[malanj]

Space shuttle's main engine was the "boosters". A huge liquid (very cold hydrogen and oxygen) tank which supplied the fuel to the actual shuttle during launch, and two smaller solid fuel boosters. The tank and boosters were all destroyed on launch.

SpaceX rockets use a much simpler engines, that burn oxygen and kerosene. The main cost is in the first stage of the engine - think two rockets on top of each other, the first stage is the bottom rocket that first first. When the first rocket is done, it falls away. This first stage accounts for the majority of the cost of the launch. Think of it was being equivalent to the main tank and 2 boosters of the shuttle.

What SpaceX manages, which no-one has done before, is to retrieve that big + expensive first stage for reuse.

[bluehawk]

The boosters were actually parachuted back down to earth and reused. Though the general consensus is that it didn't save any money, and may have been more expensive than if they had just been disposable.

[mikeyouse]

Yeah they would parachute into the ocean, get filled with air, then literally dragged back to port:

http://www.gettyimages.com/detail/news-photo/solid-rocket-bo...

All that stress + salt water meant a fairly extensive refurb process.

[sqeaky]

These seem like problems with that design, not something fundamental.

Could one conceivably use different materials (that maybe didn't exist back then) resistant to aquatic stress and salt, to have made the old plan much more cost effective?

Following this line of thought I think you wind up with something close to what SpaceX does. Because the next largest save-able cost would be the boat crew to go recover it. So attach a propeller to the rocket to have it come back on its own. Then you want to save that cost and complexity so have it come to your boat with no crew and touch down gently.

[greglindahl]

The solid rocket boosters (SRBs) for the Space Shuttle provided 83% of the thrust at takeoff. The main engines were the other 17%, and continued to fire after the SRBs dropped off and parachuted into the sea. The main engines perform the function of part of SpaceX's booster stage and also SpaceX's upper stage.