[AR] Re: Issues with operating at low chamber pressure
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 6 Sep 2016 14:31:25 -0400 (EDT)
On Tue, 6 Sep 2016, Troy Prideaux wrote:
Anyway, it turned out the combination producing the lowest Isp actually
produced the highest delta V return primarily due to the respective
densities on offer which directly affected the respective mass ratios for
the volume fixed analysis...
There are occasional observations going back to the 1950s about how denser
fuels often seemed to produce higher performance in real rockets, even if
they incurred an Isp penalty.
That said, any constant-volume analysis is going to be somewhat biased in
favor of denser fuels, in the same way that any constant-gross-mass
analysis is going to favor the highest possible Isp: the conditions of
the analysis have stacked the deck somewhat. The yardstick that's really
of the most interest is not volume or mass, but cost -- defined broadly,
to include issues like operations difficulty as well as cash outlay -- but
that's harder to estimate well for a paper design.
Henry
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