“John Hunter wants to shoot stuff into space with a 3,600-foot gun. And he’s dead serious–he’s done the math. Making deliveries to an orbital outpost on a rocket costs $5,000 per pound, but using a space gun would cost just $250 per pound.
How to Shoot Stuff into Space
STEP 1: HEAT IT
The gun combusts natural gas in a heat exchanger within a
chamber of hydrogen gas, heating the hydrogen to 2,600˚F and causing a 500 percent increase in pressure.
STEP 2: LET THE HYDROGEN LOOSE
Operators open the valve, and the hot, pressurized hydrogen quickly expands down the tube, pushing the payload forward.
STEP 3: TO INFINITY AND BEYOND
After speeding down the 3,300-foot-long barrel, the projectile shoots out of the gun at 13,000 mph. An iris at the end of the gun closes, capturing the hydrogen gas to use again.” via PopSci