Read: NASA is rushing to the moon

The flight is an important milestone for the American space program. The United States hasn’t launched astronauts from American soil since 2011, when the space shuttle Atlantis closed out a 30-year program that folded under the weight of cost, political will, and safety concerns. Americans continued to fly to space. They hitched rides on a Russian launch system, the Soyuz, operated in Kazakhstan, in the middle of the desert—an expensive situation, but necessary to keep the ISS staffed.

In 2014, NASA awarded two American companies, SpaceX and Boeing, billion-dollar contracts to build the next generation of astronaut transportation. SpaceX would build a passenger-safe version of its uncrewed Dragon spacecraft, which already delivers cargo to the ISS, to fly on a Falcon 9. Boeing would develop the Starliner, to launch on the Atlas V, a rocket manufactured by the United Launch Alliance, Boeing’s venture with Lockheed Martin.

After schedule delays and technical issues at both companies, SpaceX has beaten Boeing to the launchpad for the NASA program’s first significant test. The firms have always resisted describing the efforts as a race, but surely there’s something juicy about a billionaire-run start-up edging out a longtime government contractor.

Competition aside, the companies must do the same thing: prove to NASA that they can safely send astronauts to space.

“The task ahead of us is really historic,” Hans Koenigsmann, the vice president for build and flight reliability at SpaceX, told reporters on Thursday. “We’ve done an incredible amount of testing together with NASA to make sure everything is safe and ready to go.”

That sense of history is baked into the concrete here at the launch site. The mission will depart from the Kennedy Space Center’s launchpad 39A, right along the water, the site of many historic launches in American spaceflight history, including the Apollo and Space Shuttle programs.

When the final space-shuttle mission flew, in 2011, the fate of the program had already been decided years earlier. After the Columbia disaster in 2003, which killed all seven crew members upon reentry, the United States shut down the program to conduct a lengthy review. As investigators worked to determine the cause of the tragedy, the Bush administration considered the future of American spaceflight. National-security officials spent the year in meetings to discuss what the country should do next, Sean O’Keefe, the NASA administrator at the time, said.

Former President George W. Bush announced the result of these discussions in a speech in January 2004. “America has not developed a new vehicle to advance human exploration in space in nearly a quarter century,” he said. “It is time for America to take the next steps.”

The president proposed the construction of a brand-new launch system that could carry astronauts not just to low-Earth orbit, but also farther—to the moon and Mars, journeys the space shuttle was not designed to make. The government couldn’t fund both efforts at the same time, so it was decided that the space shuttles would be retired after they finished delivering the hardware necessary to construct the new ISS, which was being built in orbit, piece by piece, at the time.