A seven-seat space taxi backed by NASA to ferry astronauts to the International Space Station will make a high-altitude test flight next summer, officials said on Tuesday.

Sierra Nevada Corp's Dream Chaser space plane, which resembles a miniature space shuttle, is one of four space taxis being developed by private industry with backing from the U.S. government.

For the unmanned test flight, it will be carried into the skies by WhiteKnightTwo, the carrier aircraft for the commercial suborbital passenger ship SpaceShipTwo, backed by Virgin Galactic, a U.S. company owned by Richard Branson's London-based Virgin Group.

The test flight was added after privately held Sierra Nevada got a $25.6-million boost to its existing $80 million contract with NASA.

The test flight will take place from either Edwards Air Force Base in California's Mojave Desert, or from the White Sands Missile Range in New Mexico, Ed Mango, manager of NASA's Commercial Crew Program, said at a community briefing at the Kennedy Space Center in Florida.

With the retirement of the space shuttles this summer, NASA is now dependent on Russia to fly astronauts to the space station, at a cost of more than $50 million per person.

The agency hopes to turn over crew transportation services to one or more commercial firms before the end of 2016, Mango said.

In addition to Sierra Nevada, NASA is funding spaceship development work at Boeing Co, Space Exploration Technologies, and Blue Origin, a start-up firm owned by Amazon founder Jeff Bezos.

Having only one way to get crew to the station is a limitation, NASA astronaut Mike Fossum, who is currently living aboard the outpost, said during an in-flight interview last week.

The station, a $100 billion project of 16 nations, was finished this year after more than a decade of construction 225 miles above the planet. The outpost, which is about the size of a five-bedroom house, supports a variety of scientific research and technology demonstrations.

Along with helping to develop commercial space taxis, NASA is working on a heavy-lift rocket and capsule to fly astronauts and cargo to asteroids, the moon, Mars and other destinations beyond the space station's orbit.

Drawing heavily on equipment originally built for predecessor programs, including the space shuttle and the canceled Constellation moon exploration initiative, the new rocket, called the Space Launch System or SLS, is scheduled to debut in 2017.

That unmanned test flight would be followed in 2021 by a trial run with astronauts, said Kennedy Space Center director Bob Cabana.

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