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Official Armadillo Q&A thread

Posted by: John Carmack - Tue Jun 15, 2004 8:01 am
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Official Armadillo Q&A thread 
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Spaceflight Enthusiast
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Post    Posted on: Wed Jul 21, 2004 7:01 pm
luke.r wrote:
Enough with the computer games chat! If you want to talk about them, find another site. :evil:


Sorry. :(


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Spaceflight Enthusiast
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Post    Posted on: Wed Jul 21, 2004 7:02 pm
Matthew Ross wrote:
luke.r wrote:
Enough with the computer games chat! If you want to talk about them, find another site.


John's comment about his time at id Software vs. Armadillo got quoted on a computer games web site, and this thread was linked - I think that's why we're seeing the sudden influx of such questions.


Well, you can't really blame them. JC is the guy responsible for the creation of the FPS genre and all.


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Rocket Constructor
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Post    Posted on: Wed Jul 21, 2004 7:13 pm
OfF3nSiV3 wrote:
Not sure if it's off topic but i'm curious about the scientifical knowledge you demonstrate.
Being computer programmer and designing a rocket capable of flight requires a certain level of scientific knowlegde
Computer programming requires lot's of time, for a guru like you, inovating in all ways, which doom3 is the best example
But designing rockets is a complete different thing, which requires a bigger amount of knowledge including chemistry, physics and dynamics
Enough with the long writing, what i'd like to know is what are your habilitations, such as university degree or something.
I know you're a genious, but it can't be just hobbie knowledge!
Keep up the good work and good luck!


While John Carmack undoubtedly has a powerful intellect, I think his accurate and wide randing knowledge of scientific principles is more a credit to his inspiring work ethic than anything else.

Being really smart doesn't mean you know chemistry. It just means you are really smart.:)

Carmack just works with focus and patience on the things that interest him, to the exclusion of all distraction. That is probably the key to his skills and definately why he is so inspirational.:)


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Spaceflight Trainee
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Post    Posted on: Wed Jul 21, 2004 7:57 pm
Wow, the Comp-L engine looks like a proven COTS system. It makes me think that Armadillo should just buy an engine and focus on the VTVL guidance software. Of course, Comp-L was developed with government money so it would disqualify them for the X-Prize.

Some stats from the web site:
· Vacuum ISP of up to 330 seconds can be achieved.
· Propellant mass fractions > 90% can be achieved.

Plugging in to the famous rocket equation:
Delta_V = Isp * g * ln(Mo/Mf)
Delta_V = 330s * 9.8m/s^2 * ln(1.0/0.1)
Delta_V = 7400m/s

Hmmm, not quite orbital velocity (7800m/s) even if all of your losses are paid by a boost stage a la Rocket Company. 91% mass fraction would make orbit with no payload.

OrenT wrote:
Yes, Bruce Dunn's self-pressurizing concept should be a good candidate for a peroxide/hydrocarbon upper stage. What it wastes on a high molecular weight pressurant it gains in simplicity and structural weight. Just a few notes:

The concept is patented, with the patent held by the university where Bruce worked on this.

The fuel can be any combination of ethane, propane and butane so you can basically dial-a-vapor-pressure.

Dan Moser of compositex has built a prototype of this design called Comp-L (google it up).

It's pretty easy to think up a couple of other configurations that keep the fuel and oxidizer in pressure communication without the use of things like flexible feed lines or even bladders.


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Post    Posted on: Thu Jul 22, 2004 1:46 am
John Carmack is my idol, thats why I posted here hoping he would acknowledge my post...ah well people can dream cant they?


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Post    Posted on: Thu Jul 22, 2004 8:04 am
>Hmmm, not quite orbital velocity (7800m/s) even if all of your losses are
>paid by a boost stage a la Rocket Company. 91% mass fraction would
>make orbit with no payload.

No it won't. Orbital velocity and characteristic velocity for a real system to reach orbit are different thing. 7800 m/s will be enough only:
1. The body is already at the orbital altitude (at least 100 statute miles).
2. The impulse of thrust has a zero or very close to zero duration (like a gun shot).

On a real system, you are subject to huge losses to the following factors:
1. You need to climb from 0 to the target altitude.
2. You need to compensate for the pressure of the stream of air you pass through.
3. You need to compensate for the gravity losses during the orbit insertion (some part of thrust will be lost just to keep the rocket flying).
4. Also, Isp of the engine goes down in the atmosphere, depending on the expansion ratio of the engine and chamber pressure.

So, a real system needs at least 9000 m/s to reach orbit, not 7800. This is for most effective ones. Average one will need near 9500 m/s and some as much as 10000 or close to it. So SSTO with any known fuel is impossible.

On the matter of upper stages: a have reviewed all known types of upper stages and found that only one of them will go to orbit atop Armadillo's 1600 gal, carbon fiber vehicle: Star 48B. But it's a solid. This is to demostrate that creating such a stage (liquid) will be a huge (but likeliy solvable) task even in professional environment. Pros would likely go into pressure-fed, simple LH2/LOX system with Isp around 410 and mass ratio around 6. Without cryogenic fuel that would be likely impossible even in a pro envoronment, they would prefer solid...


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Post    Posted on: Thu Jul 22, 2004 5:09 pm
anovikov wrote:
>even if all of your losses are paid by a boost stage a la Rocket Company.

On a real system, you are subject to huge losses to the following factors:
...


Actually, I was considering the case of a stage and a half system described in the novel "The Rocket Company." The first stage flies straight up and comes straight down to land. The upper stage starts out at orbital altitude and thrusts straight sideways so it doesn't suffer from drag losses, gravity losses, etc. So the boost stage effectively pays all of the losses while the orbital stage pays all of the velocity change. You are right that the thrust will not have zero duration, and that will be a loss. There will also be steering losses. But I was just doing a back of the envelope calculation.

Carmack has already posted on this thread that the orbital launch scheme he likes best is a vertical boost plus an orbital stage with an extremely high mass ratio (10 or 15). I was just running some numbers to see if this engine could fit that scenario.

And I agree that the boost stage would have to be higher performance than Armadillo's current rocket. But that shouldn't be hard. They're only using 50% Hydrogen peroxide right now.


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Post    Posted on: Thu Jul 22, 2004 7:39 pm
OK, here's you right. Black Armadillo will be the best first stage imaginable for such a scernario. And if the staging will not be done in apogee, but at some 60-80 km altitude after first stage burnout, it will eliminate the gravity losses (second stage could fire directly sideways), so your estimate is right.

Of course, it is still doubtful that a 330s/10x mass ratio stage is feasible... Well it IS feasible on a larger scale (like, Soyuz FG third stage, 359s/11x), but it weights 30 tonnes and costs several millions... I don't really think anything other than an ultralight solid will work here.


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Post    Posted on: Thu Jul 22, 2004 9:28 pm
i'm not sure about this, but is there any reason why you have to reach orbital velocity with your burn to get into an orbit? can't you just climb to a certain height above the desired orbit, then the velocity gained by "falling" back to earth should be sufficient, with some adjustments from short-duration burns, to place the vehicle into its target orbit without actually reaching orbital velocity. instead of needing to produce enough thrust to make the orbital insertion as soon as you reach that height, you overshoot at a lower speed and go in on the way down. would that potentially work?

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Post    Posted on: Thu Jul 22, 2004 9:51 pm
TerraMrs wrote:
i'm not sure about this, but is there any reason why you have to reach orbital velocity with your burn to get into an orbit? can't you just climb to a certain height above the desired orbit, then the velocity gained by "falling" back to earth should be sufficient, with some adjustments from short-duration burns, to place the vehicle into its target orbit without actually reaching orbital velocity. instead of needing to produce enough thrust to make the orbital insertion as soon as you reach that height, you overshoot at a lower speed and go in on the way down. would that potentially work?


Well, orbital velocity is lower at higher altitudes. I found a calculator on the web here:

http://liftoff.msfc.nasa.gov/academy/ro ... _calc.html

Here's a few samples:

altitude, orbital velocity (circular orbits, elliptical could be less)
200km, 7.8km/s
1000km, 7.4km/s
2000km, 6.9km/s

So If your upper stage can't make orbit you could always beef up the lower stage and throw it to a higher altitude. Not a very efficient way to add delta V, but it has the operational advantages of straight up/straight down.

However, no matter how high you go you will always need some sideways kick to avoid hitting the earth on the way down.


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Post    Posted on: Fri Jul 23, 2004 10:52 am
wow :P i read some about armadillo project but what are you plainnig with this i didnt understant fully my english is not very well :P. Liquid fules :P good but what is your h2o2 conc. (is that a real space launch preoject???) i am making rocket too :P but they are solid fuels and it is my hobby :P (what is taht armadillo from the pictures i can see taht you are making a serious thing)
-------------------
Wooooowwwwwwwwwwwwwwww i watched the video and i am shocked stupified,terrified this is imposibbleeeeeee rocket launched and than come back again with the same movement haha how can it be posibble :P

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Post    Posted on: Fri Jul 23, 2004 2:25 pm
Hooray for enthusiasm!! :D I know roughly how Armadillo does what it does, and I now it can take off and land vertically, but when I saw that video I still can't believe that it really does it. It is severely cool.

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Last edited by luke.r on Fri Jul 23, 2004 7:47 pm, edited 1 time in total.



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Post    Posted on: Fri Jul 23, 2004 4:20 pm
but John Carmack is really brave because of playing with high concentration of H2O2 :P i cant play with that :P solid fuels are okay for me :P

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Post More answers   Posted on: Fri Jul 23, 2004 10:18 pm
more on mass ratios:
There are some not-obvious things to keep in mind when comparing commercial stages.

The delta RS-68 booster stage has a mass ratio of 8.5 with lox / lh2. It was mentioned that an empty centaur has a MR of 10, but I didn't double check that.

Lox/LH2 has a combined bulk density of 0.28 g/cc. If you filled the exact same tanks with 98% peroxide and kerosene, which has a bulk density of 1.31, you would wind up with a MR of 40. Propellant density makes a big difference.

In fact, the tankage difference should be even greater, because you don't need any insulation. Plumbing scales somewhere between linearly with density and the square root of density, depending on flow speeds, but combustion chambers and nozzles don't improve, so you do need bigger engines for the 4x heavier vehicle.

Commercial upper stage solids are operating at MR of 18 or so, and they have bulk densities a bit better than peroxide / kerosene, and less weight for combustion chambers. However, they operate at quite high pressures, usually 800+ psi. A space engine can operate just fine at 200 or 100 psi, and possibly even lower. You trade a bulkier and heavier expansion nozzle for lighter tank weight, but since most of the empty mass of these solids is tank (and liner insulation), there is a large benefit to be had by using a dense liquid.

This is why I say making an expendable, exoatmospheric peroxide / kerosene vehicle with a MR of 15 isn't all that aggressive. We are basically talking about two very thin walled spheres (or one sphere with a bladder inside) with an engine stuck on one end and a flight computer stuck on the other end. This would be a sputnik like stunt, with little useful ability other than operating as an amateur radio packet repeater, but it is my idea of a good first step towards useful orbital capability.

self-pressurized peroxide / propane / ethane:

Engines like this aren't suitable for high mass ratio upper stages, because the pressurizing gas mass winds up being quite significant at burnout. Pump fed rockets can live with evaporating oxygen to keep lox tanks at a few dozen psi, but if you want a couple hundred psi, you really want to use helium. For example, in our test hops of the big vehicle, we actually use 100 pounds of nitrogen, or almost 6% of the dry weight of the vehicle, into it. A gaseous hydrocarbon would be worse.

Also note that these engines are ablative, and that there is a big difference between a motor that has been built and fired a few times and a COTS product.

low pressure testing on electronics:

Our electronics ride in the pressurized cabin.

dual engines:

We might try making a dual 12" engine vehicle, but I honestly think it would be easier to just make an 18" or larger engine.

engine commercialization:

I have offered assistance to some people interested in pursuing similar engine development, and I have no intention of attempting to patent anything. We are willing to sell engines to government agencies right now, but a commercial company would have to sign some iron clad liability waivers. A 12" engine "as-is" would probably be around $50,000. Extensive testing and characterization can run the price up as high as you want to go.

safeguards:

The master cutoff watchdog is completely independent of the main system, and it shuts the cutoff valve if the main computer fails in any way. We have unfortunately tested this a great many times with the big vehicle in the last several months...

Safety of third parties is the dominant driver, not safety of passengers. A rocket dropping like a rock is much more appealing to the licensing teams than one flying off towards Vegas.

mini-nozzles:

The all share the same catalyst packs, it is just a replacement of a single big nozzle with lots of little ones.

cabin-at-the-bottom:

You get a lot more cabin room in the cylinder than in the cone. Three people could fit in the cone, but they were only "virtual" passengers for the X-Prize rules. The cylinder is plenty roomy for three real people.

We want to be able to do all operations without needing to climb up on a ladder.

If the vehicle tips over on landing, you don't want to be 16' up in the air.

h2o2 concentration:

We used to use 90% concentration, but when we could no longer buy it, we developed a new propellant combination using 50% concentration peroxide with methanol mixed in. This is a much more troublesome propellant, requiring staged catalysts and flame holders instead of a simple screen pack, but it is cheap and we can get as much of it as we want.

John Carmack


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Post    Posted on: Sat Jul 24, 2004 12:08 am
i know mr Carmack would be well aware of the british efforts with HTP from the 50's to 70's
this site may be of interest
http://www.spaceuk.org/index.htm
the Black Knight and Black Arrow page are of particular relavance
having lifted thier first Satellite the rocket engineers found that politicians
were to dense to follow.


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