After the shuttle Atlantis made its final flight this summer, NASA is shutting down the program responsible for 135 manned space flights since 1981.

Now, NASA is turning to commercial companies to develop space-flight capabilities through its Commercial Crew Development program, which has doled out $320 million in funds since 2009.

Here’s a look at the top four contenders for developing the next spacecraft, how much funding they have received through the program, and how close they are to sending a crewed flight into orbit.

Sierra Nevada Corporation, Richard Branson