LOS ANGELES, July 9 -- U.S. space agency NASA on Thursday took a key step forward in the goal to land a person on Mars, naming the first four astronauts to train for commercial spaceflights.

The three men and one woman -- astronauts and test pilots Robert Behnken, Eric Boe, Douglas Hurley and Sunita Williams -- were selected to train and prepare for the commercial spaceflights that will return American launches to the U.S. soil and further open up low-Earth orbit transportation to the private sector, NASA said in a statement.

"These distinguished, veteran astronauts are blazing a new trail -- a trail that will one day land them in the history books and Americans on the surface of Mars," said NASA Administrator Charles Bolden.

The selections are the latest major milestone in the Obama Administration's plan to partner with U.S. industry to transport astronauts to space, create good-paying American jobs, and end the nation's sole reliance on Russia for space travel.

Boeing and SpaceX were selected in September 2014 to build the United States' commercial passenger spacecraft, the Crew Space Transportation (CST)-100 and Dragon, respectively. The vehicles' first flights were currently planned for 2017. NASA has ordered the first-ever commercial crew flight to the International Space Station from the Boeing Company in May.

The commercial crew astronauts will work closely with company-led teams to understand their designs and operations as they finalize their Boeing CST-100 and SpaceX Crew Dragon spacecraft and operational strategies in support of their crewed flight tests and certification activities as part of their contracts with NASA.

SpaceX received 2.6 billion U.S. dollars to create on an updated design of its Dragon cargo spacecraft, while Boeing received 4.2 billion dollars to turn the design of its CST-100 into reality.

NASA has had to rely on Russian spacecraft to transport its astronauts to the International Space Station and back since the space shuttle program retired in 2011. Sending a single NASA astronaut on the Soyuz costs the agency upwards of 70 million dollars. Relations between the United States and Russia have been strained since the Ukraine crisis.