Boeing Crew Flight Test

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Boeing Crew Flight Test (Boe-CFT) is the first crewed mission of the Boeing Starliner and the third orbital flight test of the Starliner overall after the two uncrewed orbital flight tests, Boe-OFT and Boe-OFT 2 in 2019 and 2022. The mission entails flying a crew of two NASA astronauts, Barry E. Wilmore and Sunita Williams, from Cape Canaveral Space Force Station to the International Space Station for a two-week test flight and then returning to the American Southwest for a ground landing. The flight test was initially planned to occur in 2017. However, various delays pushed back the launch.

Boeing Crew Flight Test
Boeing Starliner Calypso launches on the Crew Flight Test atop an Atlas V rocket
Mission typeFlight test
OperatorBoeing Defense, Space & Security
COSPAR ID2024-109A Edit this at Wikidata
SATCAT no.59968
Mission duration14 days, 3 hours and 10 minutes (in progress)
~21 days (planned)
Spacecraft properties
SpacecraftBoeing Starliner Calypso
Spacecraft typeBoeing Starliner
ManufacturerBoeing Defense, Space & Security
Crew size2
Start of mission
Launch date5 June 2024, 14:52:15 UTC
RocketAtlas V N22
Launch siteCape Canaveral, SLC-41
ContractorUnited Launch Alliance
End of mission
Landing dateNET 26 June 2024 08:51 UTC (planned)
Landing siteWhite Sands Missile Range
Orbital parameters
Reference systemGeocentric orbit
RegimeLow Earth orbit
Docking with ISS
Docking portHarmony forward
Docking date6 June 2024, 17:34 UTC
Undocking dateNET 26 June 2024 02:10 UTC (planned)
Time docked13 days and 28 minutes (in progress)

Boeing Crew Flight Test mission patch

Williams (left) and Wilmore (right) 

The spacecraft was integrated with the Atlas launch vehicle on 16 April 2024 in preparation for launch. The flight was scheduled for 7 May 2024 but was scrubbed about two hours before liftoff due to an oxygen valve problem on the United Launch Alliance's (ULA) Atlas V. After the initial scrub, the launch was repeatedly delayed due to a helium leak in the Starliner service module. The second launch attempt was on 1 June, but was scrubbed 3 minutes, 50 seconds before liftoff when the ground launch sequencer computer registered a loss of redundancy due to a faulty power supply. The third launch attempt, on 5 June at 14:52 UTC, was successful.

During the flight to the ISS, additional helium leaks were discovered, though these were still too small to threaten the mission. As Starliner approached the ISS, five reaction control system thrusters failed, likely unrelated to the helium leaks. Resetting and firing the thrusters eventually made four out of five work again, and the Starliner safely docked with the ISS after a delay. The thruster malfunction looks identical to unresolved problems encountered during OFT 2 and will likely have to be resolved before Starliner is certified by NASA.


The first delay occurred as a result of the first uncrewed test of Starliner failing to reach the ISS in 2019. A second uncrewed test flight launched in 2022 and succeeded in all flight objectives. This led to the scheduling of the first crewed test flight. However, Boeing announced in August 2023 that it would be delayed to no earlier than March 2024 due to issues with the strength of certain joints within the parachute system and concerns over the potential for combustion of the wiring harnesses. As a result, Boeing had to undergo multiple investigations before another flight test would be permitted.


CFT is the second mission for the Starliner Calypso capsule, which was first used on the first Orbital Flight Test. NASA announced that Boeing prepared to reassemble the vehicle for flight, following multiple checkouts, for the CFT mission in August 2020, and that new parachutes and airbags would be fitted. The CFT capsule's docking system was modified to accommodate the new re-entry cover that debuted on the OFT 2 test flight.


Nicole Aunapu Mann was initially assigned to this mission, which would have made her the first woman to fly on the maiden crewed flight of an orbital spacecraft, but was subsequently re-assigned to the SpaceX Crew-5 mission as the first female commander of a NASA Commercial Crew Program launch. For medical reasons, Eric Boe, who was originally assigned to the mission in August 2018 as the pilot, was replaced by Michael Fincke on 22 January 2019. Boe replaced Fincke as the assistant to the chief for commercial crew in the astronaut office at NASA's Johnson Space Center. Boeing astronaut Chris Ferguson was originally assigned to the flight as commander, but he was replaced by NASA astronaut Barry E. Wilmore on 7 October 2020. Ferguson cited family reasons for the replacement. Matthew Dominick replaced him on the backup crew.

On 18 April 2022, NASA said that it had not finalized which of the cadre of Starliner astronauts, including Barry E. Wilmore, Michael Fincke, and Sunita Williams, would fly on this mission or the first operational Starliner mission. On 16 June 2022, NASA confirmed that this CFT mission is a two-person flight test, consisting of Wilmore and Williams; Fincke is to train as the backup spacecraft test pilot and remains eligible for assignment to a future mission. Williams is the first woman to fly on a maiden crewed flight of an orbital spacecraft type (Judith Resnik was the first female crew member on the maiden flight of an orbital spacecraft, the Space Shuttle Discovery).

Prime crew
Position Crew member
Spacecraft commander   Barry E. Wilmore, NASA
Third spaceflight
Pilot   Sunita Williams, NASA
Third spaceflight
Backup crew
Position Crew member
Spacecraft commander   Michael Fincke, NASA



The third launch of the Atlas V N22 variant launched Starliner with a crew of two. The vehicle docked with the International Space Station, and will return to Earth for a ground landing in the southwestern United States.

Boe-CFT is the first launch of a crewed spacecraft by an Atlas V launch vehicle. In addition, the mission is the first launch of a crewed spacecraft utilizing a member of the Atlas family of launch vehicles since Mercury-Atlas 9 flown by Gordon Cooper in May 1963 and the first launch of a crewed spacecraft from Cape Canaveral Space Force Station since that of Apollo 7 in October 1968.

A short-duration mission with two astronaut test pilots is sufficient to meet all NASA and Boeing test objectives for CFT, which include demonstrating Starliner's ability to safely fly operational crewed missions to and from the space station. However, to protect against unforeseen events aboard the station, NASA has added the flexibility to extend the duration of the CFT docking for up to six months.

The Starliner will make a ground landing in the Western United States, a first for a crewed capsule mission launched from the United States, which have all made a splashdown in an ocean.


Starliner capsule stacked on top the Atlas V rocket prior to launch

In 2023, following the discovery of a technical issue with the spacecraft's parachute system and a flammability concern on the spacecraft's wiring, CFT was delayed to no earlier than March 2024. In November 2023, NASA announced that the mission was on track for an April 2024 launch, with most of the flammable material removed from the spacecraft and a drop-test of the redesigned parachute system planned for January 2024. This test was successful, allowing NASA and Boeing to proceed into launch preparations. In February 2024, the Atlas V rocket was moved into ULA's Vertical Integration Facility at Space Launch Complex-41, starting preparations for stacking ahead of the launch. In March 2024, the launch was rescheduled from 22 April to early May due to scheduling conflicts on the ISS, with a launch date of 6 May announced in early April. Work on the Starliner spacecraft inside Boeing's production facility was completed on 15 April, and the spacecraft was moved to the launch pad and stacked on top the Atlas V rocket the following day. The crew arrived at Kennedy Space Center on 25 April, and on the same day the mission concluded its Flight Test Readiness Review, officially approving the mission to proceed. On 2 May, the SpaceX Crew-8 Dragon spacecraft relocated from the forward port of the ISS Harmony module to the zenith port, to make room for the CFT mission, which is only approved to dock on the forward port. Following the completion of ULA's Launch Readiness Review, the Atlas V rocket rolled to its launch pad on 4 May.

The first attempt to launch CFT, on 6 May, was scrubbed around 2 hours before launch due to a problem with an oxygen valve on the rocket's Centaur upper stage. While this problem had been seen in previous Atlas V flights and could be resolved simply by closing and reopening the valve, new flight rules prohibited doing so with crew on board, which forced the decision to scrub the launch. The next day, the launch team determined that this faulty valve would need to be replaced, with the rocket having to be rolled back to its Vertical Integration Facility, delaying the launch to 17 May. Meanwhile, in an unrelated issue, NASA and Boeing discovered a small helium leak on Starliner's propulsion system, which delayed the launch further to allow the teams to assess the situation. On 24 May, following several days of analysis, NASA and Boeing announced plans to launch CFT on 1 June without repairing the helium leak, determining that the spacecraft was safe to fly even if the leak rate worsened by many times. This review also uncovered a "design vulnerability" in the propulsion system that could prevent the spacecraft from completing a deorbit burn in a very remote failure mode; engineers then devised a new reentry mode to employ should this failure mode occur. Astronauts Butch Wilmore and Suni Williams, after returning to Houston following the previous scrub, flew back to Kennedy Space Center on 28 May. On 29 May, during a Delta-Agency Flight Test Readiness Review, teams from NASA, Boeing, and ULA confirmed readiness for a 1 June launch.

The second launch attempt, on 1 June, was scrubbed 3 minutes and 50 seconds before liftoff after an automatic hold triggered after one of three redundant ground computers gave slower-than-normal readings. The issue was pinned down on a single faulty power supply unit connected to that computer. On 2 June, an ULA team replaced the computer chassis containing this power supply and verified that the new hardware was performing normally. The launch was rescheduled to the next available opportunity on 5 June.

CFT successfully lifted off on the Atlas V rocket on its third launch attempt, on 5 June at 10:52 am EDT. The mission was launched from ULA's SLC-41 launch site at Cape Canaveral Space Force Station, Florida, and was Atlas V's 100th flight. The rocket flew in the N22 configuration, with no payload fairing, two GEM 63 solid rocket boosters, and two RL10A-4-2 engines on the Centaur upper stage. The solid rocket boosters separated from the rocket 2 minutes and 20 seconds after liftoff. The core stage continued firing until 4 minutes and 28 seconds after launch and was separated shortly thereafter. The Centaur upper stage then began firing until 11 minutes and 52 seconds after launch. The Starliner spacecraft separated from the upper stage about 15 minutes after liftoff. To maximize safety, it was placed in a sub-orbital trajectory by the rocket and used its own thrusters to enter orbit about 31 minutes after launch.

Attempt Planned Result Turnaround Reason Decision point Weather go (%) Notes
1 6 May 2024, 10:34:14 pm Scrubbed Centaur LOX valve issue 6 May 2024, 8:32 pm ​(T-02:01:30) 95
2 1 Jun 2024, 12:25:40 pm Scrubbed 25 days, 13 hours, 51 minutes Ground launch sequencer computer fault 1 Jun 2024, 12:22 pm ​(T-00:03:35) 90
3 5 Jun 2024, 10:52:15 am Success 3 days, 22 hours, 27 minutes 90
CFT mission launch events
Time Event
L−6:00:00 Atlas V cryo load
L−4:00:00 Atlas V cryo load complete/stable configuration
L−4:30:00 Crew suit-up begins
L−4:04:00 T-4 minute hold begins
L−3:20:00 Crew suit-up complete/departs for launch pad
L−3:10:00 Crew Module preps begin
L−2:50:00 Crew arrives for insertion
L−1:20:00 Hatch closure complete
L−0:50:00 Cabin leak checks/cabin pressurization complete
L−0:35:00 Crew space to ground communication checks
L−0:22:00 Flight Director Poll: Go for terminal count
L−0:20:00 Crew visors configured for launch
L−0:18:00 Starliner poll for terminal count
L−0:18:00 Starliner to internal power
L−0:11:00 Crew access arm retracted
L−0:07:00 Atlas V launch vehicle poll for terminal count
L−0:07:00 Starliner configured for terminal count
L−0:05:00 Starliner configured for ascent
L−0:04:00 T-4 minute hold releases
L−0:00:02.7 RD-180 engine ignition
L+0:00:01.1 Liftoff (thrust to weight > 1)
L+0:00:06.0 Begin pitch/yaw maneuver
L+0:01:01.7 Maximum dynamic pressure
L+0:01:05.3 Mach 1
L+0:02:20.4 SRB jettison
L+0:04:28.9 Atlas Booster Engine Cutoff (BECO)
L+0:04:34.9 Atlas Centaur separation
L+0:04:40.9 Ascent cover jettison
L+0:04:44.9 Centaur First Main Engine Start (MES-1)
L+0:05:04.9 Aeroskirt jettison
L+0:11:55.4 Centaur First Main Engine Cutoff (MECO-1)
L+0:14:55.4 Starliner Separation

Cruise and docking

Starliner approaching the ISS during the Crew Flight Test (CFT)

In the hours after getting into orbit, the crew performed several manual maneuvering exercises, including pointing the antenna towards the TDRSS communications satellites, pointing the solar panels towards the sun, manually using the star tracker, manually braking and accelerating the spacecraft to perform orbital maneuvers, and manually orienting the spacecraft for reentry. Although the Starliner spacecraft is designed to operate autonomously and these capabilities are not required in a nominal mission, these tests showed that the crew can successfully take over many functions of the craft during an emergency.

Late 5 June, just before the crew's sleep time, flight controllers on the ground detected two additional helium leaks in different parts of Starliner's propulsion system, in addition to the one that was already known before the flight. To manage these leaks, flight controllers temporarily closed the two helium manifolds associated with the new leaks, which had the effect of disabling 6 of the spacecraft's 28 reaction control system thrusters. The leaks were described as small and the spacecraft still had plenty of excess helium to complete its mission, so managers gave permission to proceed with docking operations. The helium manifolds were reopened during rendezvous and docking and were subsequently closed once the spacecraft docked, as is standard procedure. A fourth leak, smaller than the other three, was detected after docking. The cause of the helium leaks is not yet known, but NASA and Boeing managers acknowledged that this appears to be a systemic problem with the propulsion system, contrary to their expectations before the mission that the first helium leak was an isolated issue caused by one defective seal.

As Starliner approached the ISS, another problem appeared when five reaction control system thrusters were deactivated during flight. Mission teams managed to bring back four of the thrusters by doing a series of resets and hot-fire tests on them, during which the crew manually held the spacecraft just outside the station's 200-meter keep-out zone. After verifying that the thrusters were operating normally, Starliner was permitted to dock with the station. The problem with the thrusters was similar to what happened during the uncrewed OFT 2 mission in 2022 when thrusters in the same location in the spacecraft were deactivated during approach. Mission managers believe the failure of the thrusters could be related to input data being outside some predetermined limits rather than being a software or hardware problem, although the exact cause is unknown.

Starliner successfully docked to the forward port of the Harmony module on the ISS on 6 June at 1:34 pm EDT, nearly 27 hours after launch. Docking was delayed by over an hour due to problems with the spacecraft's reaction control thrusters. Astronauts Butch Wilmore and Suni Williams entered the station at 3:45 pm EDT, joining Expedition 71 crewmembers Jeanette Epps, Matthew Dominick, Tracy C. Dyson, and Michael Barratt of NASA, and Oleg Kononenko, Nikolai Chub, and Alexander Grebenkin of Roscosmos.

ISS stay

Starliner docked to the ISS as seen from the Crew-8 Dragon spacecraft

On 7 June, the CFT astronauts spent their first full day aboard the ISS transferring cargo and emergency gear in and out of Starliner. They were helped by ISS crewmates Michael Barratt and Matthew Dominick. Among the items unpacked was a new pump for the station's urine processing facility, which converts urine into drinking water. It was added as a last-minute change to Starliner's cargo manifest after the station's old pump malfunctioned on 29 May. By the next day, the new pump was already installed and operating properly.

On 8 June, the crew tested the ability of the Starliner vehicle to act as a "safe haven" in the event of an emergency at the ISS, which includes sheltering the crew for an extended time or quickly departing the station if needed. This is a requirement for any crewed vehicle that visits the ISS. The CFT astronauts were also joined by Matthew Dominick and Tracy C. Dyson to test the living conditions on Starliner with a crew of four inside. On 9 June, the CFT crew continued performing checks on Starliner as part of their flight test objectives. The spacecraft was then switched to a low power mode, which it will stay on until undocking preparations begin at the end of the mission.

On 10 June, with all their initial Starliner testing completed, the CFT crew started working on general ISS maintenance and research activities. They started their day with health checks measuring their temperature, blood pressure, pulse, and respiratory rate. Later, Wilmore worked on maintenance of a computer connected to the Microgravity Science Glovebox, while Williams installed hardware to support a space fire investigation. They also participated in a number of public relations events where they talked to people on Earth, including a call to the Sunita L. Williams elementary school, located in Williams' hometown of Needham, Massachusetts and named after her. On June 11, the astronauts spent their time on biomedical activities, with Wilmore organizing the inventory of the Human Research Facility, and Williams working on procedures to collect microbe samples and sequence their genes. They also participated in an event with Tennessee Tech, Wilmore's home university. On 12 June, Wilmore checked cargo in the Harmony module and worked on maintenance of the station's bathroom, while Williams continued her gene sequencing work from the day before. On 13 June, the CFT crew worked to support a planned spacewalk by astronauts Matt Dominick and Tracy Dyson; they helped the pair during the suit-up process, and, once the spacewalk was canceled, helped them get out of their spacesuits. Later in the day, they took an inventory of the personal consumables they had used up to that point and worked with flight controllers to update their tablets with emergency procedures.

On 14 June, after their planned undocking date got pushed back to 22 June, the CFT astronauts had a call with Boeing mission managers to discuss the end of the mission, and then entered Starliner to review the spacecraft’s flight operations and procedures. On the weekend of 15 and 16 June, they performed various tasks related to their CFT mission and to assist the ISS crew. On 17 June, Williams worked on various maintenance task and prepared the Advanced Plant Habitat for future experiments, and on 18 June she continued working on the gene sequencing study from the week before. Meanwhile Wilmore spent the two days working on a study of the behavior of flowing liquids in space.

While Starliner is docked to the ISS, NASA and Boeing teams have continued to assess the spacecraft's performance up to this point, especially relating to the helium leaks and RCS thrusters issues that occurred in the beginning of the mission. These issues have made NASA delay the end of the mission multiple times to give teams more time to test the spacecraft while it is in space; since the service module in discarded on reentry, NASA and Boeing will not have another opportunity to collect data from it. On a 10 June update, NASA reported a fifth small helium leak in the service module, in addition to a new issue with an RCS oxidizer isolation valve that did not close properly. On 15 June, the spacecraft was powered on for a test of the aft-facing RCS thrusters, during which seven of eight thrusters performed nominally, including four of the five that had malfunctioned during docking. One thruster, which could not be restored during docking, was deemed unusable and will not be used for the remainder of the mission. This test also provided an opportunity for engineers to measure the helium leaks of the spacecraft, and all five leak rates were found to have decreased. While the cause of the helium and thrusters issues are still unknown, NASA managers speculated that, while not directly related to one another, the intense "dynamic operations" during the docking sequence could have contributed to both of these issues.

Return to Earth

NASA's original plan was for Starliner to undock from the ISS and return to Earth on 14 June. This has been pushed back several times to 26 June to allow engineers work to understand what has caused the helium leaks and thruster issues.

Once the crew closes the hatch of the Starliner, it will take about three hours before the crew will be ready to undock from the ISS. Once undocked, the crew plans to make a flight around the station before firing the service module thrusters to begin the trip back to the Western United States, where the capsule will land about six and a half hours later.

The Starliner will make a ground landing, a first for a crewed capsule mission launched from the United States. After reentering the atmosphere, three parachutes will be deployed, slowing the capsule to approximately 4 miles per hour (350 ft/min; 1.8 m/s). Before reaching the ground, six airbags will deploy to cushion the landing. For this mission, the prime landing targets are two locations inside the White Sands Missile Range in New Mexico. Other potential landing locations include the Willcox Playa in Arizona and the Dugway Proving Ground in Utah. Edwards Air Force Base in California serves as a contingency landing location. All of the landing sites are in the Western United States, allowing the service module to be jettisoned for a destructive reentry over the Pacific Ocean.

See also

  Media related to Boeing Crew Flight Test at Wikimedia Commons