ORLANDO, Fla. — NASA plans to complete by the middle of March a contingency plan for ensuring access to the International Space Station should its two commercial crew partners suffer additional delays.

In a response included in a U.S. Government Accountability Office report issued Feb. 16, Bill Gerstenmaier, NASA associate administrator for human exploration and operations, concurred with a report recommendation that NASA develop alternative ways of getting astronauts to and from the ISS if commercial crew vehicles are not certified once NASA’s current contract with Russia for Soyuz flights expires at the end of 2018.

“NASA will develop a contingency plan for maintaining a presence on the ISS beyond 2018 if the Commercial Crew Program’s partners experience additional schedule delays,” Gerstenmaier wrote. That report, he said, would be completed by March 13.

The GAO recommended the report because of concerns that Boeing and SpaceX will not have their commercial crew vehicles certified to carry astronauts by the end of 2018. Those certification reviews, which will come after both uncrewed and crewed test flights of their vehicles, are intended to confirm that the vehicles are able to safely transport astronauts to and from the station.

The certification review for SpaceX’s Crew Dragon vehicle is currently planned for the third quarter of 2018, after an uncrewed test flight in November 2017 and a crewed test flight in May 2018. That review is at least 15 months later than the original schedule for the vehicle in SpaceX’s contract with NASA.

Boeing’s CST-100 Starliner is currently scheduled to have its certification review in the fourth quarter of 2018, after an uncrewed flight test in June 2018 and a crewed flight test in August 2018. That review is at least 14 months behind the original schedule in Boeing’s contract.

While both companies state they are making good progress on their vehicles after encountering a range of technical issues, NASA is less confident in their ability to remain on their revised schedule. “The Commercial Crew Program is tracking risks that both contractors could experience additional schedule delays and its own analysis indicates that certification is likely to slip into 2019,” the GAO report stated.

One challenge in coming up with a contingency plan is that the advance time for purchasing Soyuz seats from the Russian space agency Roscosmos has traditionally been three years, which would have required NASA to purchase seats for 2019 flights to the ISS in 2016. As of last fall, NASA officials had indicated that they had no plans to purchase additional seats.

According to the GAO report, NASA and Roscosmos are discussing one option where they would repeat the “year in space” experiment of 2015 and 2016, when NASA astronaut Scott Kelly and Roscosmos cosmonaut Mikhail Kornienko spent nearly one year on the ISS. A second one-year mission, starting in late 2018, would eliminate NASA’s need for one seat in mid-2019 as that astronaut would remain on the station until late 2019.

Another option not directly addressed in the report is for NASA to purchase Soyuz seats from Boeing. In January, NASA announced it was considering a Boeing proposal to purchase two Soyuz seats in the fall of 2017 and spring of 2018, with an option for three additional seats in 2019. Boeing acquired the seats from Russian company RSC Energia as part of a settlement of a lawsuit between the two companies about the Sea Launch joint venture.

NASA issued a “sources sought” announcement Jan. 17 seeking responses from companies before entering into negotiations with Boeing for a sole-source contract to acquire the seats. Neither Boeing nor NASA have provided an update about any negotiations since that announcement. According to the announcement, NASA has until the fall of 2017 to exercise the option for the Soyuz seats in 2019.

As NASA examines its options, Boeing and SpaceX are dealing with technical issues with their vehicle designs. Boeing’s top risks, according to the GAO report, include obtaining adequate information about the capsule’s parachute system and getting data on the design of Russian-built RD-180 engines used by the CST-100’s launch vehicle, the Atlas 5. The engine data is needed by NASA to verify the engine meets human certification requirements, but access to the data is restricted.

SpaceX’s risks involve a number of issues with the design of the Falcon 9, including a concern that frequent updates hinder the development of a stable design of the vehicle. Another issue is previously-reported criticism by some NASA advisers about SpaceX’s plans to fuel the Falcon 9 after astronauts have boarded the Dragon spacecraft, rather than fueling the rocket first.

A recent news report stated that NASA had also raised concerns about cracks seen in the turbines of the Falcon 9’s engines that NASA deemed an “unacceptable risk” for crewed launches. That issue was included in the GAO report, but it also noted that SpaceX has already made design changes to the turbine that “did not result in any cracking during initial life testing.”