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Carmack's Throatless Rocket Engine
Baldrson writes "John Carmack is working a potentially disruptive technology: A throatless rocket engine. Its made from plain aluminum pipes with few machined fittings. Carmack says: "The great thing about these engines is that it only takes me two nights to machine the parts, so we can test two engines a week if necessary." It scales too: "If this line of tube engine development works out, we can make a 5,000 lbf engine with very little more effort than the test engine." This is what makes disruptive technology development work: Cheap, fast turnaround on on redesign producing technologies that scale. If this works, the NASCAR guys may really start entering space competitions like the X-Cup."
the Pipedream finally becomes reality.
I mean, why have a genius like Carmack working on shooting rockets into space, when what the world really needs is a better personal rocket launcher... for shooting rockets into other people.
In an effort to propel himself high enough to reach the Quad Damage, John Carmack fragged himself with his own rocket launcher. He will be remembered by a rabid community of gamers. We will all miss you John.
Not that I'm one to criticize (large liquid-prop rockets built by Skyshadow: 0), but everytime they get an engine together and start encountering difficulties it seems like they scrap it and just go to another design. Assuming that rockets are anything like the mechanical things that I understand (cars), this just isn't how you can go about these things -- you've got to settle on a promising, well thought-out design and then dedicate your efforts towards ironing out the kinks or you'll perpetually be just past "go".
Anyhow, just the impression I get from reading the updates.
Every year during my review, I just pray the words "slashdot.org" aren't mentioned.
If you would have read through armadillo's website you would see that he has been putting a serious effort in. As an aerospace engineer who has been keeping tabs on John for several years I can assure you he's got his design well thought out.
Throatless rockets aren't new... they've been around for awhile. They aren't as efficient as a throated rocket but they offer some operational advantages (namely in throttling, which is nice for a powered reentry).
-everphilski-
since I'm not a rocket scientist, I fail to understand the importance of what John is doing (or has discovered? surely throatless engines aren't an entirely new concept are they?).
I understand that this *might* impact manufactoring costs, but exactly how is this revolutionary, or going to affect us? Are we going to sport some pocket engines in the future? Are they more environmental friendly? Do they scale well? Will it run Linux?
Seriously, after reading the story and the article a few times I haven't yet understood half of it.
Hack your mind out of its sandbox.
I'm miffed that he didn't express it in stone-furlongs.
Before.....
After.
No, we are not "stubborn". And yes, the standard system SUCKS. The reason we haven't moved to metric is that we have too much momentum built up in society for anyone to switch over. What needs to happen in America is a migration. This is slowly being done, but it will take many more generations beyond me.
I was tought the metric system in grade school. However, I only use it personally when working on cars. Most of the time GM will have a mix of standard and metric bolts these days.
Life is not for the lazy.
I think Mr. Carmack has a bit of a Pygmalion complex with Commander Keen. To the heavens!
If you read the link, the X-Prize people are talking about starting the X-Cup, a regular space competition.
Well then, that's no problem, as lbf means "pounds-force", not pounds*feet (which would be a measure of torque).
Here's a hint: a serving of beer weighs about a pound. One lbf is how much force you must use to hold it up (assuming you're drinking it somewhere on Earth).
It's also equivalent to about 4.44 newtons, but that unit is too small to provide a satisfactory serving.
From the site ...
"Too many users... blah blah blah
Probable cause: http://www.slashdot.org/
Try again in a few seconds...
-xian@idsoftware.com"
That has to be the best 'server down' message I've seen in years
"If you would have read through armadillo's website you would see that he has been putting a serious effort in. As an aerospace engineer who has been keeping tabs on John for several years I can assure you he's got his design well thought out." - by everphilski (877346) on Sunday August 07, @11:07AM
:)
That is good to hear, that another pro from that SPECIFIC field is seconding his designs, and as far as thinking things out (when it comes to this guy, Mr. Carmack)?
I believe you.
E.G.=> Ever heard of "Carmack's Reverse"? If not, look it up, & check it out... this showed me this guy can THINK, & "outside of/above & beyond the box"...
Not every computer scientist has things like that to his credit!
IMO, these types of things (engines/algorithms) to overcome limitations ARE the mark of what others called him here:
A genius.
IMO, he is.
After all, his wares from IDSoftware & contributions in the OpenSource world show it. There's little arguing with that & little arguing with success.
*
APK
P.S.=> I wish him the best of luck to be quite blunt & honest about it...
Like he himself has said (not a direct quote):
Once you've accomplished a decent amount in 1 particular field? It's good to take a "hard right turn" into another one that interests you and make a career of it!
In his case it would NOT surprise me one iota if he does not end up becoming a breakthru maker in it as he did in computer science...
People like these, just give them time & experience: They're the types that always come thru!
Yes, this is "intellectual/technical hero worship" & he is one of the few out there I give that much credit to!
He, along with Mr. Anders Hejlsberg (of Borland (TurboPascal/Delphi designer) & Microsoft (C# & Visual Studio improvements) fame)... they're 2 of the 'outstanding' individuals in THIS field (computers) out there now, truly outstanding ones.
There IS a diff. between pretty good, good, great, & absolutely outstanding/in a league of their own.
Never underestimate folks like those, they often surprise... apk
What the hell is a lbf? Is North America really so backwards and stubborn they refuse to use units that the rest of the world is perfectly happy with.
;)
Yes. We are able to use non-decimal units because, quite frankly, most applications call for non-decimal units.
Once you've been to the moon and back, THEN maybe we'll consider your ideas on measurement.
If this line of tube engine development works out, we can make a 5,000 lbf engine with very little more effort than the test engine."
Interestingly enough, as a kid I made my own alcohol fueled rocket motor, based around a bottle filled with a alcohol/oxygen mix, a small orifice, and an ignition source.
If thing were the way I'd like them to be, I could have scaled it up to be something like twice the power of the Saturn V rocket. But after the first successful test, I was unable to scale the device.
Best of luck to John, may he do better than I did.
I know it sounds crazy, but sometimes it is much easier to evolve a nice solution to an engineering problem than to calculate one. For example calculating robustness and reliability is very difficult. It is much easier to simply measure it.
Change the unreliable bits to something else, and see if it breaks. If you kill off the most unreliable part of your design each time, I guess you can work out what happens.
I'm not saying that you shouldn't use simulations or calculate anything at all. Use them as guiding hands, but don't let them alter the process. The problem is many people think that it is easy to create some sort of `breakthrough' design. It isn't; if it was, then everyone would have them.
Per Carmack's writeup, 1.5% ISP loss, which is lost in the noise for their purposes. He also mentions that he thinks he can get about a 15% increase over their initial tested ISP, which was about 190 seconds, and that that would put the ISP very close to the maximum value for the propellant of 220 seconds.
Property law should use #'EQ, not #'EQUAL.
*ahem*
/
http://www.cnn.com/TECH/space/9909/30/mars.metric
Do not trust this signature.
This "throatless" engine seems more useful for testing injectors than actually extracting impluse (propulsion). The narrow throat of engine followed by a expanding nozzle allows for the chamber pressure to be high (good) while the exhaust pressure is lower (also good). This site explains much this and in fact says, "If the pressure ratio (and thus expansion ratio) [like Carmak's design] is 1, then F = 0. The only thrust produced by such a nozzle is the pressure thrust, or Ftotal = (Pe-Pa)Ae. Such a nozzle, of course, would have no divergent portion, since A*/Ae=1, and would be a badly designed rocket nozzle!"
;)
Simon
Ok, first, you don't get shockwaves in nozzles- not unless you've got a rough nozzle surface, which is a bad idea, because the hot gas comes to a screaming halt ("stagnates") and the local temperature goes way up, and then the nozzle melts. And yeah, Carmack knows that a nozzle and throat needs to be smooth, this isn't the first bipropellent engine he's built, and he's widely known not to be stupid. :-).
Oh yeah and actually, even these 'throatless' engines has a throat, but it's kinda hard to spot :-), the gas makes up its own mind where to put the throat, in realtime- the throat is defined to be where the gas goes sonic, and this always happens when the combustion pressure is more than 2.7 times the ambient.
You mainly get shockwaves in air inlets in jet engines, not in the nozzle. You also get shockwaves in the exhaust plume of rocket engines where the exhaust kinda bounces of the external atmosphere, but that's harmless (actually kinda pretty google on "mach diamonds"), and they form wayyy downstream of the exit. Oh yeah, and a rocket launching, once it passes about mach 0.85 gives transonic shockwave around its nosecone, and then later supersonic shockwaves there, those can cause damage, but they rarely do.
So, these non existent shockwaves can't damage any equipment, or waste any energy. Oh yeah, and did I mention there aren't any shockwaves? :-)
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"He reports only an ISP only in the low 200s, this is not efficent enought to get to orbit.
TFA is unavailable due to slashdotting, but low 200's will get you ~5km/s with a 90% mass ratio. It's plenty for sub-orbital work, and useful for the first stage if you're not trying for Single Stage To Orbit.
The shuttle SRBs have an ISP of 273 seconds.
Yes, However the Shuttle's 470ish ISP SSMEs do most of the work in getting it to orbit. If he could get the rating around 250 I would say he has a chance at maybe a first stage.
It's actually a misnomer; provided the chamber pressure is more than 2.7x the atmospheric pressure (which it always will be if you stuff enough propellant in through the injectors) then a throat spontaneously forms near where the nozzle widens out. The throat is defined to be the place in the combustion chamber where the gas goes faster than sound. Normally that would happen at the narrowest point of the nozzle, but in this case it may even move around in the combustion chamber, but it can't leave because the nozzle widening out stops it.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"From Mirror:
http://www.mirrordot.org/stories/8f5373b24e35f5c45 3edf914cc953eff/index.html
Armadillo Aerospace News Archive
>
Servo regulator, Throatless engines, Hold down test
Aug 4, 2005 notes
Despite not having time to do an update for a while, we have been steadily working...
Servo regulator
When we last worked with it, the setup showed what seemed to be a valve lash problem - flow would begin when the high pressure ball valve reached 15% open, but it wouldn't shut off until it was closed all the way back to 5%. Since we had fabricated our own actuator to valve adapter, we thought we might have allowed too much lash into the coupling. We built a new mount using helical beam couplers with zero lash, but that turned out not to help. The coupling seems tighter, with the valve following every little jitter of the actuator, but the flow behavior seems to be an aspect of the seals in the ball valve, not the linkage between the actuator and the valve.
This cracking problem is only really an issue at very low flow rates, so we were able to do some flow tests at roughly the performance levels that our single-man space shot vehicle will use. With a single large nitrogen bottle feeding the servo regulator, we did the following test:
2700 psi initial bottle pressure
60 gallons of water at 230 psi and 215 gpm flow rate
1800 psi final bottle pressure
2" plumbing, 1" valve
The small fittings at the bottle valve became the limiting factor as the pressure dropped below about 2200 psi, with the servo valve eventually going wide open and still not quite being able to keep up. Our flight vehicle pressurant tanks will manifold directly out of bottle necks with a -10 fitting, so they won't become flow limited at all. When our new 36" hemispheres arrive, we will be welding up the full tankage and pressurization system for the big vehicle and doing water flow tests in preparation for testing a 5,000 lbf class engine.
Speaking of spheres, here are a couple pictures of the tear area on the burst one:
http://media.armadilloaerospace.com/2005_08_03/tor nSphere.jpg
http://media.armadilloaerospace.com/2005_08_03/tor nSphere2.jpg
Throatless engine
I was recently looking at the table in Sutton regarding losses due to small chamber to throat contraction ratios, and they weren't as significant as I had remembered them. A chamber with no contraction ratio at all will lose 20% of its thrust due to pressure losses from accelerating gasses in the straight section, but the Isp loss is only 1.5%. The text mentions "throatless rockets" being used in some missile applications to minimize chamber length and dry mass at the expense of Isp. The text doesn't say if these were liquids or solids, but I assume they were solids.
However, this does open up the question of building liquid engines like that. If L* remained constant, you would have an extremely long engine that would probably be impossible to cool, but I could imagine the accelerating, high speed flow could reduce required combustion stay times significantly. A 1.5% Isp loss is utterly meaningless for our purposes, so a configuration that traded that for fabrication benefits could be quite useful.
We fired a few crude throatless lox / ethanol chambers, and the results were surprisingly encouraging. With a very crude injector (a spray nozzle for the lox and four straight horizontal jets for the ethanol), we measured a 190 Isp from a 12" long straight pipe combustion chamber. It melted in a couple seconds, but this was still very impressive. With a 3:1 expansion cone added, performance should increase about 15% to around 220 Isp. That would be right at theoretical va
"If all the world's a stage, I want to operate the trap door." - Paul Beatty
Is North America really so backwards and stubborn they refuse to use units that the rest of the world is perfectly happy with.
Ok, it's a 5klbf engine. Happy?
If I have been able to see further than others, it is because I bought a pair of binoculars.
but he doesn't work for NASA
Neither does Burt Rutan.
Unfortunately, no. Chemically fueled rockets are just barely capable of making it to orbit. They're mostly fuel tankage. Single stage to orbit craft must have at least a 90% fuel fraction. At least. Any serious inefficiency or weight growth kills the design, as happened for Rotary Rocket.
Staging helps. Two stages will get you to low earth orbit. Beyond low orbit usually requires three. This reduces the fuel fraction, but by less than one would hope. The Shuttle's fuel fraction is around 89%.
So space flight is all about weight reduction. Which is why everything is so fragile and unreliable. If you could build a launch system with a fuel fraction of 50%, which is roughly where most aircraft live, it would be a straightforward job.
lbf is "pounds-force", a slightly more specific unit than "lb", which could refer to a mass (0.454 kg) or a force (4.54 N).
As a scientist I think in SI these days though it took years to unlearn the training of my youth, and I still vascillate between F and C for my preferred temperature unit.
Nobody uses perfect units. Why aren't you measuring your car's efficiency in inverse square millimeters?
We all know what this administration does to people who purchase large numbers of aluminum tubes.
That, and he makes video games! Ones that might possibly have boobie-enabling mods!
I am no longer wasting my time with slashdot
I always thought one of the more interesting things about Carmack wasn't his original work (which is impressive) but his ability to mine academic papers for techniques useful to him. Most of the really cool things he introduced to the gaming world came from research in CGI and such (BSP's, etc). The point is, while everyone else was writing what they know, John was learning what he needed to know to make his vision.
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
I myself try to stay with DD-cup or smaller.
Screw that! Rocket-jump, baby!
Freedom: "I won't!"
Yes. We are able to use non-decimal units because, quite frankly, most applications call for non-decimal units.
Which is the standard, utterly nonsensical, argument. These are only measurement systems. You can use either to express anything. However, one of them (and I'll let you figure out which) makes it MUCH easier to do conversions and allows useful equations (like e=mc^2) to actually work without inventing new units to fit. So yes, something which is an inch today may be 2.54cm, which isn't as convenient to write. But guess what, that same thing in a metric country would be 2.5cm, or maybe even 3cm. Which is 1.18110236. I'll let you work out what fraction that is....
---- Den ene knappen er powerknapp, den andre er Bender voice knapp "Bite My Shiny Metal Ass"
Its strange how positive experimentation such as this is dubbed distruptive.
According to the X Cup Schedule, Armadillo will be conducting a demo flight out in New Mexico. (Check out Oct 9th activities).
I wonder if he'll be showing off the BFG as well... =p
A concise explanation of shock diamonds(mach diamonds) here.
You've got your judgement of Carmack's mentality exactly backwards. From the Armadillo site:
"A chamber with no contraction ratio at all will lose 20% of its thrust due to pressure losses from accelerating gasses in the straight section, but the Isp loss is only 1.5%."
"ISP loss"? "maximum propelleant value"?
Sheesh, what do you guys think this is, rocket science?
It is a pound-force, as distinguished from the pound-mass, which weighs 1 pound-force when sitting in 1 normal g acceleartion at Earth's surface.
It is true, this is a hard to learn and obsolete system of units. But since some of the most advanced machinery in the history of the world was developed in it, and we have a whole industrial base that can crank out devices and gadgets practically on demand that revolve around it, we are loathe to give it up just so we can be like the French.
By the way, Pound-feet is abbreviated lb-ft and indicates a torque as opposed to ft-lbs, which would be an energy. Probably. You need to actually Understand what you are doing over here.
ps. 1 pound (lbf) is equal to 4.448 Newtons. Which most metric people would call 2.205 kilos anyway, because they don't know a force from a mass.
Behold, this dreamer cometh. Come now, and let us slay him... and we shall see what will become of his dreams.
He should have just used the jump pads.
---
PS - This is what part of the alphabet would look like if Q and R were eliminated.
Generated by SlashdotRndSig via GreaseMonkey
Why is it that when you believe something it's an opinion, but when I believe something it's a manifesto?
The problem was hydrogen peroxide. His first engines were built around the stuff. The way hydrogen peroxide works is you catalyze it - that is run it through a mesh of material that reacts with it to liberate steam and hot oxygen, which you then combust with a fuel. Hydrogen Peroxide is a nasty beast. It's hard to find vendors to sell to you (at rocket grade concentrations, 90-98%), and combustion is tricky. After a lot of experimenting (and he himself will tell you - a lot of valuable data gained; he was able to test at rates higher than using other fuel combos) they gave up on it.
Now they are using liquid oxygen as an oxidizer. They aren't stalled. They are exploring their options. If you look at NASA they have really only done things one way, the convergent-divergent regeneratively cooled nozzle, using O2 and H2, occasionally kero. He's sticking his neck out trying something new, it just takes awhile with limited funds. He's not stalled now.
-everphilski-
How much *design* is actually going into these if they are expecting to build 2-3 a week???
What does it matter? Rapid turnaround means he can develop a lot of them, and pick the best performers.
Maybe John, as brilliant as he is, should go to school for awhile to learn a bit about fluid dynamics and thermal dynamics and the equations that govern those sciences.
Why would you assume that he doesn't already know a great deal about these subjects?
I really don't get the knee-jerk reaction around here. Whenever someone does something interesting and potentially significant, there's always this chorus of people looking for something to bitch about to try to look cleverer than the guy who's acually doing something.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
Plus it gives people something to bitch about and blame pretty much everything that goes wrong on. They always appreciate that.
Switch back to Slashdot's D1 system.
NASA did things based on previous research by Goddard, Von Braun, and others. H2/LOX fueled engines didn't materialize until the Apollo program. Kero/LOX was the status quo for big liquid fueled boosters before that. And it is still used by the Russians. Is your argument that NASA has only done things one way, and hasn't explored other options? What about the Soviet space program, did they steal the design from NASA, or did the also come up with it through research? If alien cultures ever made cars, do you think they would have round wheels? Some times the optimum solution is the same, no matter where it is invented. I don't think that chemical rockets are the end all be all of rocketry, but they are a mature technology, and everyone who has achived orbit has used convergent-divergent nozzles. The revolutionary step is mass production, to bring the cost down. Making parts from aerospace alloys is difficult. Tubular shapes are easy because tubing is mass produced. If you want to bring the cost down, one needs to find cheaper ways of making rockets. Liquid fueled rockets are complex and require turbo machinery. Maybe he should look to solid fueled rockets. There isn't as much complexity in them.
The Russian approach to rocket science was along the lines of "let's see how it blows up and make sure it blows up in a different way next time".
That's a complete crock. The Russians, just like the USA, started from the V2s they captured, and applied the best engineering practices that were known at the time. They blew up a lot of rockets, and so did anyone else who every tried to build a rocket.
The fact that they got Sputnik into orbit first, and got Gagarin into space before anyone else is a testament to their skill.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
A more serious effort for SSTO was DC-X. The full size version probably wouldn't quite have made it to orbit, but it would have been close enough to know if it was possible to do it with a reasonable payload. Unfortunately, after two successful Air Force flights, NASA took over and the craft was destroyed because a technician didn't hook up a hydraulic line to one of the landing "legs". Then NASA cancelled it in favor of X-33, a project with no hope of success. X-33 allowed NASA to say, with a straight face, "SSTO doesn't work", when what they proved was X-33 doesn't work.
Staging helps. Two stages will get you to low earth orbit. Beyond low orbit usually requires three. This reduces the fuel fraction, but by less than one would hope. The Shuttle's fuel fraction is around 89%.
Yes, and staging also complicates the design, making it more expensive. You get those one-shot parts you throw away, which means doing lots of extra work (ie spending $$) to make sure they work the first and only time. I suppose you could have some kind of flyback reuseable stage, but that's complicated enough that it won't save you any money.
So space flight is all about weight reduction. Which is why everything is so fragile and unreliable. If you could build a launch system with a fuel fraction of 50%, which is roughly where most aircraft live, it would be a straightforward job.
Everything is fragile and unreliable because the design philosophy is wrong. It's a question of designing for perfomance when we should be designing for operational efficiency. In the end the mass fraction doesn't matter - what matters is reliability and $/lb. to orbit. There will always be a market for heavy lift launchers, but for manned flight you'd rather have frequency and reliability.
The benefit to VTVL SSTO is you can launch it more frequently, since all you have to do for the next flight is inspect it and fill up the tanks. The reentry is powered, so you don't have thermal problems, and since you don't need a runway you can land it on the same spot you launched it.
Look at it this way - the amount of fuel it takes to get to orbit will get you from the US to Australia in a 747. The reason it's cheaper to go to Australia is they don't throw away the plane when you get there (expendables) or take it apart and rebuild it (the shuttle) before the next flight.
This also has implications for safety. Would you rather fly a 747 for its maiden flight or its 100th? If you fly the same craft more than once you're much less likely to be bitten by manufacturing defects.
We've been using staged rockets for fifty years now, and the price is still a huge multiple of fuel costs. Time to try something different.
Yes, I'd say his Internet Service Provider is in the low 200s as well.
This idiot should stick to games.
Well, thank you for that well-reasoned critique of his efforts.
I have to wonder, what is it about achievement, or even effort, that brings people like you out of the woodwork? Why are you so jealous of him?
'Disruptive' is one of those buzzwords that business school types throw around when they are trying to deceive investors.
It's also a term that describes any number of scientific and technological advances that came from private effort like John's. In any case, he's doing this with his own money, so what's it to you?
What is the advantage of this engine design? What are the reactants, ISP?
Hey, here's a wild idea: why not RTFA and find out?
Meaningful details like that don't get you posted on slashdot I guess.
The same could be said for meaningful critiques. Better luck next time.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
Psst, here is another secret: Most of the rocket engines made weren't designed by NASA either. The were built by Pratt and Whitney, Rocketdyne, and others. But NASA managed the project and doled out the money because rocket engine design and manufacturing is expensive and not very profitable unless you're working for the government, which has all this taxpayer money to spend and wants some rockets. So it isn't a government bureacracy that has a monopoly on rockets. There is nothing stopping a private company building rockets, but they are expensive to build and not very profitable.
There was never suppose to be a fleet of shuttles. They were supposed to have such a fast turnaround that the capital cost of each shuttle would be amortized over zillions of launches. It was originally sold to Congress as having a turnaround of a week. It was never sold as being cheap to mass produce a fleet of them. You wouldn't need a fleet if they had a one week turnaround.
Infuriate left and right
Yes! For the slight inconvenience of having to work with four different length units (inch, foot, yard, mile) with easily remembered conversion factors, we can finally express lengths of 1/3 or 1/6 inch as umm... 10.667/32 in, or... 0.3333 mill. Better example: Highway exit signs. The Englisch system is obviously superior, since we can easily say 1/4 mile, where you only need to divide 1760 by 4 to get yards. Easy! Converting something like 1/4 kilometer to meters would involve dividing 1000 by 4: Totally ARBITRARY!
You win, I'm switching over to Imperial today.
chl
PS: Is 543 yards plus 1563 yards longer than 1-1/4 mile? I lost my calculator.
PPS: Sarcasm is not funny. Mod this insightful.
http://www.xcor.com/engines.html X-cor has been making "throatless" motors for some time. Very nice and simple.
So space flight is all about weight reduction.
That's the NASA myth, and why they build crappy spacecraft.
Certainly weight reduction is important, but if you don't keep looking at the overall system, and the trade-offs, you'll fuck up the design. The focus on Isp is a symptom of that. The Shuttle is a prime example of it.
Sure, high Isp means you need less weight of propellant per unit of impulse (thrust * time), which sounds great. So the propulsion guys start focusing on Isp and design exotic high-pressure engines that use fuels like LH2 which is really light and gives you an engine with a 400-range Isp. Never mind that you have to practically rebuild the thing after every flight. (It also gives you a relatively low thrust to weight ratio, so you end up having to augment it at launch with something with high thrust even if crappy Isp, like SRBs)
The propellant guys figure LH2 is cool too -- highest energy per unit weight, and all that.
And the airframe guys just build the lightest structure they can to hold what the propulsion and propulsion guys give them.
All of which leads to a suboptimal design.
LH2 is about the lowest density liquid around. High density urethane foam would sink in the stuff, it's about the same density as lighter weight foams. Which means you need a bloody big tank to put the stuff in. The Shuttle uses 8 times, by weight, as much LOX as LH2, but the LH2 tank is about three times bigger than the LOX tank.
Tankage is heavy. The portion of airframe weight devoted to tankage scales as the volume of the propellant, not the weight.
Replace LH2 with something like liquid methane and your tankage -- and its weight -- becomes much less, which ends up improving your fuel fraction, even with the slightly lower Isp of methane-LOX.
The original Atlas launch vehicle, which used LOX and kerosene and stainless steel tankage, could reach orbit without shedding any stages. (Although it did shed two of its three engines.) It also couldn't carry much payload that way, but we're talking late 1950s technology.
NASA technology is fragile and unreliable because they're more interested in engineering projects for the sake of engineering projects, and then have to hack it back because of budget limitations. Anyone in software development who has seen a project get designed with all sorts of bells and whistles and the designers' favorite new technlogies, only to be turned into some ugly hacks toward the end when deadlines are looming and the budget has run out, will understand this.
-- Alastair
The DC-X saw a lot more than two successful flights. At one point in its SDIO (not just Air Force) operated test series, it did two flights with a 24 hour turnaround.
I had the privilege of attending the first public flight, which was the second real flight. Seeing a rocket climb out and then just stop in mid-air is quite something. Then it flew sideways a hundred yards or so and descended tail first to a perfect landing.
Later flights went higher and faster, and one demonstrated its survivability when an at-launch explosion of vented hydrogen blew off part of the aeroshell, and the thing was dropping bits and pieces as it climbed out. The remote pilot (Pete Conrad) just clicked the emergency autoland button and the thing hovered until it had burned off enough fuel to land (the landing gear wasn't designed to support fully fueled weight, it sat on a "milk stool" for launch).
Then NASA took it over and, as you mention, fucked up their first flight. The unconnected leg folded up on landing and the thing fell over, broke apart and burned.
Given the huge workforce that NASA keeps employed to fly the Shuttle (or rather, to act like they're keeping it flying while keeping the actual number of launches to a minimum -- reduces the career risk for NASA managers), it's not surprising that they don't like anything that might threaten that turf. Not that, as you point out, the ridiculous design of X-33 ever remotely threatened it, and gave NASA engineers (and their LockMart, etc, buddies) something else to spend money on.
-- Alastair
It's a force equivalent to that of Earth's gravity (at the surface) exerted on a roughly half-kilogram mass (0.454 kg, to be precise). About four and a half newtons.
(lbf = pounds force, not pounds feet)
-- Alastair
In mechanical engineering, a throat is a channel through which fluids move that has a narrowing followed by an expansion (so that the cross sectional area of the channel decreases and then increases). When a compressible fluid flows through a channel that narrows, its velocity increases. Normally, when the channel expands again, the fluid will slow back down. However, with a properly designed throat and a low enough backpressure, the fluid will accelerate to speed of sound at the throat and then, instead of slowing down, continue to accelerate beyond Mach 1 as the channel expands. I don't know anything about "throatless" rockets, but I suspect that they are able to accelerate the rocket exhaust above Mach 1 by forcing the exhaust gases to contract and then expand even though there is no channel forcing them to.
NASA is a sham, a front, a cover for the real space program. The real U.S. space program exists in military black-projects and that is where 2000s level technology is being developed and used. You think UFOs are alien? Ha!
Do your own research, but I will present you with the basic idea that ZPE and antigravity are a reality within military black-ops and has been for decades.
It is your personal duty to fight for what is right on a daily basis. Ignoring injustice is identical to approving
I'm with you. From now on, days are the equivelant of 3.6525 current days, and there are 100 days in a year. Months are now ten days long, and we'll just get rid of February and May, because February sucks, and May already has its own day.
Ah, the ideas.. my mind feels like it's running at 5,280 ft. per minute!
https://www.eff.org/https-everywhere
"Look at it this way - the amount of fuel it takes to get to orbit will get you from the US to Australia in a 747. The reason it's cheaper to go to Australia is they don't throw away the plane when you get there (expendables) or take it apart and rebuild it (the shuttle) before the next flight."
I do love this old chestnut: it's perfectly true, and yet so misleading.
Helpful Hint #1: How long does it take to fly the 747 to Australia? What would happen if you took that long getting to orbit?
Helpful Hint #2: What is the difference between energy and power? If two machines release the same total energy, but machine #2 must release it much more quickly with equal or greater precision, which is likely to be more complex and expensive?