NASA on Friday named four crews of astronauts that it says will begin "a new era in American spaceflight" by flying the first commercial spaceships, built by Boeing and SpaceX, in a series of test launches.

"For the first time since 2011, we are on the brink of launching American astronauts from American rockets on American soil," NASA Administrator Jim Bridenstine said during a televised briefing on Friday.

Crew Dragon, designed and built by Elon Musk's SpaceX, and the CST-100 Starliner, made by Boeing, are the two spacecraft being developed for NASA as part of its Commercial Crew Program. Each ship requires two crewed test launches before NASA will certify it for routine flight.

The astronauts named Friday (see the full list below) are tasked with those missions, all four of which are set to happen sometime in 2019.

NASA started the Commercial Crew Program in 2010, just before it retired the last space shuttle in July 2011. The competition asked private spaceflight companies to develop new astronaut-ready spacecraft — and Boeing and SpaceX emerged as the winners. The agency has doled out more than $8 billion in awards and contracts over the past decade.

The program's core goals are to get American-made ships able to reach the International Space Station and to reduce or eliminate the US's reliance on Russia's ever more expensive Soyuz spaceships to fly there.

Boeing and SpaceX were supposed to have their systems certified by 2017, according to a recent report from the Government Accountability Office, but the program has met multiple setbacks. Some delays stemmed from launch vehicles, such as the September 2016 launchpad explosion of an uncrewed SpaceX Falcon 9 rocket, while others came during spaceship development; Boeing, for example, recently discovered a fuel leak in its Starliner system.

If the spacecraft aren't certified and ready by the end of 2019, NASA could temporarily lose access to the ISS. But the agency is confident that the Boeing and SpaceX missions are moving toward completion — a sentiment underscored by Friday's announcement.

NASA selected eight active astronauts and one retired astronaut from a wide array of backgrounds. The group includes former space-shuttle flyers, ex-military test pilots, rookies, and — critically — a cadre of four astronauts who've already been testing and providing feedback on the new commercial ships for years.

Here's what we know about the first astronauts to take part in a new space race.

This story was updated with new information. Dana Varinsky contributed to this post.