(no subject)

[inahandbasket]

brain fart that I need to let out...

So there's a lot of chatter lately about resurrecting/creating Jules Verne's old spaceship launching cannon - essentially a big gun on/in the ground that shoots objects into space.
(See this boingboing post for some more info and jump-off links.)

The major issue is one of friction and heat, namely any projectile moving through low atmosphere at enough speed to hit orbit would burn up well before it got there.

So here's a thought.
Let's use the big gun to launch a projectile, but instead of full velocity at exiting the muzzle you make the projectile a SCRAMjet. It'll leave the gun at well above Mach5, trigger the SCRAMjet engine, and roar vertically into orbit, accelerating the whole way. The momentum it's got should coast it through the upper atmosphere where the air's too thin for the SCRAMjet to function, perhaps needing a small booster for the last push to orbit.

Comments

[komos.livejournal.com]

Would you have the same heat issues if you were to use a railgun or some other electromagnetic setup rather than chemical explosives and mechanical pistons? Or do we just need frictionless surfaces?

[inahandbasket]

the issue's actually air friction. Escape velocity from earth's surface is roughly 7 miles per second, which is how fast the projectile would have to be moving when it left the barrel of the gun.
Dat's a lotta air friction. ^_^

[komos.livejournal.com]

I was thinking that might be the problem. Frictionless surfaces it is.

'Course, I'm still opting for a space elevator and solar sailers.

[wanderyng1.livejournal.com]

There's two major issues with this:

#1 - No scramjet has ever survived its test flight.
#2 - Scramjets don't work below super-sonic speeds.

You could get the jet into space, but it would essentially be stranded at that point.

[inahandbasket]

#1. feh, prototypes have flown. details. ;-)
#2. It shouldn't ever be below super-sonic, that's what the big 'ole gun is for. Starting speed will be at the muzzle of the launcher.

The discussion around the railgun launcher is mostly for sattelites, so stranded isn't a problem. ^_^

[wanderyng1.livejournal.com]

I've flown too, and I crash each and every time...just like the scramjet. Albeit the scramjet makes it a bit higher than I can. They've just never managed to design one yet that can possibly survive a test flight. Their current designs are flawed and they know it. I'm not poo-pooing the idea of a scramjet entirely; they're just not quite there yet.

I thought we were talking about this from the standpoint of a spaceship, as in one involving passengers (hence the need for a return trip).

Also, it will drop below super-sonic as soon as it hits orbit. Orbit = no oxygen = no combustion = no scramjet propulsion.

Now railguns on the other hand are fun toys :)

[jjjiii]

I would think the acceleration would be too severe for most payloads, and more of an issue than friction and heat. Can you imagine the G-forces involved in being shot out of a cannon with sufficient muzzle velocity to escape Earth's gravity well?

I think the SCRAMjet idea has some merit, though.

We really could use something to lower the cost of getting to orbit.