Troy,
Density is veery important. Keroxide gives the same or better
performance as Kerolox, and in fact, in single stage to orbit configurations,
peroxide beats every other propellant. A while back I ran some numbers which
showed a 10% payload to LEO increase for a Falcon 9 FT loaded with H2O2. And
that was assuming that the engine efficiency would be kept the same, which is
not entirely true because staged combustion is "easy" with peroxide. The killer
combo is a peroxide first stage and a Lox Methane or Lox Hydrogen second stage
for higher energy missions. That is a 30% increase in payload for an equal
volume rocket.
You might think a 10% or a 20% improvement isn't much, but that's a
cost reduction in the same park as what SpaceX loves to blob on and on about.
There is also the fact that using a room temperature liquid would take away the
complexities of handling a cryo propellant and could simplify some of the
operations.
Just my 2 cents,
IB
Subject: [AR] Re: Issues with operating at low chamber pressure
To: arocket@xxxxxxxxxxxxx
From: daze39@xxxxxxxxxxxxx
Date: Mon, 5 Sep 2016 21:03:30 -0700
On 09/05/2016 08:49 PM, 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. Anyway, it raised a few
eyebrows if I vaguely recall.
I remember running some calcs for pure peroxide and different fuels -
it was interesting to see how much of an influence density did have
on overall stage delta-V when I assumed a given incremental tank mass
cost per unit volume (i.e., a given wall density and working strength).
Peroxide + DMAZ has noticeably better Isp than peroxide + a hydrocarbon
(such as RP-1, which being the liquid hydrocarbon fuel for which the
software had an entry in the data table; assuming commercial low-sulfur
#2 diesel might be fairly similar.) DMAZ (at about 0.92) has a slightly
better density than the kerosene. However, overall density, and hence
overall propellant quantity for a given total tank volume, is somewhat
worse, simply because the mixture ratio is less lopsided (about 3.5 vs.
7 for HP/DMAZ vs. HP/kero), and thus less of the propellant is the
denser peroxide. This tended to cancel out a significant fraction of
the Isp advantage. (I suspect, however, that DMAZ may be much easier
to ignite and burn smoothly in a peroxide rocket without the cat pack
commonly used with hydrocarbon fuels - this could have implications
for a lightweight low-pressure system.)
-dave w
