[AR] Re: Issues with operating at low chamber pressure
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Tue, 6 Sep 2016 20:39:00 -0400 (EDT)
On Tue, 6 Sep 2016, ignacio belieres wrote:
Well if you accept the correlation that cost tends to go up
with dry mass, and that volume is in a direct relationship to dry mass...
Which are reasonable rules of thumb for scaling *the same technology*.
Comparing different technologies is much trickier; this is another case of
rules that are true when other things are equal, but other things are
rarely equal.
...with a room temperature liquid propellant you dont have to deal with
cryofluids, prechills, cryovalves, insulation, reaally good thermal
control, lox vents, and extra annoying stuff.
You only have to deal with passivation, much more restricted materials
choices, the difficulties of clearing a low-vapor-pressure fluid out of
the plumbing afterward, oxygen venting (for any plumbing you can't 100%
reliably clear out), corrosion, and extra annoying stuff. :-) It's not a
question of peroxide being carefree, but of dealing with a different set
of difficulties.
Oh, and I forgot to mention the supply problem. :-) LOX you can get most
anywhere. Unless things have changed when I wasn't looking, HTP on
amateur-friendly terms still comes from a single supplier; XL is a good
outfit, but what happens if they go out of business? Having a second
source would be a lot more comfortable.
A peroxide compatible 1 inch ball valve will probably be 20 times
less expensive than an equivalent Lox valve.
Not if you want it certified peroxide compatible, the same way the LOX
valve is certified LOX compatible. With both oxidizers, you can get
perfectly usable valves much more cheaply if you're prepared to do some of
the legwork on materials checking etc. yourself. And some of that legwork
you really ought to do yourself anyway, if it's your equipment and your
extremities that will be at risk -- suppliers have been known to goof.
Henry
P.S. My opinion? Best choice depends somewhat on the application. That
said, I think the balance would often tip in favor of peroxide if there
were multiple friendly suppliers for 98%+, but as it is there's a lot to
be said for LOX.
Other related posts:
