NASA says three commercial companies now are engaged in activities to confirm commercial spacecraft are safe to carry crews to the International Space Station.

It's a crucial next step toward launching astronauts to the orbiting station from the United States under the Commercial Crew Program, the space agency said.

Three companies are working under contract with CCP to develop products to implement the agency's flight safety and performance standards and requirements, NASA said.

They are the Boeing Company of Houston developing the CST-100 spacecraft that will launch atop a United Launch Alliance (ULA) Atlas V rocket; Sierra Nevada Corp. Space System of Louisville, Colo., building the Dream Chaser also set to launch on an Atlas V; and Space Exploration Technologies Corp. (SpaceX) of Hawthorne, Calif., developing its Dragon capsule and Falcon 9 rocket for crewed missions.

"Throughout the phases of this program, we've really been creating a capability for the nation to use for low-Earth orbit transportation," Ed Mango, CCP manager at NASA's Kennedy Space Center, said. "As we create that capability, then NASA will become a customer so that we can move our flight crew to the International Space Station and continue our critical science."