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Re: Re: Arcjet Motor



I like verbose. Thanks to all that answered my question!

Gene Harlan - WB9MMM
Harlan Technologies - publisher of
OSCAR Satellite Report - OSR@hampubs.com
Amateur Television Quarterly - ATVQ@hampubs.com
http://www.hampubs.com


----- Original Message -----
From: "John P. Toscano" <tosca005@tc.umn.edu>
To: "Gene Harlan" <atvq@hampubs.com>
Cc: "i8cvs" <domenico.i8cvs@tin.it>; "Edward R. Cole" <al7eb@ptialaska.net>;
"AMSAT-BB" <amsat-bb@AMSAT.Org>
Sent: Wednesday, June 06, 2001 1:13 AM
Subject: Re: [amsat-bb] Re: Arcjet Motor


> Gene Harlan wrote:
> >
> > Not knowing anything about rocket motors, is a burn really a "burn". I
guess
> > I am asking if there is a flame, is it ignited, and by what? Or is it
> > a chemical reaction?
>
> It depends.  In the case of the Ammonia ArcJet motor, the answer is NO.
> This is described in the message you are quoting:
>
> > -----Original Message-----
> > From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> > Behalf Of i8cvs
> >
> > The ArcJect thruster is about 100 mN,giving an acceleration of order
> > 0,0002 m/s^2 provided the ammonia is heated by electric arc, then
> > the heated gas is expanded via a nozzle and thermal energy is
> > converted into kinetic energy.
>
> In the case of the liquid fuel motor, the answer is YES.  Monomethyl
> Hydrazine (MMH) is mixed with Nitrogen Tetroxide (N2O4).  The MMH
> burns (is oxidized) by the N2O4.  This is a chemical reaction,
> similar to what happens when you light a match to gasoline.  In that
> case, hydrocarbons (gasoline) are oxidized by atmospheric oxygen (O2)
> to produce mostly carbon monoxide (CO), carbon dioxide (CO2), and
> water (H2O).  The advantage of MMH + N2O4 is that they are
> "hypergolic", which means that the simple act of mixing them together
> causes spontaneous combustion to occur.  No spark, heat, or other
> external ignition is needed.
>
> But the word "burn" is used loosely in either case.  With the
> ammonia arcjet, there will be heat involved during normal operation,
> but the heat is provided by stored electrical energy (originally
> produced by the photocells), and is used to accelerate the speed of
> propellant expulsion as described above.  So heat is not a RESULT
> of firing the motor, it is a method of increasing the output of
> the motor.
>
> Just for completeness' sake (some would say just because I am too
> verbose when I compose email ;-), people also use the word "burn"
> when they talk about recording a compact disc in a CD-R or CD-RW
> drive.  I don't really know if the chemical reaction in the disc
> is an oxidation/reduction reaction ("burning"), but it has gotten
> that name at a minimum because a (relatively) high-power laser beam
> is focused on the disc and produces local heating that causes a
> chemical reaction that produces a change in optical characteristics
> of the disc that can be detected (read back) with a low-power laser
> beam later on.
>
> John (KB0ZEV)
>

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