Gentlefolk << ...while still being able to throttle back sufficiently by shutting down engines. How does/did Atlas accomplish this with only 2 engines ? >>
The classic Atlas had three engines, two boosters outboard (later dropped) and a sustainer on the center line. If memory serves, only the sustainer could be throttled and this may have been a later refinement. Russian space booster engines used clustered combustion chambers fed by a single pump system. The term "engine" in Soviet rocketry often refers to a chamber cluster/pump system. I like clustering smaller engines for a variety of reasons: 1) Lower development cost; this tends to scale with engine mass 2) Greater system reliability. One or even two out doesn't necessarily kill the mission. 3) Less room for certain acoustical and fluid dynamics phenomena, the study, modeling and control of which is needed for big engines. 4) Manufacturing learning curve; one gets well down that curve in production of the first cluster, as opposed to, say, the tenth rocket. 5) Size and expense of manufacturing, maintenance and check-out equipment. 6) Turnaround. This seems counterintuitive, but checking out many engines with bench top equipment may prove faster, easier, and safer than manhandling a large engine through a garage-scale maintenance procedure. The cluster, of course, needs to be designed for easy engine swapping. The main drawback on clusters is mass. For the same chamber pressure, a single large engine is likely to have a better thrust-to-mass ratio for cube/square law reasons. But this trade curve tends to be somewhat flat at ERPS thrust levels contemplated. Also, engine mass tends to scale with power, and an application using dense propellants and lower specific impulse means higher thrust for a given power. (But higher thrust is needed because of the higher mass ratio.) I think ERPS is going in the right direction. --Best, Gerald _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
