> Putting it on the top of the stack would prevent the first stage engines from being reused. That's true, but reusability was the wrong goal. It forced a bad

> Putting it on the top of the stack would prevent the first stage engines from being reused. That's true, but reusability was the wrong goal. It forced a bad design to be adopted. It also led directly to the wishful thinking (50 flights per year!) that caused the schedule pressure on the Challenger. The actual goal should've been low cost. Instead of designing the most awesome closed-cycle engine that we could, we should've mass-produced a low-tech and low-cost engine. That's what the Russians did, and that's what SpaceX is doing today.