Panacea

Combustion rockets, not chemical rockets.

Suggesting that Isp doesn't in any meaningful way correlate with cost is utter and complete poppycock, Rand, and I suspect you actually know it. Every element of the rocket equation affects cost. Isp is a poor variable to judge launchers on anyway, which is probably why they didn't do it. That's your strawman, not theirs.

Even the two factors that you mention matter -"fly a lot and don't throw the vehicle away" are directly correlated to cost of design. In fact, the cost of designing to those two standards is so challenging that NO ONE has been able to do it yet; shuttle does it only partially, and expensively--but no one else does it at all, not even partially. Besides, getting to space isn't the hard part--we've been doing that since the fifties. The hard part of an RLV is bringing everything back.

While there's a negative correlation with cost between 320s and 420s (ker-LOX to LH-L2), what you're omitting from the Orion story is that a reliable launcher with an an Isp > 1500s would allow you to pretty much forget about TPS, since you wouldn't have to take off your orbital speed with a clunky, heavy, one-way component that takes up a huge chunk of your available dry mass. More to the point, you could drastically increase your drymass and still reach orbit, a bonus that allows you to increase structural rigidity, etc. Unfortunately, anything above 500s Isp requires non-chemical rockets. so chemical rockets leaves you 2 orders of magnitude below where you'd need to be.

I say all this knowing Nuke-to-orbit is a non-starter politically. But chemical rockets

One wonders if the writer has "target fixation" with nuclear pulse rockets or just does not understand the process of launch vehicle design.

Personally, I don't think that nuclear pulse rockets will be used in space exploration. I fully expect some of the more esoteric plasma systems to yield real high performance engines for "in space" use. I would like to extrapolate the argument for plasma systems to launching from the surface of the Earth but I cannot make it work at the moment.

So, for the forseeable future we will haves to use chemical propellants to launch from the Earth to LEO. We know how to do this quite well. The design of a launch vehicle is an exercise in compromise. Isp is just one part of the problem; but I guess if you're wed to just one thing and know nothing else then you pick on what you think may be a problem!

Suggesting that Isp doesn't in any meaningful way correlate with cost is utter and complete poppycock, Rand, and I suspect you actually know it. Every element of the rocket equation affects cost.

I didn't say that it doesn't affect cost. I said it doesn't correlate with it. That is, there is no equation, either theoretical or empirical, that goes "higher Isp" = "lower (or higher) cost." Technical design issues are a second-order term in driving launch costs. Scale of operations are a first-order term.

Hmmm.

This is way off the reservation for me but I'm curious:

What about ground based electromagnetic coil acceleration systems?

Make it big enough to handle spaceworthy capsules that can take a standard shipping container. Build it as long as necessary to maintain a 3g-4g acceleration rate and power it with a nuclear power plant.

Wouldn't that work? Even if it cost $50 billion wouldn't that be a drop in the bucket compared to what we're prepared to spend just to boost mass for every other project?

I'm not a rocket scientist, but I am an economist (among other things) and I'm used to using big numbers and looking at scaling things like business models, networks, etc.

Perhaps I used specific impulse inappropriately, but I still think I'm correct about nuclear (or some derivative: fusion, anti-mater, whatever) being the only thing that has enough energy density to get a lot of mass into orbit and beyond. I'm not talking about putting a few people into orbit, after all chemical propellants are fine for that.

I'm talking about the billions of tons of mass that are going to have to be lifted out of a gravity well if we're ever going to have any kind of meaningful human presence in space. I'm not considering cost either for that matter. At a certain point a chemical rocket, no matter how energy dense the fuel, will reach what I would call declining and even negative marginal returns when it comes to increasing payload size per launch. I know I'm not expressing this idea in the proper terminology, but you probably know what I mean.

Is there any other type of propulsion that could even theoretically lift a few million payload tons into orbit at one time?

Technical design issues are a second-order term in driving launch costs. Scale of operations are a first-order term.

incorrect. For current & forseeable space launch markets, amortization of development cost is a magnitude of order above "scale of operations," or operational cost.

i.e. Amortization of development cost is a first-order term. Technical design issues are a first-order term in driving development cost. Operational cost is a third-order driver in development cost and, barring a drastically larger market (by 100-1000 times current levels), a second or third-order driver in actual launch costs.

SpaceX's pricing, for example, although *pricing* and not *costing*, reflects this reality very closely.

I should add that the market size matters because, with chemical rockets, there is no near term development that can occur to drastically change the market, at least within our lifetime.

This sad fact follows from understanding that there is actually only a very small technical delta between low-performance and high-performance orbital launch vehicles: they are ALL very difficult to build and make reliable, much less reusable.

Alan's proposal, then is to stop building rockets and start building spaceships. Yes, you really do need to build an SSTO to build a spaceship. Unfortunately, chemical SSTOs are literally impossible to build (adequate reliability, safety, cargo, etc) with current materials and available levels of development funding.

Using Isp to compare fuels makes the assumption that all the supporting hardware, pumps, tanks, etc are the same. They clearly aren't when some of the fuels require cryogenic storage.

One way to compare fuels is to see what delta-v they produce on their own mass and their hardware without a payload. A fuel that comes out well in this comparison is hydrogen peroxide/JP4.

NASA will never develop a spacecraft that operates like a airliner. To do so would require them to do away with thousands of ground support personal and no government agency will reduce their workforce.

Ah, the thorny problem of the first hundred miles strikes again.

Rockets of any sort are not the optimum solution, unless someone manages to turn a Polywell proton/B11 reactor into a rocket engine with a thrust/weight ratio well over 1. This may or may not be possible, but it certainly isn't going to happen soon. (I specified proton/B11 because large numbers of neutrons and/or radioactive fallout are an unacceptable cost of operations in atmosphere.)

However, there are other ideas floating around, and one or more of them may work. An electromagnetic accelerator at ground level will not work - the payload would melt and possibly vapourise. Air-breathing engines for the first couple of hundred thousand feet and first 10,000MPH may help, by economising on propellant weight. Balloon launch for the first 100,000 feet or so might help.

One rather eccentric idea that I have seen somewhere is an EM accelerator - but thirty miles up. The idea is basically that the launch system is suspended from really big aerostats, and the payload is got to the "breech" end of it by any of a number of methods - lighter than air being the most likely to work, perhaps.

That high up, weather is not really a problem; and neither is excessive frictional heating at launch velocities.

Then there are laser launch systems. But if we can possibly get it built (and carbon nanotubes make it at least conceivable) then the best route to space, in the long term, is a Beanstalk.

For space operations, at least with large payloads, the engines really have to be some sort of nuke. For smaller loads, perhaps some sort of mass-driver engine would work.

i.e. Amortization of development cost is a first-order term.

Of course it is. That's my point. You have to have a high flight rate to amortize your fixed costs.

If you don't have a high level of activity, it doesn't matter what the design is--it will he horrifically expensive (as it currently is). If you do have a high level of activity, there are many designs that will work. That's why it is the first-order effect, and others are second order.

Air-breathing engines for the first couple of hundred thousand feet and first 10,000MPH may help, by economising on propellant weight. Balloon launch for the first 100,000 feet or so might help.

No, they won't. Rockets are just fine, as long as we operate them at a high rate.

"Rockets are just fine, as long as we operate them at a high rate."

Fine for what purpose, weekend getaways to LEO?

I'm talking about what's going to be required to have a permanent human presence in space. Thousands of people if not millions.

I'm still looking for an explanation of how chemical rockets are going to get millions of tons of mass off earth.

The Saturn V only put 50 tons into Lunar orbit. But to build even one large habitat in space we'd need thousands of Saturn V equivalents. Sure, that's a high rate, but it's also ridiculous. The same applies to putting people on other planets.

Say you want to colonize Mars. How are chemical rockets going to move thousands (or even millions) of people to Mars when the best we can do with rockets is five or six to LEO?.

I don't think you can realistically operate enough chemical rockets at a high enough rate to make that possible.

I suspect that if it could be done the Russians and/or Chinese (who have fewer issues with pollution) would have launched a test Orion by now. I imagine the two could dominate space rather quickly.

I'm also amazed the North Koreans (or someone else) hasn't made such a claim to justify their own nuclear efforts.

Fine for what purpose, weekend getaways to LEO?

Sure. Whatever works.

The Saturn V only put 50 tons into Lunar orbit. But to build even one large habitat in space we'd need thousands of Saturn V equivalents.

I already said that you don't throw the hardware away, so obviously I'm not proposing Saturn V equivalents. Low-cost rockets will take off from spaceports, on a daily or hourly basis, just as aircraft take off from airports.

In any event, the purpose of getting low-cost launch is to enable the use of extraterrestrial materials for energy and construction--it's silly to think that we'll launch space habitats from the earth, at any launch cost.

Existing chemical rockets are just fine for the existing marketplace. But to get *me* into space, it will have to use a system that operates like an airline. I.E. the turnaround times must be in the 24 hour range, zero hardware can be thrown away, allowing millions of people to travel into space in order to amortize the development costs.

Even if you could build a vertical takeoff chemical rocket that was 100% reusable, the monkey motion of flying it, recovering it, inspecting it, and hoisting it back to a vertical launcher just won't be done in 24 hours. Weeks, more likely.

The only option I see that can do the requirements are horizontal takeoff/landing air breathing two stage systems. Yeah, it's a bit of a pain to join the vehicles, but it can be done in a short time if the vehicles are built right.

The Air Force did a study several years ago that developed charts showing fuel costs and weight into orbit performance for air breathing first stages. If you can get the first stage into the Mach III range (within the performance of a 1960's XB-70 bomber), then the concept begins to pay off. Although a genuine orbital system would have to be much bigger and first stage faster.

If you can get the first stage to Mach 10, and air breathing aircraft have done this, then it gets to be pretty easy. The air breathing vehicle ends it's boost with a zoom past 100k feet before the rocket stage ever ignites, eliminating aerodynamic drag and maximizing the use of the atmosphere as a component of the thrust.

Assuming the second stage delivers my backside to an space station of some sort, it returns and flies again in the 24 hour window. The first stage might be turned around even faster to boost a different second stage.

The X-20 Dyna Soar program in the early 60's is remembered as being boosted on the top of a Titan III. But the reality is that it was a successor to the X-15, and would have first been launched on a B-52, and then a B-70 at supersonic speeds. This could easily have been the rumored "BlackStar" that Aviation Week believes flew in the 90's. Had the Air Force continued that program in the early 60's, and continued development beyond it, instead of using that time to make a moon landing stunt, I feel confident that I would have already spent a week or two on vacation in LEO.

Vertical throw away rockets are the perfect solution for companies offering occasional high priced satellite launches, and for keeping the monopoly a government bureaucracy has in the human space flight business. Both these entities have a huge vested interest in making sure a low cost, high turn around orbital system never gets built. That they will say and do anything to prevent such a system from existing is obvious.

Obviously there are a lot of people who are smarter than me that have given this a lot of thought.

That said, there's a world of difference between putting a few tons into LEO and getting to the point where millions or even billions of people are living somewhere besides Earth.

I still don't think chemical rockets can scale enough to make that possible.

That said, there's a world of difference between putting a few tons into LEO and getting to the point where millions or even billions of people are living somewhere besides Earth.

I still don't think chemical rockets can scale enough to make that possible.

Of course they can (though that's not necessarily a desirable goal--most likely most people living off planet will have been born there, not exported from earth). Take just two or three major airports, such as Hartsfield, DFW and O'Hare. They move hundreds of millions of people per year. There is no technical or economic reason that space transports couldn't operate at the same scale. The amount of energy it takes to get to orbit is similar to the amount needed for a transpacific flight. The difference is power, not energy, because the energy has to be expended much more quickly for the rocket.

It is not a problem of Isp, or "energy density." It is simply a problem of not having invested in the infrastructure. Rockets will work just fine, once we decide as a society that space is important. To date we have not made that decision.

I think it is obvious that the solution is to use the limited lift capabilit we have to get seed equipment up, then use that to develop infrastucture, and following that, industry, and with that, a culture. There currently isn't remotely near enough economic pressure on earth to motivate development of the massive earth based launch capability mentioned in the above posts, but perhaps enough to get the starts out of the gravity well that all of us would like see. With a little foresight and planning these starts would build the rest. Like compound interest, the beginning would appear to move very slowly, but would gain and build powerful momentum until it is independent of earth completely.

A couple of thoughts: I suspect serious space colonization will proceed only when we have off earth resource and manufacturing capacity. The moon, with 1/8 the gravity well of Earth, is a place to start.

Second, if the massive stuff is made on the moon - likely robotically - then the payloads from earth can be high value, low weight and chemical rockets will work fine.

Most importantly, so far as is possible, nothing which leaves Earth's gravity well should be allowed to return. Better to end a satellites' useful life by firing it to a Legrange point or even crashing it on the moon for later recovery.

Finally, it is vital that we think of the conquest of space as both urgent and lengthy. It may well take another 100 years to have a really viable colony on the moon. But we should be planning that right now.

Cheap spaceflight DOES depend on ISP because it determines what you have to build. Assume: you want a spacecraft that's SSTO (operationally simple), reusable (to save money), non-exotic fuelled (say kerosene/LOX - Isp~260 seconds).

The rocket equation is:
Initial-Mass = Final-Mass * exp( delta-V / (g * Isp)).

Mass fraction (mass of fuel / total takeoff weight) = 1-Initial-Mass/Final-Mass = 1-exp( - delta-V / (g*Isp))

Ignoring atmospheric drag and gravity losses, delta-V to LEO is about 8000 m/s. Plug in the numbers and your mass fraction is 0.95. So your kerosene/LOX spaceplane, sitting on the runway for takeoff, has to be 95% fuel&oxidizer by weight. That's really hard to achieve.

What aircraft are comparable? A Boeing 747-400ER, no payload, max fuel load? About 51% fuel by weight. KC-10A tanker, fully loaded with fuel? About 60% fuel by weight. Rutan Voyager? About 77% fuel by weight. Remember how wobbly and fragile that looked at takeoff? And you need to build something to get into orbit, and reenter and fly to a landing, and carry a useful payload, with far less structure than that. I don't think you can do it, or if you can it will be VERY expensive and VERY fragile.

What if you go to LH/LOX with and ISP about 450? Now your mass fraction is down to 83%. At least you're in the same ballpark as an existing vehicle (Voyager) although this is still not going to be very practical.

What if you can achieve nuclear propulsion with an ISP around 1500? Now you're talking. Mass fraction is down to 41% so you can build something beefier than a 747, include structures and components for take-off, re-entry and landing, still get into orbit with a single stage.

So, yes, ISP does matter very much.

Your analysis applies only to single-stage vehicles. That's why staging was invented.

I never said that Isp doesn't matter. I said that it doesn't correlate to cost. Obviously, all things being equal, higher Isp is better than lower. But all things are never equal.

Well, you said that "It is not a problem of Isp". I think it is.

Obviously, staging improves performance or we'd never have got into orbit. But, as I think you'll agree, it would be great to have spaceplanes launching from runways, landing on runways, being refuelled and reloaded and taking off on a short cycle. In my book, that's single stage, and it can't be done with kerosene/LOX range Isp, and probably can't be done with a LH/LOX range Isp.

...it would be great to have spaceplanes launching from runways, landing on runways, being refuelled and reloaded and taking off on a short cycle.

No doubt it would be great. But it's not necessary to have that to do a lot better than we are now. A fully-reusable two-stage rocket could be very cost effective, at a high flight rate. You can't draw any useful conclusions about the potential for chemical rockets from history.

A fully-reusable two-stage rocket might be cost effective and have a high flight rate. Any idea how to build one?

The original space shuttle design was supposed to be like that but they couldn't figure out a way to make it work, which is why we have the kludge we do now.

The Rutan SpaceShipOne/White Knight combo is kind of like that (as was the B-52/X-15) but although they reach the altitude of space they don't get close to orbital speed.

Pegasus looks like one, but of course the rocket itself is a 3-stage non-reusable one, and the launch aircraft is more of a mobile launch platform and doesn't contribute much to altitude or velocity.

It's a tough problem. Let's hear some brilliance.

Any idea how to build one?

A lot of people have ideas how to build one. They haven't been funded, to date. But they'll likely evolve out of suborbital systems.

The original space shuttle design was supposed to be like that but they couldn't figure out a way to make it work, which is why we have the kludge we do now.

No, the Shuttle was a failure because it was overspecified (payload way too big, with a thousand miles cross range, and too many requirements that it be a space station as well as a space transport), and didn't get the development budget it would have needed. Very few useful conclusions can be drawn from the Shuttle about future reusable space transports. The only useful conclusion we can draw is to not allow the government to develop a launch system, if you want it to be cost effective.

Let's hear some brilliance.

Lack of "brilliance" is not the problem. Lack of funding and market is. Those problems are being addressed, by the private sector and (perhaps) the Air Force. But not by NASA.

Well, I'm 100% with you that the government shouldn't be the ones building launch systems.

"A lot of people have ideas of how to build one" - examples?

...examples?

You probably wouldn't have heard of most of them.

> While nuclear-pulse propulsion may be an interesting technology for in-space transportation, where the radiation level is pretty high to start with, it was never going to be used for earth-to-orbit transportation. One does not have to be a luddite to believe this. I'm all in favor of getting access to orbit as low cost as possible, as soon as possible, but I think that the notion of using Orion for this is nuts ...

I think it would be ok to use an Orion type for Earth to Orbit once. Get a huge load of useful stuff up there and use it (and the spacecraft) to set up a colony and start mining so you can make more spaceships without needing to get more huge loads of stuff from earth.

2 obvious problems. First, fallout. I think the estimate in the 60s was that there might be 10 (working from memory - I might be WAY off) extra cancer fatalities from the fallout. On the other hand, there would be many deaths from all sorts of accidents from launching 100s of rockets instead of one Orion. (both accidents during the launch and those involved in building the rockets, mining the materials and so forth).

Second, reliability. That Earth to Orbit Orion launch has to work the FIRST time and it's hard to see how you're going to test the entire system before. Wow. Super complicated mechanical bomb throwers and it's gotta work the first time. Very exciting. Maybe too exciting.

Try me.

Are you thinking of something like Skylon? Can they get those combined cycle engines to work? If they can, then their Isp for the airbreathing part goes off the scale, which might make it possible (back to my point about the importance of Isp). But it looks very challenging with a lot of unproven technology.

Planetspace Silver Dart? Is the booster reusable as well as the hypersonic glider?

SpaceX Falcon? Basically a two-stage standard rocket, but they're trying to return the stages via parachute for re-use. That's still got to really affect the operational pace if they need to be refurbished and reassembled (see Shuttle SRBs).

I'm not saying these aren't worth pursuing (and putting development money into) but they don't (with the exception of Skylon, if that can be made to work) really fit the bill of what we were talking about.

Any others I should hear about?

No, I wasn't thinking of airbreathers. As I said, they're all unfunded, and you've probably not heard of them. I don't really have time for a tutorial, sorry.

The point is that no one knows what the right answer is, and we won't until we try a few things and let the market sort it out.

They could do Orion in the 50's, but they can't do it today? Interesting.

Radiation and EMP can be mitigated. The real issue is who's going to provide a sufficient supply of nukes to do the job?

I agree it's not going to happen... unless some funny looking elephants arrive to be our masters...

http://www.amazon.com/Footfall-Larry-Niven/dp/0345323440?tag=particculturf-20

Here's hoping SpaceX's 3rd is a success.

They could do Orion in the 50's, but they can't do it today? Interesting.

They didn't do Orion in the 50s. Or the 60s. And, if they had gone ahead and tried, I am pretty sure they still wouldn't have ended up making it work. A number of complicated technologies were needed, technologies that would have been difficult to meaningfully test in isolation or at smaller scale. Grief is the overwhelmingly most likely outcome, optimistic paper engineering notwithstanding.

Like Rand, I think Orion, if it is ever developed at all, will only come when the development and testing can be done in space. You can static test an Orion at full scale in space. You can't on Earth.

Mr. Simberg, I don't think anyone is asking for a tutorial when they request names of systems you offer up to show that "a lot of people have ideas of how to build one." System and designer names would be just fine, even if we plebs haven't heard of them yet. I'm curious as well, and I'm willing to do my own tutorial if you'll give a name or three.

System and designer names would be just fine, even if we plebs haven't heard of them yet.

The systems I'm talking about, in general, don't have "names." They are concepts that have been kicked around for years, by many people, at many companies, but have never been funded. I'm sorry, but I do not have the time to sit down and research back papers, and plumb my memory, to write a history, unless you're an interested investor and want to compensate me for it. But now that the market is finally starting to work in space transportation, many new things will be tried. My only point is that there are many promising rocket concepts, and that we don't need to do nukes in the atmosphere to get into space in an affordable and large-scale way.

>>John wrote:
Mr. Simberg, I don't think anyone is asking for a tutorial when they request names of systems you offer up to show that "a lot of people have ideas of how to build one." System and designer names would be just fine, even if we plebs haven't heard of them yet. I'm curious as well, and I'm willing to do my own tutorial if you'll give a name or three.

July 20, 2008 7:58 PM

You might check out Len Cormier, Economics of X Van. It is quite informative. Selenian Boondocks (blog) has a good series on launch methods.

Watch your assumptions. New York City could not have been built with imports by Spanish galleons. The Empire State building alone would have bankrupted Europe if that was the requirement.

There are thousands to millions of articles on the web of varying quality. You must have a functioning BS detector to wade through on your own. Any time you read one, you must consider the slant of the party writing it. Many are so heavily biased as to be useless. Orion papers will normally assume that it is necessary to get massive cargos to orbit at one shot. Govt cheerleaders will focus on convincing the president/congress/voters to fund pet ideas. Most will use baseline assumptions that rule out as many competing methods as possible.

My slant is commercial. Don't give subsidies in any form to anyone. Let the markets decide. If no is the answer, I can live with that until no is not the answer. I don't believe in top down decisions and operation for the whole industry. Armadillo, Masten, and XCOR are my favorite start ups with friends in all three. One or more of them will fail. That is business. If there is a better way, all of them might fail. That is also business. Just don't use an arbitrary baseline that rules out new (or old) methods.

John (not John Hare, great post by the way) it's easier the other way around, what has been used so far to get to orbit?

Surface launches staging nonreusable and nonrecoverable one-time-only chemical rockets, solid, liquid, hybrid, etc. and all exclusively using fairly conservative bell nozzles. The exceptions can be counted on two fingers (the Space Shuttles and Pegasus) and are only partial exceptions.

That's all, there's a lot of unexplored or only partially explored ideas and approaches.

Purely as an example of how much hasn't been thoroughly looked at the first launch of an annular aerospike engine in the US was not done by NASA but by a student group working under an independent company-university partnership and they did it in this century (a few years later NASA played catch-up together with the DoD). Now maybe annular aerospikes are a dead end (and for sure it's not a silver bullet) but even so the point remains and you can only get real data by doing it. No aerospike design, annular or linear, has been used all the way to orbit to validate the theoretical difference to bell nozzles.

That's an example of a single possible tweak that might be incorporated into existing and imagined launch systems/vehicles and one that has been somewhat commonly/publicly known about for a long period of time. There are plenty more.

One of the areas about rocket launching that has been toyed with is to come up with alternatives to a traditional ground-launch system. I'll admit that this is hinted above, but not the fundamental issue involved.

An embarrassingly large amount of fuel is usually spent for any rocket system just to clear the tower. Some of that is engine start-up, when the engine isn't working at an efficient level and often with the rocket "being held down" to get the engines going. A great deal of that has to do with simply trying to get the whole thing accelerated to any reasonable degree. Furthermore, engines designed for use in space have very different characteristics and design issues than operating at sea-level pressures... giving further design compromises that negatively impact performance. Keep in mind that the tanks and the vehicle infrastructure must be there to deal with this fuel even though it is used mainly on the ground. I should note this is just as true for the Space Shuttle as it is for an Estes rocket, and is hard physics.

None of this is new, and indeed some "alternative" approaches have been created to deal with this "clearing the tower" issue. Spaceship 2, designed by Scaled Composites, is going to fly the tower at between 40k and 60k feet and flying at about 500 mph, which certainly is an interesting solution to this problem. Railguns and other more bizzare solutions attempt to address this problem by giving the rocket a huge boost and an initial velocity vector even before the engines start up.

All of this said, I think the conjecture you are making here, Rand, is that mass production of rocketry is the key to reducing the costs and not necessarily dealing with exotic systems that try crazy schemes to get the vehicles up. Again going back the the Estes rockets, that is one launch system that is in mass production... so much so that you can go down to your local Wal-Mart and pick up not just the rocket but a complete launch system for the price to feed a large family a Thanksgiving dinner (actually, a bit less I might note).

I'm not suggesting you will be able to purchase a Falcon 9 at Wal-Mart (other than the Estes model kit of one) but mass production is something that could make a huge difference. The real question there is: who is going to use a mass-produced and presumably manned rocket system?

No, not mass production (though that would be nice, too). Mass operation. Don't throw the vehicles away.

Rand is totally right here (as almost always when it comes to rockets). Cheers!

Many of the people writing the comments have such a huge number of incorrect assumptions that the questions posed are not really well founded.

I am pretty sure they still wouldn't have ended up making [Orion] work.

Good grief! There NEVER was a question of whether it would work. They made a scale model using conventional explosives work. It is HARDER to make the scale model work than it was to make the real thing. The more massive you make it the WIDER the tolerances. The project stopped for other reasons.

Too bad, because if you can take a thousand people up with a single craft a lot of them would be regular people (engineers, technicians, hands-on workers) instead of a few elite chosen ones. You could take an entire factory to the belt and really start cranking out product.

That doesn't mean chemical rockets can't get us from here to there and I expect they will.

The systems I'm talking about, in general, don't have "names." They are concepts that have been kicked around for years, by many people, at many companies, but have never been funded. I'm sorry, but I do not have the time to sit down and research back papers, and plumb my memory, to write a history

Would it be asking too much for a 30 second brain dump of common names for these concepts? That's all I wanted, not a history, not a research project, not a series of blog posts, and not a tutorial. I'm sorry that I was unable to communicate this in a simple way. I just wanted to understand what you were thinking of when you mentioned a lot of people had ideas. I can do research myself, but a quick concept list from a very knowledgeable person would be worth quite a bit. And if it is too much, well, thanks for all the stuff you already write about here.

Would it be asking too much for a 30 second brain dump of common names for these concepts?

Yes, sorry. There is no such thing as "common names" for them. The best I could do is describe them, but I can't do that in thirty seconds. It really would require expenditure of brainpower. As John Hare suggested, go over to Selenian Boondocks, and look through some of Jon Goff's recent posts for the past couple months. He lays out some interesting generic ideas.

There was an engineering test conducted by the original Orion (nuclear) rocket team that placed a full-scale heat shield like would have to be used for the rocket during one of the Pacific nuclear tests.

The main goal of the test was to see if __*ANYTHING*__ could survive structurally at ground zero in a nuclear blast. I think it was a 3-5 megaton test... and if memory serves me correctly it was the test at Bikini Atoll. It also had some huge springs to see if it could mechanically operate under those kind of conditions.

The result of the test was quite promising, at least in terms of material science and mechanical engineering and seeing the whole thing survive and work in those conditions. It also increased their confidence that their model they did test with chemical explosives could be scaled up to full sized devices, and some hard data to do more than an educated guess for what a full sized vehicle would require for materials.

Unfortunately/fortunately tests of that nature are a relic of the past. There certainly would be no practical value to such a test just to refine such data... particularly atmospheric tests.

Ken Anthony wrote:

Good grief! There NEVER was a question of whether it would work. They made a scale model using conventional explosives work. It is HARDER to make the scale model work than it was to make the real thing.

I am flabbergasted by the manifest absurdity of your argument.

The scale model was far simpler, and asked to do far less, than a full up Orion launcher. The latter would have entire systems lacking in the scale model. It would operate in a much different physics regime.

The showstopper for Orion is the great complexity of the idea ("Rube Goldberg" springs to mind as you look at some of the design concepts), coupled with the inability to meaningfully test the system except by flying it. Compare this to chemical rocket engines, for which a much larger fraction of testing can be done on static test stands (since the behavior of the fluid flow before the choke in the nozzle is independent of what happens afterwards). In this sense, Orion is akin to scramjets, where development has also been glacially slow.

Even with their testability advantage, rockets only became as reliable as they are because of a large base of accumulated experience. There was no budget for a similar experience base to have been accumulated for Orion. Reliability would have been horrible, and I suggest it would never have risen to the point that they could consider the concept to have 'worked', even to the extent of getting a single one of them to orbit.

I've always liked NERVA style engines because they let you radically improve the inert mass fraction of a rocket stage. With NERVA, you might just have the structural beef required to build a rugged reusable rocket - something that actually can stand up to the stresses that spacecraft necessarily endure for multiple launches, and do it in a single stage as well.

SSTO without significantly higher Isp can't be completely reusable. Completely reusable vehicles with current propellants would have to be staged - which adds to vehicle complexity.

But then again - if there were a way to mass-produce cheap drop-tanks you could get the benifits of staging without needing to throw away the important bits - the engine, ect. Just need a good way of arranging the propellant mass about the reusable engine support (maybe have the drop tanks over the vehicle capsule?)

There may not be one true way - but propellant mass does get to be a pain in the ass (especially once you're halfway to anywhere and most-of-the-way out of gas - especially acute in interplanetary propulsion) and the only way to reduce it is increase the overall specific energy of the vehicle. Nukes in various configurations do that.