Since the retirement of the space shuttle in 2011, the USA has been relying on Russian Soyuz rockets, launched from Kazakhstan, to get astronauts to the ISS.
"This is a big deal for our country, and we want America to know we're back", Bridenstine said in a speech. "We congratulate all the astronauts chosen to fly to the space station on commercially developed systems".
Since her selection as an astronaut in 1998, she has spent 322 days aboard the International Space Station (ISS) for Expeditions 14/15 and Expeditions 32/33, commanded the space station and performed seven spacewalks, the USA space agency said in a statement.
The astronauts assignments will be for both the test flights of Boeing CST-100 Starliner and SpaceX Crew Dragon, which won't dock with the ISS, as well as the first post-certification missions for both private companies, which will head to the space station.
Behnken, Boe, Hurley, and Williams were named in 2015 as NASA's "commercial crew cadre" and have been working with Boeing and SpaceX on the development of the spacecraft and the simulators that will be used to train astronauts to fly.
Both spacecraft are now undergoing hardware tests, with final processing ahead as launch dates hover closer.
Recent delays have pushed back the first flights of the Starliner and crewed Dragon to 2019, with uncrewed test flights hopefully happening in November for SpaceX or late this year, early next year for Boeing. That flight is now projected to lift off in April of 2019.
Trump wasn't the only one heralding NASA's commercial crew announcement today. "The first flight is something you dream about as a test pilot", Hurley said.
Victor Glover and Mike Hopkins, who has spent more than 160 days in space, were selected to crew SpaceX's first full mission.
It's been a long trip for these astronauts.
The U.S. space agency NASA on Friday introduced the nine astronauts who will ride the first commercial space capsules into orbit next year.
The CST-100 test flight will also include Christopher Ferguson, a former NASA astronaut and current Boeing commercial astronaut.
The SpaceX Crew Dragon that will be used for Demo-1 arrived at Cape Canaveral Air Force Station in July. Those were Behnken, Boe, Hurley and Williams.
The two pairs of NASA crewmates will be accompanied to the station by Russian cosmonauts and global astronauts, to be announced at a later date. He retired from NASA after commanding the final shuttle mission in 2011, and eventually joined Boeing to help develop Starliner. Since then, it has relied on Russian Federation to fly USA astronauts into space, with each ride on Russia's Soyuz spacecraft costing NASA about $80 million.
"Once you get into the spacecraft, you're on your way, you've got a mission, you're focused, and it's really exciting", she said.
"It's absolutely an opportunity of a lifetime", said Mann, who was selected as an astronaut in 2013. He also serves as a Navy commander, naval aviator and was a test pilot.
The new schedule of launches will see up to four astronauts carried to the ISS at a time ensuring the station's crew of seven is always maintained. Both vehicles are reusable. Boeing said only that it would fly NASA's astronauts by sometime in the middle of next year.
SpaceX's first flight test is scheduled for April 2019, while Boeing's is planned for mid-2019.
Those launch targets may change. Boeing most recently suffered a problem while testing its emergency abort system and its first test flight won't be until at least mid-2019. The first crewed flights would then follow by the end of 2018.