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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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Post    Posted on: Mon Jul 19, 2004 7:49 am
From your latest update:
"Unfortunately, there is so much backlash in the huge gear train and mounting play that it isn’t very good at making small flow changes."

If backlash is a problem, look for harmonic drive valves.


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Post more answers   Posted on: Tue Jul 20, 2004 12:37 am
avionics:
The system uses a three axis fiber optic gyro, three axis accelerometer, and an unrestricted high update rate GPS.

failure modes:
We may experiment with using two engines, each controlled by an independent computer system, and each capable of landing the vehicle. When we were working on differentially throttled engines this involved eight engines around the outside of the cabin-at-the-bottom, but with jet vanes the vehicle would have to fly at a fairly high angle of attack with an engine out to get the CG above the thrust vector.

We expect to have a stabilization drogue that can be manually triggered by the pilot to make sure things are slowed down enough for a bail out. If we can get sufficient reliability out of a single string flight system, we may still fly with a theoretical dead zone shortly after liftoff.

pilot controls:
Two buttons: abort boost and land normally, and force cutoff and pop stabilization drogue. Its an elevator, not an airplane.

mininozzles:
They save vehicle height, a bit of weight, some money (but more labor), and, most importantly, guarantee that the jet vanes will still engage flow even at very low chamber pressures where the stream would be separated from the nozzle edges.

ceramic jet vanes:
Yes, that should be possible. We have talked about looking into some carbide fabrication techniquies, but Rene-41 was recommended to us by some military folks that have worked with jet vanes before.

reentry:
The vehicle should be stable base first, and should not break apart under any possible aerodynamic load (no wings hanging out in single shear...), but it may well be capable of tumbling if it was spun hard enough. There are pretty good odds that we are going to find out about the dynamic stability of the unpowered vehicle during our test flights, wether we want to or not...

engine / tank sizes:
One 24" engine + 63" 850 gallon fiberglass tank = 1 person to 100km
One 24" engine + 63" 850 gallon carbon fiber tank = 3 people to 100km
Two 24" engines + 63" 1600 gallon fiberglass tank = 3 people to 100km
A high performance 600 pound upper stage replacing the people could basically just orbit itself, giving a packet radio relay.
To orbit a person in a recoverable capsule, you would need a very large booster, like a cluster of four stretched 63" diameter carbon fiber tanks, each with a 36" engine, and probably also a middle stage.

deep throttling:
We have operated our engines over a 10:1 throttling range, but we have to be careful not to go subcritical at landing, or the thrust can drop sharply with only a small drop in chamber pressure. Keeping the narrow jet of a deeply throttled engine engaged with the jet vanes is one of the major pushes for the mininozzles.

To do a powered landing you MUST drop thrust, even if you had a fully pressurized feed system instead of a blowdown system. The vehicle must be able to descend the final couple meters at a constant rate, which is the same as hovering. Landing weight is close to one fifth takeoff weight, and you want to have at least 1.5 G takeoff acceleration, so you really need 8:1 or better throttling.

multiple engine, single nozzle:
We have considered making a cluster of four 12" engines and only putting a single vane under each one, because we have all the materials for 12" engines, but engine variability bothers us a lot. We would add interconnect pipes between the engines under the cold packs and above the nozzles, but there could easily still be warming issues.

Id vs Armadillo:
I am working on the rendering technology for the next game right now, so it looks like the balance will stay about the same for a while at least.

balanced two-stage:
Pragmatic reasons argue for an unbalanced pop up / side boost combination. With balanced staging, your first stage is going to go a long ways down range, which realistically means that it is going out over the ocean, and you aren't going to get it back. We think that it is easier to make a single, high performance upper stage for use on top of a well tested up / down booster, than to make two new medium performance stages that are going to be lost a lot in testing.

I'm not a fan of solids.

solid state IMU:
The accelerometers are micromachined, but the gyros are fiber optic. We used gyration gyros in our very first vehicle, but they were very, very sensitive to shock. In the larger scheme of things, paying $11k for an IMU that is completely insensitive to acceleration and vibration is money well spent. We communicate with the IMU over normal RS232 at 19kbaud.

harmonic drive gearing:
Thanks for the pointer, that is an interesting technology I didn't know about.

John Carmack


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Post Self-pressurized rockets   Posted on: Tue Jul 20, 2004 5:09 am
http://www.dunnspace.com/self_pressurized_rockets.htm

Here's a link to an interesting idea for pressure fed rockets using the vapor pressure of the fuel for pressurization. It's like the VaPak system, except the fuel and oxidizer are kept in the same pressure vessel separated by a flexible plastic membrane. So only one of the components has to be near it's boiling point to pressurize both. This means you don't take as much of a hit on propellant density.

Another advantage is no intertank structure. You mentioned designing an upper stage with an extreme mass ratio. A single sphere with an engine sticking out the side and no internal structure may fit the bill.

The propellant combination they suggest is H2O2/Propane. It's similar to H2O2/Kerosene except that Propane has a high vapor pressure at room temperature. I thought you might want to take a look at it since you are thinking about H2O2/Kerosene and you use a blow-down pressure fed system.


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Post    Posted on: Tue Jul 20, 2004 5:26 pm
Have you done any low pressure testing on your electronics? It occurs to me that canister capacitors could pop as gasses come out of solution at low pressures.


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Post    Posted on: Wed Jul 21, 2004 12:32 am
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!


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Post    Posted on: Wed Jul 21, 2004 2:36 am
*cough* already working on a new game? Can't wait to see what you got up your sleeve this time.

Good luck with the Armadillo project.

-qw


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Post    Posted on: Wed Jul 21, 2004 2:46 am
John Carmack! First off I'd like to say good luck with the Armadillo Aerospace project!!! Second, how do you do it?? Programming the next game engine for id, which will be revoulutionary when it comes out, AND do this Armadillo Aerospace at the same time!

Since I'm a big id software fan and a fan of yours, could you clarify what you mean by "Id vs Armadillo:
I am working on the rendering technology for the next game right now, so it looks like the balance will stay about the same for a while at least."?

Ok here's the real Question...are you leaving id anytime soon?? (im hoping not!!)

-Intel17


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Post    Posted on: Wed Jul 21, 2004 3:23 am
Ah.. we are going off topic here. Let's stick to the spirit of this thread. 8)


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Post    Posted on: Wed Jul 21, 2004 5:09 am
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: Wed Jul 21, 2004 7:47 am
John, I know this question is off-topic, but I figure I might as well ask it while you're here.

Is your next project at Id going to be Quake 4? Ive heard rumours about it, just wanted to know if it's true or not. Of course, I understand if you're not allowed to say anything on that subject. Thanks in advance, im a huge fan.

P.S, Good work on Doom 3, it looks fantastic.


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Post    Posted on: Wed Jul 21, 2004 7:54 am
Enough with the computer games chat! If you want to talk about them, find another site. :evil:

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Post    Posted on: Wed Jul 21, 2004 10:03 am
I read back and am still intregued about multiple engines. specifically Dual engines.
1) you stated that you still had the 12" parts so i was thinking a Dual setup akin to other rockets or (excuse the reference) star wars A wing type design. as you could keep the current cabin, and basically would just bolt on the engines to the side (bolt on is quite an understatement, as supports and other things would be needed to be taken into consideration)
also a redisign of the software and actuaters would be needed, two engines would still allow for Roll controll, and provide a safegaurd agianst single engine failure. (which is something i worry about with an experimental engine, especially after you mentioned in re-entry you would need short burns to keep it warmed up)
It would be nice to see such a design, though i doubt your current timeframe would allow it.

2) Commercialization of the engine. I'm more intregued about the engine itself, on how it works, ect. you mentioned that everything you have on the engine is considered public domain, so i would assume that no patents would be filed under Armadillo Aerospace, and that it would be unlikely that one would be filed in the future. (If so, my hats off to you, I applaud the Open source model)

3) IS there, or are there plans to have any papers written on the current engine model? or will you leave any details to the public to assemble? I would be interested to see if the same engine could be used for small scale hobby use, say around 2-3" engine on a small scale vehicle. or if this engine would be capable of horizontal uses like a plane.
from my limited knowledge, could I assume that this engine would also work underwater givin the proper preparations?

4) What Hardware or software safeguards are implemented or will be implemented in the event of an electronics failure or software failure. say, a fuse blows, or a transister shorts.

-Steve


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Post    Posted on: Wed Jul 21, 2004 12:34 pm
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.


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Post    Posted on: Wed Jul 21, 2004 1:17 pm
Raven is doing Quake 4, id software is doing a completely different game based on a new engine...


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Post    Posted on: Wed Jul 21, 2004 3:01 pm
John,

In your last update you showed pictures of the mini-nozzle setup Armadillo is going to test. But now that you have moved to a simpler 1 engine design vs. 4 engines, won't switching to mini-nozzles once again cause similar multi-engine problems? Or will there still be only one "catalyst chamber"? (or whatever it is called)

Also, what was the reason(s) behind moving the cabin under the tank on your full-scale vehicle? Center of mass during descent? Easier entry/exit for pilot/passengers? Something else?

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