Boeing Starliner's ISS Departure Postponed for In-Depth Propulsion System Review

NASA and Boeing have decided to postpone the undocking of the CST-100 Starliner spacecraft from the International Space Station (ISS). This extension allows mission teams to conduct a comprehensive analysis of the spacecraft's service module propulsion system, which has exhibited several small helium leaks and unexpected thruster performance during its inaugural crewed flight test.

Crew Flight Test: A Critical Certification Mission

The Starliner's Crew Flight Test (CFT) is the final major milestone required before NASA certifies the spacecraft for routine crew rotation missions to the ISS. Astronauts Barry "Butch" Wilmore and Sunita "Suni" Williams are currently on board the station, participating in this critical test phase, which provides invaluable data on the vehicle's performance in a real-world space environment.

Analyzing On-Orbit Anomalies

During its journey to the ISS, mission controllers identified five small leaks in the helium manifolds of the service module's propulsion system. Helium is a non-combustible gas used to pressurize the propellant lines for the Reaction Control System (RCS) thrusters. Additionally, five of the 28 RCS thrusters failed during the final phases of docking, although four were later successfully recovered through software commands.

1. Helium System Leaks: Teams are analyzing the propagation and stability of five distinct leaks to understand their root cause and ensure they pose no risk for the deorbit burn.
2. RCS Thruster Performance: Engineers are evaluating the data from the thruster failures to understand the thermal and operational parameters that may have contributed to their temporary shutdown.
3. Propellant Valve Health: A previously known issue with a propellant valve is also under review to ensure it functions as expected for the return journey.

The Importance of Rigorous Testing

This extended stay is a testament to the rigorous safety protocols governing human spaceflight. Using the ISS as a testbed allows engineers to gather extensive data and perform system checks that would be impossible on the ground. The ultimate goal is to validate the Starliner's systems with a high degree of confidence before it enters operational service.

We are taking our time and following our standard mission management team process. Starliner is performing well in orbit while docked to the space station. We are strategically using the extra time to clear a path for some critical station activities while completing readiness for Butch and Suni's return.

Next Steps and Return Profile

Engineers will continue to analyze flight data and conduct hot-fire tests of the RCS thrusters to model system performance for the return trip. Once teams are satisfied with the analysis and have a complete understanding of the issues, a new target date for undocking and landing at White Sands Space Harbor in New Mexico will be announced.

The delay underscores the complex, iterative nature of spacecraft development. Every anomaly presents a crucial learning opportunity, contributing to the robustness and safety of future missions and reaffirming NASA's commitment to crew safety above all else.