Kennedy Space Center

This is the rear end of the Saturn V Rocket's secondary booster stage. There are 5 J-2 hydrogen-fueled rocket engines here. There is a single J-2 on the third stage of the rocket, which was used to push the command module and Apollo capsule out of earth orbit. Each J-2 can produce 250,000lbs of thrust. Interestingly, an advanced version of the J-2 will replace the Space Shuttle Main Engines (SSMEs) that were going to be re-purposed for the Constellation/Ares program. Why the J-2? It's less than half the price of an SSME, which was designed to be re-usable. The J-2X variant will produce 294,000lbs of thrust, and the Ares booster will only be carrying one for it's Earth Departure Stage on the Ares I manned rocket -- just like the third stage of the Saturn V. For primary ascent the Ares I will use an updated version of the Space Shuttle Solid rocket booster (SRB). The main boost stage on the heavy-lift Ares V variant for moving large cargo items into space will use five RS-68 engines, which are used on the Delta-IV unmanned rockets, and will also use the J-2X on it's Earth Departure Stage.