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Sorry, but a railgun-based launcher doesn't make sense at all. There's all sorts of gun-based launchers that do, but railguns are hard enough on relatively easier (lower velocity, lower projectile mass) specs such as the US Navy's projects. Something like tbfg.org's proposed ram accelerator is much more feasible.

Might we, someday, be good enough at ultra-low-impedance machines that a railgun-to-space becomes feasible? Sure... but why wait around for that day when we have a good working grasp of the technology behind other designs? There's a world of cheap satellite comms* just waiting for cheap rides to LEO which will amply recoup the capital costs for the launch system, and meanwhile we can figure out the other applications (on-orbit fuel depots, space-based solar power, etc.).

* could/should end up as ubiquitous as cellular mobiles, but without the dead spots throughout most of the plains states, without needing a different phone for boaters over the horizon from land, etc. The only thing stopping this now is the ridiculous cost of launching the huge constellation you need for full coverage.

Here's another way to express it: you cannot achieve a repeating orbit whose low point (perigee) is higher than the last point at which thrust was applied. For a simple gun, that point is the muzzle.

Wow... Excellent point! Rail guns are pretty worthless on their own when trying to achieve a useful orbit.

On their own, yes. (And it applies more generally to all linear accelerators.) But the circularization burn can be quite small, so they are worth considering. But IMO ram accelerators as promoted by tbfg are a better bet than railguns.

And you lost way to much energy in the lower atmosphere (and create incredible heat loads) trying to ram through it at super-orbital speeds (in fact the G-loading from this deceleration alone will probably be prohibitive for humans).

For human spaceflight, it's obviously a no-go. For satellites, it's not so obvious you lose "way too much" -- see tbfg for some papers regarding this.

See the BFG for an even better choice for propulsion -- saves accelerating all that propellant down the track before burning it -- even if you did end up needing maglev for stabilization/guidance in the tube. (They think it can be done aerodynamically, I'm not convinced.) But neither option is particularly attractive for SHLV work, since they don't scale well. Basically, after you build your proof-of-concept/commercial launcher for putting satellites in LEO, you have to build a whole new system for HLV capability, then another for SHLV; with rockets, OTOH, there's reasonable commonality of components between multiple HLVs over a factor of 10 or more payload.

Of course, long-term, we need truly cheap and high capacity LEO capacity, which IMO means partial-orbital-ring/launch-loop, but I think a rail launcher of some sort for light payloads with chemical HLV/SHLVs will be the best compromise until then.

No. Sorry to disappoint all the folks who just don't get it, but this is not going to be a railgun. As a software engineer, your confusion on this is certainly excusable -- after all, even SF and video games, by and large, seem determined to make sure nobody understands what a railgun is.

At present, railguns suck -- even the Navy's version (the only thing close to being productized) is anticipated to need rail replacement/rebuild every dozen shots or so at first, with the hope that they can improve on that once it's operational. That's entirely feasible for a weapon that fires what's essentially a metal slug (perhaps a few hundred or thousand dollars) with range, accuracy, and damage on par with a $500,000 cruise missile; the money saved more than allows for having a bunch of replacement rails (only a few feet long) on hand, and replacing them can be done fairly quickly. They suck, it's just that cruise missiles suck even more.

But on a miles-long track, replacing or refinishing the rails is an insanely slow and expensive undertaking -- not that it's completely infeasible (after all, rockets, short of SSTO, suck pretty hard too), but you'd have a hard time solidly beating rocket launch rates and costs, and with the enormous capital outlay to build the launch ramp, you've gotta be sure you can undercut the competition and make it back. No, the reason it's called "railgun-like" in TFT, and "an electrified track" in TFS, rather than simply a railgun, is because it's going to be a linear induction motor or similar (in fact, probably a LIM to get up to Mach ~2, then a scramjet the rest of the way), not a linear homopolar motor, or (as the LHM with a projectile-armature is commonly known) railgun.

Oh, and FWIW, another quite interesting launch-ramp concept is the BFG's ram accelerator concept -- IMHO the most promising of the various alternative-launch-schemes-with-websites (aka crazy bastards looking for VC). Highly recommended reading for alternative launch geeks, especially those with enough sense to realize they won't see a geosynch space elevator in their lifetime...

You mean The BFG? (Not a cannon, but if you knew more of what you were talking about, you wouldn't have said cannon anyway. Ram launchers are much cooler and more feasible, especially since they can go hypersonic, where cannon can only go sonic (WRT hot propellant gas or, for an LGG, whatever light gas you use).)

I make that 10,000 launches which over 30 years is nearly a launch a day. I was under the impression that rocket launches have a negative environmental impact not including the impact of actually building so many.

The obvious solution here is to build an orbital cannon. The biggest built and successfully used was in the 60s by the U.S. Navy to launch atmospheric probes up to 100 miles into the atmosphere. Building a 50-100m long gun up the side of a mountain(or even underground in a mine shaft or silo) isn't that technically hard. Estimates for the gun itself run about 200 million to build. The idea is to have each payload have its own small positioning rocket and external case. Drop the mirrors in the case and lob into space - the small engine moves it out to the proper position. Since we're talking just scattering the mirrors, there's nothing else required here - just position and open it up. Once a day is trivial. 10,000 launches would cost a mere 1-2 billion dollars. Even if it required 10x that many launches, with it firing off every couple of hours, it would be simple enough to accomplish. With ten of them, this could be done in just 3-5 years.

2-3 billion for an array of ten of these. Problem solved in a new years.

http://www.tbfg.org/
This is the latest company that is working on this. They will have a test-launch next year.