Starliner spacecraft’s propulsion system. Hydrazine fuel ignites when mixed with the oxidizer, generating thrust from the spacecraft’s rocket jets — supplied by Aerojet Rocketdyne — for in-space maneuvers and docking at the space station.
The stuck valves are used to isolate the thrusters from the nitrogen tetroxide tank, and need to open in flight to operate the thrusters for maneuvers or a launch abort.
Engineers from Boeing, NASA, Aerojet Rocketdyne, and Marotta, which produced the valves, honed in the cause of the problem during an eight-month investigation.
Technicians detached the service module from the Starliner’s crew module in January for shipment to a test facility in New Mexico, where teams performed tests to better understand the valve problem. The OFT-2 mission will fly with a new service module, one originally assigned to the first Starliner mission with astronauts.
The investigation revealed nitrogen tetroxide vapors seeped through Teflon seals in the valves, an occurrence that was known to happen in similar systems on other spacecraft. But moisture from the humid Florida air — not from rainfall, officials said — somehow made its way into the service module and reacted with the nitrogen tetroxide to create nitric acid.
The nitric acid then reacted with aluminum material in the valve housings to create aluminum nitrate deposits, leading to corrosion.
“Those corrosion products then resulted in and preventing valve motion,” said Michelle Parker Boeing’s deputy general manager for space deputy launch programs.
Engineers have not redesigned the valves on the new Starliner service module, but added “mitigations” to help prevent moisture from entering the propulsion system.
“If you eliminate the moisture from the valve, you won’t have this reaction and it won’t lead to corrosion,” Parker said.
The valves will be purged with nitrogen gas to prevent moisture build-up, and Boeing added sealant around an electrical connector that provided a path for humidity to get into the valves.
“Those two things will prevent the moisture from getting into the valve to start that reaction at all,” Parker said.
Boeing also made process changes, and loaded the nitrogen tetroxide into the service module closer the time the spacecraft rolled out of the factory at the Kennedy Space Center. Teams will also command valve cycles every two to five days through launch day to ensure that the valves remain operational, Parker said.
The final pre-launch valve cycle test will occur during the countdown May 19.
“We are confident that we have the right mitigations in place,” said Mark Nappi, Boeing’s program manager for the Starliner. “We’ve also cycled the valves several times. We’ll continue to cycle the valves until we get to launch day to boost the confidence that we have a system that’s working.”
Stich, a former space shuttle flight director, said valves on the shuttle’s reaction control system jets were also susceptible to moisture corrosion causing.
“These prop iso valves, especially with NTO, they’re the bane of our existence,” said Kathy Lueders, associate administrator of NASA’s space operations mission directorate. “This is something that is not a new phenomenon on the spacecraft side.
“If you’ve been Florida in July, just imagine being outside,” Lueders said. “It’s just the ambient humidity. This is kind of an insidious thing because you have a vehicle on the pad.”
With SpaceX now providing regular crew transportation services to the space station, there’s no rush to make the Starliner spacecraft operational. Nevertheless, NASA is eager to have two crew transportation providers to avoid again relying on Russia’s Soyuz spacecraft for astronaut flights in the SpaceX event runs into any significant delays.
NASA has signed a series of contracts with Boeing, valued at more than $5 billion, since 2010 for Starliner development, test flights, and operations. The contracts include agreements for six crew rotation flights to the space station — each with a four-person crew — following the completion of the OFT-2 mission and the short-duration Crew Flight Test, or CFT, with three NASA astronauts on-board .
NASA and Boeing officials declined to set a target schedule for the Crew Flight Test, only saying that preparations on the capsule for the first astronaut mission were on track to have the vehicle ready for launch by the end of this year.
“The best path to CFT is a successful OFT-2 flight because this is the time that the vehicle is put through its paces in the space environment, through the complex rendezvous and docking sequence with the navigation sensors,” Stich said. “And really the only way to test that, we’ve found, is in the space environment.”
Email the author.
Follow Stephen Clark on Twitter: @StephenClark1.