Community > Forum > Official Armadillo Aerospace Forum > Official Armadillo Q&A thread

Official Armadillo Q&A thread

Posted by: John Carmack - Tue Jun 15, 2004 8:01 am
Post new topic Reply to topic
 [ 2523 posts ] 
Go to page Previous  1 ... 124, 125, 126, 127, 128, 129, 130 ... 169  Next
Official Armadillo Q&A thread 
Author Message
Moderator
Moderator
avatar
Joined: Mon Feb 09, 2004 4:01 am
Posts: 747
Location: New Zealand
Post Re: Bell-Shaped Pendulum?   Posted on: Thu Sep 17, 2009 11:51 am
sanman wrote:
Another different idea that just came to me relates to the "pendulum fallacy", whereby people mistakenly think that a rocket is hanging by the nose from an imaginary string, instead of actually resting on top of its tail/thruster.

So then, what if you could position a lot more of the lander's mass below the thruster?
Then you really would have a little more basis for pendulum paradigm.
And a pendulum is a little more easy to balance on a vertical centerline than a pencil standing on its end is.

So what if your rocket/lander looked more like a bell shape, where the thruster was located on the inside of the bell near the top, and the fuel tanks with their propellant mass were located on the outside of the bell near the bottom?
Wouldn't that type of mass distribution make it easier to do your balancing act, since your vehicle's mass distribution would be helping you rather than working against you?

Comments? Thoughts?


The Pendulum fallacy is the idea that if you put the entire rocket beneath the engine it would behave any differently than if the engine was at the bottom. Goddards Rocket had the fuel tanks beneath the rocket in the center of the plume. It didn't help.

_________________
What goes up better doggone well stay up! - Morgan Gravitronics, Company Slogan.


Back to top
Profile ICQ YIM
Spaceflight Participant
Spaceflight Participant
User avatar
Joined: Sun Sep 13, 2009 2:29 am
Posts: 64
Location: South Africa
Post Re: Official Armadillo Q&A thread   Posted on: Thu Sep 17, 2009 2:08 pm
I see that the ARCA team is planning to launch soon with just such a pendulum rocket! First a balloon and then rocket engines all tied together like a line of hotdogs!

_________________
Johann Grobler
AeroSpace Research
http://www.aerospace-research.co.za


Back to top
Profile WWW
Space Walker
Space Walker
User avatar
Joined: Thu Jun 17, 2004 3:01 am
Posts: 173
Location: Dallas, TX
Post Re: Official Armadillo Q&A thread   Posted on: Thu Sep 17, 2009 3:32 pm
sanman wrote:
Could you for instance have 3 different thrusters attached to the vehicle at fixed positions, and just vary the thrust between them to maintain balance and altitude?

Differential throttling. Yep, we've done that (with four engines, back in the peroxide days):

http://media.armadilloaerospace.com/200 ... Hover2.mpg

sanman wrote:
Or could you instead have some kind of slats under the single rocket thruster, to perhaps deflect that thrust in a particular direction?

Jet vanes. Yep, we've done that too (also in the peroxide days):

http://media.armadilloaerospace.com/200 ... tedHop.mpg

sanman wrote:
Or could you just have the lone main rocket thruster fixed in position, and then have some additional smaller thrusters at the very top of the craft to tip the nose in the right direction to maintain balance?

Attitude thrusters. And yes, we've done that too (in the really early days, and the thrusters were small peroxide engines, outboard instead of at the top):

http://media.armadilloaerospace.com/mis ... _short.mpg

I don't think we'll ever do spin-stabilization since manned flights are the ultimate main thrust of our program.

All of these control methods have their pluses and minuses, but we'll probably be going back to differentially throttled soon when we're flying with four Mods bolted together.


Back to top
Profile WWW
Space Station Member
Space Station Member
User avatar
Joined: Mon Feb 25, 2008 9:51 am
Posts: 448
Location: Vienna, Austria, Europe, Earth
Post Re: Bell-Shaped Pendulum?   Posted on: Thu Sep 17, 2009 3:43 pm
sanman wrote:
Another different idea that just came to me relates to the "pendulum fallacy", whereby people mistakenly think that a rocket is hanging by the nose from an imaginary string, instead of actually resting on top of its tail/thruster.

So then, what if you could position a lot more of the lander's mass below the thruster?
Then you really would have a little more basis for pendulum paradigm.
And a pendulum is a little more easy to balance on a vertical centerline than a pencil standing on its end is.

So what if your rocket/lander looked more like a bell shape, where the thruster was located on the inside of the bell near the top, and the fuel tanks with their propellant mass were located on the outside of the bell near the bottom?
Wouldn't that type of mass distribution make it easier to do your balancing act, since your vehicle's mass distribution would be helping you rather than working against you?

Comments? Thoughts?

As idiom has already pointed out, your idea is exactly the "pendulum rocket fallacy". It would only work IF a rocket would behave like a pendulum.
See http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy and http://www.geocities.com/jim_bowery/pendrock.html (the second one with some nice and helpful graphics)

SA_Rocket_Guy wrote:
I see that the ARCA team is planning to launch soon with just such a pendulum rocket! First a balloon and then rocket engines all tied together like a line of hotdogs!


What has that to do with the pendulum rocket fallacy? Yes, their rocket IS hanging from the balloon like a pendulum to gain altitude, but it has nothing to do with a "self-stabilizing" rocket, it just launches from a balloon ;).

_________________
pride comes before a fall


Back to top
Profile
Moderator
Moderator
avatar
Joined: Mon Feb 09, 2004 4:01 am
Posts: 747
Location: New Zealand
Post Re: Official Armadillo Q&A thread   Posted on: Thu Sep 17, 2009 9:16 pm
The later stages of the ARCA rocket use non-rigid mechanics (cables) between the stages.

Quote:
Helen will be using a gravitational stability method in vertical flight without aerodynamic surfaces or jet commands, by towing the component stages and payload. The towing can be made by cable, or rigid-articulated system.
In order to have a stabilized rocket in vertical flight, in gravitational field, this method is using a towed mass in the same direction with the thrust. This mass consists in the next rocket stages and payload. The stability effect depends of several elements: the mass of the stabilized body, the mass of the towed mass and the length between the centers of gravity of the stabilized body and the stabilizer body.
This method can be applied in the extra atmospheric space on vertical ascendant or descendent trajectory under the influence of gravitational field.


This Thread for more info.

_________________
What goes up better doggone well stay up! - Morgan Gravitronics, Company Slogan.


Back to top
Profile ICQ YIM
Space Station Member
Space Station Member
User avatar
Joined: Mon Feb 25, 2008 9:51 am
Posts: 448
Location: Vienna, Austria, Europe, Earth
Post Re: Official Armadillo Q&A thread   Posted on: Thu Sep 17, 2009 11:31 pm
Thanks, guess I wasn't up to date any more.

Though I don't have any way of proving this, I believe that this really is just another case of the pendulum rocket fallacy. If this does anything to stabilize the rocket, then it does it aerodynamically. I would really like to know the reasoning behind their statement, that this works with gravity and can be used outside the atmosphere...

_________________
pride comes before a fall


Back to top
Profile
Space Station Member
Space Station Member
User avatar
Joined: Wed Jul 30, 2008 9:39 pm
Posts: 266
Location: Denmark
Post Re: Official Armadillo Q&A thread   Posted on: Fri Sep 18, 2009 1:03 am
John, for all the achievements of AA, a decade has passed and you are still bouncing on the ground, no disrespect intended. But at this pace and with the commitment to bouncing turists (which I assume will be very demanding on AA time) when will you go for orbit?
have you done the math and the design for a low weight payload vehicle to orbit?
do you realize that a space telescope (both for looking up and down) can be made very light and even a 50cm mirror can resolve 20cm resolution from 250km up? is there not commercial application to that? mapping companies and universities buying telescope time? indeed someone like google might well want to pay for everything just for the mapping capability or the chance of it.

I believe it is/was your stated motivation of AA that Nasa is far too ineffective and slow, yet a decade has passed and it looks like some measure of subconscious capitulation has taken place, being distracted by competitions, small contracts and now bouncing turists. When will you go for orbit? Can you promise that another decade will not pass without at least seriously trying for orbit?

This might be hard to hear when used to all the praise of people here but I feel very strongly that you are missing a great opportunity to do something that really will make a difference because unlike most, AA is a combination of your skill and your financial means and orbit is where the difference is made, that's where Nasa will be put to shame and it is so needed.

I would ask that you at least do a design and do the math projections on how it would be and what it would cost so you will at least have seriously considered the possibility. So you are armed with the awareness of the possibility.
I would ask that you do the math on the diffraction limit of a 50cm mirror and compare the values to the hubble telescope pixel size. I think you will find it interesting. hubble doesn't even have color and only a 1024x1024 imager.

ask yourself, how light can a space mirror be, how light can an imager be, how light can a radiocircuit be, how light can a battery be, the solar film, the controlling electronics, the gyro mechanics for orientation. and how light can the rocket be to lift it there. and how many universities would stand in line to manufacture the mirror for you if you can put it in space for them.

imagine seeing that live HD image of the earth rolling by and being able to switch to 20cm resolution on the ground as it rushes by. you could see yourself wave to it.

and that would only be the beginning

ADMIN NOTICE:
Limit your replies to this post to this topic:
viewtopic.php?f=23&t=10511


Back to top
Profile
Space Walker
Space Walker
avatar
Joined: Tue Sep 15, 2009 11:59 pm
Posts: 188
Post Re: why not chemical + electric?   Posted on: Fri Sep 18, 2009 2:35 am
Pooua wrote:
I am not a rocket scientist, but I suspect that a turbine + generator large enough to produce sufficient electrical power to an arcjet would be heavier than the gimbals you are attempting to replace. Also, I've read that the typical life of an arcjet assembly is about 1500 hours of operation. If the price of an arcjet is higher than that of the gimbals, then this solution increases the weight and cost of the rocket. I'm not sure that it necessarily increases the reliability of the rocket.


Hi,

Thanks for that response. Yeah, I was wondering about that too, after I posted. So what is the mechanism used for gimbaling? Is it some sort of electrical/magnetic solenoid type of actuator?

Quote:
Helium is a nice gas to use in a cryogenic system. It is lightweight, won't liquify or freeze against LOX and it is non-flammable.


Well, they say that Helium is a precious and dwindling substance, so I certainly hope there's enough of it left to supply frequent lunar travel in the later part of this century.

Meanwhile, I feel that energy is a more fungible and abundant commodity in space, which also happens to have a lot of raw energy coursing through it, so that a space vehicle which is extravagant on energy while being conservative on propellant might be the best compromise. Electric thrusters seem to lean in that direction.


Back to top
Profile
Spaceflight Trainee
Spaceflight Trainee
avatar
Joined: Mon Sep 14, 2009 12:59 am
Posts: 44
Post Re: why not chemical + electric?   Posted on: Fri Sep 18, 2009 3:29 am
sanman wrote:
Thanks for that response. Yeah, I was wondering about that too, after I posted. So what is the mechanism used for gimbaling? Is it some sort of electrical/magnetic solenoid type of actuator?


That's something that team Armadillo needs to answer. I don't know what they are using. I suspect it would be something like a solenoid.

sanman wrote:
Well, they say that Helium is a precious and dwindling substance, so I certainly hope there's enough of it left to supply frequent lunar travel in the later part of this century.


I've read some people speaking with alarm at the casual way we use helium these days (filling party balloons with it seems like a waste to these people). I don't know what to think of their warnings. Helium is produced naturally by radioactive decay.

As for space flight, it is my understanding that pumps reduce or eliminate the need for gas pressurization.


Back to top
Profile
Launch Director
Launch Director
avatar
Joined: Fri Apr 18, 2008 2:25 am
Posts: 11
Post Re: Official Armadillo Q&A thread   Posted on: Fri Sep 18, 2009 5:58 pm
Hey Armadillo, per the Xprize rules, are you allowed a second chance at the Level-2 competition in order to improve the accuracy of your landing?


Last edited by dannyTX2 on Fri Sep 18, 2009 8:07 pm, edited 1 time in total.



Back to top
Profile
Spaceflight Participant
Spaceflight Participant
User avatar
Joined: Mon Apr 24, 2006 1:05 pm
Posts: 62
Location: Dallas, Texas
Post Re: Official Armadillo Q&A thread   Posted on: Fri Sep 18, 2009 6:43 pm
dannyTX2 wrote:
Hey Armadillo, per the Xprize rules, are you allowed a second chance at the Level-2 competition in order to improve the accuracy of you landing?

We were, but the time to register for it has already passed.


Back to top
Profile WWW
Spaceflight Participant
Spaceflight Participant
User avatar
Joined: Mon Apr 24, 2006 1:05 pm
Posts: 62
Location: Dallas, Texas
Post Re: why not chemical + electric?   Posted on: Fri Sep 18, 2009 6:48 pm
Pooua wrote:
sanman wrote:
Thanks for that response. Yeah, I was wondering about that too, after I posted. So what is the mechanism used for gimbaling? Is it some sort of electrical/magnetic solenoid type of actuator?

http://www.ultramotion.com/
I do not know exactly which ones we use though.


Back to top
Profile WWW
Spaceflight Trainee
Spaceflight Trainee
avatar
Joined: Mon Sep 14, 2009 12:59 am
Posts: 44
Post Re: Official Armadillo Q&A thread   Posted on: Fri Sep 18, 2009 11:07 pm
Has Armadillo Aerospace experimented, or considered experimenting, with aerospike engines?


Back to top
Profile
Space Walker
Space Walker
avatar
Joined: Tue Sep 15, 2009 11:59 pm
Posts: 188
Post Re: Official Armadillo Q&A thread   Posted on: Fri Sep 18, 2009 11:44 pm
An aerospike engine is only useful across a wider range of ambient pressure, whereas with a lunar lander you've got no atmosphere at all, and even for the purpose of this Level2 test, you weren't going upto a very high altitude.

So aerospike would be good if you're going from ground to orbit, and thus going across the full range of ambient pressure.


Back to top
Profile
Space Walker
Space Walker
User avatar
Joined: Wed Mar 07, 2007 3:30 am
Posts: 213
Location: USA
Post Re: Official Armadillo Q&A thread   Posted on: Fri Sep 18, 2009 11:49 pm
The aerospike issue was sort of covered awhile back in this very thread.

http://spacefellowship.com/Forum/viewtopic.php?f=23&t=396&p=27945&hilit=compensation#p27945

They have since tried a two stage expansion bell that does similar things. It is not continuous like an aerospike but much simpler.

Anyway read the posts surrounding the one I pointed to.


Back to top
Profile WWW
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 2523 posts ] 
Go to page Previous  1 ... 124, 125, 126, 127, 128, 129, 130 ... 169  Next

Who is online 

Users browsing this forum: No registered users and 12 guests


© 2014 The International Space Fellowship, developed by Gabitasoft Interactive. All Rights Reserved.  Privacy Policy | Terms of Use