Peter Fairbrother wrote in message ...
John Schilling wrote

Because conventional powder guns absolutely cannot accelerate a
projectile to even one-quarter the necessary velocity.

I'd have thought a Yank would know about guns.

Let's say for argument the necessary velocity is 8.5 km/s.

Bull got around 3.6 km/s at (S)HARP.


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

SHARP (the large, Lawrence Livermore gas gun built in the mid 90's)
got to 3 km/s, but the projectile only massed a few kilograms.

The engineering of building a larger light gas gun (larger than SHARP)
is *extremely* challenging. The 40 ton breech block of SHARP was the
largest forging of high-cobalt, high-nickel steel ever attempted.


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


A slight variation is the two-stage gasgun, which can reach about 8 km/s. I
believe the first was built in 1957. LLNL built one in 1972 and is still
using it. It's powered by gunpowder.


Two-stage gas guns have demonstrated velocities of 10 km/s, but with
projectiles only massing a few grams. See my comment above regarding
scaling of gas guns.


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.
--
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/