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Comparisons - expend./reusable,heavy/light,theory/practice

Posted by: Ekkehard Augustin - Thu Mar 30, 2006 8:38 am
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Comparisons - expend./reusable,heavy/light,theory/practice 
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Post Comparisons - expend./reusable,heavy/light,theory/practice   Posted on: Thu Mar 30, 2006 8:38 am
It seems to be required to consider the whole family as a whole - to compare each rocket to another rocket.

It is required to that technically and technologically in this thread.

I am already thinking about applying formulars etc, but there are already some non-formular hints and aspects.

The Ziolkovsky-formualr says that the required amount of energy and thus propellant increases exponentially when weight increases linearily. Logically the required amount of propellant increases linearily only if the weight is spread over several launches .

This is the heavy/light-aspect.

If a rocket or vehicle is expendable it has to built each time again when another fraction of the weight has to be lifted. This seems to mean that there as much sources of failures, errors, mistakes and delays as launches required. On the other hand this is not the case if the rocket or vehicle is reusable - the sources od failures etc. are reduced then.

This is the expendable/reusable aspect.

Next there are the rockets/vehicles existing, being in use, having flown already - they are all distinct instances of rockets/vehicles. They don't represent all rockets/vehicles which can be cosntructed technically and using the budgets, ressources, funds, capital available. They are the practice while the theory may allow for rockets and vehicles that allow the combination between linearity of required amount of propellant and reduction of the sources of failures etc.

This is the theory/practice-aspect.



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Last edited by Ekkehard Augustin on Sat Apr 01, 2006 10:56 am, edited 1 time in total.



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Post Re: Comparisons - expendable/reusable, hevy/light, theory/pr   Posted on: Thu Mar 30, 2006 2:53 pm
Ekkehard Augustin wrote:
The Ziolkovsky-formualr says that the required amount of energy and thus propellant increases exponentially when weight increases linearily.
If by the Ziolkovsky-formualr you mean this equation:

M0 = M1 ( e ^ DeltaV/Ve )
where:
M0 is the combined mass of the propellant, rocket and payload.
M1 is the mass of the rocket and payload only.
Ve is the exhaust velocity
DeltaV is the total change in velocity that M1 gets.
http://en.wikipedia.org/wiki/Rocket_equation

then it says nothing about energy.

It only says propellant increases exponentially with the total change in velocity (DeltaV).

If DeltaV and Ve remain the same, then ( e ^ DeltaV/Ve ) is constant and the equation simplifies to M0 = M1 * C, which says propellant increases linearly with weight.


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Post    Posted on: Fri Mar 31, 2006 6:14 am
Of course I am speaking about that formular since I do not know another formular by that title or name.

My focus is on the propellant of course but the propellant is the source of energy to be activated by the engines.

And I didn't apply the formular in any particular way yet. To apply M0 = M1 doesn't make sense no way since it would mean that no propellant is in the rocket - so it couldn't take off nor reach any orbit.




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Post    Posted on: Fri Mar 31, 2006 1:46 pm
Ekkehard Augustin wrote:
To apply M0 = M1 doesn't make sense no way
:?: :?: :?: :?:
You are right, that makes no sense. That is why I didn't say that.


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Post    Posted on: Fri Mar 31, 2006 1:57 pm
The problems are the spaces in your equation(s) and that you used an upper case C which appeared in the line follwoing M0 = M1 on my display. I would have written your equation as follows: M0=M1*const or M0 = M1*const. I even would prefer c instead of const but I suppose then you would argue that c is the speed of light ...

But I still don't have in mind to keep DeltaV and Ve remaining the same - this would be a special case which doesn't cover all possible results and thus isn't valid generally. It would mean to keep the problems ocurring when something like that is done in my science.



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Post    Posted on: Fri Mar 31, 2006 2:21 pm
He never used an upper case C..... For that matter, he never used a lower case c. The equation is Msub0 = Msub1 * (e ^ ∆V/VsubE). In case that one symbol before the first V didn't come through, it's a Delta. It means that the initial mass equals the empty mass times e (2.71828) raised to the power of (∆V/VsubE), the total change in velocity divided by the exhaust velocity. It's a simple Conservation-Of-Mass statement, really.

Later, he said that IF the two were constant, then it was equivalent to Msub0 = Msub1 * C (or, if you prefer, K, or any other letter that you wish to use for an arbitrarily-named constant). This is not equivalent to Msub0 = Msub1, which is obviously wrong. Also, C≠c; C is just an arbitrary number, while c is defined as 3*10^9 m/s. (Of course, c should not be confused with such numbers as csubl or csubd, which are coefficients of lift and drag, respectively, per unit span... Bah, we ran out of letters decades ago, and we keep coming up with new constants..... But that's another story.)

(Damn, we need an equation editor around here.)

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Post Re: Comparisons - expendable/reusable, hevy/light, theory/pr   Posted on: Fri Mar 31, 2006 2:30 pm
My point is that this statement
Quote:
The Ziolkovsky-formualr says that the required amount of energy and thus propellant increases exponentially when weight increases linearily.
is wrong. The required amount of propellant does NOT increase exponentially when weight increases linearly, it increases linearly when weight increases linearly. And you need another formula (E=1/2MV^2) to calculate energy, but energy also increases linearly when weight increases linearly.


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Post    Posted on: Sat Apr 01, 2006 11:17 am
Hello, spacecowboy,

of course you are right so far regarding the formular as Ziolkovsky writes it but Peter used the uppar case C. under www.bernd-leitenberger.de the equation is given also but using different symbols due to language.

Peter, you are doing another of the mistakes you are causing threads to go spirally by - you are complicating the topic by a lot of whens and ifs. While such whens and ifs are useful under one or another aspect they all cause a set of special solutions. And this complexifies considerations and discussions - it causes confusions and can result in logical, mathematical and calculation eroors and mistakes.

I will simply use the equation as I find it and - I will not start by
Quote:
If DeltaV and Ve remain the same
, but simply by the equation itself. There are four parameters involved in the formular which allows for several different combinations of keeping two parameters as parameters plus using one of the remaining as an independent variable while making the remaining parameter the dependent variable.

There are more posibilities what to do with the formular.

It is far too ea4rly to introduce constraints like that you are mentioning and you don't know yet, what I have in mind.

Peter, avoid doing any errors and in particular those I already listed to you - I still can intensify my handling of your errors and mistakes like interpretation and the like. I am doing that as a poster who doesn't want his posts to be abused to make threads go spirally.



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Post    Posted on: Sat Apr 01, 2006 7:17 pm
Ekkehard Augustin wrote:
I will simply use the equation as I find it
Here is the equation simply as it is:
M0=M1(e^DeltaV/Ve)
It clearly says that propellant does NOT increase exponentially with weight. It DOES say that propellant increases exponentially with VELOCITY. Your statement that
Quote:
propellant increases exponentially when weight increases linearily
is wrong and I do not want to see a spiraling discussion started here based on the false premise that propellant increases exponentially with weight.


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Post    Posted on: Sun Apr 02, 2006 12:47 pm
Peter, I shouldn't answer to your posts no more since they more and more sound or look suspicious to me - more about that later in thi spost.

Propellant is involved implicitly in that formulat since the velocity can be got only by using propellant. You are responding to thoughts of mine you don't know yet and you already have experienced in another section that it is likely that your assumptions and images what my thoughts are tends to be wrong - which is the next error, mistake,failure to be listed. There is another one - you already have experienced that your assumptions and thoughts about what instruments, methods etc. are avilable to me tend to be errant, false etc. also.

And I dectect a third error etc. to be listed here - I knew the formular before you listed it here - I do not know why you seem to assume something different - there was no reason to do so, since everyone who is interested can search the Internet for it, can read a lot of articles and much more.

Personal reanrk as poster simply

Now the remark regarding my suspicions. Your are trying to act here as well as in other answers to me like people who want to giude off a person from his straight way of thinking and arguing, off the logic and off the topic. Managers etc. are sent to classes, courses and the like to learn that. Partially it's called Dialectic but what you are doing isn't Dialectic yet - you are simply disturbing the straight way of thoughts. Either you don't know to do better or there is an intention behind that.

To continue - I am informed that in the angloamerican region of this planet there is a tradition of debating, There are real debating clubs. And as far as I know further the focus of those debates is on using Rhetorics etc. to get rid of others - regardless of those others being correct. When something like that is done in parliaments often damge to the economy, culture, foreign affairs, history, justice and more can be observed - the only way to go against that to many people appeares to be to apply that way also.

So debating has a bad image to me mostly - I don't like it really and in Germany there is no such tradition of debating.

Sigurd one day told me that this message board isn't meant to debate but simply to do conservation. I don't know what caused him the impression that I want to debate but this doesn't matter here - I am not out on debating and never was.

What I am out on here is to assist the evolution of private space flight, mankind becoming a space fairing civilisation, and find new ideas, ways, aspects etc. to enable that. I want to be constructive here, to add my thoughts, ideas, questions, abilities, knowledge, methods, creativity etc. to those of others for positive goals I share with them. When I entered the board there was nothing to complain about. In between this has been reduced a bit - by you and one other poster. There is no reason for me to leave the board but it has become a little less positive.

Pleas reamrk: I AM NOT OUT ON DEBATING but I am out on finding ways and perspectives and to further positive goals like private spaceflight toegther with others. But you and the other poster are negative experiences compared to to other posters here.

End of personal remark



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Post    Posted on: Sun Apr 02, 2006 3:51 pm
Hey Ekkehard Augustin,

I really see nothing wrong in campbelp2002 style of posting..
Maybe you're just making wrong assumptions about what he's trying to say or achieve... And if you don't like what he's saying.. you always have the option of ignoring him, or just with noting, you won't react on his posts, as you do not see it valid or so..

You can't change or remove people who do not share the same way of thinking.. so I think your pesonal remark, will have almost no effect what so ever in the end. The best solution I see, is to change the way you're responding to him, don't give your frustrations a chance to run away with yourself...

If you have frustrations, it are "your" frustrations. And you want to get rid of them.. so try to find a solution.. but making an open remark to him, is not a solution that will help you, nor him in this case I think. So sometimes you just have to clearly put your own red line.. and say.. no I do not continue or respond to "someones" questions or remarks, cause I personally don't agree with them and I don't want to put my time into it.

Cause if you keep defending yourself.. frustrated and angered.. you often won't find a solution, both sides will be frustrated and it will cost a lot more energy and time than just ignoring or writing a short message explaining why you do go into his discussion.. without hate and frustrations..



About the discussion itself..

I think campbelp2002 has valid arguments, maybe you're less focussed on how "correct" things are.. but even in economics writing a formula wrong, even if it's just with words, a wrong explenation.. it may really confuse other people, or provide them with wrong answers.

And with that "discussion" I think it's only finding common way of describing and noting the things down like they really are.. I fear Ekkehard, you where confused with the way the mathemathics was written down.. but campbelp2002 is correct. While you made some wrong assumptions and unable to read the mathemathics correctly, possible because you learned it with writing it diffrently (and a forum isn''t really able to use the right Mathemathics writing style)

So please don't make it too personal.. this stays a forum.. and you do not have to reply to everyone or explain always everything to everyone..

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Post    Posted on: Sun Apr 02, 2006 4:28 pm
Hello, Sigurd,

throughout my life I have experienced that it is better to clarify what someone feels or thinks about someone else experiencing his behaviour. What I said isn't meant to change him nor it is meant to solve something - it's only meant to clarify it. Peter should know it and so I said it.

Up to now I didn't apply any mathematics here in the meaning of modifying formulars and the like. There only was a problem when Peter's formular was displayed on my screen - of course I was in error but simply because of the display.

Under www.bernd-leitenberger.de the formular is written
Quote:
Geschwindigkeit einer Rakete = Ausströmgeschwindigkeit der Verbrennungsgase mal natürlicher Logarithmus des Verhältnisses von Vollmasse zu Leermasse.

...

v = ve * ln (Mv / Ml)

v: Endgeschwindigkeit der Rakete (in m/s)

ve: Ausströmgeschwindigkeit der Gase (in m/s)

Mv: Masse der Rakete beim Start

Ml: Masse der Rakete nach Verbrauch des Treibstoffs.
.

"Treibstoff" means propellant - the difference between Mv and Ml is the mass of the propellant. This is the reason why I said that propellant is involved in the formular.

Modifications:

0: v = ve*ln(Mv/Ml)
1: v/ve = ln(Mv/Ml)
2: e^(v/ve) = Mv/Ml

At launch from surface the propellant is used to accelerate the vehicle to achieve the velocity v. Given a certain v ve determines the amount of propellant required. Then the amount of propellant increases exponentially the less ve is - and ve depends on the chemical(s) used. And the more of the chemicals is required the more the Ml is increased - not proportionally I suppose but it is increased. This I am talking about

And so on. I am still working on it and investigating it all even beyond that formular - I haven't it ready yet and because of this Peter should be patient.

The symbol Mv means "Masse voll" which means "tank filled with propellant" while Ml menas "Masse leer" which means "tank empty". Peter's M0 is Mv and Peter's M1 is Ml.


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Post    Posted on: Mon Apr 03, 2006 3:50 pm
Good post Ekkehard.
Ekkehard Augustin wrote:
Then the amount of propellant increases exponentially the less ve is - and ve depends on the chemical(s) used. And the more of the chemicals is required the more the Ml is increased - not proportionally I suppose but it is increased. This I am talking about
Exactly so. Lowering Ve (or increasing V) will require exponentially more propellant (exponentially more Mv for a given Ml). This is why I say propellant varies exponentially with velocity.

Quote:
Logically the required amount of propellant increases linearily only if the weight is spread over several launches
You can launch double the Ml into the same orbit (same V) with the same exhaust velocity (same Ve) with one rocket by only doubling the Mv. There is no exponential increase in Mv. It is linear.


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Post    Posted on: Tue Apr 04, 2006 6:50 am
To keep the thread up to date regarding my "work" on the comparison I am in between including the reusability-aspect. Partially this means a system of equations at present.



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Post    Posted on: Mon Apr 24, 2006 9:14 am
Thinking about the reusability/expendability-aspect there is one function that meets some aspects of one or two other threads here.

The function says that the less the reusability the longer the time required until the next launch. Of course expendable rockets can be stored which reduces the time until the next launch.

I don't have ready the function-equation yet.

The function for the link between reusability/expendability and the number of sources of errors I am still thinking about.



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