Coil guns vs. mass drivers

Bill,

The timing circuit must apply a magnetic field to "pull" the payload until it is centered with the magnetic coil at which time the power is dropped. It is after this point that the passing magnetic will induce their voltage. Hence, if there is a way to transfer the magnetic field/current to the next magnetic coil and to open the circuit up so that it does not conduct electricity, then there will be no induced current to impede the payload.

Tom
From: bill t
To: spacesettlers@egroups.com
Sent: Sunday, December 31, 2000 9:03 AM
Subject: [spacesettlers] Re: Coil guns vs. mass drivers

A diagram would be great if had a scanner to scan it in.

I think you are looking at it from the wrong point of view. The moving
magnetic field will cause induction in the stationary coils. This
induction will cause a decrese in current flow. The capsule acts like
a linear generator. It is acedemic though. For long induction motors
(which is what this is) this doesn't become a problem.

Being straight is not a real prblem. In fact the structure will be
curved since it is on a planet.

This post was to answer that the maximum speed was limited to about 2
km/s. This is true only for short high acceleration coil guns. For
longer guns the induction problem is still there but the maximum
velocity is much higher for longer (1000 km length) designs.

Bill

--- In spacesettlers@egroups.com, "Tom Tucker (Olympia)"
wrote:
> Bill,
>
> It would be helpful to see a sketch of the design being considered.
If the acceleration is similar to the linear motor concept being used
for maglev trains, then I don't understand the design limitation. At
the higher velocity sections, the propulsion magnets could be spaced
further apart if timing becomes an issue. In a vacuum, the only
constraint I am aware of is the ability to construct the magnetic
support rails exceedingly straight. The structure might be blown
around by the solar wind :-)
>
> Tom
> From: bill t
> To: spacesettlers@egroups.com
> Sent: Wednesday, December 27, 2000 7:36 PM
> Subject: [spacesettlers] Re: Coil guns vs. mass drivers
>
> The inductance will limit the acceleration not the velocity. The
DOD
> were building high acceleration devices (>100 g). I had did the
> calculations about a decade ago, and came up with a safe
acceleration
> to escape velocity of about 70 m/s^2. I'll try to dig up my old
notes
> and transcribe it for everyone and you can try to find problems
with
> the physics.
>
> Bill
>
> --- In spacesettlers@egroups.com, "Mike Combs"
wrote:
> > --- In spacesettlers@egroups.com, Ian Woollard

> > wrote:
> > >
> > > Coil guns can do about 2.5 km/s which is enough for the
> > > moon (or punching though armour plate), but I think it runs
> > > out of 'steam' after that. The inductance of the coils gets
> > > to be a huge problem.
> >
> > Actually, I've heard pessimists proclaim that coil guns can't
even
> > get up to 1 km/s, which would mean that they couldn't even be
used
> as
> > a lunar launcher. But as I remarked in "Making Dreams from
> > Moondust", I'm not sure a direct comparison can be drawn between
the
> > kind of coil gun that the DoD funded, and the kind of mass
driver
> > O'Neill was experimenting with. I know I did get a reply from
Dr.
> > Les Snively, who worked with O'Neill on Mass Driver 3. He said
that
> > the coil rise time the critics were pointing to as an
insuperable
> > problem was an implicit part of their models.
> >
> > I still consider it within the realm of possibility that those
who
> > built that coilgun for the military simply erred in some
fundamental
> > way, and that the mass driver may still work as anticipated.
> >
> > And as you say later, the erosure problem rail guns have may be
a
> > show stopper there.
> >
> > Regards,
> > Mike Combs
>

The timing circuit must apply a magnetic field to "pull" the payload until it is centered with the magnetic coil at which time the power is dropped. It is after this point that the passing magnetic will induce their voltage. Hence, if there is a way to transfer the magnetic field/current to the next magnetic coil and to open the circuit up so that it does not conduct electricity, then there will be no induced current to impede the payload.

Tom
From:
bill t
To:
spacesettlers@...m
Sent:
Sunday, December 31, 2000 9:03 AM
Subject:
[spacesettlers] Re: Coil guns vs. mass drivers
A diagram would be great if had a scanner to scan it in.
I think you are looking at it from the wrong point of view. The moving
magnetic field will cause induction in the stationary coils. This
induction will cause a decrese in current flow. The capsule acts like
a linear generator. It is acedemic though. For long induction motors
(which is what this is) this doesn't become a problem.
Being straight is not a real prblem. In fact the structure will be
curved since it is on a planet.
This post was to answer that the maximum speed was limited to about 2
km/s. This is true only for short high acceleration coil guns. For
longer guns the induction problem is still there but the maximum
velocity is much higher for longer (1000 km length) designs.
Bill
--- In spacesettlers@egroups.com, "Tom Tucker (Olympia)"
> Bill,
>
It would be helpful to see a sketch of the design being considered.
If the acceleration is similar to the linear motor concept being used
for maglev trains, then I don't understand the design limitation. At
the higher velocity sections, the propulsion magnets could be spaced
further apart if timing becomes an issue. In a vacuum, the only
constraint I am aware of is the ability to construct the magnetic
support rails exceedingly straight. The structure might be blown
around by the solar wind :-)
>
> Tom
> From: bill t
To: spacesettlers@egroups.com
> Sent: Wednesday, December 27, 2000 7:36 PM
> Subject: [spacesettlers] Re: Coil guns vs. mass drivers
>
The inductance will limit the acceleration not the velocity. The
DOD
> were building high acceleration devices (>100 g). I had did the
> calculations about a decade ago, and came up with a safe
acceleration
> to escape velocity of about 70 m/s^2. I'll try to dig up my old
notes
> and transcribe it for everyone and you can try to find problems
with
> the physics.
>
> Bill
>
> --- In spacesettlers@egroups.com, "Mike Combs"
> > --- In spacesettlers@egroups.com, Ian Woollard
> > wrote:
> > >
> > > Coil guns can do about 2.5 km/s which is enough for the
> > > moon (or punching though armour plate), but I think it runs
> > > out of 'steam' after that. The inductance of the coils gets
> > > to be a huge problem.
>
> > Actually, I've heard pessimists proclaim that coil guns can't
even
> > get up to 1 km/s, which would mean that they couldn't even be
used
> as
> > a lunar launcher. But as I remarked in "Making Dreams from
> > Moondust", I'm not sure a direct comparison can be drawn between
the
> > kind of coil gun that the DoD funded, and the kind of mass
driver
> > O'Neill was experimenting with. I know I did get a reply from
Dr.
> > Les Snively, who worked with O'Neill on Mass Driver 3. He said
that
> > the coil rise time the critics were pointing to as an
insuperable
> > problem was an implicit part of their models.
> >
> > I still consider it within the realm of possibility that those
who
> built that coilgun for the military simply erred in some
fundamental
> > way, and that the mass driver may still work as anticipated.
> >
> > And as you say later, the erosure problem rail guns have may be
a