I may be coming around on the cluster-of-engines concept for economic reasons.
A lot of manufacturing costs (machining and tooling) scale with volume, while thrust scales with area, which makes larger engines start to cost more than I like. There are lots of variables, but I know that right now, I can make eight six inch motors for the price of one twelve inch motor, even after tooling costs are amortized. Including the tooling costs more than doubles the advantage. There is a huge benefit to trying to design things that can be done on common CNC machining centers. If you are pushed that way for economics, you might as well use differential throttling on the big engines instead of attitude jets, and if have eight engines (say, for an X-Prize vehicle) and a 2x T/W at liftoff, you might as well set up for full engine-out operation. Clusters trade against a few other design decisions -- hybrids look worse, and radiative cooling may not be workable with multiple hot radiators nearby. John Carmack _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
