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R: Re: Arcjet Motor




Ed and all:

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.
Is AO40 there is ammonia for about 500 hours of operation offering a total
delta-V
of up to 470 m/s

On the other side, 400 Newton is the nominal thrust of the rocket liquid
propellant motor.
Since spacecraft launch mass is 632 Kg,the motor,if no problems occurred,was
able to  impart an initial acceleration of typ,400/632 = 0,6m/s^2 or about
0,06 g.
Total delta-V available is about 1100 m/s

The 100 mN thrust of ArcJect motor is 1/4000 of the main motor,but can fire
for long periods,giving significant velocity changes.

 The kick motor used on AMSAT Phase III-A was a solid propellant Thiokol TEM
345-12 containing approximately 35 kg of a mixture of powdered aluminum and
organic chemicals in a spherical shell with a single exit nozzle.
The unit was capable of producing a velocity change of about 1600 m/s
during its single 20 second burn but unfortunately this AMSAT Phase III-A
satellite was lost in the Atlantic with ARIANE-4

OSCAR-10 and 13  used a liquid-fuel roket produced by the German company
Messerschmitt .
This unit produces a thrust of 400 Newton  with the advantage to be ignited
several time and is similar to that used on AO40

All tree satellites OSCAR-10,13 and AO40 had problems with the 400 N liquid
propellant motor and no one of it was able to reach the final orbit
inclination.

I hope this information is usefull for the ArcJect Motor forum.

73 de i8CVS Domenico


----- Original Message -----
From: Edward R. Cole <al7eb@ptialaska.net>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, June 05, 2001 4:29 AM
Subject: [amsat-bb] Re: Arcjet Motor


> WA4SCO, and all:
>
> I think that one should realize that the arc-jet is a very low thrust
> engine.  I believe it is considered high impulse, but even that does not
> replace "pounds of push"!  The arc-jet is the "little engine that barely
> can".  It shines as a highly controllable motor for fine tuning an orbit,
> but its unlikely that it has sufficient fuel to accomplish any major
> orbital shift.  This would be true on future ham satellites, too.
>
> The solid propellant engine "idea" might just be a viable alternative to a
> liquid fuel engine.  Obviously, they burn until fuel is expended, so there
> is less control and much more orbit pre-planning will be required.  I
> suppose our orbit experts are reading and maybe they will take a look
> (again?).  The multi-engine proposal has some merit, especially if engines
> with different thrust and burn times were combined.  Under software
> control, the appropriate engines could be chosen for a given burn.  Of
> course it would be less refined than using a liquid fuel rocket.
>
> I have a little experience with solid rockets...launched many in the
1950's
> as a teenager ;-)  Never got as good as Homer Hickam, though.  {It was
> 1952-age eight, that I decided to become either a "spaceman"...the term of
> astronaut not being coined, yet...or a "rocket engineer"}  Never quite
> realized that; best I came to that goal was working for NASA.  My
> participation in ham-sats gives me an outlet for those early dreams.
>
> Ed
>
>
>
> ----
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>








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