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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 more answers   Posted on: Mon Jul 12, 2004 9:09 pm
orbital performance:
We expect any upper stage to use 98% peroxide + kerosene, or possibly a sodium borohydride spiked fuel for a performance boost. The mixed monoprop can get 200s Isp with a high expansion vacuum nozzle, so it would be possible to make a 3 stage orbital vehicle, but we think it would be simpler to make a single really good upper stage, rather than two simpler upper stages stages. A mass ratio of 10 for an unstreamlined, non reusable vehicle is trivial, and we actually don't think 15 will be that hard. Our opinions may change as we develop things, of course.

carbon fiber:
Carbon fiber composites have great strength, but it is better at making extremely strong things (like tanks or wing spars) much lighter than at making already light things (like our aluminum cones) even lighter. There is a significant "minimum gauge" issue, so there wouldn't be much savings in making our nosecones or cabins out of composits, and it would be much more expensive. Rolled and welded aluminum is a very cheap fabrication method, and it is much more convenient for drill and welding on the various tabs and brackets that are necessary.

multiple engines:
Our lives really did get a lot simpler when we moved from four engines to a single engine. There is a slight temptation to use multiple 12" engines because we have all the parts for them on hand, but we think it is going to be easier to just build a bigger engine instead.

John Carmack


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Post    Posted on: Tue Jul 13, 2004 4:37 am
I have three questions.

1. What sort of avionics are you planning on using. I am wondering if you have installed any independant gryro instruments such as those found in general aviation aircraft. I'm thinking of these in the context of instrument that are tried and true non-digital instruments that only require power and don't rely on any computer or computerized sensors whatsoever. Something like a attitude indicator, etc.

2. Since you are having several computer failures, what have you considered for your GOne To Hell (GOTH) plan. Are you thinking of using a redundant control system, some sort of electric manual control bypassing the normal flight software, a nonballistic parachute?

3. What kind of control layout are you planning for the pilot?

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Last edited by i2blind on Mon Jul 19, 2004 9:56 pm, edited 1 time in total.



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Post Thank you / Multi-nozzle engine?   Posted on: Tue Jul 13, 2004 5:27 pm
Are you the second coming JC? Come to take those who believe up into the sky? In the beginning, you brought us Doom, now conversely Rapture.

Kidding aside,

You gave us a tantalizing peek at your experimental multi-nozzle engine. Can you tell us anything more about it?

It's a pleasure to follow your thoughts Mr. Carmack.

Your faithful Disciple.
Richard Janicek


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Post Ceramic jet vanes   Posted on: Tue Jul 13, 2004 8:08 pm
Is it possible to use ceramic jet vanes? Would that prevent the problematic warping problem? Would the issue be attaching it to the actuator or is there some other issue with going non-metallic?


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Post    Posted on: Wed Jul 14, 2004 12:15 pm
John, have you done an analysis of how the structure of the vehicle holds up under the reentry forces? Is reentry in a bottom-first orientation necessary to prevent breakup of the vehicle or can you basically throw the Black Armadillo at the atmosphere in any which way without it losing structural integrity (not even considering what this would imply for the health of the passengers)? Or is this a question that doesn't need answering, because the vehicle would be lost anyway if it was unable to orient itself correctly?

Hmm, I take back this last question, because if you are carrying passengers, being able to survive a reentry without having control authority would at least give you the opportunity to bail out after reentry. So basically, my question is simply: does the Black Armadillo allow for a care-free reentry (as Burt likes to call it)?

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Post    Posted on: Wed Jul 14, 2004 6:08 pm
Okay, let me just make sure I've got it. Two 12'' engines+ a ~1,000 gallon tank= one person to 100K. Four 12''ers+ a 1600 gallon tank= X Prize vehicle. Some larger reusable first stage burning monoprop+ an expendable second stage burning H2O2/Kerosene= orbit! How big would it need to be to get a human up there in orbit?

Your last update was interesting, I loved the picutre with everything laid out like it'd be in the trailer, it finally gave a decent sense of scale. I'm just wondering, what exactly are the tiny penny-size engine bells for?

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Post deep throttling   Posted on: Thu Jul 15, 2004 12:57 am
Hi John,

You've been working to improve your mass fraction, so your future vehicle's thrust-to-mass ratio will be considerably higher coming down than going up.
How deeply can you throttle your engine, and still have it work? Also, your tank pressure, and therefore thrust, will be lower on the descent than the ascent. Is this a good thing or a bad thing? How much ullage volume do you start with?

- Ashley


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Post    Posted on: Thu Jul 15, 2004 11:28 am
Abit off topic here. I read from The Register that Doom 3 has gone RTM and will be hitting the stores by next month.

Just want to say thanks for the great work. Unfortunately, I will not be getting it as my PC is too slow to run the game and I am also using a PowerBook as my laptop.

Doom had gave me great pleasures in the past. I will forever remember the times in polytechnic where we play Doom under the noses of my lecturers and the pesky technical officers those many years ago. 8)

Hope that once this is out, you would have more time for Armadillo!


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Post deep throttling correction   Posted on: Thu Jul 15, 2004 11:50 am
Sorry, I didn't mean "mass fraction". I meant to say, you're lowering the vehicle's dry weight as a fraction of the total launch weight.
- Ashley


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Post    Posted on: Thu Jul 15, 2004 4:55 pm
Quote:
multiple engines:
Our lives really did get a lot simpler when we moved from four engines to a single engine. There is a slight temptation to use multiple 12" engines because we have all the parts for them on hand, but we think it is going to be easier to just build a bigger engine instead.


have you considerd multiple engines but a single nozzle?
it would give engine out protection,increase thrust but still with only one set
of control vanes.
a three chamber design would seem the most sensible.

i was very impressed by the test flight landing BTW.


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Post    Posted on: Thu Jul 15, 2004 5:44 pm
koxinga wrote:
Abit off topic here. I read from The Register that Doom 3 has gone RTM and will be hitting the stores by next month.

Just want to say thanks for the great work. Unfortunately, I will not be getting it as my PC is too slow to run the game and I am also using a PowerBook as my laptop.

Doom had gave me great pleasures in the past. I will forever remember the times in polytechnic where we play Doom under the noses of my lecturers and the pesky technical officers those many years ago. 8)

Hope that once this is out, you would have more time for Armadillo!


sigurd has said off topic questions are unacceptable, but seeing as there's no question involved, and it's tied in with armadillo, complements are just fine 8) . btw, i agree completely, awesome job on doom 3, i'll probably be getting it, though that might depend on half-life 2's release date. i guess i might as well phrase it as a question, but will you be working more on armadillo once doom 3 hits stores, or will it still just be a weekend/tuesday job?

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Post    Posted on: Fri Jul 16, 2004 7:13 am
>simpler upper stages stages. A mass ratio of 10 for an unstreamlined, >non reusable vehicle is trivial, and we actually don't think 15 will be that >hard. Our opinions may change as we develop things, of course.

Still sounds like a very risky, marginal design. Say you have a 1650 gal (or is it 1600 gal?) fuel tank on the main vehicle, it weight 1700 pounds dry with a 850 gal tank, switching to 1650 gal will add 800 pounds. So we have 15000 pounds of propellant and (1700+800=2500) pounds vehicle. Engines for the liftoff weight of over 20000 pounds, so having at least 25000 lbf thrust will be over 500 lb. This is over 3000 lb of dry vehicle mass, add 10% for fuel for powered landing, it will be 3300-3400 lb. Isp is 190s.

Second stage weights, say 2000 lb, and 1/15 mass ratio.

To get a minimal total characteristic velocity of 9300-9400 m/s to get to orbit, you'll have to get vacuum Isp of second stage at 260s with 1/15 mass ratio and no payload, or 300s with 1/10 mass ratio. Both seem impossible or extremely hard to achieve... Even no "professional" upper stage has 1/15 mass ratio, Centaur B or C with a single RL/10 is a lightest one with about 1/11 or so. 300s Isp will bring extremely complex cooling problems...


Last edited by anovikov on Fri Jul 16, 2004 7:20 am, edited 1 time in total.



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Post    Posted on: Fri Jul 16, 2004 7:15 am
Why don't switch to a simple, reusable two-stage combination with a total characteristic velocity of 5-6 km/s and a third solid-fueled stage, or Jupiter-C style solid fuel stage pack?


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Post IMU and solid state gyro questions   Posted on: Fri Jul 16, 2004 11:12 pm
Hi again, John
I think that you tested some of the solid state mems type accelerometers and said they were to noisy at low G, which is why your running the fiber optic gyro. (at least that's the impression I got)
Which specific parts were those? the analog devices ADXL-202's ? There is also some brand new accelerometers out that might be worth trying.

What specs do you need from your IMU? If someone (me!) were to build an IMU with solid state accelerometers & angular rate sensors for only a couple hundred dollars or less, what specs (drift, error, frequency response) do you require? What interface would you like it to have back to your CPU? (serial, parallel, I hope not USB)?

Doesn't your GPS handle any small drifts ithat the IMU might have?

Brynn Rogers

http://www.visi.com/~brynn/tryclops to see my robot


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Post    Posted on: Sat Jul 17, 2004 6:35 am
Our local Russian guys are experimenting with regen-cooled kerosene/nitric acid engines and plan to build a vehicle, they also tried solid-state gyros and found them completely unusable.


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