NASA and Boeing Co. agreed to turn the initial test flight of the company’s commercial crewed capsule into an operational mission, one of several recent signs officials are hedging their bets on when U.S. spacecraft will start regularly ferrying astronauts to the international space station.

Thursday’s disclosure by the National Aeronautics and Space Administration suggests a previously planned two-person flight, slated for November 2018, is now likely to occur in 2019 or 2020 and would likely carry one additional crew member along with extra supplies. Instead of staying for two weeks as originally envisioned, NASA said the expanded crew could stay at the station for as long as six months conducting experiments and carrying out maintenance tasks.

The agency’s agreement to use Russian rockets and capsules to carry astronauts to and from the international laboratory ends in late 2019.

That is prompting NASA leaders to seek contingency plans to carry American astronauts into orbit—and keep them there for extended periods—in the event U.S. providers aren’t ready to assume routine transportation responsibilities by the deadline. Maintaining a continuous U.S. presence on the international space station is important to NASA.

Even after a successful crewed test flight, it could take NASA several months or longer to authorize routine missions, according to outside experts, agency advisory committees and senior NASA officials. The process could leave the U.S. scrambling for stopgap measures unless alternate options are put in place relatively soon.