NEW YORK (CNNMoney) -- Boeing and SpaceX have been awarded NASA contracts to transport astronauts to and from the International Space Station, the agency announced Tuesday.
"This wasn't an easy choice but its the best choice for NASA and the nation," said NASA administrator Charlie Bolden.
NASA ended its Space Shuttle program in 2011 after a review of the shuttle program and amid a shift in priorities to exploring deep space, including sending humans to Mars.
Bolden called the companies' contracts, worth $6.8 billion, a "seminal moment" in NASA history.
Since the shuttle program was retired, NASA crewmembers have been hitching rides on Russian Soyuz spacecraft, at a cost of $70 million per seat, according to a NASA spokeswoman. The agency typically purchases six seats per year.
Boeing and SpaceX, which is backed by Tesla CEO Elon Musk, did not comment about the announcement.
NASA created the Commercial Crew Program to help private companies develop spacecraft to carry astronauts into low Earth orbit by 2017. The agency has invested more than $1.4 billion in contracts and special agreements with private companies for the two phase program.
The goal, according to NASA's website, is "to establish safe, reliable and cost-effective access to space." Once the new transportation system is up and running, NASA says it will use private spacecraft to "meet its space station crew rotation and emergency return obligations."
Boeing, which has received more than $100 million in NASA funding, is working on the Crew Space Transportation 100 as part of the program. The CST-100, which will accommodate up to seven passengers or a mix of humans and cargo, and will be capable of reaching the space station.
Meanwhile, the SpaceX Dragon became the first commercial spacecraft to deliver cargo to the space station in 2012. The Dragon currently only carries cargo, but SpaceX says it will be able to transport humans as well.
Sierra Nevada Corp., an aerospace company based in Nevada, is working on the Dream Chaser, a winged spacecraft designed to fly into orbit.
--CNN's Rachel Crane contributed to this story.