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Yeah, when you start applying space elevator class building materials to your rocket tankage, the usual assumptions simply don't apply. For example: with 65GPa tensile strength (the low end of the strength range Wikipedia gives for an elevator material) material for tankage, a 1000 psi tank filled with dense propellants (which, depending upon your models, might be better) has a mass ratio of somewhere over 1000. The exact number depends on your assumptions about anisotropic winding strength efficiency, but is probably around 1500 before you include a safety margin.

The helium to pressurize it with is actually the most problematic part -- but with that kind of tank mass ratio, it's not unreasonable to decide you're going to operate in blowdown mode (or regulated, but decaying to a lower final pressure) so that you have less helium mass at burnout. That lets you get the high initial chamber pressure (good atmospheric expansion ratio) without all the helium mass required to pressurize the entire tank. And using the ullage helium for the circularizing burn isn't hard (you could even include a peroxide monoprop heater and get a reasonable Isp out of it).

Which kind? The open-core, spewing radioactive gas into the atmosphere kind? Or, the closed-core, made of unobtainium that is transparent and physically stable at all temperatures even under the influence of heavy radiation.

There's at least one alternative that's at the same time highly efficient, being able to be throttled in a wide range of power, has all the radioactive material contained, and needs no exotic materials. It was called the "DUmbo" project (a rather dumb name, IMHO), a top-secret development started in 1958.

A Google search gave me this document, the best description I could find online, but the December 1975 Analog magazine has a good article by Donald Kingsbury called "Atomic Rockets" (page 38) with an excellent description of the basic principles involved, with simple but good calculations of the thermodynamic effects involved.

You are absolutely right.
Instead of using water as the propellant directly, have the water press against a piston that compresses hot hydrogen.
The seal issues have been addressed for the HARP gun:
http://www.dunnspace.com/harp.htm
http://www.astronautix.com/lvs/sharp.htm
http://www.astronautix.com/lvfam/gunnched.htm
http://en.wikipedia.org/wiki/Light_Gas_Gun

I don't know if heat buildup is more of an issue with a longer, lower G force tube.

Actually aren't most of our space launch vehicles essentially modified ICBMs? I mean, isn't that true of most space launch vehicles? Von Braun and all that?

I think the general idea, as discussed in documents like this one, is that the primary design goal with ICBMs was maximizing the ratio between payload weight and rocket weight/size. This is great for ICBMs, where you want to cram missiles into tiny places, but not so good for space launches, where you should ideally be maximizing the payload/cost ratio. However, since most modern rockets are direct descendants of ICBMs, the original design constraints are still present in their current design, and are arguably embedded in the rocket engineering culture.

Most people say that the solution is then to pursue things like space elevators and scramjets, but groups like SpaceX are trying to show that low-cost rockets can still be developed if one designs them from the beginning to maximize the payload/cost ratio.

Now the NASA has gotten into 'competition' maybe they could review some older 'decisions'.
Big Dumb Boosters over the shuttle?
EELV's over the shuttle?
EELV's over the CLV?

Moderators, read the motherfucking link before marking that as a Goodwin troll. The "LEO on the cheap" study uses the NAZI V2 program as a case study. Their program was sixty years ago . If you can't improve upon their efficiency, maybe you should study how they did things.

But before going down that path, the folks in India should listen to this guy http://www.dunnspace.com/home.html#Columns. Getting into orbit is fundamentally different than flying an aircraft, and this Arthur Schnitt fellow argues that the max performance route used in aircraft is too costly. He got this idea of Minimum Cost Design from the Thor-Agena launcher for the Corona-Discoverer spy satellite -- the Thor booster was a lot cheaper than the Agena upper stage on top -- that cost had little to do with size in rockets, and by building big rockets with cheap methods (the Big Dumb Booster), you could reduce the cost of space launch

The NAZIs did it why can't you dopes figure it out? The secret is to bang the rocks together guys!

IIRC some of the solid core nuclear thermal rocket designs were supposed to have good enough thrust to weight ratios to escape Earth's gravity under their own power (e.g. DUMBO).

Is this the report you're thinking of? DUMBO was indeed a paper design intended to show that the engines could be lighter and more powerful. Even so, I don't think the design was ever sufficient to reach orbit. Project Timberwind continued the work for the StarWars project and had a thrust to weight of 30:1. In comparison, the Space Shuttle Main Engines have a 73:1 thrust ratio and they still need assistance from the higher thrust SRBs. (The SRBs provide 71.4% of the Space Shuttle's thrust during liftoff, each providing 3,300,000 lbf vs. the 400,000 lbf each SSME generates.)

The only reliable way to overcome the thrust-to-weight problems that plague the NTR engines is to run the reactor so hot it melts the uranium fuel. As you can imagine, anything that can melt Uranium can melt most materials we have available. The solution to this problem is the Gas Core Nuclear Rocket which relies on the "nuclear lightbulb" concept to keep the reactor gasses from interacting with the walls of the engine. I've spoken with a former NASA Nuclear Propulsion engineer on the issue, however, and he's very concerned about whether the concept is feasible or not. It seems that there's a lot of research that still needs to be done on the subject. It's a wonderful dream, however. :-)

Besides those, you have nuclear pulse propulsion (e.g. Orion), which most definitively would have a good enough thrust to weight ratio.

I do believe we were talking about NTR engines, but Orion can certainly attain orbit. The only problem (which is also one of the reasons why the Orion was never built) is that the Nuclear Test Ban Treaty of 1963 made it illegal to launch an Orion from inside the atmosphere. This relegates it to being a space-only engine, and/or a useful craft for Moon or Mars launches.

NASA have needed a heavy lifter

Actually, I've heard about studies stating that the main driver for launch cost is neither the total payload nor the technology but the launch rate. That is, for the same payload weight, a light booster that flies a hundred times a year will probably be cheaper than a heavy lifter that flies only a few times a year. It doesn't really matter if they are expendable, reusable, cryogenic or whatever.

See for example this 1994 study ("This indicates a potential paradox in the commercial space transportation market. High flight rates appear to be necessary to reduce the price per flight. However, reduced prices per flight reduces the revenue per flight, and consequently the cash flow available for investment payback.") or A Rocket a Day Keeps the High Costs Away.

Sure, a lower payload capacity means more orbital assembly required, more modular systems, which will make them heavier. But they will be more versatile, possibly cheaper, and the lower launch cost will offset the added weight.

OTOH, developing a heavy lifter starts from the opposite premise: a launch has to be expensive, so their number has to be minimized, with more payload per launch. This makes low flight rate a self-fulfilling prophecy and almost calls for a high cost.

The funny thing is that NASA arbitrarily set the CEV weight at 25 tonnes, just above the LEO capability of the heaviest rocket currently available (Delta 4 Heavy). Almost as if they wanted to need a new launcher, which then could be developed from Shuttle parts, keeping the existing workforce with a job, maybe even the very same job...

One point the author makes is that it's almost worth launching a inert payload just to keep the pipeline and infrastrucucture running than it is to stop and restart the process. Imagine the kind of payloads that could be waiting on standby for a free launch -- oh wait, you CAN'T because this is by definition an enabling technology.

Get the damn bueracrats out of the picture.

The SSME is probably the most magnificent piece of high performance rocket engineering achieved by man to date. It pushes the limits of what is possible with chemical propulsion. But it achieves that high performance at the cost of incredible complexity, and a design that may be operational, but is certainly not operable (in the sense that it supports overall system operability). I would also dispute the assertion that the SSME is truly capable of "being reused". While it is true that pieces of the engine are flown more than once, an individual SSME is essentially completely disassembled after each flight, and then inspected and rebuilt. That is not what I would call real reuse: you might as well just build a new engine. Ok, the material costs might be a little higher, but you'd potentially save a bunch on having to do fatigue and wear checks on parts that have done a flight or two. A real reusable engine would support multiple flights before needing more than light maintenance, and tens-hundreds of flights before a complete teardown was needed.

This is one of the new technologies that we needed to develop, and without the Space Shuttle it would become unneccessary.

No, it really isn't a necessary technology. It provides performance at the expense of everything else. Good system design requires paying attention to aspects such as reliability, maintainability, operability, and cost, as well as performance. There are existing designs that could do more and better than the shuttle, and cost significantly less. Take a look at "LEO on the Cheap: Methods for Achieving Drastic Reductions In Space Launch Costs" by Lt Col Jack London for examples of some of these designs, as well as a good articulation of the root causes of high launch costs, and the principles and strategies for reducing those costs.

They only had to kill thirteen astronauts to come to the same conclusion!

Sounds like a viable justification for this plan! And additional side-effect is that we get a reasonably priced launch system out of the deal!!

How many times do we have to tell you?!!!
Big, dumb boosters for cargo.
Little, safe (99.999%) rockets for crew!

• Have seperate systems for Humans & Cargo - because it cost a lot more to make a man-rated system safe
• Build big, dumb cargo lifters. The Russians know how to do this. Build it like a ship, not like a missile.
• Privatize it - NASA specifies requirements, private companies contract to fill those requirements
• Standardize it. Specify a standard payload size, sell launches to anyone with : 1)$, 2)compatible (safe) payload.
• Prime the pump - buy a launch a week for five years (at ~$10e6 per launch, IIRC?) even if you're just launching dead weight and dropping it into the ocean. Let the market get established.
• ???
• PROFIT!

The Russians aren't as risk adverse as NASA. (Hell, they're less risk adverse than I am!)

As described in LEO on the Cheap, the Russians do have a more realistic and economical approach to spaceflight. That is, they build their rockets with shipyard-level technology, not ballistic missile-level technology. Big, heavy, tough and dumb vs light, high-performance and expensive.

On point made in "LEO ..." is to split your man rated (99.99% reliable) boosters from your cargo haulers (99% (95%?) reliable). Exactly NOT what NASA did when they designed the space camel, err... shuttle.

And for God's sake, have a plan with a definate goal, not "lets get everybody together and put on a show"!

Let NASA commercialize their cutting-edge stuff but for crissake get NASA out of the launching business. Let them deploy probes to other planets, study the Earth and environment, develop advanced interplanetary propulsion concepts, build space habitats, study space medicine - but don't let them anywhere near the drawing board of a launch vehicle. Ground to LEO transport should be off-limits for NASA.

Cargo launch vehicles don't need to be cutting edge. They don't need to be advanced - they need to be dumb, big, reliable andcheap. Crew space taxis need to be ultra-reliable, small and relatively cheap. NASA is apparently incapable of achieving any of these goals.

Subsidizing shuttle payloads has nearly killed the private space industry. Instead of competing with it with tax dollars NASA should promote it by buying launch services.

See this report by Lt. Col. John R. London III to find the historical reasons for the cost of launching and how it can be drastically reduced.