Sometime this month, NASA is expected to announce which private spaceflight company (or companies) will ferry astronauts to the International Space Station. Since the retirement of the space shuttle in 2011, the United States has been booking rides on Russian Soyuz flights, and that's expected to continue through 2017. But NASA's commercial spaceflight program is making steady progress. SpaceX and Orbital Sciences Corporation are already making regular ISS supply runs, and SpaceX's Dragon capsule is capable of returning cargo and experiments to Earth.

This phase of the selection process is called Commercial Crew integrated Capability, or CCiCap. It kicked off in 2012. The three contending spacecraft are Boeing's CST-100 capsule, SpaceX's Dragon Version 2 capsule and Sierra Nevada Corporation's Dream Chaser space plane. Both the CST-100 and Dream Chaser launch on top of an Atlas V rocket, which currently uses a Russian-built RD-180 engine. SpaceX's Dragon launches on a Falcon 9.

Since most of us aren't privy to NASA's behind-the-scenes decision making process, I thought it would be helpful to take a look at each company's CCiCap milestones. All three companies received fixed-price funding awards tied to a series of progress milestones. When a company completes a milestone, it earns another portion of its award.

Finding an up-to-date list of these milestones is surprisingly difficult, so I created my own. The data for my list come from NASA's Return on Investment Reports, Space Act Agreement amendments, press releases, and NASA email correspondence. My list also includes SpaceX's new milestones, 13A through 13D, as well as the new due dates for SpaceX and Sierra Nevada.

I plotted out the percentage of milestones each company has completed over the duration of CCiCap. Boeing has finished their milestones, Sierra Nevada has completed 85 percent and SpaceX has completed 70 percent.