Astronauts Eric Boe, right, and Bob Behnken work in a mock-up of the SpaceX Crew Dragon flight deck at the company's Hawthorne, California, headquarters as development of the crew systems continues for eventual missions to the International Space Station.

Astronauts Bob Behnken, left, and Eric Boe work in a mock-up of the SpaceX Crew Dragon flight deck at the company's Hawthorne, California, headquarters as development of the crew systems continues for eventual missions to the International Space Station.

Astronauts Bob Behnken, left, and Eric Boe work in a mock-up of the SpaceX Crew Dragon flight deck at the company's Hawthorne, California, headquarters as development of the crew systems continues for eventual missions to the International Space Station.

Astronaut Bob Behnken, work in a mock-up of the SpaceX Crew Dragon flight deck at the company's Hawthorne, California, headquarters as development of the crew systems continues for eventual missions to the International Space Station.