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by DanielBMarkham 3216 days ago
And the math and models all say it isn't possible, these days you could run the CFD analysis yourself on a high end desktop if you had the software.

Just spent about an hour poking around the internet. Fun subject! I believe you are stating this as far too certain of a thing when it's not. But hey, an hour doesn't mean much :)

There are three issues. Issue #1: without some way of correcting orbit, all you could ever get is some crazy long ballistic orbit (Which is another way of saying an elliptical orbit which intersects the ground). Solution? A sabot with standard space-capable gear inside.

Issue #2: hard acceleration needed. Solution? Not as big of a problem for cargo as you would think. Bull encased his gear in wet clay and it worked in a cannon setup. Some proposals calls for a 2km track with a 100G load, which is fine for a lot of cargo.

Issue #3: the atmosphere is basically a brick at the speed required. This sounds like much more of a problem than it is. Think about it: we have capsules re-entering Earth's atmosphere all the time, sometimes as fast as 12km/sec -- and that's at an very slight angle. Shooting more directly into space, the atmosphere would be mostly cleared in an extremely small amount of time. Bull was working with about 1/4 escape velocity decades ago. Even with gear like the Navy's new railgun, you're in the ballpark.

On my cusory search, I couldn't find other commenters as pessimistic as you are. If you have links, please share! I'd love to learn more. In the meantime, here's a paper that studies the issue. https://research.lifeboat.com/ieee.em.pdf

ADD: I by no means intended to imply this problem is easy or trivial, just as far as I can tell, it's nowhere in the neighborhood of being as open-and-shut as "the math doesn't work out"

1 comments

I wonder if you could "blow a hole" through the atmosphere (very briefly) and send your real payload after. Sounds absurd, but then so did Orion. I expect you could only manage a transient rarefication behind a rapidly-slowing "rabbit", alas.
There's definitely some interesting math going on. For example, max aerodynamic pressure happens immediately, on launch, with each additional millisecond decreasing stress on the payload.

At high enough speeds, does the atmosphere supercavitate? Could you use a double-shot, with the first projectile basically ablating away and creating a "wake" for the second to fly through?

I think the aerospike concept is related to this solution.

https://en.m.wikipedia.org/wiki/Drag-reducing_aerospike

Interesting. The "air spike" referenced there is like another idea I was wondering about: cross a bunch of laser beams ahead of the bullet, from a spread-out set of ground-based lasers. Like laser launch, but for rarefying the air in front instead of for powering a rocket.