Boeing's crew system and CST-100 spacecraft, has advanced through various commercial crew development and certification phases. Image source: Nasa.comNASA’s Commercial Crew program ordered its first crew rotation mission from Boeing. Meanwhile, SpaceX successfully performed a pad abort test of its flight vehicle in May and expects to receive its first order later this year.

NASA will determine which company will fly its mission to the station first at a later time.

Boeing’s crew transportation system, including the CST-100 spacecraft, has advanced through various commercial crew development and certification phases, NASA says. The company recently completed the fourth milestone in the Commercial Crew Transportation Capability (CCtCap) phase of the program, the “delta integrated” critical design review. NASA says this milestone demonstrates the transportation system has reached design maturity appropriate to proceed with assembly, integration and test activities.

"We’re on track to fly in 2017, and this critical milestone moves us another step closer in fully maturing the CST-100 design," says John Mulholland, Boeing’s vice president of Commercial Programs. "Our integrated and measured approach to spacecraft design ensures quality performance, technical excellence and early risk mitigation."

The spacecraft will stay at the ISS for up to 210 days and act as an emergency lifeboat during that time. A standard mission to the station will carry four NASA or NASA-sponsored crew members and about 220 pounds of pressurized cargo. Each contract includes a minimum of two and a maximum potential of six missions.