Amazon.com founder Jeff Bezos plans to build a rocket engine that would eventually replace the Russian mainstay used in many American unmanned launches.
United Launch Alliance, a collaboration of two aerospace giants that launches unmanned rockets, announced on Wednesday that it will pay Bezos' Blue Origin space firm to develop new rocket engines.
In about four years, the launch alliance hopes to start using the new engines in Delta and Atlas rockets.
Some experts worry that tensions over Ukraine might interrupt the supply of Russian engines, but alliance chief Tory Bruno said that's not a problem.
Bezos said he will proceed with plans for his private human space capsule to launch later this decade.
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However, Bezos' firm wasn't picked on Tuesday by NASA for its $US6.8 billion ($A7.3 billion) private space taxi program.
