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Posted by BDH on September 17, 2006, 8:55 am
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Supposedly the slingatron is one of the more sound and more thoroughly
reviewed of potential hypervelocity systems, but there are a few
problems I can't figure out a way around.
Suppose you use conventional or gas bearings. The best I've seen is
.001 for a friction coefficient. At a few km/s (below which why
bother!) because the projectile makes many trips the heating seems to
be unacceptable and destroys the projectile. Also gas bearings
obviously introduce gas into the track.
On to magnetic levitation. Type 1 superconductors and rare earth
magnets seem to be too weak for reasonably sized slingatrons. All of
the type 2 superconductors I know of, even single grain YBCO, seem to
have magnetization losses such that the losses of the track
superconductors as the projectile electromagnet approaches and leaves
are unacceptably high, requiring overly high track speeds and leaving
very low efficiency. These losses go down with projectile length but
not really enough.
Further, as a projectile moves around a track, it exerts an outward
force of the track at a point that moves around the track, and the
track bends in response. Are people designing variable resonance masses
that cancel this out and move with the gyration? Planning on very
massive stiff tracks? Both? Otherwise you lose a bunch of energy.
So are people planning 100m projectiles on a 1km diameter fast moving,
massive, stiff, ring, with large amounts of well cooled
superconductors, and active vibration cancellation handling variable
frequency and exerting thousands of tons of force? And still being
inefficient, with power supplies and motors scaled accordingly? Doesn't
seem so cheap...
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Posted by delt0r on September 19, 2006, 7:45 am
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Well this is the first i have heard of slingatrons. Would make a real
nice problem for a mechnics class. Anyway...
Yes yes and yes. Dealing with a curved track makes all the "mass
driver" problems worse IMO. I can't see this as a improvment over other
mass driver ideas.
Futher i really can't see mass drivers as the way ahead to CATS. First
off it will be a rocket, plain and simple with lower operational costs
and the next will be tethers in LEO. All IMHO. Maybee Space Elevators
will "fly" but the numbers don't look good unless there is some nano
tube fab breakthrough.
Greg
BDH wrote:
show/hide quoted text
> Supposedly the slingatron is one of the more sound and more thoroughly
> reviewed of potential hypervelocity systems, but there are a few
> problems I can't figure out a way around.
> Suppose you use conventional or gas bearings. The best I've seen is
> .001 for a friction coefficient. At a few km/s (below which why
> bother!) because the projectile makes many trips the heating seems to
> be unacceptable and destroys the projectile. Also gas bearings
> obviously introduce gas into the track.
> On to magnetic levitation. Type 1 superconductors and rare earth
> magnets seem to be too weak for reasonably sized slingatrons. All of
> the type 2 superconductors I know of, even single grain YBCO, seem to
> have magnetization losses such that the losses of the track
> superconductors as the projectile electromagnet approaches and leaves
> are unacceptably high, requiring overly high track speeds and leaving
> very low efficiency. These losses go down with projectile length but
> not really enough.
> Further, as a projectile moves around a track, it exerts an outward
> force of the track at a point that moves around the track, and the
> track bends in response. Are people designing variable resonance masses
> that cancel this out and move with the gyration? Planning on very
> massive stiff tracks? Both? Otherwise you lose a bunch of energy.
> So are people planning 100m projectiles on a 1km diameter fast moving,
> massive, stiff, ring, with large amounts of well cooled
> superconductors, and active vibration cancellation handling variable
> frequency and exerting thousands of tons of force? And still being
> inefficient, with power supplies and motors scaled accordingly? Doesn't
> seem so cheap...
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Posted by Kent Paul Dolan on September 20, 2006, 2:21 pm
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show/hide quoted text
> Supposedly the slingatron is one of the more sound
> and more thoroughly reviewed of potential
> hypervelocity systems, but there are a few
> problems I can't figure out a way around.
[snip]
show/hide quoted text
> On to magnetic levitation. Type 1 superconductors
> and rare earth magnets seem to be too weak for
> reasonably sized slingatrons. All of the type 2
> superconductors I know of, even single grain YBCO,
> seem to have magnetization losses such that the
> losses of the track superconductors as the
> projectile electromagnet approaches and leaves are
> unacceptably high, requiring overly high track
> speeds and leaving very low efficiency. These
> losses go down with projectile length but not
> really enough.
Well, if a maglev train can work, and lots of smart
people seem to believe so, then what you want
is just a very fast annulus-shatped train with no
head and no tail running on a track that happens to
be more _beside_ it than under it. Unless there are
some show stoppers for that train as a train, it
could even carry a railgun around with it from which
to shoot the projectile, combining two technologies
to gain extra velocity.
Depending mostly on size of projectile versus mass
of "train", it might or might not be necessary to
shoot a sabot from the opposite side to balance the
forces, but if you're gathering solar power to keep
the whole kit going, there's _lots_ of available
power, close to free, so cost of construction,
rather than cost of operation, seems to be the
stopping point.
My feeling is that a "train" about the mass of the
Hoover Dam would work best.
Since you'd want to put the device at one or other
lunar pole, to avoid precession forces, you'd also
have the advantage of solar power being available
from one direction or another nearly constantly,
missing only eclipses.
xanthian, not even pretending to be able to do the
math.
--
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> reviewed of potential hypervelocity systems, but there are a few
> problems I can't figure out a way around.
> Suppose you use conventional or gas bearings. The best I've seen is
> .001 for a friction coefficient. At a few km/s (below which why
> bother!) because the projectile makes many trips the heating seems to
> be unacceptable and destroys the projectile. Also gas bearings
> obviously introduce gas into the track.
> On to magnetic levitation. Type 1 superconductors and rare earth
> magnets seem to be too weak for reasonably sized slingatrons. All of
> the type 2 superconductors I know of, even single grain YBCO, seem to
> have magnetization losses such that the losses of the track
> superconductors as the projectile electromagnet approaches and leaves
> are unacceptably high, requiring overly high track speeds and leaving
> very low efficiency. These losses go down with projectile length but
> not really enough.
> Further, as a projectile moves around a track, it exerts an outward
> force of the track at a point that moves around the track, and the
> track bends in response. Are people designing variable resonance masses
> that cancel this out and move with the gyration? Planning on very
> massive stiff tracks? Both? Otherwise you lose a bunch of energy.
> So are people planning 100m projectiles on a 1km diameter fast moving,
> massive, stiff, ring, with large amounts of well cooled
> superconductors, and active vibration cancellation handling variable
> frequency and exerting thousands of tons of force? And still being
> inefficient, with power supplies and motors scaled accordingly? Doesn't
> seem so cheap...