Cheaper way to space!? A supergun.

On 4 Oct 2003 23:27:00 -0700, (George William
Herbert) wrote, in part:
Paul F. Dietz wrote:
George William Herbert wrote:

I think that's not true with a travelling charge;
but nobody has made reliable travelling charge guns.

Has anyone mentioned ram accelerators in this thread?

Andrew Higgins posted in the thread, so I think it's
got to have been part of some included library function
or something.

A railgun, or mass driver, built, say, on a gentle slope leading to
the top of a 20-mile-high artificial mountain wouldn't be as good as a
"space elevator", as it would only allow one to eliminate the *first*
stage of a rocket and replace it with electrical power...

but it wouldn't require exotic materials like carbon nanotubes, I
would think. Still, the square-cube law does mean there would be some
problems, and maybe we could get away with a lower height.

I base 20 miles on the fact that rockets generally remain in vertical
flight up to about 20-25 miles to minimize air resistance losses, but
after 20 miles (where the atmosphere is less than 1/1000 of that at
sea level) air resistance tends to be regarded as unimportant. But I
admit I'm no expert at this, and of course every mile shaved off of
the needed height would greatly reduce the cost of such an artificial
mountain.

John Savard

John Savard
http://home.ecn.ab.ca/~jsavard/index.html

Andrew Higgins wrote

The maximum muzzle velocity of the 1960's era HARP gun never exceeded
2 km/s.

My bad. The figure I gave was a projection, and wasn't actually achieved.

However, I've seen several ref's to a 2.3 km/s shot, from the Canadian guy
who wrote a paper on the HARP in about 1966. Whether that was actually shot
or not, I don't know.

There are a few 13,000 fps (~4km/s)
powder guns around today, and I've heard of plans for a 5km/s one


Reference, please.

Working on it. The 5 kps gun is more likely to yield results, I know some
guys involved. I've a feeling the 4 kps one is too classified.

You can prove on gasdynamics grounds that a powder
gun can *never* exceed 3 km/s muzzle velocity.

The "gas speed" limit in a "gun" is not the speed of sound in the gas,
assuming no projectile.

Ignoring for the moment wall effects, the mass of gas in the "barrel" can be
bulk accelerated to some velocity by pressure from behind - and a _very
light_ projectile can then be accelerated to the speed of sound relative to
the travelling mass of gas, by it's expansion. Which is more than the speed
of sound relative to the breech.

Of course, it's far more complex than that.

Experimental railguns have already achieved 30,000+ fps, well over orbital
velocity,


References, please. I am not aware of any railguns exceeding 6 km/s.

The 30,000 fps plus figure came from a USN press report, with no details. I
think it slipped out. I don't know if it's right, but for sure some research
and development on railguns is classified. The same is even more true of
travelling charge guns (which, btw, the 5 kps gun is not).

However, these guys reportedly got 7.1 km/s:
http://www.ioffe.rssi.ru/PAPERS/94w06.pdf

and a railgun at ISAS (in Japan) gets 7+ km/s too, or so they've said, but
they are a bit reticent. They are also working on a 10 kps+ shaped-charge
"thrower".

I have the impression that considerable unannounced progress has been made.
This looks interesting:
http://library.kmitnb.ac.th/df/ieee40/370192.pdf




By the way, does anyone know anything about an "electric gun" at LLNL? Not a
railgun, I'd guess, they were talking about 15-18 kps?



--
Peter Fairbrother

How about a series of superguns of different sizes? You start with a small gun,
it fires a projectile that hits an object hovering in front of it. The
projectile knocks the object forward and in front of a second slightly larger
gun which fires a projectile hitting. The target goes faster and higher each
time it is hit by projectiles fired by increasingly larger superguns. The guns
are igged to fire at a precisely timed moment hitting the target as it passes
in front of it. The projectiles never have a fast enough relative velocity to
actually destroy the target, only to push it faster and higher. Eventually you
need superguns to push the target to near orbital velocities. Each supergun
only fires once for the launch of the payload. Does this sound like a good
idea?

Tom

Peter Fairbrother wrote in message ...
Andrew Higgins wrote

You can prove on gasdynamics grounds that a powder
gun can *never* exceed 3 km/s muzzle velocity.

The "gas speed" limit in a "gun" is not the speed of sound
in the gas, assuming no projectile.


Correct: maximum velocity is *not* equal sound speed in propellant
gas, but they *are* directly related.

In fact, as can be shown from the Method of Characteristics for
unsteady gasdynamics, the maximum velocity of a gas expansion is:

Vmax = 2 a0/(g-1)

....where "g" is the ratio of specific heats and a0 is the *initial*
speed of sound of the propellant. For g = 1.4, for example, Vmax = 5
a0. This is for a complete expansion to vacuum, only realizable with
a zero mass projectile.

In practice, actual guns get nowhere near this limit. The base
pressure drops off exponentially as the projectile accelerates,
approximately as:

p/p0 ~ exp(-g * V/a0)

....where p0 is the initial pressure (before projectile started
moving). Once the projectile has reached twice a0, the base pressure
is only about 5% its initial value, and guns can rarely accelerate
projectiles any faster than this.

For powder guns, the gaseous propellant is the combustion products of
the powder, which typically have an initial sound speed around 1 km/s.
Hence, the speed limit of about 2 km/s for powder guns. I am very
skeptical of claims of a 3+ km/s powder gun.

Experimental railguns have already achieved 30,000+ fps,
well over orbital velocity,


References, please. I am not aware of any railguns
exceeding 6 km/s.

The 30,000 fps plus figure came from a USN press report, with no details. I
think it slipped out. I don't know if it's right, but for sure some research
and development on railguns is classified. The same is even more true of
travelling charge guns (which, btw, the 5 kps gun is not).

Traveling charge guns, as far as I am aware, have *never* demonstrated
a boost in muzzle velocity over conventional, breech-fed guns. The
last review I've seen was:

Baer, P.G., and I.W. May, "Traveling-Charge Effect" in "Gun
Propulsion Technology" ed. L. Stiefel, Vol 109, AIAA Progress in
Astronautics and Aeronautics, 1988, pp. 499-536.

....and I am not aware of any new experimental results since then.


However, these guys reportedly got 7.1 km/s:
http://www.ioffe.rssi.ru/PAPERS/94w06.pdf


Thanks for the reference; this claim, if true, would be a new velocity
record for a rail gun.

However, I would need to see more data from the actual test before
being convinced; some claims at record muzzle velocities from rail
guns have actually been jets of plasma squirting from the end of the
rails, not coherent projectiles.


I have the impression that considerable unannounced progress has been made.
This looks interesting:
http://library.kmitnb.ac.th/df/ieee40/370192.pdf


I think "Promising but unconfirmed theoretical study" is more
appropriate description of this paper, rather than "considerable
unannounced progress."


By the way, does anyone know anything about an "electric gun" at LLNL? Not a
railgun, I'd guess, they were talking about 15-18 kps?


I am not aware of a 15-18 km/s gun at LLNL, although certain there is
interest there (an elsewhere) in such a device.

You may be thinking of two different, recent developments:

One is the use of the Sandia Z machine (basically, a very, very large
pulsed power supply) to launch thin metal foils to velocities of 15-20
km/s via magnetic loading:

http://www.sandia.gov/media/NewsRel/NR2001/flyer.htm

The other is a 3-stage gun at Sandia that has also accelerated small
flyer plates ( 1g) to 15 km/s:

http://www.cs.sandia.gov/HPCCIT/hyprvel.html

Note that the third stage of this 3-stage gun is basically the
2nd-stage projectile impacting a special, density-gradient material
that "smoothly" shocks the smaller flyer to the final velocity.

In both of these devices, there are still concerns if the projectile
is actually intact, or has been "spalled" by the acceleration process.

Note that all of this work uses projectiles smaller than 1 g, and is
used exclusively for fundamental equation of state studies motivated
by inertial confinement fusion studies, H-bomb physics, and
fundamental planetary physics.

Other than as a possible simulator for micrometeoroid and orbital
debris impact, these devices have no relevance to the subject of this
thread ("Cheaper way to space!? A supergun.") because they cannot
scale and because they violently shock their projectiles to their
yield strength.

As for concepts that are scalable for "soft" direct space launch, the
two most interesting concepts (the Ram Accelerator and, more
speculatively, the Slingatron) remain too underdeveloped to make
definitively assessments of feasibility. Neither of these concepts
have ever had the funding support necessary to determine what the
maximum velocities achievable are, although a small amount of basic
research is continuing on both.
--
Andrew J. Higgins Mechanical Engineering Dept.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://www.mcgill.ca/mecheng/staff/academic/higgins/

Peter Fairbrother wrote in message ...
Andrew Higgins wrote

You can prove on gasdynamics grounds that a powder
gun can *never* exceed 3 km/s muzzle velocity.

The "gas speed" limit in a "gun" is not the speed of sound
in the gas, assuming no projectile.


Correct: maximum velocity is *not* equal sound speed in propellant
gas, but they *are* directly related.

In fact, as can be shown from the Method of Characteristics for
unsteady gasdynamics, the maximum velocity of a gas expansion is:

Vmax = 2 a0/(g-1)

....where "g" is the ratio of specific heats and a0 is the *initial*
speed of sound of the propellant. For g = 1.4, for example, Vmax = 5
a0. This is for a complete expansion to vacuum, only realizable with
a zero mass projectile.

In practice, actual guns get nowhere near this limit. The base
pressure drops off exponentially as the projectile accelerates,
approximately as:

p/p0 ~ exp(-g * V/a0)

....where p0 is the initial pressure (before projectile started
moving). Once the projectile has reached twice a0, the base pressure
is only about 5% its initial value, and guns can rarely accelerate
projectiles any faster than this.

For powder guns, the gaseous propellant is the combustion products of
the powder, which typically have an initial sound speed around 1 km/s.
Hence, the speed limit of about 2 km/s for powder guns. I am very
skeptical of claims of a 3+ km/s powder gun.

Experimental railguns have already achieved 30,000+ fps,
well over orbital velocity,


References, please. I am not aware of any railguns
exceeding 6 km/s.

The 30,000 fps plus figure came from a USN press report, with no details. I
think it slipped out. I don't know if it's right, but for sure some research
and development on railguns is classified. The same is even more true of
travelling charge guns (which, btw, the 5 kps gun is not).

Traveling charge guns, as far as I am aware, have *never* demonstrated
a boost in muzzle velocity over conventional, breech-fed guns. The
last review I've seen was:

Baer, P.G., and I.W. May, "Traveling-Charge Effect" in "Gun
Propulsion Technology" ed. L. Stiefel, Vol 109, AIAA Progress in
Astronautics and Aeronautics, 1988, pp. 499-536.

....and I am not aware of any new experimental results since then.


However, these guys reportedly got 7.1 km/s:
http://www.ioffe.rssi.ru/PAPERS/94w06.pdf


Thanks for the reference; this claim, if true, would be a new velocity
record for a rail gun.

However, I would need to see more data from the actual test before
being convinced; some claims at record muzzle velocities from rail
guns have actually been jets of plasma squirting from the end of the
rails, not coherent projectiles.


I have the impression that considerable unannounced progress has been made.
This looks interesting:
http://library.kmitnb.ac.th/df/ieee40/370192.pdf


I think "Promising but unconfirmed theoretical study" is more
appropriate description of this paper, rather than "considerable
unannounced progress."


By the way, does anyone know anything about an "electric gun" at LLNL? Not a
railgun, I'd guess, they were talking about 15-18 kps?


I am not aware of a 15-18 km/s gun at LLNL, although certain there is
interest there (an elsewhere) in such a device.

You may be thinking of two different, recent developments:

One is the use of the Sandia Z machine (basically, a very, very large
pulsed power supply) to launch thin metal foils to velocities of 15-20
km/s via magnetic loading:

http://www.sandia.gov/media/NewsRel/NR2001/flyer.htm

The other is a 3-stage gun at Sandia that has also accelerated small
flyer plates ( 1g) to 15 km/s:

http://www.cs.sandia.gov/HPCCIT/hyprvel.html

Note that the third stage of this 3-stage gun is basically the
2nd-stage projectile impacting a special, density-gradient material
that "smoothly" shocks the smaller flyer to the final velocity.

In both of these devices, there are still concerns if the projectile
is actually intact, or has been "spalled" by the acceleration process.

Note that all of this work uses projectiles smaller than 1 g, and is
used exclusively for fundamental equation of state studies motivated
by inertial confinement fusion studies, H-bomb physics, and
fundamental planetary physics.

Other than as a possible simulator for micrometeoroid and orbital
debris impact, these devices have no relevance to the subject of this
thread ("Cheaper way to space!? A supergun.") because they cannot
scale and because they violently shock their projectiles to their
yield strength.

As for concepts that are scalable for "soft" direct space launch, the
two most interesting concepts (the Ram Accelerator and, more
speculatively, the Slingatron) remain too underdeveloped to make
definitively assessments of feasibility. Neither of these concepts
have ever had the funding support necessary to determine what the
maximum velocities achievable are, although a small amount of basic
research is continuing on both.
--
Andrew J. Higgins Mechanical Engineering Dept.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://www.mcgill.ca/mecheng/staff/academic/higgins/

Peter Fairbrother wrote in message ...
Andrew Higgins wrote

You can prove on gasdynamics grounds that a powder
gun can *never* exceed 3 km/s muzzle velocity.

The "gas speed" limit in a "gun" is not the speed of sound
in the gas, assuming no projectile.


Correct: maximum velocity is *not* equal sound speed in propellant
gas, but they *are* directly related.

In fact, as can be shown from the Method of Characteristics for
unsteady gasdynamics, the maximum velocity of a gas expansion is:

Vmax = 2 a0/(g-1)

....where "g" is the ratio of specific heats and a0 is the *initial*
speed of sound of the propellant. For g = 1.4, for example, Vmax = 5
a0. This is for a complete expansion to vacuum, only realizable with
a zero mass projectile.

In practice, actual guns get nowhere near this limit. The base
pressure drops off exponentially as the projectile accelerates,
approximately as:

p/p0 ~ exp(-g * V/a0)

....where p0 is the initial pressure (before projectile started
moving). Once the projectile has reached twice a0, the base pressure
is only about 5% its initial value, and guns can rarely accelerate
projectiles any faster than this.

For powder guns, the gaseous propellant is the combustion products of
the powder, which typically have an initial sound speed around 1 km/s.
Hence, the speed limit of about 2 km/s for powder guns. I am very
skeptical of claims of a 3+ km/s powder gun.

Experimental railguns have already achieved 30,000+ fps,
well over orbital velocity,


References, please. I am not aware of any railguns
exceeding 6 km/s.

The 30,000 fps plus figure came from a USN press report, with no details. I
think it slipped out. I don't know if it's right, but for sure some research
and development on railguns is classified. The same is even more true of
travelling charge guns (which, btw, the 5 kps gun is not).

Traveling charge guns, as far as I am aware, have *never* demonstrated
a boost in muzzle velocity over conventional, breech-fed guns. The
last review I've seen was:

Baer, P.G., and I.W. May, "Traveling-Charge Effect" in "Gun
Propulsion Technology" ed. L. Stiefel, Vol 109, AIAA Progress in
Astronautics and Aeronautics, 1988, pp. 499-536.

....and I am not aware of any new experimental results since then.


However, these guys reportedly got 7.1 km/s:
http://www.ioffe.rssi.ru/PAPERS/94w06.pdf


Thanks for the reference; this claim, if true, would be a new velocity
record for a rail gun.

However, I would need to see more data from the actual test before
being convinced; some claims at record muzzle velocities from rail
guns have actually been jets of plasma squirting from the end of the
rails, not coherent projectiles.


I have the impression that considerable unannounced progress has been made.
This looks interesting:
http://library.kmitnb.ac.th/df/ieee40/370192.pdf


I think "Promising but unconfirmed theoretical study" is more
appropriate description of this paper, rather than "considerable
unannounced progress."


By the way, does anyone know anything about an "electric gun" at LLNL? Not a
railgun, I'd guess, they were talking about 15-18 kps?


I am not aware of a 15-18 km/s gun at LLNL, although certain there is
interest there (an elsewhere) in such a device.

You may be thinking of two different, recent developments:

One is the use of the Sandia Z machine (basically, a very, very large
pulsed power supply) to launch thin metal foils to velocities of 15-20
km/s via magnetic loading:

http://www.sandia.gov/media/NewsRel/NR2001/flyer.htm

The other is a 3-stage gun at Sandia that has also accelerated small
flyer plates ( 1g) to 15 km/s:

http://www.cs.sandia.gov/HPCCIT/hyprvel.html

Note that the third stage of this 3-stage gun is basically the
2nd-stage projectile impacting a special, density-gradient material
that "smoothly" shocks the smaller flyer to the final velocity.

In both of these devices, there are still concerns if the projectile
is actually intact, or has been "spalled" by the acceleration process.

Note that all of this work uses projectiles smaller than 1 g, and is
used exclusively for fundamental equation of state studies motivated
by inertial confinement fusion studies, H-bomb physics, and
fundamental planetary physics.

Other than as a possible simulator for micrometeoroid and orbital
debris impact, these devices have no relevance to the subject of this
thread ("Cheaper way to space!? A supergun.") because they cannot
scale and because they violently shock their projectiles to their
yield strength.

As for concepts that are scalable for "soft" direct space launch, the
two most interesting concepts (the Ram Accelerator and, more
speculatively, the Slingatron) remain too underdeveloped to make
definitively assessments of feasibility. Neither of these concepts
have ever had the funding support necessary to determine what the
maximum velocities achievable are, although a small amount of basic
research is continuing on both.
--
Andrew J. Higgins Mechanical Engineering Dept.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://www.mcgill.ca/mecheng/staff/academic/higgins/

Peter Fairbrother wrote in message ...

and a railgun at ISAS (in Japan) gets 7+ km/s too, or so they've said, but
they are a bit reticent. They are also working on a 10 kps+ shaped-charge
"thrower".


Shaped charge explosives capable of producing 10+ km/s metallic jets
have been around since the Second World War.

In fact, Fritz Zwicky can lay claim (albeit tenuous) to having
launched the first artificial object into solar orbit in 1957 (just 12
days after Sputnik 1) by using a Aerobee rocket to launch a shaped
charge to high altitude, then detonating the explosive to send out
jets at 15 km/s. Similar work was also done by Zwicky and Fred
Whipple in 1946, using captured V-2's.

You can read more about this fascinating story he

http://utenti.lycos.it/paoloulivi/aerobee.html
http://www.slac.stanford.edu/pubs/be...1-1-maurer.pdf
http://www.ufx.org/gfb/zwickoralhist.htm
http://www.ufx.org/gfb/artifmet.htm
--
Andrew J. Higgins Mechanical Engineering Dept.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://www.mcgill.ca/mecheng/staff/academic/higgins/

Andrew Higgins wrote

However, these guys reportedly got 7.1 km/s:
http://www.ioffe.rssi.ru/PAPERS/94w06.pdf


Thanks for the reference; this claim, if true, would be a new velocity
record for a rail gun.

However, I would need to see more data from the actual test before
being convinced; some claims at record muzzle velocities from rail
guns have actually been jets of plasma squirting from the end of the
rails, not coherent projectiles.

http://ieeexplore.ieee.org:80/xpl/ab...rod=JNL&arnumb
er=195613&arSt=431&ared=434&arAuthor=Kawashima%2C+ N.%3B+Yamori%2C+A.%3B+Yana
gisawa%2C+M.%3B+Kubo%2C+H.%3B+Kohno%2C+M.%3B+Teii% 2C+S.&arNumber=195613&a_id
0=195609&a_id1=195610&a_id2=195611&a_id3=195612&a_ id4=195613&a_id5=195614&a_
id6=195615&a_id7=195616&a_id8=195617&a_id9=195618& a_id10=195619&a_id11=19562
0&a_id12=195621&a_id13=195622&a_id14=195623&count= 15

reports 7.45 km/s max, and always 6+ kps, again quite a few years ago.

There's a figure at
http://www.ted.isas.ac.jp/spc/railgun/railgun.html

that gives ~7.8 km/s max, but I don't know if it's actual shots or projected
results - it looks like shots, but I don't read Japanese. Anyone?


Thanks for the Sandia ref's. The guys were working at LLNL tho', so I'm
unsure whether they meant the Sandia stuff or something else, I'll ask.


BTW, the 10 km/s+ shaped-charge "thrower" isn't from ISAS as I said, but
NAL/Mitsubishi. I don't know if it's much more than a design study.


--
Peter Fairbrother