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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 Rockets vs. Airbreathers   Posted on: Thu May 26, 2005 12:44 pm
If the mods would be kind enough to cut and paste the last few posts from the "Venus-Fit Technology" thread, then we can get on with the discussion.

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Post Re: Rockets vs. Airbreathers   Posted on: Thu May 26, 2005 12:50 pm
spacecowboy wrote:
If the mods would be kind enough to cut and paste the last few posts from the "Venus-Fit Technology" thread, then we can get on with the discussion.

Phpbb forums does not allow to split and merge again, or to move posts to an other topic.
Please qoute from the previous topic, the text you're replying on.

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Post    Posted on: Thu May 26, 2005 1:44 pm
Okay, quotemania it is…

publiusr wrote:
No--I do respect Rutan's ability to build airframes. A MAKS type craft would be perfect for his 'scale' of work. But the actual boosters need to be done by someone else.

A "Rutan Buran" would be perfect--NASA makes an Energiya type HLLV with an RS-68 equipped ET--instead of Energiya's ET with four RD-0120 hydrogen engines.

Rutan could build Buran very easily. Buran only had orbital insertion engines--not ponderous huge SSMEs. Its near SS1 scale insertion engines burned Lox/kerosene, which could be used for landing jets--and the O2 for emergency life-support. Had we flown a (metal heat-shielded) Buran in a heads-up profile--out of foam fall--which has to be fixed for any TSTO (which would also have to use parallel staging / side payload mount) we would't have had the Columbia Disaster.

If we had Energiya and the Russians had STS--the world would have been better off.

The US would have had the EELV-class Zenits (not SRBs) to replace the older Delta's and Atlas--and the orbiters could be switched out for 100 ton payloads--since the engines would be on the ET and not the blasted orbiter.

Large scale hypersonic boilerplates could be launched in the same position as the orbiter--after being released by 747 orbiter ferry for low-speed tests. Hypersonic needs near ful scale tests--not surfboard sized X-43s.

Energiya would have launched 100 ton ISS segments--and it would have been finished--with simpler Buran orbiters leaving 30 tonnes of raw material and recovering the same mass as processed goods. Each 100 ton payload--launched in place of Buran--could have been like the Columbus Free-Flyer the Euros wanted.

We could have had true modularity--and the orbiters down-lift and mass (stable for 100 ton segment construction) would have been an asset instead of a liability.

It wasn't mixing crew-and cargo that doomed the STS--it was putting over-complicated SSMEs on the orbiter.

Big engines on a fly-back with no heat shield is fine. A spaceplane with only insertion engines is good. A plane with that and huge engines both--that becomes ponderous.


I actually challenge the 'don't-mix crew-and-cargo' mantra. Very small top-mount spaceplanes run out of room--and run into weight creep really fast--as do SSTOs that are cryogenic blimps/hypersonic eggshells. By keeping high density crew and cargo together--but by keeping heavy engines and bulky propellant mass outside the airframe--you have an orbiter scaled up big enough to be useful (unlike an X-37 only mini-me could fit in)--but compact enough to be buildable--unlike VentureStar.

You don't use row-boats or super-tankers to visit oil derricks--but mid-sized tugs and such.

But people have been brainwashed into hating such orbiters, so a hypergolic Martin Astro-rocket type TSTO with non-cryogenic porpellants or something like MAKS or HOTOL are what pretty much what is left--apart from SpaceDev's orbital version of their X-34 based Dream Chaser--which looks a lot like a mini, hybrid version of Energiya-Buran--only with tourists and light cargo. They will have no ice or foam problems--and the side-mount reduces pitch-loads and bending moments that threaten to tear top-mount mini-spaceplanes off their rides.

The LockMart OSP/CEV had a picture of a tiny escape tower(AV WEEK) that I doubt could tear that slab off an EELV during max Q. EELVs like axial loads--and that will probably mean capsules for CEV.

Dennis Smith--the X-37 huckster from Marshall--tried to sell Congress a $13 billion OSP program and got laughed off the hill--and this LockMart OSP has his name written all over it. He wanted X-37 launched inside a shroud--for he knew what pitch-loads could do to it.

Hard to bail out through a shroud.


spacecowboy wrote:
Y'know.... This guy keeps on making more and more sense.

By the way, what do you think of SSTO airbreathers, such as this one and this one? Those two designs aren't that great, but the concept seems pretty good.


publiusr wrote:
Sadly, I must say that I don't think that much of them. Since you are going to need a rocket at some point--save a step and go all rocket. Hu Davis thinks that Air Launch doesn't get you that much BTW.

The problem behind airbreathers is that--while they omit some of the oxidizer mass--you are left with even more severe thermal issues, andthe airframe must be burdened with large scramjet intakes, jets, etc. A rocket is a simple tube--with as much wing as you need. Hard to beat that for simplicity's sake. Plus, the rocket can pop up through the atmosphere and get over it quickly--hypersonics must stay in atmo for oxidant

Let's compare two vehicles. An airbreather is like a sprinter who has to eat his way through flaming jello and build up speed. A rocket is like a fat man who climbs a ladder and loses ten pounds with every step (staging prop mass as thrust). He then is on an upper story race course.


The fat man beats the sprinter every time.


Large scale hypersonic boilerplates--would give good full scale tests. I have heard some good news coming from a contact I have in the Pentagon--who spoke with Pete Worden. He can't say much--but he did say it was "all good news." I think airbreathers will be possible after, say, 2050. Self ferry capability is nice--but a rocket that burns kerosene can have that too.

Ironically--there were some plans for Buran to have jets. The analogue did, and unlike our Enterprise--the Buran analogue could take off under its own power.

With Orbital insertion engines where we put our SSMEs--turbojets could be placed on Buran where we place our OMS pods. I would put them in a mount atop the wing--and have the fuel cells keep them warm with some tubing. Then returning orbiters only need keosene for both orbital insertion and ferry. Extra kero tanks could go in the payload bay for Buran--and extra lox. Buran could fly much higher--take more to orbit--return with more--was simpler--etc.

Plus, by keeping its engines under an ET (Energiya) it gave us a heavy lifter that could be used independantly.

This was the STS we could have had.


Marshall wrote:
publiusR wrote:
publiusr wrote:
Let's compare two vehicles. An airbreather is like a sprinter who has to eat his way through flaming jello and build up speed. A rocket is like a fat man who climbs a ladder and loses ten pounds with every step (staging prop mass as thrust). He then is on an upper story race course.


The fat man beats the sprinter every time


Good visual .


spacecowboy wrote:
I tend to like airbreathers because they have the capacity to be a true SSTO, whereas the best rocket designs tend to be two- or three-stage. The airbreathers (while admittedly taking their sweet time to get to orbit) are completely reusable and also offer an outstanding compromise between Isp and thrust-to-weight ratio. Rockets are great at T/W, but usually throw away their lower segments (or said segments have to be completely rebuilt after each launch, as the SRBs), and have a lousy Isp.

[edit]Outstanding visual, by the way.[/edit]


DUN

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Post    Posted on: Thu May 26, 2005 5:47 pm
Actually, the staging interfaces can cause weight penalties themselves--this was why the Shuttle--and the original Atlas rockets are thought of as stage-and-a-half vehicles.

If any of you remember the old SCORE program--what they did was to place an entire Atlas body in orbit. This led to the idea of the Convair Atlas station. By having propellants in one container--that could pop up through the atmosphere without having to stay in it as long as hypersonics--you had a simple system.

Atlas had a thrust ring--three engines--one on the body of the rocket itself as a sustainer--and two more on the thrust/support ring which fell away in flight--leaving the whole body of the rocket to go to space--with the oxygen tank capabile of being usable hab-space--the fuel tank too with cleaning. A winged Atlas was proposed but never followed up on--and Atlas was a simple tube good for rising up like a nail--coming in belly first would not have been good for its balloon tank structure.

Saturn VB was to have been a similar Stage-and-A-Half system--and the Saturn IB with a cluster of tanks is probably strong enough for wings.

The original R-7 Sputnik rocket was a stage and a half system--the conical strap-ons falling away and the core section that kept rising. Later, as heavy upper-stages were added, it fell away as normal.

The shuttle could take its External Tank into LEO with it--as it stands--it has to go in a shallow dive, blow the tank--then burn its OMS for that last little boost. The ET has propellant left over--and the SSME's shut down early. One ET has more volume than ISS--more than Skylab even--and would have been perfect as a station. Energia, with a lighter side payload could also be taken to space.

One big rocket--perhaps with strap-on jets/fall away take off gear is about as simple as an SSTO gets.


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Post    Posted on: Thu May 26, 2005 5:56 pm
Forgot something. Liquid hydrogen likes big, simply shaped high volume metal tanks. It does not like conformal, composite multi-lobed tanks and will burst them every time.

A hydrogen scramjet must face this problem--and do it better than Venture Star.

A big ET is good for LH2--can be used as hab space--and, with three RS-68s--gives us an HLLV with engine-out. Delta IV has cores that are more narrow--not as efficent--and only have one egnine each.

A winged Zenit like the Zvityaz air-launched system might work--and it took AN-225 for that--but was never done. Hypergolics are desnse and allow for more narrow tankage--and the spaceframe resembles an eggshell less (the ET is quite strong compared with Atlas however--it has to be).

But an All hypergolic SSTO or TSTO will probably not sit well with the Greens and EPA--especial;y after the Nedalin disaster--that shows what hypergolics can do to human flesh all too clearly. The only reason our STS orbiters use in in those OMS pods, is because the SSMEs take up all the asft boat-tail. The hypergolic fuel tanks are the size of beach balls.

Buran had no such problem--being all OMS--and had nice big kerosene and lox tanks in place of the SSMEs--and no need for OMS pods--thus its smooth backside. Buran was about as simple as a spaceplane could be--and was just one of Energiya's many planned payloads. Buran's tankage was compact--rather like Dyna-Soar's trans-stage--but was re-used as part of the orbiter. Dyna-Soar was too small in my book, and the Titan III it needed could have put an entire Gemini-equipped MOL up in orbit instead--if you don't mind crawling through a hatch through Gemini's heat-shield to get to the MOL, that is.


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Post    Posted on: Tue May 31, 2005 12:55 pm
Is it possible to build a human-friendly HLLV -- i.e. one that does not pogo noticeably, has considerably lower acceleration than most other rockets, and provides for a smooth, comfortable ride?

Second question: okay, so we've got this big beautiful rocket, and we've even taken the whole damned thing to orbit. So now how do we get it back down in one piece (or at least so that we can put it back together)?

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Post    Posted on: Thu Jun 02, 2005 10:06 pm
I don't know that we have to get it back down. ET's can be left in orbit for spacehabs.

This is where Single-Stage and Stage And-A-Half designs and space architecture share a certain design--large simple tubes.

It is much easier to put floors across anti-slosh baffles and call it a deck than it is to get a large tank--put wings on it, landing gear in it, and heat shield under it--to call it an RLV.

Some of the old hybrid rocket designs--Amroc, I think, wanted to keep one big oxygen tank under the payload, atop all fuel lower stages that fell away. With modifications, you could leave this oxygen tank on the payload (capsule, cargo, etc) and back the tank with a combination LOX/hatch pass thru to a station. The gaseous lox becomes propellant for stealth cold-gas thrusters, and new oxygen is left on the station--which just got larger.

The payload separates from the tank and heads for Earth.

As far as winged craft--esp. hypersonics...I think another materials revolution with mass production of borazon is needed.

I like www.spaceislandgroup.com

They are the only company outside starbooster talking about finding private markets for heavy lift.

Everyone else plays with toys, call the HLLV folks dreamers, while getting little support themselves. We need to remember that containerships work because they are big. I just wish people understood that. Usually when folks invest in space--they invest small amounts--which doesn't really advance us. We need big supporters to reach economies of scale. Griff will give us that--and Tom Delay too I hope.


I always liked the look of Star Raker myself--as far as hypersonics go.


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Post    Posted on: Mon Jun 06, 2005 12:41 pm
How would the borazon be used? Tiles like on the Shuttle (and everything else so far)? Or a one-piece hull, constructed entirely out of the stuff? Ah, but if only we could build nanomachines, and have them build us a spaceship....

The Star Raker's a decent design -- for the '70s. I tend to prefer the newer, more advanced designs. I have a feeling your preference for the Star Raker was based at least partially on size -- but doesn't that $22 per pound payload price sound beautiful!

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Post    Posted on: Wed Jun 08, 2005 6:12 pm
Size is the number one factor when it comes to profitability. There are two ways to reduce launch costs per pound. The easiest way is to increase throw-weight per launch. (the BIG DUMB BOOSTER approach). The second is with an increased number of flights. Star Raker was to launch 100 tons with each flight--combining the best of both worlds.

I think that and that alone will revolutionize space flight. Borazon tiles may come first. Amorphous steels are strong--but are limited to coatings, and can be brittle.

Here is what I would like to see:

Shuttle Derived Heavy Lift for now--small space factories, etc.New materials

Even larger boosters like Sea Dragon for true space platforms--serviced by--

Star Rakers for the future.

As it stands--no one launches more than 20 tons. If it were up to me--there would be no craft capable to lofting less than 100. Star Raker does that--or would.


The idea that we need RLVs first--to build grand structures--was the STS approach.

My approach would be to build large space factories, grow hulls in zero-g and fly them back. A top down--not a bottom up approach. A large, one piece crystal grown in a template would work. It becomes an RLV.

So it is not SSTO to space and back--but SSTO from space and back. It might be that the materials needed for better heat shields can only be grown in bulk in the actual space environment we want to reach. So we have to take the Big Dumb Booster approach now--to get the next series of materials revolutions we need to fly often.

Otherwise, things continue to stagnate.

Fly big now--fly often...later.

Then fly big and often.


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Post    Posted on: Wed Jun 15, 2005 1:34 pm
Y'know, boys and girls, it really truly makes sense.

And I certainly agree that we desparately need in-orbit materials research.

Question, though: you mentioned problems with storing the LOX/LH2 fuel earlier. What is it about the Star Raker's design and construction that makes it better able to handle the fuel tanks?

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Post    Posted on: Wed Jun 15, 2005 7:56 pm
There are five size-ranges of vehicles out there.

Three size ranges work, two do not.

Small top-mounted spaceplanes that are manned are hurt by weight creep. Scale it up a bit where it becomes Buran or Dream Chaser sized and it works. Scale it down for it to become un-manned and you have an agile warhead, and that works. But OSP itself was like Hermes--which would have cost as much as Buran--but was far more cramped.

Venture tard was a little larger than Shuttle. Something very much larger like Sea Dragon is scaled up so f--ing big that the high volume is such that you can use heavy maranging steel and it works. Star Raker is more of that class than Venture Star--but even it is likely to need a new class of materials to really work.

Just my opinion, mind you.

Agile warhead------OSP----------Buran/Dream Chaser-------VentureStar-----Sea Dragon/Star Raker
GOOD......................BAD.......................GOOD.............................BAD...................GOOD


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Post    Posted on: Thu Jun 16, 2005 1:43 pm
Okay, that makes sense: make it small and unmanned, and you don't have to deal with life support, g-requirements, etc. All your weight goes into heavy-duty materials. Try and make it larger and cram people inside, and you won't have the room to stuff in a big enough engine to push the structure. A little bigger, and it works, because you can put in a big enough engine. Try and scale it up a bit larger, and again, you need heavier materials to handle the bigger structure, but then you won't have a big enough engine to push it. Keep going up in size, though, and you'll finally hit a threshold where you can build a stable, strong structure and can put in a big enough engine.

:idea:

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Post    Posted on: Thu Jun 16, 2005 6:54 pm
Exactly. A lot of things are that way. Some things work out a bit differently, tho'

. A one piece doghouse won't topple during an temblor (though it can be pushed around). A midsized building of only a few floors with un-reinforced masonry will come down on you--but a steel megaskyscraper will give and (usually) not collapse during tremors.


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Post    Posted on: Thu Jun 16, 2005 8:49 pm
That's about materials and methods of construction, not scale.

Cowboy stands to lose nothing by exposure to such ignorance, because he's going to be properly edjumacated at GT. As such, by next year he'll be able (for example) to answer his own question (not this thread, I know) about Musk's turbopumps (it's about performance, Cowboy) but not everyone on this board has the advantage of a future education of that quality.

If you could make a real min/max graph out of your "five sizes" position, it might hold a little sway. But as it stands, it is (as you did correctly say, thank you) just your opinion. I'm not saying your opinion doesn't have merit, it just doesn't have any factual basis given its delivery.


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Post    Posted on: Mon Jun 20, 2005 1:21 pm
Yes, and my first couple of instructors are probably going to hate me for all the idiotic ideas I'm going to bring with me. What he said makes sense: for example, 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. The one is an example of trying to use the wrong type of engine for a particular purpose, the other an example of a vehicle that has no market value (it would cost too much to operate for the average private pilot, and could never make any money for a commercial operator). Could you build them? Sure... But why?

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