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Rockets vs. Airbreathers

Posted by: spacecowboy - Thu May 26, 2005 12:44 pm
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Rockets vs. Airbreathers 
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Post    Posted on: Mon Jun 20, 2005 1:35 pm
spacecowboy wrote:
Yes you don't make a helicopter that can carry 500 people and fly three thousand miles like the A380; nor do you build a turbojet aircraft that is only big enough for two... Could you build them? Sure... But why?
That is a really telling statement. I wonder where rockets fit into that paradigm? What worries me is that they may be like the 500 passenger helicopter.


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Post    Posted on: Mon Jun 20, 2005 3:03 pm
spacecowboy wrote:
What he said makes sense


Well, yes, it has some basis in fact. I expect some general statement could be made about scale of launch platforms and operational efficiency versus practical utility. I just think that somebody who speaks with as much conviction as publi is better off being more technically specific. I mean, we're all smart fellas here, right? The collective gray matter which is pointed at this forum is better served by statements of the form "this is what I found/learned/discovered" than those which say "this is what I think"

Publi is a passionate fellow, and though some of his positions are perhaps controversial, he does have a contribution to make to this community. I don't want to silence him, I just want him to be easier for folks to hear.

P.S.: If someone did design (let alone build) a 500 passenger transatlantic helicopter, it would have a cult of followers whom thought it was the greatest machine ever invented, and whom would endlessly spam every aviation and aerospace forum about how it never should have been canceled and how Boeing/Government/Military conspiracies/collusion/favoritism was responsible for ruining a masterpiece and that it should be built/rebuilt/restored immediately by introducing a special tax on "ordinary" air travel.


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Post    Posted on: Mon Jun 20, 2005 4:06 pm
Hrm... Excellent points -- especially the part about the cult following.

Peter: I doubt it very seriously, and besides: if they are, then the whole forum is kind of pointless, no? Besides, I thought Elon, Burt, and John have already pretty much proven that kind of thinking erroneous.

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Post    Posted on: Mon Jun 20, 2005 4:35 pm
spacecowboy wrote:
Peter: I doubt it very seriously, and besides: if they are, then the whole forum is kind of pointless, no?
Yes, that is what it would mean. :(

I recall reading somewhere long ago (I wish I could remember where) that Arthur C Clark once said that chemical rockets would be hideously expensive and clumsy space vehicles.

Falcon drops the first stage into the ocean by parachute for recovery and refurbishment, can you imagine the airlines doing something like that? By comparison a transatlantic helicopter seems reasonable. Or maybe a transatlantic airship. Possible, or even done before, but not practical.

SS1 is not orbital and still has two parts, only one of which gets to the intended ultimate destination. If that destination was orbit, I would be a lot more upbeat though, as both pieces land normally and do not need to be recovered or refurbished.


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Post    Posted on: Mon Jun 20, 2005 4:41 pm
Which is why I still like the idea of a hybrid airbreather such as the hypersonic critters I mentioned earlier.

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Post    Posted on: Mon Jun 20, 2005 5:31 pm
So do I.


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Post    Posted on: Thu Jun 23, 2005 7:59 pm
The relationship of scale to materials is not to be dismissed lightly.

[P.S.: If someone did design (let alone build) a 500 passenger transatlantic helicopter, it would have a cult of followers whom thought it was the greatest machine ever invented, and whom would endlessly spam every aviation and aerospace forum about how it never should have been canceled and how Boeing/Government/Military conspiracies/collusion/favoritism was responsible for ruining a masterpiece and that it should be built/rebuilt/restored immediately by introducing a special tax on "ordinary" air travel.

Cute. :roll:

I can think of worse:

"Containerships? Made of metal? Ha! Our Clipper Ships (read..Delta II) do just fine thank you. The next thing you know--you'll be expecting to haul oil in huge crude carriers, instead of doing the smart thing--and using a million motorboats to cross the Atlantic. Gotta walk before you can run."

Thankfully--Mike Griffin is too smart to listen to this kind of stupidity.

"Lets launch a whole bunch of EELVs, dock six times--turn around and touch your nose..."

And get astronauts killed.

Besides, big autogyros are in a good size range--and can have good wings for back up.

EELV's have no engine-out--and therefore, no backup.


Remember the commercial where Columbus was in a rowboat and said "Take me to my flagship!"?

"This is your flagship."

That is how not to do things.


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Post    Posted on: Fri Jun 24, 2005 3:35 pm
publiusr wrote:
The relationship of scale to materials is not to be dismissed lightly.


Nor is it to be RENDERED lightly. You presume to speak with authority, but all you offer is opinion. Where is the substance? If you want to sway the thinking of others, particularly in any technology-related field, your arguments need to have significant numercial import. The only way to teach others is to share what you yourself have learned; so come on, man, show us what you KNOW... everybody here already knows what you THINK.


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Post    Posted on: Sat Jun 25, 2005 1:37 am
SawSS1Jun21 wrote:
publiusr wrote:
The relationship of scale to materials is not to be dismissed lightly.


Nor is it to be RENDERED lightly..../quote]

I agree with both these statements, but the second is usually dominant. Scale is a significant but WEAK factor in most human enterprise. Scale factor is commonly used to justify the heavy burden of using the wrong ORGANIZATION (with disproportionate overhead) for small scale work.

Real estate people use cost per square foot, with small scale changes (when the same type of construction is used) over ranges of more than 100 in size.

“Scaling Up” from a Cessna 172 to an Airbus 380, the cost per pound dry weight GOES UP by a factor of about 2. Small, fast turboprops exceed the operational speed (not peak, but door to door) of the Airbus, and erase most of this cost differential.

You might notice that most human transportation in the US (Long as well as Short range), is done in 4 to 6 passenger vehicles.

The 500 passenger Helicopter is an irrelevant concept, since there is no need to use a specialized, high drag system to haul people over the Atlantic.

When the economy of scale – NUMERICAL PRODUCTION RATE – is included, a few large vehicles usually cost proportionally much more than a lot of small ones. The economy of scale (production numbers) is the most reliable and significant scale factor, with unit cost reductions of from 20% to 50% with every factor of ten increase in sustained production rate. Don’t try to match the achieved reductions with theoretical modeling! The historic results include the benefit of bringing in (or inventing) new production processes as volume increases. This effort and investment is only made attractive by the demonstrated demand.

It is insane to think that some economy of LINEAR SCALE is going to fix a seriously overweight design and make the bloated result economical!

Granted, getting a twenty man research team to Mars, or major mining systems on the Moon, looks like work for heavy lift vehicles – if and when anyone wants to pay the cost. But to argue that “Going Big” will fix everything is the same failed theory proposed for aircraft – before and after 1903! And, most certainly, if you are going to argue the “Big is Cheaper” line, you need to have a very good explanation for why the Space Shuttle was an economic disaster (compared to the program’s promises), and why the same organization, with the same operating procedures, will achieve the promised results now, while following a very similar development process!


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Post    Posted on: Mon Jun 27, 2005 12:36 pm
Hrmph. Anyways, my other example of a two-person turbojet seems to have come back to haunt me: ATG is currently developing a two-person supersonic jet for civilian courier use. Of course, I merely argued that it's uneconomical, not un-designable.... Hey, gimme credit for at least trying to save my butt here...

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Post    Posted on: Wed Jun 29, 2005 3:16 pm
You presume to speak with authority, but all you offer is opinion.

The same opinion as the NASA Chief--or perhaps you don't believe him either.

Where is the substance? If you want to sway the thinking of others, particularly in any technology-related field, your arguments need to have significant numercial import.


Read Spaceflight in The Era of Aerospaceplanes by Russ Hannigan--esp. that point about small spaceplanes being of limited utlilty. Or just remember how Dennis Smith tried to snowball Congress into funding an OSP that was just as expensive as the larger Energiya--you do remember that--don't you?

The only way to teach others is to share what you yourself have learned; so come on, man, show us what you KNOW... everybody here already knows what you THINK

I could say the same thing to you--but suffice it to say that...

I know that Mike Griffin knows a lot more about our launch needs than most. And for that reason--I think I will support him instead of backbiting him.

If that is permitted, imperious leader...


On to other matters. Designing big makes more sense than designing complex.
Big Dumb Boosters have had advocates for many years, and there are all kinds of papers out there on the subject. One you might like to look at is John London's book LEO ON THE CHEAP. He works Marshall and I speak with him on a regular basis.

Sadly, the Goldin/Gore types gave us the X-33 debacle--and we all know what happened with that. So it should be obvious that the 'fly often and sophisticated' approach has nothing on the 'fly big and simple' approach. That should be common sense to all by now--and I find it surprising that a lot of people still don't get it.

Even Rutan is going to have to learn to build larger--if he is to field a VLA for t/Space. VLA for Very Large Aircraft. So as you can see--one way or the other....it's a heavy-lift world.

We have been conditioned to think that spacecraft have to be small and complex--and yet we spend a lot of money on megaprojects like Kansei and Troll that make even Sea Dragon look tiny by comparison. That is the approach space advocates need to embrace--not fight.


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Post    Posted on: Wed Jun 29, 2005 7:07 pm
You're missing the point, publi.

I don't dispute that heavy-lift makes sense. I absolutely support what Griffin wants to do about it. I actually
said that Griffin was probably going to tell the primes that he already has a heavy-lift rocket http://www.xprizenews.org/forum/viewtop ... ght=#13706
and lo, and behold, he says just exactly that last week at the Space Transportation Association breakfast
NASA Administrator Mike Griffin wrote:
For the heavy lifter, I am looking to adapt shuttle-derived systems to the needs of Moon-Mars because we already have a vehicle that is in the class that I want.

...you can find this at http://www.spaceref.com/news/viewnews.html?id=1035, but surely you are aware of his position on this issue.

My point in all of this is that big isn't always best simply on account of being big. There is a reason that Sea Dragon was not built, and it isn't Vietnam or Apollo or STS. Sea Dragon wasn't built because nobody believed that there was a practical reason to loft 500 tons in a single launch. They didn't believe it because noone was able to provide a convincing rationale. If you want people to believe you, publi, you are going to need convincing rationale.

Someday, someone will build a launch vehicle with that kind of capacity. Griffin is NOT going to do it because he doesn't NEED to. When there is valid cause and appropriate demand for a vehicle in that class, it will become a reality. If someone builds it just because "bigger is best," it won't survive. One of your favorite birds, Energyia, is a perfect example of that principle.

publiusr wrote:
the X-33 debacle--and we all know what happened with that

Do we, really? Can you provide us with a treatise on cryopumping and what really caused the composite LH2 tank failure? Can I safely assume everyone here has read the extensive and technically complicated literature which deals with the behavior of cryogenic fluids in laminated composite structures? I don't suppose I can. Was the failure of the x-33 program a consequence of insurmountable engineering problems? No, it was not. Was it doomed to the scrap heap by socio-economic forces because its backers lacked convincing rationale? Possibly. Did congress pull the funding because they felt that it wasn't NEEDED? I expect so.

Are socio-economic forces a reliable gauge of what is the best engineering choice? Most certainly not. Are socio-economic forces the ultimate deciding factor in what does and does not get built and used? Every time. Does that mean we should give up trying new things like linear aerospikes and SSTO and 500 ton HLLVs and other technically challenging goals? I certainly hope not.

Given the resources, a motivated team of bright people can conquer any problem. But the "resources" is the one box you CAN'T think outside. Otherwise all you'll ever be is a dreamer.


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Post    Posted on: Thu Jun 30, 2005 12:00 pm
Damned good post.

Isn't the full structure of the X-33 sitting in a hangar somewhere in the Southwest waiting to be assembled, because they cut the program before they bothered to put the thing together? Or am I completely off-base?

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Post    Posted on: Thu Jun 30, 2005 6:37 pm
SawSS1Jun21 Wrote :
There is a reason that Sea Dragon was not built, and it isn't Vietnam or Apollo or STS. Sea Dragon wasn't built because nobody believed that there was a practical reason to loft 500 tons in a single launch.

We have to agree to disagree on that one. Check with Lowther's APR or the astronautix website. Vietnam had everything to do with it. Sea Dragon just did not have the advocacy it needed to prove its utility--commercial or otherwise. General Atomics actually got pretty far along with the early prep work for Orion--but Von Braun was A#1 at that time.

As far as X-33 you don't need to ask around very much to speak with engineers who understand that you don't put liquid hydrogen in conformal composite tanks--when metal tanks of simple shapes are best--that is why they were going to metal tanks in the end--the weight then got to them--and then they blame other factors. Don't fall for that--you are too smart.

You did ask, after all:

"Are socio-economic forces a reliable gauge of what is the best engineering choice? Most certainly not."

Agreed.


"Given the resources, a motivated team of bright people can conquer any problem. But the "resources" is the one box you CAN'T think outside. Otherwise all you'll ever be is a dreamer."

Dreamers come up with cockied plans to break the laws of physics when big dumb boosters will do the job just fine thank you. We are ALL dreamers here--and a very few of us also add the "--shaper, thinker, maker." to our names. Resources are such that large but simple designs are what is best.

We have been brainwashed into thinking small is good for so long that we have begun to buy into it. That is one "socio" force that really is a hold back--and Griff could explain that to you very well from experience --since he gets the old "we-don't-need-heavy-lift" lie spouted at him at every turn by EELV hucksters who also realize that there isn't much of a market for EELV either. They want us to pay for their needs--and not build for ours.

People like Griffin and I refuse to buy into this--because our scales of thinking are such that we understand that scale opens up new vistas. In the era of Kansei, and other mega-projects that started off as dreams--no violation of the laws of physics is needed.

The problem as I see it is this. People want the easy way out. There are a lot of Art Bell types working on small "anti-gravity" machines, 100 mile per gallon contraptions and such. It doesn't take a lot of money to build a lifter--and fool yourself into thinking that you are on to something--explaining away the ion wind effect.

X-33 was this kind of thinking done by a company fooled by the "Why waste time with 'dinosaur' boosters when we can do smaller and smarter?" line that just doesn't work. The Soviets got ahead because they built rockets bigger than 'needed.' and that works for them just fine. Where our rockets were over-optimised, underpowered and over-complicated--Russian boosters were underoptimised, overpowerd, and simple. At the time--it took lots of money--but it was worth it in the end.

Ask Dennis Tito.

As long as people keep fooling themselves with small-scale nonsense we are never going anywhere as a species.

Instead of making anti-gravity playthings (or X-33s for that matter) out of matchsticks to cross a gorge--it is best to buckle down, buy some steel--and make a big stout bridge.

It is hard? Yes--but hard beats impossible.

The problem with investors is that, with regard to space--they think the impossible is easy and the hard is impossible (or foolish)--and that mindset holds us back.


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Post    Posted on: Thu Jun 30, 2005 9:33 pm
publiusr wrote:
Sea Dragon just did not have the advocacy it needed to prove its utility--commercial or otherwise.


...isn't that what I said? I'm sorry if I wasn't clear.

Quote:
As far as X-33 ....... --that is why they were going to metal tanks in the end--the weight then got to them--and then they blame other factors.


I don't know what was blamed by the LockMart brass. I couldn't care less. I read the engineering reports on that project religiously during its development and testing and I know that the aluminum tanks would still have flown. It was a subscale demonstrator after all, it wasn't going to orbit in any case.

If you feel they spent too much money for a subscale demonstrator, well, I can't argue with that. But again, that's not an engineering issue.

Quote:
Dreamers come up with cockied plans to break the laws of physics when big dumb boosters will do the job just fine thank you. ........ Resources are such that large but simple designs are what is best.


Sure, I think we need to put our resources into what works, but we need innovation, too. I hope like hell that my grandkids won't live in a world where the only way to orbit is in a pressure-fed iron-hulled behemoth. And the notion of "growing crystalline airframes in zero-G orbital factories" seems a lot more far-fetched to this engineer than does the notion of conformal composite LH2 tanks.

Quote:
The Soviets got ahead


Ahead by what measure? They offer the most affordable launch options on this dirt clod, they build thier rockets for peanuts, they should have put everybody else out of the business by now. But even in the most prohibitive regulatory environment (i.e. the US), we have multiple startups (one about to fly now) whom are saying they can do it cheaper... with smaller birds?

Musk is building his bird for the MARKET, which is the only force which can drive space travel over the long haul. When the market wants a 500-ton payload launcher, it will get one. Your containerships vs. clippers is a good example. The clippers disappeared because the containerships made more economic sense, not because some 'visionary' shipwright built them ahead of the shipping market's demand for capacity. Instead of putting the cart before the horse, you're putting the launcher before the payload (this analogy is only valid in it's linguistic context, not the mechanical one :) )

Or, to put it another way, the pharmaceutical researcher calls his patron one day and says, "Hey, I have a formula that can grow hair on a billiard ball!"

...to which the reply is "Who wants hair on a billiard ball?"


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