Agreed. I don't think there's anything there that couldn't be
reproduced by most people on this list with a few hours and a
spreadsheet. I was intending it more as an aid to those trying to
follow along than as adding anything new to the discussion; that's the
role I found it useful in when reading past SSTO discussions.
The "Dry Mass" and "Limitations" sections are useful and informative,
but more for pointing out things to look at than for actually
answering questions or justifying assumptions.
And if you're looking seriously at tripropellants, presumably it's
also worth looking seriously at things like LOX/LH2 with variable mix
ratio.
Evan Daniel
On Tue, Feb 13, 2018 at 9:14 PM, William Claybaugh
<wclaybaugh2@xxxxxxxxx> wrote:
Evan:
I have seen that paper. For something as technically (much less
economically) difficult as SSTO it seems a little light: even much more
detailed analysis doesn’t often lead to much confidence that I ought to
recommend dropping $20 or $40 billion on one solution over another.
The little bit of possible gain from propane (which cokes) or the rest seems
to me to probably only play as a tripropellant where there is an additional
small gain, maybe.
But this is all hints and whispers; which specific technical recommendation
to make seems to be obscured by the very considerable variance in our
knowledge.
Bill
On Tue, Feb 13, 2018 at 1:29 PM Evan Daniel <evanbd@xxxxxxxxx> wrote:
Dunn on SSTO propellants is a useful survey of rough numbers. (I'm
assuming both Henry and Bill have read it, but might be of interest to
others.) PDF:
http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=34919.0;attach=587468
Relevantly, Dunn concludes that propane has a slight advantage if
prechilled. Propyne, propene, and MAPP gas are also worth looking at.
The paper doesn't really look at detailed assumptions about things
like combustion efficiency or tank masses. It uses a
fixed-propellant-volume comparison, which seems a slightly odd choice
IMHO.
Evan Daniel
On Tue, Feb 13, 2018 at 2:39 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Tue, 13 Feb 2018, William Claybaugh wrote:
Is anyone aware of a careful comparison of LH2 vs. Propane fueled SSTO?
James Martin (of Langley) looked at this in some detail back in the
1980s,
generally concluding that propane showed a small advantage. I'm not
aware
of a more recent equivalent.
One issue he noted is that the outcome is rather sensitive to
assumptions
about things like combustion efficiency.
Hydrogen tanks generally weigh around 10% of the fuel mass whereas
Propane
tanks are closer to 1%....
Some years ago, Jordin Kare was describing some NASA-funded studies of
laser
launch that he'd been involved in, and he said that there actually
seemed to
be considerable disagreement about just how much a hydrogen tank weighs.
(Probably people making different underlying assumptions.)
Henry