We have a space station in permanent orbit ... but not a lot of rockets that can get there. 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 SCIENCES Rocket: Antares

Capsule: Cygnus 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. Also, both the Cygnus and the Antares immolate in the atmosphere on the way down, which means Orbital avoids the headaches of reentry, like heat shields and splashdown prep. And no people on board means no cumbersome life-support systems. Orbital will get $43,000 per pound from NASA—$1.9 billion for eight deliveries to the ISS—and a demo resupply mission is scheduled to dock with the ISS in mid-September. It's no frills and no drama—getting to the ISS is the only point. Capsule Height: 32.5 feet

Rocket Height: 131.2 feet

Cargo Mass (going up): 4,409 lbs.

Cargo Mass (going down—in the form of trash to be incinerated in the atmosphere on the way back): 4,409 lbs.

SPACEX Rocket: Falcon 9

Capsule: Dragon CEO Elon Musk is getting $1.6 billion for 12 deliveries (it works out to $36,000 per pound) to be completed by 2016. And so far, so good: The first unmanned Dragon capsule successfully docked with the ISS in May 2012. (Manned Dragons will come later.) The goal, SpaceX says, is a reusable ship that can make a launchpad pit stop, then blast off into the ether the same day. The capsule even has a superstrong heat shield made of resin-enriched carbon fiber. For fuel, Falcon rockets burn liquid oxygen and RP-1, a refined form of kerosene. It's tricky to store, but it won't be hanging around on the launchpad, since SpaceX is planning those same-day turnarounds. Musk's Falcon is designed to be scalable, with more engines—because ultimately he plans to send this space Ferrari to Mars. The ISS is just a stepping stone. Capsule Height: 23.6 feet

Rocket Height: 224.4 feet*

Cargo Mass (going up): 13,228 lbs.

Cargo Mass (going down): 6,614 lbs.