Am 19.01.2018 um 23:40 schrieb Kenneth:

> If that's true, then one of the main 'set pieces' of the film-- the orbiting
> space station being destroyed by fast-moving debris hitting it-- seems
> unnatural. Wouldn't that debris naturally be in some different orbit, because of
> its different speed? (Unless the debris was from an explosion-- blasting out in
> all directions from some particular orbit.) I don't remember if such an
> explosion was the cause.

Yes, such an explosion was indeed the cause. IIRC that explosion in turn
was caused by another collision.

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"Bald Eagle" <cre### [at] netscapenet> wrote:
> > Wouldn't that debris naturally be in some different orbit, because of
> > its different speed?
>

>
> But you can have circular orbits, elliptical orbits, and you also have
> 360-degrees of rotation around both orthogonal axes - so you could
> be travellingat 70,000 mph in one direction, and get t-boned, or hit by
> an object head-on in the "oncoming lane".

Yeah, I completely forgot about those little facts; there are an infinite number
of 'great circles' around the Earth for any given orbit... as well as their
reversed directions!

> It depends on the mass.  Two equal masses [w][c]ould occupy the same orbit.

Like Clipka says, I think the different masses of the various objects (in the
same orbit) can be ignored. Let's say there are two objects: the U.S. Space
shuttle, and an apple(!) I'm guessing that both can be launched into the same
orbit, given the correct trajectories and forces. Assuming both are in nicely
circular orbits, they are actually 'falling' around the Earth. Neglecting air
resistance, any two objects 'fall' at the same rate, regardless of their masses.
(The old Galileo experiment, from the Tower of Pisa.) So it follows that the
Space shuttle and the apple-- in the same orbit-- are going at the same speed or
velocity. (If their speeds were different, one would head further off into
space-- attaining a higher orbit, or maybe a more eccentric one?)

I find that it's far more fun to CONJECTURE about things than to actually look
up the facts  :-P  Just like the ancient Greeks! (Well, they did OK with
geometry, I guess...)

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On 20/01/2018 16:09, Kenneth wrote:
>   Just like the ancient Greeks! (Well, they did OK with
> geometry, I guess...)

But not that great with Irrational numbers or beans. ;-)



-- 

Regards
     Stephen

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The main thing that bothered me was that Clooney basically tells Bullock 
to point directly toward the Chinese module and hit the gas.

But:

1. Isn't it really hard to move between two locations in a straight line 
in Space, so close to a large body such as the Earth? Aren't successful 
orbital maneuvers really complicated, time-consuming and hard to pull off?
2. Wouldn't it take a really long time to cover the distance between two 
space stations at the rate she was moving in her suit (e.g. slow enough 
so she could stop herself by grabbing on with her hands, IIRC)? Or do 
space stations typically live within a few kilometers of each other?

Never got to see the movie in imax.


Mike

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On 21/01/2018 16:37, Mike Horvath wrote:
> The main thing that bothered me was that Clooney basically tells Bullock 
> to point directly toward the Chinese module and hit the gas.
> 
> But:
> 
> 1. Isn't it really hard to move between two locations in a straight line 
> in Space, so close to a large body such as the Earth? Aren't successful 
> orbital maneuvers really complicated, time-consuming and hard to pull off?
> 2. Wouldn't it take a really long time to cover the distance between two 
> space stations at the rate she was moving in her suit (e.g. slow enough 
> so she could stop herself by grabbing on with her hands, IIRC)? Or do 
> space stations typically live within a few kilometers of each other?
> 
> Never got to see the movie in imax.
> 
> 

I think the real problem is that orbital mechanics is not cinema 
friendly. The public expect (from their experience on Earth) that if you 
accelerate towards an object you get closer, quicker in a straight line. 
Not that your orbit will get higher or lower. That is what stopped me 
watching any of the Star Wars follow ups.

-- 

Regards
     Stephen

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On 1/21/2018 12:04 PM, Stephen wrote:
> I think the real problem is that orbital mechanics is not cinema 
> friendly. The public expect (from their experience on Earth) that if you 
> accelerate towards an object you get closer, quicker in a straight line. 
> Not that your orbit will get higher or lower. That is what stopped me 
> watching any of the Star Wars follow ups.
> 

Well, that's not fair, since in Star Wars the space ships have very very 
powerful engines. If you have a powerful enough engine, you can make a 
house fly in a straight line.


Mike

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On 21/01/2018 17:11, Mike Horvath wrote:
> On 1/21/2018 12:04 PM, Stephen wrote:
>> I think the real problem is that orbital mechanics is not cinema 
>> friendly. The public expect (from their experience on Earth) that if 
>> you accelerate towards an object you get closer, quicker in a straight 
>> line. Not that your orbit will get higher or lower. That is what 
>> stopped me watching any of the Star Wars follow ups.
>>
> 
> Well, that's not fair, since in Star Wars the space ships have very very 
> powerful engines. If you have a powerful enough engine, you can make a 
> house fly in a straight line.
> 
> 

Fair or not it broke my sense of disbelief. Pedantic moi?
But then I'm not a great movie fan.

-- 

Regards
     Stephen

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Le 20/01/2018 à 17:09, Kenneth a écrit :
> So it follows that the
> Space shuttle and the apple-- in the same orbit-- are going at the same speed or
> velocity. (If their speeds were different, one would head further off into
> space-- attaining a higher orbit, or maybe a more eccentric one?)

Which remind me of a curiosity: if the apple goes faster, it goes
higher... and performs then less revolutions than the station.

When you're a satellite, if you want to move ahead of another one, you
need to SLOW to be able to jump from behind to the front.

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On 26/01/2018 17:02, Le_Forgeron wrote:
> Le 20/01/2018 à 17:09, Kenneth a écrit :
>> So it follows that the
>> Space shuttle and the apple-- in the same orbit-- are going at the same speed or
>> velocity. (If their speeds were different, one would head further off into
>> space-- attaining a higher orbit, or maybe a more eccentric one?)
> 
> Which remind me of a curiosity: if the apple goes faster, it goes
> higher... and performs then less revolutions than the station.
> 
> When you're a satellite, if you want to move ahead of another one, you
> need to SLOW to be able to jump from behind to the front.
> 

I wish someone had told the Star Wars makers, that fact.

-- 

Regards
     Stephen

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Am 26.01.2018 um 18:02 schrieb Le_Forgeron:
> Le 20/01/2018 à 17:09, Kenneth a écrit :
>> So it follows that the
>> Space shuttle and the apple-- in the same orbit-- are going at the same speed or
>> velocity. (If their speeds were different, one would head further off into
>> space-- attaining a higher orbit, or maybe a more eccentric one?)
> 
> Which remind me of a curiosity: if the apple goes faster, it goes
> higher... and performs then less revolutions than the station.
> 
> When you're a satellite, if you want to move ahead of another one, you
> need to SLOW to be able to jump from behind to the front.

Actually it depends how quickly you want to achieve this maneuver. If
you're in low earth orbit, have plenty of time on your hand, and/or have
a large distance to catch up, you may indeed want to decelerate in the
current direction of travel, wait for the peculiarities of orbital
mechanics to carry you the desired distance ahead, and then re-inject
into the original orbit, as it's probably the most fuel-efficient maneuver.

However, such a maneuver requires at least one full orbital revolution
to complete. Even in low earth orbit, that's about 1.5 hours.

Also, I guess the precision for such a maneuver may be comparatively low.


If you want to achieve the maneuver faster, you need to accelerate more
downward or even forward. For instance, in the final phase of docking
two spacecraft, orbital maneuvering is actually pretty intuitive.

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