Hey, perhaps that's something to do with no zero-speed thrust? That, plus they're not more efficient than turbojets at any speed below mach 1. Where they win is the low development cost. In obscure cases, that's a win. My claim is that this is one case where they are very probably a win; since development costs are about half of the launch costs.
But people have built ramjets before for launching stuff; IRC NACA achieved 150,000 ft and with a tiny R&D program- that's not bad at all; and that's an acceleration mission where ramjets do not especially shine.
Here's something to consider that supports Ian's argument. For any transonic jet aircraft, especially one designed for a wide range of speeds and altitudes, the inlet design is non-trivial. Since turbines require subsonic air at the first fan or compressor stage, and the design is dependent on the rest of the airframe, it's a problem of similar difficulty for both turbine and ramjet engines. Thing is that for a ramjet it's most of the design problem -- efficient burner sections and nozzles are not difficult, compared to the inlet. Therefore, using a turbine engine doesn't reduce the difficulty of the overall design nearly as much as Randall thinks it does.
BTW -- inlets of the required type are non-trivial, and generally require variable geometry in order to keep the shock waves in the right places. I read the chapter of 'The Mechanics and Thermodynamics of Propulsion' every time I get to thinking favorably of air-breathing propulsion for space launchers... it generally cures me :).
-p
Mars or Bust! www.marssociety.com
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