Boeing Starliner’s Crew Flight Delays

The path to the International Space Station (ISS) for Boeing’s CST-100 Starliner has faced another significant hurdle. NASA and Boeing have adjusted the launch timeline for the Crew Flight Test (CFT) multiple times following the discovery of a helium leak in the spacecraft’s service module. This mission represents a pivotal moment for Boeing as it attempts to certify its spacecraft to carry humans, a feat currently dominated in the commercial sector by SpaceX.

The Helium Leak Explained

The primary cause for the recent delays involves a small helium leak detected in the Starliner service module. Engineers traced the issue to a flange on a single reaction control system (RCS) thruster. Helium is critical for spaceflight not because it burns as fuel, but because it is used to pressurize the propulsion system. Without adequate pressure, the thrusters cannot fire correctly to maneuver the spacecraft for docking with the ISS or for the deorbit burn to return to Earth.

While NASA officials initially described the leak as stable, the decision to delay allows engineering teams to analyze the risk. They must determine if the leak could expand during the stress of launch or the temperature fluctuations of orbit. The service module is a disposable component that burns up upon re-entry, meaning engineers cannot inspect it after the mission. They have to be certain of its integrity while it sits on the launchpad.

A Timeline of Technical Setbacks

This specific helium issue is the latest in a series of technical pauses for the Starliner program. The timeline of the recent launch attempts highlights the complexity of sending humans to space:

• May 6 Attempt: The launch was scrubbed roughly two hours before liftoff. This was not due to the Starliner itself, but rather a buzzing oxygen relief valve on the Centaur upper stage of the United Launch Alliance (ULA) Atlas V rocket.
• Post-Scrub Discovery: While technicians were resolving the ULA rocket valve issue, they detected the separate helium leak in the Boeing spacecraft’s propulsion system.
• Subsequent Delays: The launch date was pushed from May 17 to May 21, and then to late May and early June. These shifts provided time to assess the leak rates and ensure redundant systems could handle a potential failure.

The Crew and the Stakes

Waiting in the wings are NASA astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams. Both are veteran test pilots selected specifically for their ability to handle the unpredictability of a test flight. They have remained in quarantine and training while ground teams work through the data.

The stakes for this mission are financial and reputational. Boeing developed the Starliner under a $4.2 billion fixed-price contract with NASA’s Commercial Crew Program. The goal is to provide NASA with a second reliable taxi to the ISS alongside SpaceX’s Crew Dragon. The Crew Dragon has been operational since 2020, putting pressure on Boeing to prove the Starliner is safe and ready for regular service.

Why NASA Won't Rush

NASA maintains a strict safety culture, particularly for crewed missions. The “flight readiness review” is a rigorous process where engineering teams must sign off on every anomaly. In the case of the helium leak, the team analyzed whether the leak was an isolated defect (like a bad seal) or a systemic design flaw affecting all thrusters.

Ground testing revealed that the leak rate was manageable within the spacecraft’s safety margins. However, flight rules dictate that the vehicle must maintain a certain level of redundancy. If the leak worsened, the computer might shut down that specific thruster manifold. The engineering teams spent weeks verifying that the backup manifolds could handle the full workload of ascent, docking, and re-entry without compromising crew safety.

Frequently Asked Questions

What is the specific danger of a helium leak? If too much helium escapes, the propulsion system loses pressure. This can prevent the reaction control thrusters from firing. These thrusters are necessary for small adjustments during docking maneuvers and for orienting the capsule for a safe return to Earth.

Who is launching the Starliner? The spacecraft sits atop an Atlas V rocket, built and operated by United Launch Alliance (ULA). This is a different rocket than the Falcon 9 used by SpaceX.

Has Starliner flown before? Yes. Boeing completed two uncrewed orbital flight tests. The first in 2019 failed to reach the ISS due to software clock errors. The second in 2022 successfully docked with the station and returned, paving the way for this current crewed attempt.

How long will the astronauts stay at the ISS? The Crew Flight Test was originally scheduled to last about a week. However, the duration is flexible and subject to change based on weather conditions at the landing site and station operations.

Is the helium leak the only issue? During the delay period, teams also looked at a potential design vulnerability in the propulsion system regarding rare electrical failures. However, the helium leak remained the primary focus of the schedule slips mentioned in late May reports.