ORLANDO, Fla. – NASA said on Friday it is weighing an option to buy two astronaut seats aboard a Russian rocket as a fall back plan against delays in the launch systems being developed by Elon Musk’s SpaceX and Boeing Co.

A possible purchase “provides flexibility and back-up capability” as the companies build rocket and also crew capsule launch systems to return astronauts to the International Space Station (ISS) from U.S. soil for the first time since NASA’s Space Shuttle program went offline in 2011.

NASA has had to rely on Russia’s Roscosmos to ferry astronauts to the space station at a cost of roughly $80 million per seat.

After 2019 there are no seats available on the spacecraft for U.S. crew, and a NASA advisory panel recommended that the U.S. space program develop a back up plan to guarantee access to the station in case problems delay Boeing and SpaceX any further.

A NASA spokesman characterized a solicitation request NASA filed on as a contingency plan. NASA said it could buy a seat for one astronaut in the fall and another seat in the spring of 2020.

The absence of U.S. crew members at any point would diminish ISS operations to an inoperable state

NASA

NASA awarded $6.8 billion to SpaceX and Boeing to develop separate launch systems to fly astronauts to space. Both companies have faced technical challenges and delays.

Boeing Starliner

NASA said Boeing’s un-crewed CST-100 Starliner would fly no sooner than April, with Boeing’s crewed mission is currently slated for August.

“Typically, problems will be discovered during these test flights,” NASA wrote.