From: jtkare@ibm.net (Jordin Kare)
Newsgroups: sci.space.tech
Subject: Re: More peroxide questions...
Date: Mon, 22 Jun 1998 23:35:42 -0700

In article <358dccb2.4421622@news.mindspring.com>, gpelkey@mindspring.com wrote:


> The reason for my interest is I am toying with a paper design of a
> small RLV that would use these storable propellants only, in the
> lowest tech way possible (small/dumb/reusable?).

Mitchell Burnside Clapp at one time did a design for a simple
perox/kerosene pressure fed; that basic design has been adopted by the
ERPS folks.
>
> One (of many) basic confusions I have is in engine types.  From what I
> have heard there are roughly 3 main types, in increasing order of
> complexity and weight:  Pressure fed, pump (non-turbo), and turbo
> pump.  Is this generalization correct?

Pressure fed is simpler than pump fed in general.  The difference between
turbopumps and non-turbo pumps (including reciprocating pumps and rotary
positive-displacement pumps) cannot be so easily summarized.  A very basic
summary:  turbopumps are simple in principle, and simple for large
systems, constant conditions, or low performance.  High performance over a
wide range of conditions tends to need very sophisticated design and
fabrication.  Small size is hard to do at low weight (bad scaling).
Non-turbopumps are potentially superior at small size (very roughly, <5000
lb thrust) or for widely varying flow rates.  They are also comparatively
simple to make (lathe & drill press vs. multiaxis milling machine).

If the non-turbo pump variety,
> what generally powers the pumps?   What is the highest reasonable
> pressure one can get from a pressure fed system?

No fundamental limit, but most pressure fed systems run <1000 psi, and
many run around 200 psi.

 For a pump
> (non-turbo) fed system?

LLNL's Mockingbird was designed for 1000 psi feed, 700 psi chamber, if I
recall correctly offhand.

Do you still need to pressurize the
> propellants a little in both of the pump fed types?

Less for nonturbopumps than for turbopumps.  Turbopumps operate at fixed
pressure ratio, so output is a multiple of input pressure; also turbopumps
are damaged by cavitation if input pressure drops too low.  Positive
displacement pumps do not have a fixed pressure ratio (output pressure is
set entirely by drive power and output flow) and are generally not
severely damaged by cavitation.

Was the 280 ISP
> for Black Arrow a simple pressure fed system?

No.  Black Arrow used a simple turbopump.
>
> Finally, how's this for an off the wall idea:  What would happen if
> one used gaseous O2 as the pressurizing gas for the H2O2 tank?  Would
> it make the peroxide unstable?

No.
>  Would some of it dissolve into the
> peroxide?

Very little, I believe.  The main problems are that O2 is fairly dense, so
you need a lot of it to provide much pressurization (compared to He
pressurization), and high pressure gaseous O2 is wickedly reactive
(remember the Apollo 1 fire at 17 psi O2) -- even worse if you heat it to
reduce the mass of gas required.

Jordin Kare

From: jtkare@ibm.net (Jordin Kare)
Newsgroups: sci.space.tech
Subject: Re: More peroxide questions...
Date: Wed, 24 Jun 1998 21:52:02 -0700

In article <Ev0Jzs.Dzu@spsystems.net>, henry@spsystems.net (Henry Spencer)
wrote:


> >If the non-turbo pump variety, what generally powers the pumps?
>
> Same thing as in the turbopump variety:  hot gas, either from combustion
> or decomposition of propellants (perhaps not the same propellants as the
> engine itself burns).  There is no other reasonable way of storing the
> energy required; batteries are immensely heavy for the energy they store,
> and all other possibilities are even worse.

For Mockingbird, we did look at running the pump on He, stored
cryogenically and warmed by a heat exchanger on the engine.  The main
advantage, of course, was that the hot gas driving the pump was wholly
nonreactive and noncombustible, which made the pump design a lot simpler.
It also gave reasonable performance even with the He at modest
temperatures, especially since even room temperature He can be exhausted
at something like 200 s Isp; low temperature meant we could use elastomer
seals on the pump.  Cryo storage kept the He storage tank mass
reasonable.  But the heat exchanger and associated plumbing was ugly.  The
nominal final design went back to running the pumps on decomposed peroxide
(shades of the V2!)

Jordin Kare