Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Bill White · 2004-05-19 13:58:58

TIme to fire that new fact checker. . .

Bill White · 2004-05-19 14:08:00

So, at all times stick to the principles of low cost design, as set out in "LEO on the Cheap: Methods for Acheiving Drastic Reductions in Space Launch Costs" by Lt. Col. John R London III (Air University Press, Maxwell Air Force Base, Alabama) (It's available from Amazon.)

Thank God for google and Amazon one-click. . .

http://www.dunnspace.com/index.htm]LEO on the Cheap - the top google link

JimM · 2004-05-20 01:37:51

Thank God for google and Amazon one-click. . .
LEO on the Cheap - the top google link

I suppose you could call that LEO on the Cheap on the cheap.

GCNRevenger · 2004-05-20 13:52:54

I think we've gotten quite a bit better at building high performance vehicles, and we are ready to build Shuttle-II and we should... when there is a need for it, which is a little ways down the road... A little dubious about the really high currency conversion figure; sixty five billion dollars? It hasn't been that long... Conventional rockets do become more efficent per-pound as they scale up, but to jump to this being cheaper and better is a naieve engineers' oversimplification of the matter.

Like most things economic, there does come a point of diminishing and even negative returns... big rockets deliver more payload per pound per flight, but the larger the rocket, the harder it is to build and the longer it takes to prepare and the more difficult it is to operate etc etc. There is an upper practical limit to the size of a rocket before it becomes more expensive, and not less, compared to multiple smaller vehicles even if its "refurbishable." Handling a very big rocket alone adds up to a substantial sum: the Russian insistance of railway-sized rocket stages only has some basis in good economics.

I'm not sure you are giving the X-15 enough credit... unlike most of the silly X-Prize vehicles, the X-15 did reach altitudes over 107km and nearly 8,000mph, about half way to a useful orbit, when launched from a low-altitude slow moving bomber and burning fuels with half the impulse of LOX/LH. Say the X-15 were deployed from 100,000 or 150,000 feet, already at Mach 3-4, and powerd by advanced LOX/LH engines? I think the little 50 year old airplane might have a shot at orbit if kept cool... Think what we could do today with our modern 4000K ceramics, CNT/inorganic-doped polymer composits, and fluid dynamics modeling.

Next up, any RLV will have to be quite reliable in order to avoid paying for vehicle losses too often in order to be financially worthwhile, and if said level of reliability plus crwe escape gives similar safety than conventional manned rocket, then why not use it to launch people? A manned upper stage different than the cargo one would give you room for crew growth, extra mass margins for survival hardening/gear or OMS fuel, and save money from having to operate two entirely different vehicles... And which spaceplane that carries people are you referring to concerning the safety reccord? There aren't any real spaceplanes, and there never have been, and basing such a broad accusation against spaceplanes in general on the debacle that is Shuttle is silly and steriotypical...

Conventional rockets have much higher stresses/vibration than an airplane especially with the high thrust/weight ratio needed, limited abort options in case of engine failure (i.e. you fall straight back down), and overall hold more fuel than a TSTO airplane would (bigger explosion, less chance of launch survival). I'd think an ejection pod for the crewd version of the vehicle would do just fine which are proven effective from zero-supersonic... I don't have much faith in that silly 8G+ "launch escape tower" deely on top, which has never been used, to escape the larger explosion of a conventional rocket booster when all that first-stage fuel (used to lift the first stage fuel) goes up.

As i'm sure you are aware, the development cost of a good long-lived design is not as signifigant a factor as the per-flight cost if you have a decent flight rate. If it costs $1,000,000 to save $1,000 a flight on Shuttle-II, then thats a good deal. Low cost construction is NOT automaticly preferable... KISS works with many things, but it doesn't automaticly produce the best solution, somtimes the more complex solution is well warrented.

Now let me end by staying that building Shuttle-II right now would be a mistake, and if we do seriously intend to get anywhere besides repeating Apollo we will need somthing bigger, BUT ultimatly to open space for humans in general that conventional rockets are just too expensive, no matter how big. Throwing away pieces, ocean recovery, gigantic industrial undertaking for every flight, low flight rate... these are things regular rockets cannot avoid, and while this might be okay for expensive government missions or large space construction, its simply not going to be cheap or easy enough in the long run to become a space-faring species.

Bill White · 2004-05-20 14:22:08

Whichever way the technology falls out, we need a compelling reason for high flight rates and IMHO colonization is the only motivation that will generate sufficient demand for sufficiently high flight rates to justify any of this.

"How" and "Why" are joined at the hip, like Siamese twins, at least IMHO.

GCNRevenger · 2004-05-20 15:22:29

Yeah ultimatly thats true, but I don't think colonization is that far outside our reach, the only missing piece technologicly is a high-ISP/high-thrust engine and refinements in our ability to live in space.

So, I don't think its inappropriate to talk about launch methods besides conventional rockets, if "the day after tomorrow" may be here a little sooner than later, as far as what can be done. Developing a good spaceplane will take time to make.

Bill White · 2004-05-20 15:32:16

Yeah ultimatly thats true, but I don't think colonization is that far outside our reach, the only missing piece technologicly is a high-ISP/high-thrust engine and refinements in our ability to live in space.
So, I don't think its inappropriate to talk about launch methods besides conventional rockets, if "the day after tomorrow" may be here a little sooner than later, as far as what can be done. Developing a good spaceplane will take time to make.

I agree the ability to actually settle is closer than many would like to believe. Its not here yet, but much closer than some think.

But that opens up a Pandora's Box of political issues - -sovereignty issues, property rights, exploitation of space resources (for the common benefit of all humanity?)

etc., etc., etc. . .

that we as a species have yet to even discuss in any meaningful way.

My point is that the funding sources need a persuasive reason to build a shuttle II or other low cost to LEO system. Otherwise, we are better off spending the money on other stuff.

My fear about the PlanBush EELV approach that we will not spend enough to do more than send a few military-clad "explorers" on rock collecting trips and serious colonization will be pushed off a century or more and accepted wisdom will be that such things are impossible.

If colonization is impossible, today, we have no need for the low cost lift you describe.

JimM · 2004-05-20 16:05:24

I think we've gotten quite a bit better at building high performance vehicles

Really? Can you think of a single example that is relevant (forget pure aircraft in this)?

and we are ready to build Shuttle-II and we should... when there is a need for it, which is a little ways down the road...

A few decades at least I hope, by which time we won’t build it. The single most significant thing you disregard is that the Shuttle was a kludge. It was designed as a kludge, to cover too many mission objectives, in a fit of insane optimism by everyone involved, from NASA to the Air Force, to the Government and the manufacturers. Apart from being nearly criminally irresponsible in requiring people on board just to orbit cargo, it was also designed to meet both civilian and military requirements. Naturally it failed, on all counts.

A little dubious about the really high currency conversion figure; sixty five billion dollars? It hasn't been that long...

Yes it has: a third of a century long. Two factor drive a 1970ish estimate of $7bn for Shuttle up to $65bn at today’s money. One is inflation, the other is the project’s cost overruns which even at 1970ish prices drove it to $18bn. Plug the two together and you get $65bn. Which makes ‘cheapness’ extortionately expensive.

Conventional rockets do become more efficent per-pound as they scale up, but to jump to this being cheaper and better is a naieve engineers' oversimplification of the matter.
Like most things economic, there does come a point of diminishing and even negative returns... big rockets deliver more payload per pound per flight, but the larger the rocket, the harder it is to build and the longer it takes to prepare and the more difficult it is to operate etc etc.

I am an engineer, and I am also an economist. I am not naïve. The naïve people are those who assume that because a rocket is bigger it must be more expensive. Indeed, if as you say rockets are more efficient per lb as they scale up, the naïve person is the one who does NOT see it means this is the cheaper way to deliver payloads.

The cube rule operates here. Doubling the length of a rocket means that (everything else being equal) the volume and in principle the payload is eight times greater. But beyond that, because the design and engineering work is not a function of size at all (except perhaps in an inverse way, but we’ll leave that to one side for now) that cost does not change with size. Construction is a square function of size, so doubling the length means four times the cost of materials and labor for assembly. Fuel is an almost negligible fraction of the cost, so basically, you could say that a rocket standing 400 ft tall on the launch pad will deliver eight times the payload of a 200 ft tall rocket at half the price per lb.

That is only ONE aspect of getting the cost of space down. Others involve abandoning cryogenic, low density fuels like LH2 (and LOX too please), abandon turbopump fed engines in favor of pressure feeding (an example of KISS)… there is a long list, but I think I’ve given a flavor of my argument. This is not the place for the full story. It would take far too long for the time I can spare.

There is an upper practical limit to the size of a rocket before it becomes more expensive,

Why? I hear or see no evidence of this.

the Russian insistance of railway-sized rocket stages only has some basis in good economics.

As with the Germans before them, this requirement was defined by the need to fit the standard railwayloading gauge for transportation, nothing else. It had nothing to do with economics. It’s certainly what fixed the dimensions of the A4/V2 back in the 1940s. You forget these were fundamentally military systems.

I'm not sure you are giving the X-15 enough credit... unlike most of the silly X-Prize vehicles, the X-15 did reach altitudes over 107km and nearly 8,000mph, about half way to a useful orbit…

Really, you should not be giving the X-15 so much credit. The best it ever managed was 7,273 kph (4,519 mph) on Flight 90 on 19 July 1963, and 106,010 meters (65.93 miles) altitude on Flight 188 on 3 October 1967. As you say yourself it had to be hauled up into the sky by a B-52 (acting the role of “Stage 1”) and as these corrected performance figures make clear, it came nowhere near orbital velocity; 4,500 mph is about a quarter of the delta-V required for LEO insertion. Take away the B-52 and have the X-15 fly from the deck under its own steam, and what would it have achieved? 15% LEO insertion delta-V? …that much? …would it have been able to lift itself into the air? I don’t know but doubt it. As I said, it just managed to pop its head up above the atmosphere for a couple of minutes, which is good but no cigar.

There aren't any real spaceplanes, and there never have been, and basing such a broad accusation against spaceplanes in general on the debacle that is Shuttle is silly and steriotypical...

No it’s not. Shuttle is the only thing like a spaceplane yet in existence; it’s been a lot more dangerous to fly in than any capsule.

Conventional rockets have much higher stresses/vibration than an airplane especially with the high thrust/weight ratio needed

Twaddle. A VTO booster stays in max-Q for a few seconds only. Any conceivable spaceplane would be in max-Q for at lest a good number of minutes. The stress on its structure would be correspondingly extended and greater. And the booster does not have wings to get shaken off.

I'd think an ejection pod for the crewd version of the vehicle would do just fine which are proven effective from zero-supersonic...

Every attempt to incorporate such a system in a manned space vehicle has killed the project so far, especially well documented in the case of the ESA Hermes. It just eats up mass like it’s going out of fashion.

I don't have much faith in that silly 8G+ "launch escape tower"

I think I’d bear with the 8 gees if it meant I would survive.

If it costs $1,000,000 to save $1,000 a flight on Shuttle-II, then thats a good deal.

No, it’s an utterly lousy deal. Unless you fly over a 1,000 missions, you’re out of pocket. Which is the very heart of the point I’m making. There is just not enough demand for RLSs today, or for a while, which is why ELSs are far more eeconomic.

Low cost construction is NOT automaticly preferable... KISS works with many things, but it doesn't automaticly produce the best solution, somtimes the more complex solution is well warrented.

There is no virtue in complexity for the sake of complexity, which seems to be your argument in a nutshell.

its simply not going to be cheap or easy enough in the long run to become a space-faring species.

True, but that does not mean we have to make it more expensive or harder than strictly necessary.

Euler · 2004-05-20 18:43:16

I think we've gotten quite a bit better at building high performance vehicles
Really? Can you think of a single example that is relevant (forget pure aircraft in this)?

Just look at shuttle itself. Most of the parts currently used by STS are an order of magnitude safer and significantly lighter than the parts used at the beginning of the program.

No it’s not. Shuttle is the only thing like a spaceplane yet in existence; it’s been a lot more dangerous to fly in than any capsule.

Why do people keep saying this? More people have died in shuttle than any other launch vehicle, but more people have also flown in shuttle than in all other launch vehicles combined. STS has shown a reliability greater than 98%, which is better than most capsules.

I don't think that a reusable spaceplane type of vehicle will be able to bring down the cost of getting bulk payload into orbit any time soon. However, getting people into orbit is a different story. While most cargo that is sent into space stays in space, people need to eventually return to Earth. This means that any manned spacecraft needs a heat shield and landing gear anyway, making a reusable much more competitive with expendables.

its simply not going to be cheap or easy enough in the long run to become a space-faring species.

Real GDP has been slowly rising while real cost/lb has been slowly dropping. As long as these trends continue, we should not have much trouble becoming a space fairing species eventually.

JimM · 2004-05-21 01:35:43

Most of the parts currently used by STS are an order of magnitude safer and significantly lighter than the parts used at the beginning of the program.

Then why is it if anything getting more dangerous to fly in, not less?

Why do people keep saying [Shuttle is ... a lot more dangerous to fly in than any capsule]?

Because it's true?

STS has shown a reliability greater than 98%

Man-rated is defined as 99.9%. So by your own words, Shuttle is not man-rated. Which is my point.

...which is better than most capsules.

No sorry, it's not. The Russian record is better, for a start. And America has lost not one man from a capsule accident while in flight. yet.

I don't think that a reusable spaceplane type of vehicle will be able to bring down the cost of getting bulk payload into orbit any time soon. However, getting people into orbit is a different story.

Agreed. I have always advocated complete separation of cargo and people. Failure to do this is one of the major fatal failings of Shuttle.

This means that any manned spacecraft needs a heat shield and landing gear anyway, making a reusable much more competitive with expendables.

Why is it more competitive? The evidence is in the exact opposite direction. (Shuttle again.)

its simply not going to be cheap or easy enough in the long run to become a space-faring species.

True again. But why make it more expensive and harder that it need be?

GCNRevenger · 2004-05-21 09:10:33

Really Jim, your steriotyping of Shuttle and non-KISS-o-phobia is is making it harder to take your conversations seriously. Shuttle is not a spaceplane, because during its most important function - launching - it is a pure rocket with no airplane character whatsoever, and this combined with USAF requirements strongly limits the ease of the other important part, reentry. Shuttle was also a compromise design in order to avoid cancellation, not some giddy happy spaceflight panacea around the halls at Nasa that you make it out to be, it was the only thing that carried people that Congress would let Nasa build... The vehicles that Nasa had in mind were nothing at all like Shuttle in nearly every respect until Nixon ended the Apollo era.

Ah yes, and your cost calculations about the overuns, your numbers are innacurate because of the large inflation differences for WHEN these costs were incured. "1970'sish" is not a particularly useful figure; I believe this difference would add up to a signifigant multibillion dollar sum.

"There is an upper practical limit to the size of a rocket before it becomes more expensive,

Why? I hear or see no evidence of this."

If you have taken any economics courses, then you would know better than this Jim. Diminishing returns is an inherint law of economics and cannot entirely be engineerd around... or clearly illustrates your blind infatuation with conventional rockets. Yes as rockets get bigger they hold more fuel via the cube law, but that is not the cost of launch. A larger vehicle requires a larger team of engineers to prepare and fly and likewise larger VAB and a larger crawler and a larger pad and tower etc... Rockets' efficency obeys the cube law, but the cost per flight can grow nonlinearly with bigger vehicles too... how much more does it cost to build (stronger since its so tall), assemble, and handle a rocket 400ft tall than a smaller one? A single Saturn-V costs even today costs more than six Delta-IV HLVs. Elon Musks' Falcon-I on its mobile launcher and a few rocket techs versus the army of tens of thousands needed to assemble and launch Saturn-V; the little rocket can carry only 1/50th of Saturn-V but Saturn was alot more than 50 times as expensive to fly... this ain't rocket science, past a certain point a bigger rocket is a liability, not an asset, because big things are harder to work with.

My example of the X-15 is not all invalid since I am comparing it to a hypothetical purpose-built TSTO vehicle... What if the X-15's sucessor held more fuel and built with modern materials & designs, powered by hydrogen which you forget is still extremely light weight, and what if it were launched at tripple or quadruple the height and four or five times the speed using a purpose-built launch aircraft? Then orbit is not so far away... the X-15 for being such an old fragile vehicle with such a finicky engine was about as reliable as Shuttle is today too.

And rockets do have more stress on the vehicle... no it is not for quite as long as a spaceplane, but it is certainly several times as much for the short period it is under... Apollo was near the edge of safe quantities of vibration and G-loading, and Shuttle is little better today. Also, a spaceplane need not even have such a big thrust/weight ratio, so it can get away with fewer and smaller engines that are less rough on the vehicle and easier to work with on the ground... And why must the upper stage for a spaceplane have wings at all? A lifting body would work just fine, since a huge amount of crossrange is not a requirement save for military flights. A nonballistic reentry also puts less strain on a spaceplane inherintly with its wider area than capsules and shallow angle, permitting a reuseable TPS and less strenuous return. Oh yes and lift bodies have large amounts of volume relativly speaking too.

And the escape system, where you cite the Hermes space vehicle, well guess what? Its not a space plane either, even less so than Shuttle. With a TSTO vehicle capable of carrying a reuseable unmanned upper stage for cargo (20-30MT preferably), then a different crew-only upper stage should have plenty of extra mass for an escape pod and safety systems... My issue with the launch tower schema is that I doubt that it would carry you clear of the nuclear-scale explosion of a failed booster either fast enough (to escape the explosion or a running booster ramming you) nor carry you far enough in the event of a pad explosion.

And this...: "There is no virtue in complexity for the sake of complexity, which seems to be your argument in a nutshell." Is exactly what I did not say, and an intelligent person such as yourself stating this reeks to me of haughty eliteism Jim, I suggest you learn to read the posts of lowly non-engineers more carefully and "clarify" your statement. What I stated is that sometimes the performance offerd by a more complicated solution is worthwhile, not that ALL complicated systems are ALL better by default.

Finally I would like ask, what other solutions are there? A space elevator may or may not be possible and is of dubious usefulness... railgun or cannon launch is limited in its versitility, laser/MW-assist system would be gargantuan... and so when we are ready to colonize the general populence and not military geologists what will we do, a thousand flights is no longer a dream but a need, what then? Conventional rockets will become a strangling bottleneck because they are too expensive and cannot fly often enough by the nature of their inherint size, fuels, and dynamics, what will we do? ...A spaceplane could do this, and we know that it will work.

Euler · 2004-05-21 11:06:06

Man-rated is defined as 99.9%. So by your own words, Shuttle is not man-rated. Which is my point.

Man-rated airplanes are 99.9%. No spacecraft that has ever been built has been even close to 99.9% reliable.

No sorry, it's not. The Russian record is better, for a start. And America has lost not one man from a capsule accident while in flight. yet.

No, the Russian record is not better. It is worse. And while America has not lost a capsule in flight, there were not that many capsule flights, and we did lose Apollo 1 in addition to having many close calls like Apollo 13.

This means that any manned spacecraft needs a heat shield and landing gear anyway, making a reusable much more competitive with expendables.
Why is it more competitive? The evidence is in the exact opposite direction. (Shuttle again.)

I don’t mean something like shuttle. What I am talking about is a vehicle where people are the primary cargo, and not satellites or ISS modules. If you crammed the shuttle payload bay full of people, it would be competitive with Soyuz (probably cheaper) in terms of cost per person. Of coarse, there is no reason right now why you would need to get that many people into space at once.

JimM · 2004-05-21 16:04:10

Man-rated is defined as 99.9%. So by your own words, Shuttle is not man-rated. Which is my point.
Man-rated airplanes are 99.9%. No spacecraft that has ever been built has been even close to 99.9% reliable.
No sorry, it's not. The Russian record is better, for a start. And America has lost not one man from a capsule accident while in flight. yet.
No, the Russian record is not better. It is worse. And while America has not lost a capsule in flight, there were not that many capsule flights, and we did lose Apollo 1 in addition to having many close calls like Apollo 13.
This means that any manned spacecraft needs a heat shield and landing gear anyway, making a reusable much more competitive with expendables.
Why is it more competitive? The evidence is in the exact opposite direction. (Shuttle again.)
I don’t mean something like shuttle. What I am talking about is a vehicle where people are the primary cargo, and not satellites or ISS modules. If you crammed the shuttle payload bay full of people, it would be competitive with Soyuz (probably cheaper) in terms of cost per person. Of coarse, there is no reason right now why you would need to get that many people into space at once.

Man-rated airplanes are 99.9%.

Rubbish. Man rated aircraft do not crash and burn every thousandth flight. If they did, there would be very few fairpaying passengers. Realistically, "man-rated" aircraft are more like 99.99999% or some such.

No spacecraft that has ever been built has been even close to 99.9% reliable.

In fact (If you're talking about man-carrying spacecraft) all have, except Shuttle.

No, the Russian record is not better. It is worse.

Substantiate this. (Warning before you start: You can't because you're wrong.)

And while America has not lost a capsule in flight, there were not that many capsule flights.

From memory, between Mercury, Gemini and Apollo, there were something like 40 or so. If they'd been Shuttle flights, the odds are very high (about 90%) that one would have been lost.

, and we did lose Apollo 1

... on the ground. I already allowed for that.

in addition to having many close calls like Apollo 13.

A close call is not the same as a disaster. Apollo at least had a recovery mode, unlike Shuttle.

If you crammed the shuttle payload bay full of people

...you could kill more people per disaster.

Of coarse, there is no reason right now why you would need to get that many people into space at once.

Exactly. That's why RLSs are several decades premature. You make my point for me.

Euler · 2004-05-21 16:43:24

Most of the parts currently used by STS are an order of magnitude safer and significantly lighter than the parts used at the beginning of the program.
Then why is it if anything getting more dangerous to fly in, not less?

After 88 consecutive flawless flights (a record that is not matched by any other spacecraft), you think that one accident means that shuttle is getting more dangerous?

No spacecraft that has ever been built has been even close to 99.9% reliable.
In fact (If you're talking about man-carrying spacecraft) all have, except Shuttle.

Like Shuttle, Soyuz has had two accidents where the entire crew was killed during a flight (and it has also had some incidents where the capsule failed to achieve orbit, but the crew survived). Soyuz has had less flights than Shuttle, and in fact all Russian capsules combined have less flights than STS. That means that Soyuz has demonstrated a lower reliability than Shuttle.

From memory, between Mercury, Gemini and Apollo, there were something like 40 or so. If they'd been Shuttle flights, the odds are very high (about 90%) that one would have been lost.

There were 4 Mercury, 10 Gemini, and 11 manned Apollo capsules (not counting Apollo 1). That is 25 flights. Using Shuttle's observed success rate, that gives a 36% chance that Shuttle would have had an accident.

JimM · 2004-05-21 17:56:23

Really Jim, your steriotyping of Shuttle and non-KISS-o-phobia is is making it harder to take your conversations seriously.

I don’t have to stereotype Shuttle, it does it for itself. And anything with six million parts (every one supplied by the lowest-priced vendor) is a really great argument in favor of KISS.

Shuttle is not a spaceplane, because during its most important function - launching - it is a pure rocket with no airplane character whatsoever, and this combined with USAF requirements strongly limits the ease of the other important part, reentry. Shuttle was also a compromise design in order to avoid cancellation, not some giddy happy spaceflight panacea around the halls at Nasa that you make it out to be, it was the only thing that carried people that Congress would let Nasa build...

Thank you for confirming what I said; Shuttle is a kludge, a horse designed by a committee. Moral? Don’t let politicians design spacecraft.

Ah yes, and your cost calculations about the overuns, your numbers are innacurate because of the large inflation differences for WHEN these costs were incured. "1970'sish" is not a particularly useful figure; I believe this difference would add up to a signifigant multibillion dollar sum.

You don’t know much about how cost estimates work, do you?

Shuttle was sold to Nixon on the basis of a 1971 (I think) estimate of $7bn. From 1971 to 2004 is 33 years (a third of a century) during which aerospace cost inflation has been approximately 350%. That means that at today’s prices, that $7bn would have become about $24 to 25bn. However the $7bn was, to cut a long story short, a lie. NASA knew from the very start it could never be done for that, and taking the actual cost back to 1971 dollars, it actually ended up costing $18bn. Add cost inflation to 2004 and you get $63bn. OK, I was $2bn out. What’s $2bn between friends?

"There is an upper practical limit to the size of a rocket before it becomes more expensive,
Why? I hear or see no evidence of this."
If you have taken any economics courses, then you would know better than this Jim. Diminishing returns is an inherint law of economics and cannot entirely be engineerd around... or clearly illustrates your blind infatuation with conventional rockets.

Well yes, I’ll grant you that mile-high rockets might create a problem or two. But in the sort of size/weight range we’re talking about, it’s actually not an issue. It is only those blinded by conventional rocket design that suppose it is.

And diminishing returns is an interesting point to bring up here, by the way. The thing is that there is an optimum size, efficiency and cost for most engineering and other systems. This means that, in the case of a rocket if it strays too far from the optimums, it becomes either unable to fly, too expensive to fly, or too unreliable to fly. This can mean that a vehicle is too big to be effective for one of these reasons, or too small. Too small is a “diminishing returns” effect too. What is too big or too small for a particular system depends on how the system is supposed to operate and what it is supposed to achieve. It is my view (along with many others) that the optimum size for a simple booster that does not try to get fancy with its propulsion systems, etc. (that is, a BDB) is from Saturn V size up to a liftoff mass of maybe 20,000 to 30,000 tons, which at that upper end could haul well over 1,000 tons to LEO all in one go. On the other hand, a spaceplane is just at the very limits of doable today. There are bits of it we really have still to invent (the propulsion system, for example) which means it will be extortionately expensive to develop, and then will deliver tiny payloads at extreme cost and risk. Come back in 20 or 30 years and that may have all changed, but meanwhile it’s really just pie in the sky.

A larger vehicle requires a larger team of engineers to prepare and fly and likewise larger VAB and a larger crawler and a larger pad and tower etc...

Why? Sea Dragon (mentioned earlier) weighs 20,000 tons at lift off – from the ocean.
It’s first stage would be fabricated from one inch thick steel in a shipyard… these things are far more rugged than what we’re used to up to now. The idea is to parachute the first stage back down to the ocean and re-use it, but that’s not essential for economic viability.

And give me one good reason why it would need more engineers to prepare for flight—or to fly (remember it’s unmanned) than a smaller booster. Indeed, by having sturdier components (such as tanking) and pressure fed rather than turbopumped engines, it would take far less engineering time to prep and fly than any small conventional booster. And guidance and navigation is a function of the flightpath, not the size of the vehicle.

Rockets' efficency obeys the cube law, but the cost per flight can grow nonlinearly with bigger vehicles too... how much more does it cost to build (stronger since its so tall), assemble, and handle a rocket 400ft tall than a smaller one?

Less, as I said above. It’s boilerplate assembled in a shipyard. Compared with conventional spaceframes, that’s real cheap.

A single Saturn-V costs even today costs more than six Delta-IV HLVs. Elon Musks' Falcon-I on its mobile launcher and a few rocket techs versus the army of tens of thousands needed to assemble and launch Saturn-V; the little rocket can carry only 1/50th of Saturn-V but Saturn was alot more than 50 times as expensive to fly... this ain't rocket science, past a certain point a bigger rocket is a liability, not an asset, because big things are harder to work with.

How can you say what a Saturn V would cost today? And are big things always harder to work with than smaller? Where did you get that quaint notionfrom? How big is you TV screen back home? 25 inch? 30 inch? – or your computer’s screen? Gee, if you just had a one inch screen, it would be so much easier to work with. (You said it, not me.)

What if the X-15's sucessor [was] powered by hydrogen?

Using hydrogen is a typical design error, in many cases. Yes, it’s very light. That’s half its problem. It means the size of tankage required to hold it (and so the size and weight of the spaceplane) is so much greater than most other fuel, most of the hydrogen advantage is lost right there. The other half of its problem is the difficulty of keeping it stored at its very low liquid temperature which means much heavier, thicker, better insulated tankage… before you know where you are, paying a ferocious price for the sake of what in the end is really just fashion.

And rockets do have more stress on the vehicle... no it is not for quite as long as a spaceplane, but it is certainly several times as much for the short period it is under... Apollo was near the edge of safe quantities of vibration and G-loading, and Shuttle is little better today. Also, a spaceplane need not even have such a big thrust/weight ratio, so it can get away with fewer and smaller engines that are less rough on the vehicle and easier to work with on the ground...

The spaceplane will more likely than not have engines with moving parts. That adds a lot to the stress in the environment you want to use them in. And anyway, you’re just plain wrong. Boosters, especially ones with pressure fed engines without turbopumps, have much less stress for a minute fraction of the time a spaceplane is exposed. – especially if you’re planning to have your spaceplane go through that stress environment on a regular basis, week after week after week. The BDB is exposed only once; it’s FAR safer.

And why must the upper stage for a spaceplane have wings at all?

So why call it a spaceplane?

And the escape system, where you cite the Hermes space vehicle, well guess what? Its not a space plane either, even less so than Shuttle.

You really should stick to things you know about. Of course it was, launched ontop a conventional booster because the horizontal takeoff spaceplane is about 30 years beyond today’s technology.

My issue with the launch tower schema is that I doubt that it would carry you clear of the nuclear-scale explosion of a failed booster either fast enough…

Sorry, but that’s better than no escape route whatever, which is what a spaceplane offers

And this...: "There is no virtue in complexity for the sake of complexity, which seems to be your argument in a nutshell."

Sorry, but at this point in our technology, a spaceplane (and indeed Shuttle before it) is precisely complexity for the sake of complexity. It’s like doing something to show how clever we are rather than doing what’s needed to deliver the result we all want.

Finally I would like ask, what other solutions are there? A space elevator may or may not be possible and is of dubious usefulness... ...A spaceplane could do this, and we know that it will work.

The point is, we do NOT know it will work. And I’m trying to keep away from science fiction here.

JimM · 2004-05-21 18:41:07

Like Shuttle, Soyuz has had two accidents where the entire crew was killed during a flight ... Soyuz has had less flights than Shuttle, and in fact all Russian capsules combined have less flights than STS. That means that Soyuz has demonstrated a lower reliability than Shuttle.

In fact there have been 93 Soyuz missions so far, and only one ended in disaster when the crew compartment deressurised on re-entry in 1971. That makes Soyuz 98.92% reliable: better than Shuttle, as you can see.

There were 4 Mercury, 10 Gemini, and 11 manned Apollo capsules (not counting Apollo 1). That is 25 flights.

In fact there were 6 Mercury, 10 Gemini and 15 Apollo manned flights, totaling 31. If Shuttle reliablity applied, there would have been a 54% chance of a catastrophic mission failure, not 36% as you state.

Euler · 2004-05-21 19:46:39

You are forgetting that Soyuz 1 was also destroyed during reentry, killing Vladimir Mikhailovich Komarov. I count 85 manned http://en.wikipedia.org/wiki/Soyuz_program]Soyuz missions.

The first two Mercury flights were suborbital, so they don't count. You are right about Apollo though; I forgot about Skylab and Apollo-Soyuz. That gives 29 flights, or a 40% chance that a shuttle would have failed (the probability of a failure is 1-(probability of a successful flight)^(number of flights)).

In any case, the point that I was trying to make was that a reusable (possibly winged) vehicle, or a vehicle with a reusable upper stage, could be economical for transporting people even if it is not economical for transporting most other cargoes. The converse is also true- if a reusable is not economical for transporting people, it is almost certainly not economical for transporting other cargo. That is why I think that it might be a good idea to investigate a reusable crew transfer vehicle. Reusable vehicles for other applications should be considered if and only if the CTV is successful.

JimM · 2004-05-22 03:16:52

You are forgetting that Soyuz 1 was also destroyed during reentry, killing Vladimir Mikhailovich Komarov. I count 85 manned Soyuz missions.

You’re right about Soyuz 1. I’m sorry. Somehow I missed that. I recounted and got 90 manned Soyuz missions, most recently Soyuz-TMA 4 which lifted off to delivered a new crew to ISS on 19 April this year.

Also I misread the number of Shuttle flights. It is not 115 but 113 to date. The reason for my errors was that I read the wrong numbers from the site I referred to.

Sorry.

It just goes to show I'm human after all and can make misteaks.(Make mine medium rare, please.)

The first two Mercury flights were suborbital, so they don't count.

Why not? Of course they do!

In any case, the point that I was trying to make was that a reusable (possibly winged) vehicle, or a vehicle with a reusable upper stage, could be economical for transporting people even if it is not economical for transporting most other cargoes. The converse is also true- if a reusable is not economical for transporting people, it is almost certainly not economical for transporting other cargo. That is why I think that it might be a good idea to investigate a reusable crew transfer vehicle.

Now we’re almost in agreement here. (Worrying, isn’t it?)

All I say different is that a reusable crew transport vehicle (RCTV) should be put to one side while an expendable crew transport vehicle (ECTV) to replace Shuttle in a hurry should be a capsule so as to get things going again quickly; after all we have all the pieces already designed or built for this. An Apollo CM on top a modified SM all on top a Titan (for example) should be doable as a crash program in a couple of years. Your RCTV will take a lot longer and cost mucho dinero more too.

Rxke · 2004-05-22 05:11:09

Not wanting to get this further off-topic, but 'bout the Soyuz-1...

Komarov knew in his heart he probably wouldn't come back alive, he was uncharacteristically silent before the launch, and his astronaut friends, very well knowing what bothered him, tried everything to distract him out of his morose mood...

The 3 previous (unmanned) testflights failed miserably, but the Kremlin insisted to launch anyway... Most people didn't consider Soyuz-1 operational, that more testing was needed before sending it up in a manned configuration. This was in the height of the space-race, and apparently the Kremlin was willing to take chances. And one didn't dispute orders coming from the Kremlin, if he wanted to stay out of trouble.

A brave man, with dreams of reaching beyond LEO, was killed for no good reason...

JimM · 2004-05-22 09:10:43

One of the things that a Sea Dragon-type BDB booster could make possible is the boosting to LEO of an Orion-type nuclear pulse spaceship—or better.

Those of you who have read Dyson’s “Project Orion” will recall that towards the end of the book he mentioned plans to orbit a sort of mini Orion atop a Saturn V that came to nothing. Using Sea Dragon it would still be a cutback version Orion when compared with a ground-launched one, but it would be a lot bigger and better than a Saturn-launched one. Now if instead of Orion’s klunky a-bombs we could fix it up with Daedelus-type “pellet and laser” fusion propulsion, we’d have ourselves a real spaceship at last, able to cruise around the Solar System almost at will.

I rather like the notion that the almost-retro technology of BDB could be the way to get a super-high-tech real spaceship into the skies.

In fact, with a few of these ships sailing the high ocean around the Sun, there would soon be a real space infrastructure; colonisation of the Moon and Mars would be a relative dawdle, for example. If one Orion/Deadelus ship could be launched by BDB every year, there would be 10 up there by 2025 if we had the first ready by 2015, and so on, because they would certainly be reusable. Here we have the way towards a real “space fleet”.

Why, there might even be enough Earth-to-space traffic to justify a spaceplane by that time!

Rxke · 2004-05-22 12:13:39

Just to remind people this thread is all about DS-1...

The Rocket Company story has just ended...

The last chapter is about getting to Mars 'on the cheap'

(Ok, start you fighting, sigh...)

Rxke · 2004-05-22 12:15:52

Sorry, forgot the link: http://www.hobbyspace.com/AAdmin/archiv … l]Epilogue 2: Mars for the Many

RobS · 2004-05-22 22:45:54

Thanks for the link; I had kept looking for more and looked a bit too soon! He is, shall we say. . . optimistic?

-- RobS

Rxke · 2004-05-23 00:09:41

Heh.

In a way, yes, in another, i kinda like the "slave-ship" idea... You'd only go if you were really prepared to suffer the hardships. See it as some kind of pre-selection.

But of course you'd have to be either some kind of monk or an ex-convict to stay sane that way...
Rich people, paying $$$, to get, in essence, locked-up in a tiny room for six months, in what amounts to a prison regime... I dunno. Esp. when they land, from the description, it's like landing on a penal-colony, all over again...

Mars: New Australia?

And then again... Why send up inanimate payload together with live crew? IMO he could've made it even *more* spartan/low-cost (the ship) (EDIT: Skip that, read it wrong...)

Not that far-out, though... America got colonised in exactly that way... Lots of desperate people in steamships, only the rich had comfort, the poor were stacked like sardines in a can. Not to mention the *real* slave-ships, that were at least an order of magnitude worse than that.
You could use the six months studying, flat-panel TFT screen and a keyboard takes not much place. Or you could meditate, pray, 'discover yourself' (everybody will go for a different reason, some people will be deeply religious, and a six-month experience like that might be welcome for some...)

I could see it happen, in fact. But imagine people revolting, or going nuts during the trip... Then what?

mboeller · 2004-05-23 06:16:21

Now if instead of Orion?s klunky a-bombs we could fix it up with Daedelus-type ?pellet and laser? fusion propulsion, we?d have ourselves a real spaceship at last, able to cruise around the Solar System almost at will.

IMHO this is not an good idea. Laser induced fusion is still too far away to be useful.

Use the MiniMag Orion instead.

Link : http://www.andrews-space.com/en/news/Pu … df]MiniMag Orion

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