Chair Force Engineer

Monday, February 27, 2006


NASA is reporting the names of the Project Constellation elements: Altair capsule, Artemis lander, and Ares booster.

The irony of it is that Ares was also the name of the booster in Robert Zubrin's proposed Mars mission, "Mars Direct." Further, Zubrin's Ares (publically unveiled in 1990) is almost the same as NASA's Ares-5, launched in 2005.

The differences between the Zubrin and NASA boosters are very subtle. Both are built from the Shuttle fuel tank and boosters, with an upper stage mounted axially on the vehicle.

The biggest difference is the propulsion arrangement. Zubrin used four stock shuttle engines (SSME's) mounted in a pod where the shuttle orbiter's tail would normally be. Theoretically, Zubrin's propulsion pod could re-enter the atmosphere and be recovered. Ares 5 goes to the more expensive step of designing a "low-cost, expendible SSME." The five engines are mounted axially underneath the hydrogen tank. While this is a more efficient arrangement, it requires more extensive modifications to the shuttle's launch pad.

There are other differences as well. Zubrin originally proposed using the now-moribund Advanced Solid Rocket Motors, while NASA goes with 5-segment SRB's. NASA stretches the shuttle's tank, while Zubrin uses the same volume of propellants on the first stage tank as the shuttle does. NASA has an 8.4 meter diameter upper stage (to match the first stage,) while Zubrin went to 10 meters for his (matching the Saturn V's diameter.)

An open question is the definition of "J-2X," the engine that will be used for the second stage of Ares I (The Stick) and Ares 5. While the engine is a modern replacement for the J-2 on the Saturn V's second and third stages, it's a mystery to me whether it will have any commonality with the old J-2 or J-2S. One wonders if the European Vulcain engine, fitted with a nozzle extension to compensate for upper atmospheric & vacuum conditions, would fit that bill. Of course, I smell the odor of "not invented here" creeping up on this idea.

While many groups of space enthusiasts have been disappointed with Project Constellation, Zubrin's Mars Society should not be one of them. Michael Griffin's NASA has joined Zubrin and his Zubrinistas, worshipping at the Church of Heavy-Lift.