On July 28th, the International Space Station (ISS) suffered a mishap after a new Russian module (named Nauka) fired its thrusters just hours after arriving. As a result, the entire station was temporarily pushed out of position, forcibly delaying the Orbital Flight Test-2 (OFT-2) mission. This would have been Boeing’s CT-100 Starliner second attempt to rendezvous with the ISS as part of NASA’s Commercial Crew Program (CCP).

The ISS managed to correct its orbit shortly thereafter, while the OFT-2 launch was delayed until the next available opportunity (Wednesday, Aug. 4th). Unfortunately, the mission was delayed again due to an issue with one of the valves on the spacecraft’s propulsion system. This prompted the ground crews to move the Starliner and Atlas V launch vehicle back into Vertical Integration Facility (VIF), so they can look for the source of the problem more closely.

The OFT-2 mission will be the second attempt of the Boeing CST-100 Starliner to dock with the ISS, having failed to do so during its previous attempt (in Dec. of 2019). Known as the OFT-1 mission, the Starliner successfully reached space without issue, but a clock malfunction prevented the engines from firing at the correct time. Once they did fire, they burned more fuel than anticipated, making its planned rendezvous with the ISS impossible.

A ULA Atlas V rocket with Boeing’s CST-100 Starliner spacecraft on the launch pad at Space Launch Complex 41 at Cape Canaveral Space Force Station in Florida. Credit: NASA/Aubrey Gemignani

That planned mission would have been the final uncrewed flight test, designed to validate the Starliner to conduct resupply and crewed missions to the ISS. SpaceX completed an uncrewed flight test (Demo-1) with their Crew Dragon spacecraft, which successfully rendezvoused with the ISS on March 2nd, 2019. This was followed by Demo-2, where astronauts Robert Behnken and Douglas Hurley flew to the ISS.

The OFT-2 flight would have put Boeing one step closer to securing contracts with NASA to fly cargo and crews to the ISS. Before that can happen, NASA and Boeing need to analyze the Starliner and find out why not all of its valves were in the proper configuration needed for launch. Already, NASA and Boeing have worked through several steps to troubleshoot the incorrect valve indications.

This included cycling the service module propulsion system valves while the Starliner was still in its launch configuration atop the United Launch Alliance’s (ULA) Atlas V rocket in Space Launch Complex-41 at the Cape Canaveral Space Force Station in Florida. At this juncture, the teams have also ruled out a number of other potential causes (such as a software glitch), but it was clear that additional assessment was needed.

After the engineering teams presented their initial findings to NASA and Boeing managers on August 4th, it was decided that the Atlas V and Starliner would be relocated to the VIF for further inspection and testing. With the VIF’s assembly of support structures securing the spacecraft service module, engineers now have direct access to the Starliner and can conduct a more thorough analysis.

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