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Orbital Mechanics

Posted by: campbelp2002 - Thu Dec 23, 2004 7:49 pm
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Orbital Mechanics 

Could an object spiral into the Sun?
Of course! 64%  64%  [ 16 ]
No way! 28%  28%  [ 7 ]
I used to think so, but now I don't. 0%  0%  [ 0 ]
I didn't think so before, but now I do. 8%  8%  [ 2 ]
Total votes : 25

Orbital Mechanics 
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Post Orbital Mechanics   Posted on: Thu Dec 23, 2004 7:49 pm
For some time I have been arguing in the disposal of radioactive waste topic that it is impossible for an object such as a package of radioactive waste to just spiral into the Sun. I would like to know the impact this has had on the forum as a whole.
How many people always thought spiraling into the Sun was possible and still do, how many never thought it was possible and still don't, and how many have changed their minds?

My vote is "No way!".

Peter Campbell


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Post Re: Orbital Mechanics   Posted on: Fri Dec 24, 2004 8:41 am
Your question is badly worded, you give no starting conditions and therefore the reader may assume any starting conditions are possible. So the question becomes the complement of is it impossible for something to spiral into the sun ... the answer to that one, based on observation, is "no". So the correct answer to the question you have posed, in the over-simplified way you have worded it, is "yes".

Semantics. Not just a waste of breath.

DKH

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Post    Posted on: Fri Dec 24, 2004 2:19 pm
Wow! The situation is worse than I thought.

First it is impossible to spiral into the Sun with ANY starting conditions, assuming nothing like friction or realitivity effects or continuous thrust. This would violate conservation of energy. After all, nobody would think you could spiral UP from the Sun without rocket power, would they?

It is bad enough that most people believe spiraling in is possible, but one person who used to think it as not possible now thinks that it is!

I really thought this forum would have a population who knew more about orbital mechanics than the general population. Or at least they would understand it if it was explained.
:cry:


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Post    Posted on: Fri Dec 24, 2004 9:23 pm
Why did this deserve yet another thread?

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Post    Posted on: Sat Dec 25, 2004 12:34 am
It doesn't. But it was the only way I could create a poll.


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Post    Posted on: Sat Dec 25, 2004 7:39 am
...


Last edited by whonos on Thu Jun 07, 2007 7:04 pm, edited 1 time in total.



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Post    Posted on: Sat Dec 25, 2004 11:41 am
Orbits dont last forever, and i dont see the point between 'landing' on earth and 'landing' on ths un or the moon. Spiraling down is not really possible i think, would mean that it would change direction, but just going down is no problem imo.

I don't see why it shouldnt be possible?


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Post    Posted on: Sat Dec 25, 2004 9:20 pm
Peter,

you are stating an issue but you didn't give a prove of it yet. You didn't prove that I'm wrong and I'm working to calculate mathematics to find out this way what's possible.

The true issue from me was that it is really possible to throw something into the sun without throwing the drive into the sun too.

There is one case at least which would cause the object to fall into the sun - if it is moving straight towards the sun instead of orbiting around the sun.

By speaking of a spiral I simly supposed the shape of the course but my issue is that something can be thrown into the sun without fly-bies.

I'm still doing my mathematics but I didn't find sufficient time during christmas up to now.



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Post    Posted on: Sun Dec 26, 2004 4:14 am
Ekkehard Augustin wrote:
you are stating an issue but you didn't give a prove of it yet.

I have given many proofs. You have just not accepted any of them.


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Post    Posted on: Sun Dec 26, 2004 3:42 pm
No, what I've been reading up to now doesn't be a general proof - it's a proof under special assumptions concerning the starting conditions. I still have to read the posts I explicitly didn't find the time to read yet but all you wrote before is mathematical right and correct but does exclude conditins that a possible in reality. Especially orbit.xls never can be considered to be a proof of general validity because it is restricted to objects already in an orbit and not capable of leaving the orbit by thrust etc.

I'm still calculating my mathematics but have already ready three steps which I will post step by step during the next few days.

Now I will read the posts I missed the time to read before christmas.



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Post    Posted on: Mon Dec 27, 2004 2:08 pm
whonos wrote:
If the object in question doesn't change velocity and it's perigee doesn't intersect the sun's surface then no, it will just orbit indefinitely.

Exactly!


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Post    Posted on: Mon Dec 27, 2004 2:15 pm
Too much - along an elliptical orbit the velocity is changing permanently. I personally would prefer to say that the tangential component mustn't be less then the vertical component at no point of the orbit.

Besides - at german site there is to be read that the escape velocity at the sun is 618.02 km/s.



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Post    Posted on: Mon Dec 27, 2004 10:02 pm
Orbit indefinitely? Huh?

DKH is right, your semantic issues are a bigger hurdle than the technical ones.

1.) All orbits decay... it's just a question of how long it takes
2.) Any decaying orbit's trajectory can (loosely) be described as "spiral"

This discussion was about the timeframe, efficiency, and relative safety of transolar trajectory injection as a method for removing biologically harmful radioisotopes from terrestrial or interplanetary space. If the syntax of some other poster is problematic, we should attempt to reframe the language used in the disccussion rather than repeated (and clearly futile) attempts to change somebody's interpretation of some arbitrary term.

Peter, I think your original position is justified, but you will never sway Ekke by sweating him over "spiral"


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Post    Posted on: Mon Dec 27, 2004 10:21 pm
At last - The voice of sanity, praise the lord. It was only days away from setting up an entire website devoted to "Spiral orbits" (which may or may not be possible). :lol:

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Post    Posted on: Tue Dec 28, 2004 7:31 am
I will continue my calculations I'm doing in the other thread. If they show that it is impossible to throw something into the sun without a permanent working drive or engine I have no problem to say freely that I was in error. I don't have such a problem too if someone proves by mathematical logic that my mathematics are wrong. And this is valid too if someone shows me that my mathematics don't represent physics sufficiently. At least one physical force is missing in my mathematics - the centrifugal force - but this force seems to be missing in orbit.xls too.

I don't want to insist but to check. By calculating the course etc. for each second and marking each position in a diagram, graphic or simply a coordinate system we will see what the result and the course will be looking like.

But to repeat a real example and to add another real example:

1. Smart-1 has been moving away from Earth by spirals. The probe orbited Earth and from time to time its ion drive has been igneted and then shutdowned again. The course explicitly has been called a spiral. Then this way Smart-1 reached a distance where the gravity of moon was stronger then the gravity of Earth - Smart-1 began to orbit the moon instead of Earth. It continued to ignite the ion drive and to shutdown it again and spiraled down to its final orbit. This example shows that it is not required that the drive or engine is working permanently to spiral around a gravitational center - regardless of approaching to or moving away from that center.

2. The Apollo-astronauts placed a mirror at the moons surface for an experiment which is repeated until now. Scientists use the mirrer to send a laser beam to it, let it be reflected back to Earth and to measure the distance of moon from Earth this way. The result is that the moon is moving away from Earth several meters - three if I remeber right - each year. The reason are the tidal forces of moon on Earth. These tidal forces a decelerating the rotation of Earth - they are reducing the impulse of rotation and the rotation energy. Because of the Impulse Conservation Theorem and the Energy Conservation Theorem the impulse is moving over to the moon permanently and enables it to override the gravitation of Earth - it is accelerated outwards. Now the moon is moving around Earth while moving away - its going only once throught each point. From this I imagine that the course of the moon will be a spiral in a coordinate system which the Earth would be the center of.

Am I informed wrong concerning these two examples?



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