WASHINGTON — Hedging its bets on commercial crew, NASA’s Johnson Space Center on Feb. 6 issued a formal notice of its intent to buy six more round-trip seats on Russian Soyuz spacecraft bound for the International Space Station in 2018.

“NASA/JSC intends to contract with Roscosmos for these services on a sole source basis for six (6) Soyuz seats and associated services for calendar year (CY) 2018 with rescue/return services extending through spring 2019,” NASA wrote in a procurement notice posted on the Federal Business Opportunities website.

“NASA needs to secure crew transportation with a known reliable provider to ensure a continued U.S. presence aboard the ISS until the sustained availability of a U.S. commercial vehicle” the notice continues. “The intent of this proposed action is to provide the Government the ability to procure these uninterrupted services until a U.S. provider demonstrates full operational capability.”

NASA is currently paying Russia about $76 million a round-trip seat to transport astronauts to the ISS through 2017 and provide return services into 2018 under a deal signed last April. NASA is counting on Boeing and SpaceX crew capsules now in development to be ready to start ferrying astronauts to and from the ISS by the end of 2017, ending the U.S. space agency’s dependence on Russia.

But in releasing its 2016 budget proposal Feb. 2, NASA officials said that timetable depends on Congress fully funding its $1.2 billion commercial crew request, which represents an increase of more than 50 percent from the $805 million Congress approved for 2015.

Here’s the full notice:

PROCUREMENT OF CREW TRANSPORTATION AND RESCUE SERVICES FROM ROSCOSMOS

Synopsis – Feb 06, 2015