https://en.wikipedia.org/wiki/Project_HARP https://en.wikipedia.org/wiki/Project_HARP "On November 18, 1966 the Yuma gun fired a 400 lb (180 kg) Martlet 2 proj

https://en.wikipedia.org/wiki/Project_HARP https://en.wikipedia.org/wiki/Project_HARP "On November 18, 1966 the Yuma gun fired a 400 lb (180 kg) Martlet 2 projectile at 7,000 ft/s (2,100 m/s)[4] sending it briefly into space and setting an altitude record of 180 km (590,000 ft; 110 mi)" If my math napkin correct the projectile lost less than 1.5 Mach of the speed when it reached 30km height, ie. where air is just 2% density of the sea level. https://en.wikipedia.org/wiki/Project_Babylon https://en.wikipedia.org/wiki/Project_Babylon "The second supergun, "Big Babylon", of which a pair were planned (one to be mounted horizontally, at least for test purposes), was much larger. The barrel was to be 156 metres (512 feet) long, with a bore of 1 metre (3.3 feet).[1] Originally intended to be suspended by cables from a steel framework, it would have been over 100 metres (300 feet) high at the tip. The complete device weighed about 2,100 tonnes (the barrel alone weighed 1,655 tons). It was a space gun intended to shoot projectiles into orbit, a theme of Bull's work since Project HARP." what a pity : "The project began in 1988; it was halted in 1990 after Bull was assassinated, and parts of the superguns were seized in transit around Europe. The components that remained in Iraq were destroyed by the United Nations after the 1991 Persian Gulf War. " one can dream - put such a gun on plateau at 4km altitude, half sea level pressure, somewhere in Bolivia or Peru (it is even close to equator) or may be Tibet, and shoot the fuel, food, water, etc. into the orbit to build up the Moon, Mars, etc, missions. If only we could find a few tens of millions dollars :). I'm waiting for Musk to hopefully get to it as he has a business case and money.