Nasa announced on 9 July that four astronauts had been selected to train for launch on the new commercial crew capsules built by Boeing and SpaceX enrollee to the International Space Station (Iss) beginning in 2017.

"I am pleased to announce four American space pioneers have been selected to be the first astronauts to train to fly to space on commercial crew vehicles, all part of our ambitious plan to return space launches to US soil, create good-paying American jobs and advance our goal of sending humans farther into the solar system than ever before," Nasa Administrator Charles Bolden said in a statement.

Bolden continued, "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."

The four astronauts selected are Robert Behnken, Eric Boe, Douglas Hurley and Sunita Williams. The astronauts will be working with Boeing and SpaceX to develop crew transportation systems and provide crew transportation services to and from the Iss, the statement said.

According to CBS News, Behnken said, "It's really been the dream of all of us to participate in the test of a new vehicle, and a vehicle like a spacecraft is probably the gem, if you will, of a career...I would have been embarrassed as a test pilot school graduate to not have jumped at the opportunity, if it was offered to me, to fly a new spacecraft. Hopefully, I'll get that chance soon."

Hurley added, "To be part of a new test program ... is extremely exciting. The challenge from a test pilot perspective is great, and I'm just looking forward to (getting) from today all the way up to the space station."

Popular Mechanics reported that Behnken flew on two shuttle missions and trains as a rescue crew member in case STS-125 experienced any problems while servicing Hubble. Boe and Hurley also flew on two shuttle missions. Meanwhile, Williams flew on shuttle mission STS-116 on a 192 day stay to the Iss in 2006 and would return to the space station in 2012.

John Elbon, the vice president and general manager of Boeing's Space Exploration, congratulated the four astronauts on their selection. "Congratulations to Bob, Eric, Doug and Sunita and welcome to the Commercial Crew team. We look forward to working with such a highly-skilled and experienced group of Nasa astronauts as we carve a path forward to launch in 2017."

President and COO of SpaceX Gwynne Shotwell added, "We look forward to working with them even more closely as we prepare for the first human missions to the space station on Crew Dragon. Human spaceflight is why SpaceX was founded, and we look forward to supporting our nation's exploration efforts by launching astronauts from America again."

CBS News reported that Boeing holds a $4.2b (£2.7b) contract with Nasa to develop the CST-100 capsule, which can carry at least four astronauts and will be launched on top of a United Launch Alliance Atlas 5 rocket.

Similarly, SpaceX holds a $2.6b (£1.6b) contract to build a human-rated version of the Dragon capsule used to deliver cargo to the Iss. The pilot version of the Dragon will carry at least four astronauts and fly atop the Falcon 9 rocket.