Slashdot Mirror
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-
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.
If you read the link, the X-Prize people are talking about starting the X-Cup, a regular space competition.
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
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.
*ahem*
/
http://www.cnn.com/TECH/space/9909/30/mars.metric
Do not trust this signature.
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!"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
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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?
It's more what he's doing than what he has discovered (which is nothing.)
For amateur rocket work, you spend about $1000 to burn $1 worth of propellant. Think about the logistics: site costs, setup costs, safety planning, data acquisition, etc.
Streamlining the process is where you make big wins: accept a 2% ISP loss, and test 10x more frequently. This is how you gain knowledge fast and avoid expensive dead-ends. A lot of this work is just learning skills -- build, launch, avoid dying, repeat.
More tech (GPS, computers, digital video) makes the process much easier: John is now doing 1970s era work after starting at a 1950's level a few years ago. There's a good chance that he will be able to reach earth-orbit level within a decade.
It impacts manufacturing costs, but in an interesting way. If you are NASA or General Dynamics, it would be a little bit cheaper to make, but no big deal. The interesting bit is that you should be able to make a decent nozzle with 1/10th the manufacturing/machining capability. It reduces the costs of entry, probably down to the level of a NASCAR crew's machine shop.
So, not truly revolutionary, but "disruptive" tech in the sense that it puts the ability to make decent nozzles in the hands of many many more people.
-- your Web browser is Ronald Reagan
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"
John is now doing 1970s era work after starting at a 1950's level a few years ago.
Thought: Is ANYONE doing rocketry at a 2000's level today? Most of the recent developments in orbit access (x-prize, china, india) seem have been people 'cathing up' to where the US and USSR where in the 60's or so (not that that lessens the achivements). And NASA's advanced projects tend to make the news mainly when they are cancelled...
__
Comment submitted. There will be a delay before you understand what you posted.
A problem with the current shuttle fleet is that they were designed to be mass manufactured and maintained. We were supposed to have a *fleet* of space shuttles. The cost of the shuttle would, under the original plan, be very small. We only ended up with a few of them and pretty much every part is custom made. Each shuttle has differences which exacerbate this problem.
However, it is very efficient in a number of parameters.
Armadillo Aerospace is attempting to produce a design which is easy to produce by limiting the use of custom parts and specialized work in both manufacture and maintenance. They are trading off a marginal amount of performance for a lot of manufacturability.
There the analogy ends since the space shuttle and the immediate goal of Armadillo have two completely different purposes.
The science of engines and propellants has matured, but there are so many combinations (propellant x engine design x vehicle design x etc) that it can be difficult to find exactly the kind of research you are looking for. Further, a lot of it is secret since most of this stuff was done for missile design.
Some may call this "seat of your pants" engineering, as opposed to design engineering. You try something, improve it until you find the optimum, then redesign it completely and start over. It is non-optimal for time and effort, but is low cost. It is enough to get started with something that works but has low efficiencies. Once one has a working design one can scale it only so far before having to go back to the redesign and test phase. At that point it often makes more sense to hire engineers capable of design engineering so the trial phase is shortened since the design is near optimal on the first try.
Many startups operate succesfully this way. Many have a mix of the two. Many fail when they invest all their money in engineering design, and then try to get more funding to build a prototype - it's much harder to sell an unproven paper design than it is to sell a working product that has flaws.
-Adam
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."
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."
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."
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