A new era of human spaceflight is set to begin Wednesday as America's space agency and a private company launch two astronauts bound for the International Space Station. It's the first such mission leaving from the United States in nine years. NASA astronauts Robert Behnken and Douglas Hurley will fly on SpaceX's Crew Dragon spacecraft, lifting off from Cape Canaveral, Fla., on a Falcon 9 rocket at 4:33 p.m. (Eastern time) May 27 for an extended stay at the space station, which currently has just one American on board. (The other crew members are from Russia, which has carried U.S. astronauts there until now.) This will be the first mission with passengers in the 18-year history of SpaceX, a company founded by Elon Musk, the man behind Tesla electric cars.

NASA's final space shuttle, Atlantis, took off in July 2011 as the 133rd flight of that 30-year program. No American rocket-and-spaceship system has sent astronauts into space since then, so this week's liftoff is a big deal. It's the final major step before NASA's Commercial Crew Program certifies the reusable Crew Dragon, which can carry seven people, for long-duration trips to and from the space station. It lays the groundwork for future exploration of the moon and Mars.

"So great to be back" at the Kennedy Space Center in Florida, astronaut Hurley tweeted after arriving last week from the Johnson Space Center in Houston. He and crewmate Behnken each flew aboard two space shuttles before the fleet was retired. NASA will stream a live broadcast of their launch. As well as continuous mission coverage, at www.nasa.gov/nasalive.

NASA administrator says: "This is a new generation, a new era in human spaceflight." – Jim Bridenstein

Backup launch date: In case SpaceX and NASA have to delay Wednesday's liftoff, the next opportunity will be Saturday, May 30.

Future NASA plan: A program named Artemis program intends to land the first woman and the next man on Earth's moon in 2024.