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