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New poll regarding ARCA stabilization method

Posted by: Bogdan - Tue Sep 29, 2009 11:01 am
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New poll regarding ARCA stabilization method 

What is your opinion about Popescu - Diaconu stabilization method?
It will work 29%  29%  [ 10 ]
There is a stabilization torque but it cannot be used for real rockets 3%  3%  [ 1 ]
It will fail since it's nothing more then the pendulum rocket fallacy 35%  35%  [ 12 ]
It will fail for other reasons 21%  21%  [ 7 ]
Don't know 12%  12%  [ 4 ]
Total votes : 34

New poll regarding ARCA stabilization method 
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Post New poll regarding ARCA stabilization method   Posted on: Tue Sep 29, 2009 11:01 am
Popescu - Diaconu stabilization method

In order to stabilize the rocket, this method is using a towed mass in the same direction with the exhaust, by using cables attached to the exterior of the rocket structure. This mass consists in the next rocket stages and payload.

http://www.youtube.com/watch?v=4qVuVix5kCE


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Post Re: New poll regarding ARCA stabilization method   Posted on: Tue Sep 29, 2009 12:53 pm
If the lines were rigid this would be a pendulum, which would not be stable. With non-rigid lines the rear segments will whip back and forth in the exhaust, and will be total lyunstable. Also, there will be a lot of drag from the exhaust in this configuration.


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Post Re: New poll regarding ARCA stabilization method   Posted on: Tue Sep 29, 2009 7:30 pm
I haven't calculated anything or looked at it in much detail, but my gut feel would be that it will be swinging around quite badly, break or tangle up and crash. Of course, it would be very cool if it would in fact work, and I wish them the best of luck!

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Post Re: New poll regarding ARCA stabilization method   Posted on: Wed Sep 30, 2009 10:26 am
Shouldn't this be testable with a finless Estes rocket and a tether with a weight?

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Post Re: New poll regarding ARCA stabilization method   Posted on: Fri Oct 02, 2009 1:53 am
I really like Idom's soultion!

Monroe

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Post Re: New poll regarding ARCA stabilization method   Posted on: Fri Oct 02, 2009 9:39 am
idiom wrote:
Shouldn't this be testable with a finless Estes rocket and a tether with a weight?

Yes, but please note that the stabilization (if any) takes place only during the powered flight.

Come on guys, please vote here. We need your opinion before the launch.


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Post Re: New poll regarding ARCA stabilization method   Posted on: Fri Oct 02, 2009 12:10 pm
Pendulm fallacy. Slower (maybe very slow at first getting worse as you drop stages) version, though in the end same result.

Monroe

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Post Re: New poll regarding ARCA stabilization method   Posted on: Fri Oct 02, 2009 3:07 pm
Bogdan wrote:
idiom wrote:
Shouldn't this be testable with a finless Estes rocket and a tether with a weight?

Yes, but please note that the stabilization (if any) takes place only during the powered flight.

Come on guys, please vote here. We need your opinion before the launch.

This can be tested with a model rocket by using a motor that provides slightly more than 1 G of accelaration. This way the rocket will not go very fast and it will minimize aerodynamic effects. I would recommend testing with the Apogee F10, which has a 7-second burn time.

The rocket would have to be launched from an elevated platform that would be higher than the tether. This way there would already be tension on the tether and it would be pointed in the vertical direction. I would suggest testing a simple 2-body system first.

However, your tests would show that the tethered method will not work. Even if the thrust were pefectly centered there are no correcting forces to keep the rocket pointed in the same direction. Any slight aerodynamic asymmetry will cause the rocket to slowly rotate.

If the thrust is slightly off-center, the tethered system will deflect slightly and point the thrust in the correct general direction. However, the deflection will cause the thrust vector to be even further from the center line. That is, it will not point toward the center of mass. This means that there will be a rotational component of the thrust vector. The rocket will spin out of control.

Dave


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Post Re: New poll regarding ARCA stabilization method   Posted on: Fri Oct 02, 2009 7:20 pm
Topic of some interest for passive stabilization methods


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Post Re: New poll regarding ARCA stabilization method   Posted on: Fri Oct 02, 2009 8:44 pm
I agree with Dave, but buy all means test it and show us the results. I bet the spin and arc get pretty hairy, should be a very interesting video. Goddard’s face must have dropped, what happened? I bet it was pretty catastrophic! The best way to learn though, go for it guy’s! And congratulations on making such an attempt that’s how we get there. In fact I bet your closer to doing it yourself than any other team. Good Luck! And don’t stop testing and trying your on the right track to make it happen. Make a big deal out of it eather way it will be your experience and thats worth more than gold.

Monroe

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Post Re: New poll regarding ARCA stabilization method   Posted on: Sat Oct 03, 2009 12:13 am
The trick question: How are you going to stabilize the last stage?

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Post Re: New poll regarding ARCA stabilization method   Posted on: Sun Oct 04, 2009 3:24 am
thomson wrote:
The trick question: How are you going to stabilize the last stage?

I think the intent is to tether the payload as a fourth mass element to stabalize the third (last) stage. As I stated below, this scheme will not work. In fact, as long as the rocket isn't spinning around it is really no different than a pendulum rocket. Since the force applied by a tether can only be in the direction of the tether, it doesn't matter how long the tether is. Therefore, the tether lengths can be reduced to zero. This results in a rigid rocket with the motor on the top, and this is not stable. Any off-center thrust will cause the rocket to spin.

I would suggest that the ARCA members perform ground tests before they embark on their planned mission. I understand that they will be using a naval ship as part of their mission. This is going to prove to be an embarassment to them and the navy. Several knowledgeable people have told them that this won't work. It appears that they haven't performed any ground experiments of this system. They haven't even shown any physics that backs up their claim that it is stabal.

There are only two possible outcomes to this. They will either scrap the idea and start over with a proven design, or they will proceed with their plans and look very foolish when it fails.

Dave


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Post Re: New poll regarding ARCA stabilization method   Posted on: Sun Oct 04, 2009 8:40 pm
I totally agree with "Dave Hein".
The rocket is simply turning upside down over and over again and pendulums have no stabilization effect and do not correct deviations from the vertical trajectory.
Image
Remark: The seven images are not at the same scale. For this reason, the mechanical system, in the picture, appears smaller and smaller
Source: http://forum.nasaspaceflight.com/index. ... c=18951.45

Being curious to find out the exact launch date for Helen I discovered, by chance, a foolish message, posted by ARCA a few months ago.
http://www.googlelunarxprize.org/lunar/ ... as-stabilo
They do not even know well how to interpret what they see in various pictures.


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Post Re: New poll regarding ARCA stabilization method   Posted on: Tue Oct 06, 2009 2:49 am
Quote:
Being curious to find out the exact launch date for Helen I discovered, by chance, a foolish message, posted by ARCA a few months ago.
http://www.googlelunarxprize.org/lunar/ ... as-stabilo
They do not even know well how to interpret what they see in various pictures.


Don't worry, nobody would allow a man inside of whatever ARCA wants to launch, without a very serious evaluation of safety issues. As we could see so far, there is still long way until they will build even a mock-up system able to fly in the manner described in pictures. BTW, that tractor sistem seems to have been scrapped, in favor of a more classical approach.


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Post Re: New poll regarding ARCA stabilization method   Posted on: Tue Oct 06, 2009 8:38 am
To form accurate beliefs about something, you really do have to observe it. It's a very physical, very real process: any rational mind does "work" in this sense, not just the sense of mental effort... So unless you can tell me which specific step in your argument violates the laws of physics by giving you true knowledge of the unseen, don't expect me to believe that a big, elaborate clever argument can do it either.

One of the chief morals of the constraints of probability are inescapable; probability may be a "subjective state of belief", but the laws of probability are harder than steel.

People learn under the traditional school regimen that the teacher tells you certain things, and you must believe them and recite them back; but if a mere student suggests a belief, you do not have to obey it. They map the domain of belief onto the domain of authority, and think that a certain belief is like an order that must be obeyed, but a probabilistic belief is like a mere suggestion.

They look at a lottery ticket, and say, "But you can't prove I won't win, right?" Meaning: "You may have calculated a low probability of winning, but since it is a probability, it's just a suggestion, and I am allowed to believe what I want."

Here's a little experiment: Smash an egg on the floor. The rule that says that the egg won't spontaneously reform and leap back into your hand is merely probabilistic. A suggestion, if you will. The laws are probabilistic, so they can't really be laws, the way that "Thou shalt not murder" is a law... right?

So why not just ignore the suggestion? Then the egg will unscramble itself... right?

It may help to think of it this way - if you still have some lingering intuition that uncertain beliefs are not authoritative:

In reality, there may be a very small chance that the egg spontaneously reforms. But you cannot expect it to reform. You must expect it to smash. Your mandatory belief is that the egg's probability of spontaneous reformation is ~0. Probabilities are not certainties, but the laws of probability are theorems.

If you doubt this, try dropping an egg on the floor a few decillion times, ignoring the suggestion and expecting it to spontaneously reassemble, and see what happens. Probabilities may be subjective states of belief, but the laws governing them are stronger by far than steel.

I once knew a fellow who was convinced that his system of wheels and gears would produce reactionless thrust, and he had an Excel spreadsheet that would prove this - which of course he couldn't show us because he was still developing the system. In classical mechanics, violating Conservation of Momentum is provably impossible. So any Excel spreadsheet calculated according to the rules of classical mechanics must necessarily show that no reactionless thrust exists - unless your machine is complicated enough that you have made a mistake in the calculations.

And similarly, when half-trained or tenth-trained rationalists abandon their art and try to believe without evidence just this once, they often build vast edifices of justification, confusing themselves just enough to conceal the magical steps.

It can be quite a pain to nail down where the magic occurs - their structure of argument tends to morph and squirm away as you interrogate them. But there's always some step where a tiny probability turns into a large one - where they try to believe without evidence - where they step into the unknown, thinking, "No one can prove me wrong".

Their foot naturally lands on thin air, for there is far more thin air than ground in the realms of Possibility. Ah, but there is an (exponentially tiny) amount of ground in Possibility, and you do have an (exponentially tiny) probability of hitting it by luck, so maybe this time, your foot will land in the right place! It is merely a probability, so it must be merely a suggestion.

Prove it to yourself if you really doubt (you could be right) whatever it takes ,but pick your battles wisely (weight the probability and the consequences). Learn from your mistakes and share what you learn.

Godspeed
Monroe

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