Spaceships Questions: Guns

[SuedodeuS]

Originally Posted by Langy

Very slightly. The impulse imparted by a firing cannon is nowhere near enough to really move a ship all that far away.

Indeed. Consider - an SM +8 Spinal Battery fires 20 cm rounds. For a conventional gun, these weigh 400 lbs - a good deal of which is propellant. We'll assume that the propellant is weightless, however, meaning we are launching a 400 lb projectile at 1 mile/second. The ship firing the weapon weighs 1,000 tons, or 2,000,000 lbs. A force that will send 400 lbs at 1 mile/second will send 2,000,000 lbs at, what, .0002 miles/second? That's a little over 1 ft/s, which is basically negligible.

Now let's get ridiculous and consider an SM+8 ship that the Hull consists of nothing but batteries, all facing one direction. A Major Battery fires 16 cm rounds, Medium 14, Secondary 12, Tertiary 10. To send the most mass flying, we'll want all Tertiary Batteries. Each battery sends 3/4 ton flying (again, assuming the propellant is massless), meaning 18 such batteries is going to move 13.5 tons at 1 mile/second. That will move the ship back at .0135 miles/second, or 71.28 ft/s (23.76 yards/second). That's a noticeable jump at human scales, but it's still nearly negligible for much of spaceship combat - it burns up .0135 mps of delta-v to correct for. And this is assuming a ridiculous design and massless propellant.