NASA is a giant step closer to launching Americans again from U.S. soil, after selecting Boeing and SpaceX as private partners to ferry crew to the International Space Station.

On Tuesday, NASA announced both firms would participate in the $6.8-billion contract to operate manned spacecraft.

The deal will end NASA's expensive reliance on Russian crew transport to the space station, an expensive alternative that was costing $71 million per astronaut.

"From Day 1, the Obama administration has made it clear that the greatest nation on Earth should not be dependent on other nations to get into space,” said administrator Charles Bolden in announcing the deal Tuesday.

“Turning over low-Earth orbit transportation to private industry also will allow NASA to focus on an even more ambitious mission — sending humans to Mars,” he added.

Elon Musk's Space Exploration Technologies Corp. — SpaceX for short — became the first private company to launch a spacecraft into orbit and retrieve it in 2010.  Its SpaceX Dragon capsule has been carrying cargo to astronauts on ISS for the past two years and will be adapted for human flight.

International Space Station

NASA astronauts have been riding Russian rockets to the International Space Station ever since NASA's space shuttles retired in 2011. The latest pricetag is $71 million per seat. (NASA)

Boeing's entry is a capsule, called CST-100, that will fly on top of an Atlas V rocket. Cape Canaveral will be the launch site for both.

NASA had considered dozens of proposals, with Boeing, SpaceX  and Sierra Nevada Corp, which also supplied the space station, considered the main contenders.

NASA has set a goal of 2017 for the first crewed launch under the program.

The launch date depends on when the private contractors gain NASA certification for human space transportation systems, a process that will involve rigorous safety testing.

The total potential contract value is $4.2 billion for Boeing and $2.6 billion for SpaceX.

The commercial crew program follows the successful private cargo delivery effort underway for the past two years, also under NASA contract. The objective, for years, has been for NASA to hand space station flights to private companies and focus on getting astronauts into true outer space, with destinations such as asteroids and Mars.

"The partnership with Boeing and SpaceX promises to give more people in America and around the world the opportunity to experience the wonder and exhilaration of space flight — to realize the dream of leaving Earth for even a short time to float above our planet Earth in microgravity and to see the stars and the majestic tapestry of the Milky Way unobstructed by the artificial lights and dust of our atmosphere," Bolden said.