From: Doug Jones (random@qnet.com)
Date: Thu Jul 22 1999 - 18:16:25 MDT
Eugene Leitl wrote:
>
> Doug Jones writes:
> > most critical design driver- solid state relays of the speed and
> > power needed aren't cheap. I can dig up detail information if
>
> How much power can we switch with a triggered arc discharge?
I've spent an hour or so trying to track down sources without much
luck, but from what I recall from discussions on sci.space.tech the
problem is turning *off* the current. V=Ldi/dt, and a large
negative di/dt is a bitch to terminate- like opening a circuit
breaker carrying a large DC current. Big sizzling arcs... A big
inductor with a large current flowing through it (ie lots of stored
energy) tries to be an ideal current source.
The ideal current profile in a stator coil is a square wave, going
high when the bucket is about one coil diameter away, then dropping
to zero as the bucket reaches the plane of the coil. This gives the
bucket a good pull, and doesn't need maglev guideways. More
realistically, you might get a roughly linear ramp up & ramp down
with a Bi-FET driver switch and bridge diodes- the switch closes
when the bucket is one diameter away, opens at 1/2 diameter, and the
diodes divert the negative spike back into the supply capacitor.
The cap driving each stage is oversized so that it approximates a
constant voltage supply. When the coil current goes to zero, the
diodes stop conducting, and the switch never sees more than 2x the
drive voltage.
Coils at the high speed end would still need to have fewer turns and
higher currents, to dump the stored charge faster- the total energy
delivered to the bucket is the same for each coil (if acceleration
is constant) but the time available for the current pulse goes as
1/v.
> > anyone is really truly interested.
>
> If this is not too much trouble on your part, please do.
Maybe after tomorrow morning... Rotary is supposed to fly the ATV in
a hover test, then safe the system, put it away, close the doors,
and send home everybody that's left. It's sad to see it go out with
a whimper.
-- Doug Jones, Freelance Rocket Plumber Formerly with Rotary Rocket
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