WASHINGTON — NASA is proposing to purchase, through Boeing, additional Soyuz seats for International Space Station missions to both take advantage of Russian plans to decrease the size of its crew and as insurance against potential additional commercial crew delays.

In a “sources sought” procurement filing Jan. 17, NASA said it considering plans to acquire from Boeing two Soyuz seats on missions to the ISS in the fall of 2017 and the spring of 2018, and options for three additional Soyuz seats in 2019. Boeing, the filing stated, had obtained the rights to the seats from Soyuz manufacturer RSC Energia.

The two near-term seats take advantage of seats the Russians are vacating as a cost-saving measure. Roscosmos, the Russian state space corporation, announced in September it was reducing its crew on the ISS from three to two, starting in March and until the launch of a new laboratory module, expected some time in 2018.

At the time, Roscosmos had no firm plans to make use of the seats on Soyuz spacecraft freed up by the decision to reduce its crew, but suggested it would make the seats available to the other ISS partners. “We discussed with our partners to maybe use this free seat for them,” Igor Komarov, head of Roscosmos, said at the International Astronautical Congress in September. “We expect some interest from that side.”

Boeing gained access to the seats as part of an agreement with Energia to settle a legal dispute regarding Sea Launch. Boeing won a judgment of more than $320 million against Energia from a federal court in May 2016, but subsequent legal filings indicated that the two companies were negotiating a settlement.

“We got together with Energia and discussed what in-kind things that we could perhaps put on the table that might offset this debt,” John Elbon, vice president and general manager of space exploration at Boeing, said in a Jan. 17 interview. Part of the broader agreement between the two companies included rights to the Soyuz seats, but he said specific details of the settlement agreement between the companies were proprietary.

Elbon said that Boeing then decided to offer the seats to NASA in an unsolicited proposal to the agency. “They have expressed some interest” in the proposal, he said, leading to the sources sought filing. “We’ll go through the process and figure out if there’s an opportunity for us to make a deal.”

The near-term seats will allow NASA to add an additional crewmember to the U.S. segment of the station, which the agency was already planning to do once commercial crew vehicles under development by Boeing and SpaceX enter service. “Adding an extra U.S. crewmember in 2017 and 2018 will really help with the utilization on board and getting more hours for science,” Elbon said.

What’s attracted more attention among industry observers is the option for the three additional seats on two Soyuz flights in the spring of 2019. NASA’s current contract with Roscosmos for regular crew transportation services to and from the ISS runs through 2018, at which time the agency expects either or both commercial crew companies to take over.

Both Boeing and SpaceX, though, have experienced delays with their vehicles that pushed back test flights until as late as mid-2018. That’s raised questions about whether their vehicles would be ready in time to start providing flights in 2019 should they experience additional issues.

“Although both commercial crew vehicles are on track right now to start flying in 2019, it seemed to us it might make sense to NASA to have some insurance just in case,” Elbon said, noting there are uncertainties inherent in any development program. “Some insurance or backstop in 2019 seemed like it might be prudent.”

NASA officials previous indicated that there were no plans by the agency to purchase additional Soyuz seats directly from Roscosmos. William Gerstenmaier, NASA associate administrator for human exploration and operations, said in an October interview that the deadline had passed for NASA to purchase additional Soyuz seats from Roscosmos for 2019 missions.

NASA Associate Administrator Robert Lightfoot, who will become acting administrator Jan. 20, did not mention the proposed Soyuz purchase during a Jan. 17 speech at a Maryland Space Business Roundtable luncheon in Greenbelt, Maryland. However, he said he believed the two companies developing commercial crew vehicles would be ready for flights in 2018 despite technical challenges.

“We’re continuing great development on the commercial crew program. We’re going to hopefully return flights of U.S. astronauts from U.S. soil here in 2018,” he said. “They’re running into what I would call the standard challenges that you’re going to run into when you’re trying to develop a spacecraft, and so we’re working through that.”

The sources sought statement indicates that NASA has until the fall of 2017 to decide whether to exercise the option for the 2019 seats, which could also be used in parallel with commercial crew missions “to maximize research onboard the ISS.” Elbon said Boeing agreement with Energia includes provisions should NASA decide not to purchase the 2019 seats, but he could not disclose those details.

Elbon said he expects NASA to enter into negotiations with Boeing about the 2017 and 2018 seats shortly after a Jan. 27 deadline for companies to respond to the sources sought statement, a requirement when a government agency proposes a sole-source procurement. “Assuming that goes well, I think we would sit down and, in relatively short order, negotiate the details of this kind of arrangement,” he said.

He didn’t specify how much Boeing was proposing to charge NASA for the seats. The agency announced an agreement with Roscosmos in August 2015 for six Soyuz seats in 2018 at a total cost of $490 million, or $81.7 million per seat.

“It’s a good value for NASA and the taxpayer,” Elbon said of Boeing’s proposed deal with NASA. “We wouldn’t ask them to pay more than they would have been paying before.”