Commercial space travel takes a significant step forward with the arrival of three American astronauts and one from Japan at the International Space Station aboard a craft owned by a business rather than NASA, the U.S. space agency. Last week's mission on a capsule and rocket owned by Elon Musk's SpaceX company follows a May test flight with two astronauts. The latest flight is the first of at least a half-dozen SpaceX voyages for NASA, paving the way for trips to the moon, Mars and beyond. The next trip to the station is scheduled to launch March 30.

The United States retired its Space Shuttle program in 2011 and had relied on Russian rockets to reach and return from the orbiting space station, paying $86 million per seat. Rather than building its own spacecraft, NASA decided to invest $3.1 billion in SpaceX to develop vehicles for carrying its supplies and crews on six missions. Musk founded SpaceX in 2002, a year before his Tesla electric car company. Some time in the future, the company envisions low Earth orbit flights for wealthy "space tourists."

The Los Angeles-area company's two-stage Falcon 9 rocket, which first flew in 2010, has launched nearly 100 times, carrying satellites into orbit and supplies to the space station. It's the only orbital rocket that's partially reusable — the booster section lands itself back on Earth after launch — a big money-saver. "There were quite a few people in the beginning who said we would never see this day," recalls NASA program head Phil McAlister. "But the NASA and the SpaceX teams persevered through challenges to achieve this milestone." The newly arrive astronauts are expected to spend about six months in orbit 262 miles above Earth, doing science experiments and space walks to continue updates and repairs on the space station's exterior.

Astronaut says: "That was one heck of a ride." -- Mike Hopkins, mission commander

NASA says: "Twenty years from now, we’re going to look back at this time as a major turning point in our exploration and utilization of space. With this milestone, NASA and SpaceX have changed the historical arc of human space transportation." – Phil McAlister, director of commercial spaceflight development

Elon Musk of SpaceX says: "America is still the land of opportunity more than any other place, for sure. There is definitely no other country where I could have done this."