Boeing's proposal to develop a so-called space taxi for NASA astronauts includes a seat for paying tourists to fly to the International Space Station, it has been revealed.

The $4.2 billion, five-year contract allows Boeing to sell rides to tourists, Boeing Commercial Crew Program Manager John Mulholland told Reuters, although a price has not yet been set,

Although the exact price has not been set, Boeing said that the price would be competitive with what the Russian space agency now charges to fly tourists to the orbital outpost - around $50m.

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Would you pay $50m for a seat? Boeing's proposal to develop a so-called space taxi for NASA astronauts includes a seat for paying tourists to fly to the International Space Station, it has been revealed.

FOLLOW SARAH BRIGHTMAN TO SPACE Space Adventures is scheduled in January to begin training British singer Sarah Brightman for a 10-day visit to the station, a trip costing $52 million, according to Tom Shelley, president of Space Adventures. Brightman is slated to become the eighth paying passenger to travel to the station, a $100 billion research complex that flies about 260 miles (418 km) above Earth. Advertisement

'Part of our proposal into NASA would be flying a Space Adventures spaceflight participant up to the ISS,' Mulholland said, referring to a Virginia-based space tourism company that brokers travel aboard Russian Soyuz capsules.

Now that Boeing has won a share of NASA's space taxi contract, 'we hope ... to start working with the ISS program to make it happen,' he said.

'We think it would be important to help spur this industry.'

Space Adventures is scheduled in January to begin training British singer Sarah Brightman for a 10-day visit to the station, a trip costing $52 million, according to Tom Shelley, president of Space Adventures.

Brightman is slated to become the eighth paying passenger to travel to the station, a $100 billion research complex that flies about 260 miles (418 km) above Earth.

Boeing's first test launch of the taxi is not expected until 2017.

But Boeing faces competition from rival Space Exploration Technologies, or SpaceX, which also won a NASA contract and says it can develop the taxi for nearly 40 percent less than Boeing.

SpaceX already plans to offer trips to tourists, but did not immediately respond to questions about whether it would fly tourists on its NASA missions.

An artist's rendition of the Crew Space Transportation (CST)-100 next to the International Space Station(ISS).

The NASA contracts awarded on Tuesday to Boeing and SpaceX cover design, building, testing their spaceship and up to six missions to fly astronauts to the station, a pace of roughly two per year.

California-based SpaceX, owned and operated by technology entrepreneur Elon Musk, says it can create and fly the taxi for $2.6 billion, compared to Boeing's $4.2 billion bid.

'I think it's a vital next step in SpaceX's progress,' Musk said in an interview on FOX Business Network.

The taxi project appears to be well within Boeing's core space capabilities, which suggests it will not have trouble meeting its cost and schedule targets, analysts said.

Elon Musk, CEO and CTO of SpaceX, introduces the SpaceX Dragon V2 spaceship at the SpaceX headquarters in Hawthorne. It is also expected to take tourists into orbit.

Separately, Boeing and Lockheed announced on Wednesday that United Launch Alliance would invest heavily in a new rocket engine being developed by Amazon.com founder Jeff Bezos and his private company space company Blue Origin.

The agreement is aimed at freeing the United States from its dependency on Russian-made engines for rockets for launches and is expected to have little effect on the space taxi.

Meanwhile, SpaceX has been aggressively exploiting the price advantage of its American-made rocket to try to break ULA's monopoly on launching the U.S. military's satellites.

A lawsuit contesting the Air Force's last contract with ULA is pending in a U.S. court.

The company also has been successfully wooing commercial satellite launches, a business estimated to be worth $2.4 billion a year, a 2014 Satellite Industry Association study shows.