Thanks for your input.

"I think where the real problem lies is gbaikie's inability to format clearly, which probably makes the material more irritating than it otherwise might be."

I don't know what mean exactly by this, but perhaps it is related to what you say next:

" "Thinking online" is just the sort of thing you might do if you are looking for input or correction, and unlike some others, I don't recall gbaikie refusing to take correction or advice on his work."

This is absolutely the case as far as I'm concerned

"The tube launcher is an interesting concept, but I think at some point it hits the same wall as Verne's Columbiad. Literally. Hitting the atmosphere at any kind of high speed will be like smacking into a wall, although gbaikie's concept seems to be more of a "first stage," not an orbital system."

Not even first stage but more of a zero stage or kind of launch pad.

"I don't think construction of such a system is going to be that much easier than simply building a first stage, or air-launching, but I haven't done any numbers myself."

Oh I don't think a pipelauncher would be cheaper than a first stage- I believe I heard that Sea launch buys it's Zenit for about 2 million- and then it modifies for additional cost [but Zenit is more than first stage]. My contention would that a pipelauncher would cheaper to make than a launch pad- whether on land or in comparison to second hand oil rig used by Sea Launch [I believe they spent 25 million for oil rig before doing any modification- and Russia spends more 100 million per year to use their launch area. NASA has spent something like 200 million for a specific launch pad- and I know NASA has charged 4.5 million for one Delta launch [I think it was a Delta III]
I think it's possible to build a boilerplate type of Pipelauncher for 5 million or less. And by boilerplate I mean something build quickly and cheaply and would work for purpose of launching some rockets [say something in the range of less than 25 of them]. From that experience one could make improvements and have a pipelauncher which could launch hundreds of rockets. This pipelauncher could cost anywhere from say 5 to 300 million- depending on what's needed and what is learned.