Citing extremely limited funding which hinders NASA’s own “human spaceflight efforts,” the agency has announced an extension of its contract with its Russian counterpart, Roscosmos, and will pay an additional $490mn to secure seats in Soyuz spacecraft, the only means of delivering US astronauts to the ISS.

In a letter addressed to Congress, NASA Administrator Charles Bolden blamed the lawmakers for failing to fulfill the agency’s financial backing requests for its Commercial Crew Program.

As a result NASA was “forced” to extend its existing contract with the Russian Federal Space Agency (Roscosmos) as the sole deliverer of astronauts to space, after the retirement of the space shuttle program in 2011.

“For five years now, the Congress, while incrementally increasing annual funding, has not adequately funded the Commercial Crew Program to return human spaceflight launches to American soil this year, as planned. This has resulted in continued sole reliance on the Russian Soyuz spacecraft as our crew transport vehicle for American and international partner crews to the ISS,” the Bolden letter reads.

READ MORE: Soyuz takes manned space mission to ISS, 1st time since Progress, SpaceX failures

The extended contract which will last until 2019 will cost the American tax payers $490 million. The contract covers the costs of guaranteed seats in the Soyuz spacecraft, as well as comprehensive services such as astronaut training and preparations for the launch, landing, and the rescue of space station crew members following long-duration missions.

While somewhat acknowledging current Russian superiority in manned space flights, Bolden warned that the US space program should not miss a 2017 deadline to send US crews to space onboard Boeing and SpaceX systems which are still in development.

NASA signing $490M contract with Russia for Soyuz seats through 2019 http://t.co/HswGDKMyyEpic.twitter.com/sKEHJeC5rf — Asteroid Initiatives (@AsteroidEnergy) August 5, 2015

In 2014, the space agency partnered up with private companies Boeing and SpaceX to help develop a means of transportation for NASA’s crew members to travel to the space station, investing about $1.4 billion in contracts with private contractors.

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To meet the deadline, Bolden urged lawmakers to approve President Obama’s $1.24 billion budget request for the program, saying that otherwise Boeing and SpaceX would likely suspend all operations on the projects by next spring or summer.

“Our Commercial Crew Transportation Capability (CCtCap) contractors are on track today to provide certified crew transportation systems in 2017,” Bolden stressed.

“Reductions from the FY 2016 request ... would result in NASA’s inability to fund several planned CctCap... and would likely result in funds running out for both contractors during the spring/summer of FY 2016.”

If Congress fails to agree, the NASA administrator said the existing contracts “may need to be renegotiated, likely resulting in further schedule slippage and increased cost.”

For the following year NASA has asked for $1.243 billion to support the program. However the House, in June, allocated only $1 billion, while a bill awaiting consideration by the full Senate gives the program just $900 million.