Propane *can* coke, but that can be readily avoided, remove all sulfur
from the fuel, cover any copper in the coolant passages with gold over
nickel plating, and keep the flow velocities reasonably high. At XCOR we
ran kerosene engines for hours without any hint of coking. Propane is
one hell of a lot easier to handle than LH2, and can readily be used in
gaseous form for RCS and orbital maneuvering.
On 2018-02-13 6:14 PM, William Claybaugh 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 <mailto: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 <mailto: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
>