NASA Astronauts Kick Off Boeing Starliner Flight Test

Getting Boeing’s first crewed CST-100 Starliner spacecraft to the International Space Station was a major step in the company’s 12-year program to develop a low-Earth-orbit transportation system for NASA and other customers. But it will take some luck for NASA to pick the Boeing Starliner to fly the station crew launching early next year.

So far, luck has been in short supply during Starliner’s development. It took 2.5 years for Boeing to return to flight testing after software and communications issues forced an early end to the spacecraft’s uncrewed debut in December 2019. Then another two years passed between the redo, Orbital Flight Test-2 (OFT-2), which successfully reached the station in May 2022, and the June 5 launch of the Crew Flight Test (CFT) with NASA astronauts Barry “Butch” Wilmore and Sunita Williams. 

“We would have liked to have been further along at this time—there’s no doubt about that—but we’re here now and we’re prepared,” Mark Nappi, Boeing vice president and Starliner program manager, told reporters in March. 

• ULA joins human spaceflight industry
• Starliner service module leaking helium

The mission was 2 hr. away from liftoff on May 6 when Boeing’s launch service partner, United Launch Alliance (ULA), stopped the countdown due to a problem with a pressure regulation valve on the liquid oxygen tank of the Atlas V’s Centaur upper stage. While securing Starliner after the scrub, engineers noted an unrelated slight helium leak in the spacecraft’s propulsion system. That was traced to a flange in one of the reaction control system (RCS) thrusters.

While the leak was well within safe parameters for flight, further analysis exposed a design vulnerability that could eliminate one of Starliner’s options for conducting its deorbit burn. NASA and Boeing developed an additional backup procedure, clearing the way for a second launch attempt on June 1.

That campaign ended 3 min. 50 sec. before liftoff when a failed power unit felled one of three redundant ground launch sequencer systems that control the final 4 min. of the Atlas V countdown.

A third launch attempt on June 5 sealed the deal. The Atlas V lifted off from Space Launch Complex-41 at Cape Canaveral SFS at 10:52 a.m. EDT, aiming to put Starliner into a suborbital trajectory ranging 45-113 mi. above Earth and inclined 51.6 deg. relative to the equator.

The rocket’s first stage, powered by a Russian RD-180 engine, burned out and separated as planned 4 min. 35 sec. after liftoff, leaving the Centaur, powered by a pair of Aerojet Rocketdyne RL-10 engines, to complete ULA’s first human spaceflight.

The Centaur fired for 7 min. 10 sec., coasted and then released Starliner 14 min. 55 sec. after liftoff, setting the stage for the spacecraft to fire four orbital maneuvering and attitude control (OMAC) thrusters and put itself into orbit.

The launch from Cape Canaveral marked the first crewed launch from the U.S. military side of the Cape Canaveral/Kennedy Space Center spaceport since Apollo 7 in 1968. Although early versions of Atlas boosters launched Mercury astronauts in 1962-63, CFT was the first human spaceflight aboard an Atlas V, which was making its 100th flight. “We’re very proud to join this human spaceflight community,” ULA CEO Tory Bruno told reporters after the launch. “There is absolutely nothing like this.”

In addition to the dual-engine Centaur, which provided a flatter trajectory to ensure safe abort options throughout ascent, Atlas V enhancements for crewed flight included an adapter to attach Starliner to the launch vehicle, a 70-in. aeroskirt for aerodynamic stability and an emergency detection system to monitor autonomously the health of launch vehicle systems. If necessary, the system would trigger an abort.

During Starliner’s 26-hr. approach to the International Space Station (ISS), Wilmore and Williams, both former U.S. Navy test pilots, took over manual flight control, pointing the spacecraft’s solar arrays toward the Sun and practicing other maneuvers ahead of an automated docking initially targeted for 12:15 p.m. EDT on June 6 (AW&ST May 6-19).

As the astronauts prepared for sleep after the first day of a planned two-week mission, flight controllers at Boeing Mission Control in Houston noticed that the small but persistent helium leak in Starliner’s propulsion system—discovered after the first launch scrub—had increased, and two more leaks had appeared as well.

They radioed for the crew to close the affected helium manifolds temporarily, sidelining six of Starliner’s 28 RCS thrusters and three of its 20 OMAC thrusters, so that flight controllers could analyze leak rates and mull workarounds. “This was not unexpected,” said Brandon Burroughs, a Boeing engineer and mission commentator. “The helium system remains safe for flight. We plan for cases like this.”

Ahead of docking, the manifolds were reopened, restoring pressurization for the thrusters, but as Starliner approached the ISS, five RCS jets malfunctioned due to an unrelated issue. This prompted the spacecraft to halt its approach at the designated Keep Out Sphere (KOS)—a 656-ft. zone around the ISS that is not to be entered if there are issues that add risk to flight control operations during docking.

Wilmore took over manual control of Starliner to hot-fire the affected thrusters one by one, demonstrating sufficient performance and redundancy prior to proceeding with docking. Four thrusters were recovered, providing NASA and Boeing teams with enough confidence to reschedule a one-orbit-delay docking.

The thrusters may have experienced software restrictions that can be altered to prevent premature cutoffs, said Boeing’s Nappi and Steve Stich, NASA’s Commercial Crew Program manager. Similar issues arose in the same thrusters during Starliner OFT-2 in 2022.

Just before docking—per their flight plan—Wilmore and Williams temporarily halted Starliner’s automated approach to the station to demonstrate manual piloting, a CFT objective intended to ensure that future Starliner crews could take over spacecraft piloting from the automated flight control system if needed.

The spacecraft, named Calypso, then berthed itself at the station’s forward-facing port of the Harmony module at 1:34 p.m. EDT on June 6 as the ships sailed 260 mi. over the Indian Ocean. “Nice to be attached to the big city in the sky,” radioed Williams, who was returning to the ISS for the third time.

Hatches opened at 3:45 p.m. and Wilmore and Williams were warmly greeted by the Expedition 71 crew, consisting of: Russian commander Oleg Kononenko; NASA astronauts Michael Barratt, Matthew Dominick, Tracy Dyson and Jeanette Epps; and cosmonauts Nikolai Chub and Alexander Grebenkin.

“We are glad to see you,” Kononenko said. “We want to congratulate the whole team.”

With Starliner docked, flight controllers closed all of the spacecraft’s helium manifolds as previously planned, curtailing additional helium loss. Two more helium leakswere detected after docking, suggesting a possible common cause requiring further analysis, Nappi said.

Teams assessed what impacts, if any, the helium manifold leaks would have on the remainder of the mission. NASA said on June 10 that 7 hr. of free-flight time were needed to perform a normal end of mission, and based on current leak rates, Starliner had enough helium left in its tanks to support 70 hr. of free flight after undocking.

Ground teams planned to fire all 28 RCS thrusters to collect additional data before the expendable service module was discarded as part of the normal reentry procedure.

“We have two problems on this vehicle right now: the helium leak and figuring out how to fine-tune these thrusters so that they’re not selected off [by the flight software],” Nappi said. “Those are pretty small issues to go deal with, and we’ll figure them out for the next mission. I don’t see these as significant at all.”

Wilmore, 61, and Williams, 58, are to remain aboard the ISS until at least June 18, when they are expected to undock and return to Earth, possibly touching down at NASA’s White Sands Test Facility in New Mexico, or at another site in the southwestern U.S. The departure date and landing location will depend on landing site weather conditions and progress toward achieving CFT performance objectives.

Upon docking, Starliner joined the NASA SpaceX Crew-8 Dragon spacecraft, the Russian Soyuz MS-25 capsule, a Northrop Grumman Cygnus supply ship, and two Russian Progress 86 and 87 cargo ships currently parked at the ISS. Once certified by NASA’s Commercial Crew Program, Starliner and Crew Dragon are expected to alternate ISS crew launches about once every six months.

Like Soyuz, Starliner was designed to parachute to the ground at the end of a mission, but it also could splash down in the ocean like SpaceX’s Dragon capsules. Starliner was developed to launch to the ISS with four astronauts, plus cargo, but it could launch to orbit with up to seven crewmembers.

On the CFT mission, Starliner delivered a modest cargo that included a 150-lb. replacement pump for the ISS water recovery system, which recycles urine and other wastewater into crew drinking water. The pump, which is part of the orbital lab’s life support system, failed in late May, prompting the quick addition of a replacement to the cargo aboard Starliner.

While docked to the ISS, Wilmore and Williams evaluated Starliner’s ability to function as a “safe haven,” should the ISS experience a contingency that would prompt evacuation of the crew to the docked Soyuz, Crew Dragon and Starliner capsules.

They also performed a habitability study, alongside astronauts Dyson and Dominick, to evaluate seating positions and other factors, such as air circulation, for a four-person crew. Other tasks included evaluating spacesuit and seat-fits, plus checkout of Starliner’s service module batteries.

Despite the thruster issue, helium leaks and a temporary Starliner cooling system glitch, NASA said CFT has so far provided a valuable step forward in the spacecraft’s certification.

“Advancing human spaceflight is not an easy task,” NASA Associate Administrator Jim Free told reporters after docking. “We had a vision to increase the reliability and safety of sending astronauts on their mission to the ISS while returning a capability to do so from the United States through a partnership with American private industry. We are continuing to make that vision a reality.”

When NASA retired its space shuttle program in mid-2011, it was forced to rely on Russia’s Soyuz capsules as the only means of transporting astronauts to and from the ISS until 2020. That was when SpaceX became the first commercial company to achieve NASA Commercial Crew Program certification with its Crew Dragon.

NASA selected SpaceX and Boeing in 2014 to develop, test and operate separate commercial transportation systems to and from low Earth orbit. SpaceX is in the midst of its eighth crewed mission to the ISS for NASA, with a ninth expected to launch in August. It also has flown four private Crew Dragon charters, with a fifth mission slated for mid-July.

In the long term, Boeing is eying orbital flight services beyond NASA, but not until it completes Starliner certification and begins the first of up to six operational missions for the agency under its 2014 Commercial Crew Transportation Capability contract (CCtCap), which is worth $4.45 billion as of March 31.

“We’ve been very focused on CFT,” Nappi said in March. “We cheer for SpaceX—that’s something that is very important to our country and very important to NASA to have that access—and we’re looking forward to providing that as well.

“The private astronaut missions are of interest later in the decade,” he added. “Right now, the focus is on getting CFT flown safely, getting certified and then flying the Starliner-1 mission.”

CFT follows two uncrewed flight tests of Starliner spacecraft in December 2019 and May 2022, the latter of which reached the ISS. Between the abbreviated debut mission and CFT, Boeing found and resolved issues with Starliner communications systems, software, oxidizer valves, parachutes and potentially flammable tape that was wrapped around wire harnesses throughout the spacecraft. The fixed-price, milestone-based CCtCap contract left Boeing to shoulder most of the costs to fix the technical issues, adding years of delays and about $1.4 billion to the company’s tab.

Pending the outcome of CFT, Boeing is looking to complete certification and have another Starliner spacecraft ready to fly in about six months. NASA plans to alternate ISS crew rotation missions between SpaceX and Boeing, which would like to have Starliner-1 ready to launch the ISS Crew 10 mission currently targeted for mid-February 2025.