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I would counter that the Russsian approach is why they beat us to orbit and to manned space flight and came distressingly close to beating us to the moon despite our enormous technological and engineering workforce head start and the fact that half of our country hadn't been bombed into rubble just a few years earlier.  The N-1(?) design was a poor one and crippled their space program.  However, aside from that blunder, we didn't surpass their space program until Apollo 8.  Also, bugetary constraints and the death of the head of the Russian space program (forget his name right now) also contributed to the decline of the Soviet space program.  Despite the loss of the moon, Russia went on to do some truly amazing work on Venus including the design of landers that could operate almost indefinately on the surface.

The Zenit launchers that Boeing uses for SeaLaunch are a perfect example of that philosophy.  They can be stored, fueled on their sides for transport and are just moronically simple.  I contrast that to the Arianne  which IIRC has never had a successful launch with the new first stage.  What gets me is that almost all of the rocket failures these days are due to software glitches.  Why do you need a million lines of code to point a gimbal mount?  We got to the moon with computers that would get the lunch money stolen from them by my watch.  The additional performance and capability given by all that software probably gives a minimal impact on the performance and has cost hundreds of millions due to lost reliability.

NASA has been a bit too tech happy for the last few decades.  If you read that microwave launcher proposal, there's a diagram of payload mass fractions for various different launchers.  Despite having an isp only ~75% of what modern launchers have, the Saturn V managed to deliver a payload mass fraction to orbit that was greater than what either the Titan or Shuttle can do.  An earth to LEO launcher needs to do one thing - get mass to orbit as cheaply as possible.  Reusability, efficiency, materials, and all that stuff are secondary to that objective.

I don't give modern materials credit precisely because I'm a materials engineer.   The shuttle reentry tiles went through a massive development program.  (some of which occurred in my department way back when)  They were supposed to work fine but have been nothing but problematic in use.  Therefore, I look at these grandiose claims of new materials and I take them with a BIG grain of salt.  There is areason that commercial airliners took 20 years to start using composite materials widely.  It's not because Boeing and Airbus are afraid of new ideas.  It's because composite materials come with severe reliability problems.  For a Rutan design where you aren't looking at tens of thousands of loading cycles and getting your mass to cargo ratio good as possible, composites weren't a problem.  For Boeing, it took a MASSIVE effort to get the stuff working properly.

Yes, the Shuttle was an experimental craft but it was designed to have a short turnaround time.  When I see things like estimates of the DC-X having a 24-hour turnaround, I get VERY dubious.  When we actually have a full-scale prototype that actually demonstrates that level of reliability, I'll believe it.

Incidentally, the DC-X is pretty close to the sort of approach I've been talking about.  No fancy lifting bodies, fairly non-revolutionary engines, no untried scramjets - just an ugly, squat cylinder that yoyos to space and back.  Personally, I'd like to see an estimate of the DC-X performance with a breakaway 1st stage.  Something made to be as cheap as possible and disposable.  I'd bet that you'd be able to get a significant performance increase.  As long as the disposable stage is fairly simple, it would probably lower the overall operational cost.  If the first stage is a a simple SRB, ther shouldn't be any reason that is should cost more than $1 million. 

Any time you use a part that's reusable, it means that you had to design it much more robustly so that it retains top operational performance even after a full launch cycle.  You have to then go through an extensive examination process to look for things like cracks and corrosion and fatigue.  In composite materials, this is much more difficult and prone to missing dangerous flaws.  The end result is heavier and ultimately less reliable that a disposable part. 

Here, you have to start doing cost benefit analysis.  If the cost of the disposable part exceeds the cost of inspection and occasional component replacement in the reusable part, then reusable is the way to go.  Otherwise, just trash the part.  Things like crew cabins and avionics and reentry systems are probably good examples of stuff that could be reused.  A metal can with solid rocket fuel in it is a good candidate for something that can just get tossed away.

Strict SSTO design is just like Mars In-situ propellant generation before Zubrin changed it.  They were so fixed upon living completely off the land that they concluded that it was impractical.  Zubrin simply decided to relax the rules and bring the hydrogen along. The result is a practical design.

If you are willing to drop the requirement for pure SSTO, I think that you will find that you can get much better performance for minimal additional cost.  That additional performance would have originally come from a larger, heavier design that, despite reusability, would have incurred higher maintainacne costs dues to the greater stresses on the materials involved.  My guess is the cost of a disposable stage is much less in the long run.

I am aware of the test to destruction they did with NERVA. (which incidentally sent a cloud of radioactive material right over LA) I'm referring to the routine testing.  If you go through the testing logs, you see that the vast majority of the testruns showed major engine deterioration and fissilbe material coming out in the run.  This is more than an enviromental issue, it implies that the engine is prone to failure.

Modern ceramics have gotten a bit better but not drastically so.  The big issue is that ceramics are inherently brittle and do not fail gracefully.  Since the material strength of a ceramic is largely determined by the microcracks and defects in the surcace, it is pretty much impossible to build a ceramic part that will fail reliably at a certain stress level.  The uncertainty forces you to engineer with absurd safety margins.  NTR's aren't impossible by any means but I am highly distrustful of them until we've managed to log at least several hundred hours of reliable operation from them.

The doubling of ISP is nothing to sneeze at but I think the question is just how much an actual decrease in actual launch cost you'll see.  Remember that much of the launch cost is due to manpower costs.  A standard rocket launch requires hundreds or thousands of people who tend to be expensive technicians and engineers.  Personally, I'm not certain why this is the case.  A commercial jet probably needs fewer than 20 people to complete a trip when you've averaged out all the air traffic controllers, baggage handlers  and fuel truck operators.  A rocket is much simpler  than a plane - why can't you just have an automated launch system? 

The Boeing SeaLaunch uses a conventional launcher but manages to get launch costs down tremendously by using a skeleton crew and a robust chemical launcher that is largely maintainance free. 

The problem with SSTO and NERVA is that we're going to sink billions into the development costs with a minimal return off of what we're doing now.  A modern chemical rocket gets something like 4-5% of it's mass to LEO.  Most of the SSTO designs right now realistically get 0-1% of their mass to orbit.  I don't know the figures for NERVA but I imagine that the mass fraction is more like 8-10%. 

To get launch costs down, we can do two things two things.

1: make the system as trouble free as possible so that you need a minimal number of people.  In this regard non-reusable rockets shine since you just throw away the parts.  When you analyze the costs of the rocket, the raw materials cost is fairly low.  The steel and H2/O2 aren't what make a launch cost so much - it's all the people on your payroll.  What worries me about an SSTO is that you will have the same refurbishing problems the Shuttle does now.  Heat protective tiles haven't improved substantially since the 70's unless you just use an ablative tile system which will have to be replaced with every trip.  (this actually is probably much cheaper than the reusable tile system we use now)  If each launch requires 3 months of 50 $200k a year technicians inspecting the spacecraft after every launch, you're spending $2.5 million a launch on your heat-resistant tiles alone. 

This doesn't include engine refurbishing, frame inspection or any of the other stuff.  IMO, our ability to create a reusable launcher system hasn't improved in a meaningful way since the 1970's.  The engines might have improved a bit but the rest of the system is still about the same.  The lack of an escape system isn't what bothers me about the Shuttle.  The apollo capsules had an escape system but I seriously doubt that it would have done the astronauts any good if the Saturn V had blown up under them.  My concern is that SSTO and reusable spacecraft have inherent reliability issues that outweigh any advantages gained from having a single stage.

Bringing the personnel costs down suggest that we use a simple design.  Lifting bodies are difficult to manufacture and to make replacement parts for.  The engineering costs go up enormously.  Repair and maintainance become more difficult.  The big metal tube design works well and and easy to manufacture. 

Keep the engine design simple.  Assuming that we can get NTR designs to work reliably, this is a big advantage - fewer moving parts. 

2: Bring the mass fraction of cargo up higher.  This is accomplished by higher ISP engines and NTRs are the best in this regard.  A possibility here is the use of microwave powered flight.  look here:
[http://monolith.caltech.edu/Papers/ParkinLauncher.pdf]http://monolith.caltech.edu/Papers/ParkinLauncher.pdf
It's basically a NERVA design that uses beamed microwaves instead of a nuclear reactor.  The microwave beaming technology is already possible.  I wouldn't want to have to pay the power bill though. :;): 

Ultimately, though these high ISP technologies are fairly technologically complicated.  They also tend to push materials science to the limit which is never a good idea.  NTR's and microwave beaming require thermal performance and reliability that I, frankly, find unrealistic.

SSTO's have the same problem.  In order to get your spacecraft weight to power rations good enough, your have to trim corners everywhere.  This is a guarantee for an unsafe and unreliable vehicle.  The mass fraction for an SSTO is pretty awful as well.  Plus, any technology that you can use on an SSTO such as scramjets, lifting bodies, advanced propellants, etc can be used on a disposable multistage rocket with better overall performance and lower cost.

Personally, I favor the KISS approach the Russians have taken.  Simple chemical rockets that are designed with ease of maintainance and high reliability instead of high performance like we tend to do.

The graph you mention is largely junk.  The 1GPa milestone is a cool one, it must have happened fairly recently so I missed it.  However, they are basing all those numbers off of one data point which is just moronic.  Furthermore, if you look at the lines, the lower one is the one that assumes that you use regular nanotubes and as you can see - it goes nowhere near the 100GPa requirement.  (also you really need 200GPa strength to ensure a good safety margin)  The upper line basically is a wild-guees extrapolation of doing chemical modifications to the nanotubes so that they will stick to the glue better.  HOWEVER, doing so puts defects in the nanotubes so that that they lose most of their strength.  That work will never make a rope of sufficient strength to build a safe space elevator. 

It's still cool work.  The resulting ropes will have all sorts of uses from better suspension bridges and stronger buildings to better bullet-proof vests.  However, it's just not good enough for space elevator work. 

Another problem with the space elvator that I didn't even touch on yet is space debris.  if one piece of space debris hits your hose, your whole system is broken.  And yes, space debris will but carbon nanotubes.  They may be tough but a bolt going 22,000 mph will go through those nanotubes like tissue paper.  You can't put shielding on the tube since it's barely strong enough to hold itself up.  Enough shielding to stop impacts would make the tube hundreds of times too heavy.  This is a problem that the regular space elevator faces as well.  However, for the space elevator, you have the advanntages of being able to use multiple ropes for redundancy and safety.  If one gets cut, you'll still have several others that are holding you up.

Basically, what you've designed is a variant of a space elevator.  The standard elevator has a nanotube cable that cargo cars run up and deliver cargo to geosynchronous orbit.  You basically have a hollow elevator that you are pumping liquid H2 through.  Therefore it is just as cheap to put the liquid H2 into a storage tank and have it crawl up a regular elevator.  The standard elevator is much safer and damage resistant and requires less new technology than your pipeline idea. 

I hate to be the voice of doom but your idea simply doen't work.  Even IF it ever becomes possible to make your pipeline, the same technology lets you make a regular space elevator and that is just as cheap and efficient as your pipeline.  Plus, it's safer and less trouble-prone.

It was a cool idea but most cool ideas just don't pan out when you start crunching the numbers.  I've had plenty of cool ideas and 95% of them just fall apart when I look at them more closely.  That's the unfortunate truth.  What you have to do in that case is quit beating the dead horse and start brainstorming new ideas.  Eventually, one of them will work. 

But that won't happen if you stay on the sinking ship and try and breath life into a dead idea.

GCNRevenger:  getting a 36,000 km column of liquid H2 is only feasible because liquid H2 only weighs about 7 kg per cubic meter.  If you tried to push water up the same column, the nanotube hose would burst long before you even got to LEO. 

The H2 should remain liquid even at above ambient temperatues at those pressures.  I'd expect that it would gassify at the top but the overall H2 flux would equal the pumping rate at the bottom.  The design would be cheaper in the long run becasue the energetics are equivalent to a space elevator but as mentioned above, you might as well carry the H2 up in tanks.

As for bend strength, the nanotubes are small enough that a 1 inch hose diameter might as well be flat as far as they're concerned.  You'd get horrible H2 leakage through the walls of the tube, though.  Also, the pressure involved might be enough to start getting spontaneous desaturation of the carbon bonds - basically the nanotubes would start spontaneously oxidizing the H2 and disintegrating.  And yes, assimuing the magic pump could even be built, I wouldn't want to be within 10 miles of it while it's running.  Forget flammability, a pinhole leak would have so much pressure that it would cut a building in half.

Thanks for the input.  I deliberately didn't comment about what I thought about the practicality of the various technologies since I didn't want to bias the discussion from the start. 

I agree that chemical still seems to be the way to go.

NTR rockets are nice but the overall performance gain isn't THAT spectacular and the danger of radionucleotide release is significant.  What most people forget to mention about the 60's NERVA tests is that all but the last two tests had significant amounts of engine breakup and radioactives release.  When I mean radioactives release, I mean chunks of Uranium oxides flying out of the back of the rocket - seriously.  Even with newer ceramics, I seriously doubt the ability of an engine to reliably maintain integrity with the hign temperatures, thermal gradient induced thermal shock, vibrations and action of high temperature hydrogen.  As for high altitide release, I'm almost more comfortable about doing it near the ground where the radioactivity may be more concentrated but at least it's localized. 

The whole space elevator business is a potential cool idea but relies upon the fact that we can actually build the damn thing.  Having worked with carbon nanotubes before, I am dubious about the chances of this happening.

Air breathing engines do help, especially ones that can operate hypersonically.  However, that only gives you a discount on oxidizer for the first 100,000 feet or so.  I suppose that if you try to maximize your acceleration in that part of the ascent, you might be able to eek some extra mileage out of the atmospheric O2 but you've still got to gain most of your delta V on your own oxidizer.  Plus, now you've got to lug this engine around if you're going for an SSTO design. 

Personally, SSTO designs are distasteful to me.  The whole idea of a reusable spaceship just reminds me too much of the Shuttle.  I'm afraid that we'll get another 'reusable' spacecraft that needs major reconstruction with every flight and is a disaster from a performance and safety standpoint. 

The maglev rail system has the same flaws - you do cut down on fuel by getting that initial boost but it's really a small part of the total energy requirements to get to LEO.  Every little bit helps, though.

Potentially, the microwave/laser assisted systems are very promising but I'm dubious about the ability to pump that much coherent energy through a laser.  As it is, these giant, military megawatt lasers can send a spaceship the size of your hand to about 200 ft.  I mean, I can do that with a slingshot.  Lasers don't scale up very well so I think that lightcraft are going to be impractical.  Using microwaves might work better as phased array microwave emitters do scale up fairly well and can have stupidly large power outputs.   I have no idea what sort of progress is being made on this front, though.

I'm just wondering if it would be possible to run some rough numbers for the various advantages of these systems vs the investment costs of building the infrastructures involved.  For example, if one were to build a maglev going up the side of Killiminjaro (sp?) that gets the rocket to mach 1 at 20,000 feet, kicks on some air-breathing engines that fall off at 100,000 geet and mach 6 before engaging an NTR upper stage, just how much performance increase would we see.  Would it actually be enough to justify the investment in R&D and infrastructure for these technologies?

There seems to be quite a bit of innovation going on lately with regards to interplanetary drive systems.  However, it seems as if the ground to LEO launch systems are still purely chemical in nature.  I wanted to start up a discussion about whether we're at the point where we can start talking about alternatives to chemical propulsion in the next 20 years to get cargo to LEO.

If possible, I'd like to try and actually crunch numbers.  It's easy to wave hands and talk about how such and such launch technology will make getting to LEO so cheap that everyone will move up there because of the lower housing prices up there but another thing entirely to actually prove it.

Aside from chemical propulsion, I see the following as potential alternatives/augmentations:

space elevator
rail/maglev assisted launch
air-breathing engines for 1st stage
Nuclear thermal rockets
laser/microwave assisted launches

Have I missed any?

Using an ionized gas inside a carbon nanotube will not work.  The ionization energy of Hydrogen is over 1.3 keV.  This is an energy level that is orders of magnitude greater than the C-C bond energy of the carbon atoms in the nanotube.  What will happen is your ionized hydrogen will strip electrons off of the carbon atoms and destroy your nanotube.  Basically, the ionized hydrogen will burn your nanotubes up.  And no, before you ask, there is NO way to prevent this.

FYI, the numbers you are giving arent kPa(kilopascals), those numbers should be GPa(gigapascals).  An object within the kilopascal tensile strength range is about as strong as a rubber band.  The 600 GPa figure is a purely theoretical one which has little basis in reality.  The 120-150 GPa figure comes from measurements of isolated flaw-free single walled nanotubes that whose stiffness was measured by measuring their vibration harmonics.  These tubes are difficult to make and have never been made more than a few microns in length.  The bulk nanotubes that are used for most fabrication are multi-walled nanotubes that have MUCH lower strength.  Furthermore, the cables that have been made are a bunch of nanotubes that are basically glued together.  The best figures I've seen for these are in the range of 100 MPa - 6000 times weaker than what is required for a space elevator.  There is no such thing as a long carbon nanotube and it is highly unlikely that there ever will be - these cables are basically the equivalent of a bunch o tiny nanotube fiber lint that's been glued together - your hydrogen will be lucky to make it a single millimeter before it just gets stuck in the glue.

Tensile strength is a material's strength in *tension* not compression.  A rope has high tensile strength but if you try to push a rope up into the sky, you won't get very far.  A nanotube 'rope' would be less floppy than a regular rope but you'd be lucky to get it 20 feet off the ground before it just flopped over. 

Additionally, solar cells, although having gotten cheaper in the last few decades are still a very expensive method of energy generation.  Even the best solar cells are still twice as expensive as regular fossil fuel power because of the high cost of the panels.  Plus, the kinds of power you are talking about would require a solar cell array the size of a city.  Remember that at noon at the equator on a cloudless day, you are pulling about 1500 watts/square meter in solar power.  The best commercial solar cells only get about 12% efficiency.  Therefore, you get about 180 watts per square meter.  At current market prices, the solar cells for 100 MW of power are going to cost you over $200 million.  Projected improvements over the next decade might bring that number down to $75 million but you get the idea - solar power is by no means free.

I'm familiar with the new solar/wind generation method you mention.  The problem is that noone's ever built one of these.  Furthermore, the complexity of making a mile high concrete tube is not simple.  Don't count on that technology until you actually see a working model.

Uh, no - 9.8 m/s^2 is the acceleration due to gravity at sea level.  If that were the excape velocity, the average person would be able to throw a baseball into orbit.

I also don't know the escape velocity off the top of my head but I want to say that escape velocity is something like 11-12 km/s.