A three-way race to build a commercially operated spaceship to shuttle astronauts -- and other paying customers -- to and from low-Earth orbit is close the finish line, with NASA aiming to award development and flight service contracts as early as next week.

So far, two companies favoring capsule designs -- Boeing and Space Exploration Technologies, or SpaceX -- have won the lions share of NASAs Commercial Crew program funds. The effort, which began in 2010, is intended to provide a U.S. alternative for flying crews to the International Space Station, which orbits about 260 miles above Earth.

Since NASA retired the space shuttles in 2011, the only human transportation system flying to the station is owned by Russia, which charges about $70 million per person for rides on its Soyuz capsules. NASA hopes to change that before the end of 2017.

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Along with Boeing and SpaceX, NASA has been funding space taxi design work at a third company, Colorado-based Sierra Nevada Corp., though its contracts have been about half of what Boeing and SpaceX received.

Sierra Nevada eschewed the capsule design in favor of a small winged spaceplane called Dream Chaser, which resembles a miniature space shuttle. The company has signed partnership agreements with more than 30 companies, nine universities, nine NASA field centers and three international space agencies, a strategy that could provide some flexibility if it is not selected for additional NASA funding.

Weve always looked at this as a system, with the space station being a mission. There are other missions that we are looking at. Having this wide group of companies allows us to look at construction, repair missions, the ability to do short- and long-duration science missions independent of the space station, Mark Sirangelo, Sierra Nevada Space Systems president, told Discovery News.

For us, receiving hundreds of millions of dollars less at the start of the competition put us at a schedule disadvantage -- we couldnt do as many things -- but it made us be a lot more creative in how we were going to manage the last two years, Sirangelo said.

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Showing that you can manage to a very tight budget is a pretty big thing, he added.

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Race to Build NASA Space Taxi Down to the Wire