How efficient is iron smelting ?
Not really to do with the thread, just a clarification: the solid rocket boosters from the shuttle can indeed work in a vacuum. The propellant mixture in each SRB motor consists of an ammonium perchlorate (oxidizer, 69.6 percent by weight, hence no air needed), aluminum (fuel, 16 percent), iron oxide (a catalyst, 0.4 percent), a polymer (a binder that holds the mixture together, 12.04 percent), and an epoxy curing agent (1.96 percent). The two SRB's alone provide over 70% of the initial thrust of the shuttle and all of the engines combined have more thrust than the Saturn V. This means that it wouldn't take much more of a booster to have two that would equal Saturn V thrust.
The problem with boosters is that they're like fireworks - once you light them, there's no unintended throttling back or shutting them off...