Boeing Co., one of four firms bidding on a NASA contract to create a space taxi capable of taking its astronauts to the International Space Station, say it has completed a crucial review of its spacecraft's design.

It is the first to do so in the original time period set by NASA, edging out other bidders such as SpaceX and Sierra Nevada Corp.

Those firms have asked for and received extensions to allow them until May 2014 to complete their design reviews.

SpaceX is already ferrying cargo to the ISS with its unmanned Dragon capsules launched by its own Falcon 9 rockets. Also in the bidding for the NASA project is Blue Origin, a company set up by Amazon.com founder Jeff Bezos.

NASA says it wants to offer the contract for a commercial space taxi to a U.S. firm to end its dependence on Russian Soyuz capsules to ferry astronauts to and from the ISS.

That intention has become more urgent in recent months amid increasing tension between Russian and the West over Russia's activities in the troubled Crimean region in Ukraine.

A NASA spokeswoman confirmed Boeing's completion of the design review of its candidate for the space agency's multi-billion dollar Commercial Crew Integrated Capability (CCiCap) project.

The company's data would be analyzed to see if it met the review's mandatory "success criteria," said Stephanie Martin.

Boeing officials admitted to some challenges but were quick to compliment the "excellent" feedback offered by NASA during the process.

"From a technical standpoint, the review went very well," said John Mulholland, program manager of the company's commercial space exploration programs. "To the best of my knowledge we're the only CCiCAP competitor that actually was able to complete all milestones in the period of performance."

He added that Boeing believes it can have construction of a capsule completed in time for flight tests to begin in 2017.

Those tests would involve launching the capsule atop a United Launch Alliance Atlas 5 rocket.

ULA is a collaboration between Lockheed Martin Corp. and Boeing.

The Atlas 5 utilizes a Russian-built RD-180 to power its first stage, another source of concern given current political tension between the U.S. and Russia.

Mulholland said Boeing's space taxi has been designed to work with different launch vehicles should that become necessary, although it would require some changes to the spacecraft/launcher interface.

NASA has said it plans in late August or September to designate one or more of the bidding companies to continue their work on their designs.