"Larry Gales" wrote in message
news:Pine.WNT.4.56.0311141016110.2448@homecomps...

The advantage of a pressure fed rocket, as I understand it, is much
cheaper (and somewhat smaller and lighter) engines, but at the cost of
very heavy tanks that hold propellant at 250-300 psi, compared with the
20-30 psi tanks used in pump fed rockets.

Would it not be possible to build very cheap low pressure pumps with 250
psi instead of the 1400-3600 psi used in pump fed rockets, so we would get
the low cost advantages of pressure fed rockets without the disadvantage
of
very heavy tanks? Or am I missing something?

(Apologies if I have posted this twice -- email is acting up)

-- Larry

My opinion is that the main thing holding back the cheap pumps is
the concept that they are complicated and expensive in the first place.
A reasonable effort can show that the pumps you descibe are doable
by changing a few of the assumptions in the design. One of the first
assumptions to be changed is that the thrust chamber is served by
a pump system that must be designed for it. By doing low level
systems engineering of the entire thrust package in parallel, several
options can be made available.

One of the simple ones is leaving the thrust chamber ablative or
radiative in cooling, with the pump rotors stacked directly above
the injection manifold, feeding it out of coaxial bowl volutes. Drive
the tip turbine with gasses taped off the combustion chamber.
A little thought will produce better geometries.