WASHINGTON — A new Government Accountability Office report called on NASA to develop a contingency plan to maintain access to the station after next September should commercial crew vehicles suffer additional delays.

The June 20 report by the GAO noted that both Boeing and SpaceX are making progress on the development of their commercial crew vehicles, including an uncrewed test flight of SpaceX’s Crew Dragon spacecraft in March. But a number of technical issues, coupled with a history of delays, didn’t give the organization confidence the companies would be able to maintain their current schedules.

“Both contractors have made progress building and testing hardware, including SpaceX’s uncrewed test flight,” the report stated. “But continued schedule delays and remaining work for the contractors and the program create continued uncertainty about when either contractor will be certified to begin conducting operational missions to the ISS.”

The report outlined the technical challenges both companies face to complete the development of their vehicles, topics that have also been discussed at recent meetings of the NASA Advisory Council and the Aerospace Safety Advisory Panel. For Boeing, that includes ongoing work to qualify the CST-100 Starliner’s parachute system while addressing an issue discovered during a parachute test last August. Another issue is an anomaly during an unidentified 2018 launch of the United Launch Alliance Atlas 5, the vehicle that will launch Starliner, where the engine position “deviated from commands” but did not affect the outcome of the mission.

SpaceX, besides its ongoing investigation into the April incident that destroyed a Crew Dragon vehicle being prepared for tests of its abort thrusters, is working through issues with its parachutes. The company was also working to qualify its propellant loading procedures and composite overwrapped pressure vessels to attain enough flight experience to satisfy NASA requirements for crewed missions, as well as a long-standing concern about cracks in launch vehicle engine turbines.

One reason the GAO is skeptical that the companies can meet current schedules is the number of “verification closure notices” they have obtained from NASA. Such notices verify that a company has met a requirement in their commercial crew contracts, with the expectation that nearly all requirements will be closed prior to a crewed test flight. However, as of the second quarter, Boeing had only 25 percent of its verification closure notices recorded, and SpaceX just 11 percent.

This GAO is not the first to warn of schedule delays in the program. The agency issued a similar report in July 2018, and the new report notes that, since that earlier report, Boeing has delayed the date it expects to have its Starliner vehicle certified by 12 months, while SpaceX has delayed Crew Dragon certification by seven months.

SpaceX’s certification date of September 2019 is likely to slip further because its schedules for both an in-flight abort test and crewed test flight are under review while the investigation into the April test incident continues. SpaceX recently filed for a communications license with the Federal Communications Commission for that crewed test, expecting that flight to take place in a six-month period starting Nov. 1.

Boeing is scheduled to perform an uncrewed test flight of Starliner no earlier than August, followed by a crewed flight in November. Both dates are likely to slip further, though, with the uncrewed test not expected before mid-September. Dennis Muilenburg, president and chief executive of Boeing, said in a June 19 speech that the uncrewed test flight would take place later this summer and the crewed flight “before the end of the year.”

The report reiterated a recommendation from the GAO’s 2018 report that NASA develop a contingency plan to maintain access to the station. Since that report, NASA announced it would procure two seats on Soyuz missions that will allow it to maintain a U.S. presence on the station through September 2020. NASA hasn’t disclosed the cost of those seats, the GAO report stated, but that it was five percent higher than the previous contract modification.

The GAO, though, said this seat purchase alone isn’t sufficient to meet its requirement. “NASA needs to provide additional support regarding planning efforts to ensure uninterrupted access to the ISS if delays with the Commercial Crew Program contractors continue beyond September 2020,” the report stated. “Continued NASA attention on this issue is needed given the uncertainty associated with the final certification dates.”

In a response included in the report, Bill Gerstenmaier, NASA associate administrator for human exploration and operations, said that the Soyuz seat purchases, along with plans to convert Boeing’s crewed test flight into a long-duration mission to the station, “currently provide adequate schedule margin to allow for Commercial Crew systems to become operational.”

“Should that schedule margin change in the future,” he added, “NASA will reassess our options to ensure we maintain a U.S. presence on the ISS.”