On the assumption that the free market can blast us to the ISS on the cheap, NASA has awarded resupply contracts to two private companies, Orbital Sciences and SpaceX. But the two space ferries have some key differences, and the competition between them is shaping up to be a dogfight between reliable spaceships of the past and slick ones from the future. Here's how they line up.

 

 

Orbital produces the Toyota Tacoma of the thermosphere—solid, reliable transport. The first-stage engines are stockpiled Soviet NK-33s from the early 1970s. And fuel-wise, the Antares is a sensible liquid-solid hybrid—mechanically simpler than a pure liquid-fuel craft but with more punch than a solid-fuel rocket.