[meteorite-list] Why did they not use the leftover propellantto heighten the orbit and push the rogue satellite into space?

Tue Sep 13 17:58:43 EDT 2011

Dennis, Probably you're right in this case, (and maybe even generally). 
  I think I was answering two questions at the same time, since it is 
slowed down in a higher orbit and slowed down to de-orbit.  The 
question was really, though, what is the first step taken.

1.  When you raise an orbit, if it is circular you actually do slow it 
down.  At higher altitudes, gravity is weaker,and that makes freefall 
slower to balance the forces for a stable orbit, if I'm not mistaken.

2.  To de-orbit ---like preparing for a gentle landing---, you would 
also slow it down, yes, since the idea is to change from a circular to 
an arc of entry...but I believe (without thinking too hard) that the 
orbit itself will now deform, in terms of the orbit, probably by 
increasing the eccentricity and the new shaped will now be helpful in 
determining where you will make your entry into the zone of significant 
air resistance.  Like taking a nose-dive into the atmosphere  ... 
though I am thinking once the nose dive is taken this is where the 
velocity will really increase since the situation is now dynamic(which 
was the reason for my answer you are commenting on).

But whether it increases or decreases will be determined by the point 
along the orbit that you fall since the ellipse will have faster and 
slower points.  Probably you could alsop speed it up and get a 
different ellipse that gets closer to the atmosphere than the original 
circular orbit.  But that wouldn't usually make much sense if you 
wanted to land the satellite.  Maybe to burn it up better, it would.  
The devil is in the details.

(Third) guessing, slowing it down to de-orbit makes the orbit more 
elliptical and with this you you select the closer point along the new 
ellipse to aim the puncture of the atmosphere (begin re-entry) where 
air is thick enough to "catch" it and dampen the remaining energy, like 
a calculated ripping through a spiders web.

  If you raise a circular orbit, you would thrust at a right angle to 
the orbital direction ("up" or "radially") and the satellite must slow 
down through some transfers to gain a circular orbit at the higher 
altitude.

Never had a toy satellite to play with ;-) but the mechanics of what to 
do aren't necessarily obvious when you go through more than one step in 
transfer orbits to achieve your goal.

Thanks for pointing that out, it would be nice to see a graphic 
animation of this to better visualize it!

Kindest wishes
Doug

-----Original Message-----
From: Dennis Cox <dragon-hunter at live.com>
To: Meteorite List <meteorite-list at meteoritecentral.com>; MexicoDoug 
<mexicodoug at aim.com>
Sent: Tue, Sep 13, 2011 4:56 pm
Subject: Re: [meteorite-list] Why did they not use the leftover 
propellantto heighten the orbit and push the rogue satellite into space?

You're second guessing your self Doug.

You said:

>oops:
>
> "Slow it down 600 mph (to 16,400 mph) and burn up vs. speed it up 600
> mph (to 17,600 mph) and get to an orbit 300 miles higher in altitude "
>
> should read:
>
> "Speed it up 600 mph (to 17,600 mph) and burn up vs. slow it down 600
> mph (to 16,400 mph) and get to an orbit 300 miles higher in altitude "
>
> ****

No, you got it right the first time.

You have to Decelerate the satellite to get it to fall out of orbit and 
burn
up. And accelerate it to get it to climb up into a higher orbit.

--------------------------------------------------
From: "MexicoDoug" <mexicodoug at aim.com>
Sent: Monday, September 12, 2011 9:39 AM
To: <mexicodoug at aim.com>; <jim_brady611 at o2.co.uk>;
<meteorite-list at meteoritecentral.com>
Subject: Re: [meteorite-list] Why did they not use the leftover 
propellantto
heighten the orbit and push the rogue satellite into space?

> oops:
>
> "Slow it down 600 mph (to 16,400 mph) and burn up vs. speed it up 600
> mph (to 17,600 mph) and get to an orbit 300 miles higher in altitude "
>
> should read:
>
> "Speed it up 600 mph (to 17,600 mph) and burn up vs. slow it down 600
> mph (to 16,400 mph) and get to an orbit 300 miles higher in altitude "
>
> ****
>
>
>
>
>
>
>
> -----Original Message-----
> From: MexicoDoug <mexicodoug at aim.com>
> To: jim_brady611 <jim_brady611 at o2.co.uk>; meteorite-list
> <meteorite-list at meteoritecentral.com>
> Sent: Mon, Sep 12, 2011 12:32 pm
> Subject: Re: [meteorite-list] Why did they not use the leftover 
propellant
> to heighten the orbit and push the rogue satellite into space?
>
>
> Its going a bit under 17,000 mph.
>
> Slow it down 600 mph (to 16,400 mph) and burn up vs. speed it up 600
> mph (to 17,600 mph) and get to an orbit 300 miles higher in altitude
> where gravity is still 75% what it is on earth's surface, and
> completely lost control of what happens after that since there is no
> fuel.
>
> Move it down 300 miles and you've burnt up already in the atmosphere,
> problem solved.
>
> It was a 340 miles altitude.  The gravity is about 85% the value it is
> on earth there, or about 8.31 m/s2 (at sea level g=9.8 m/s2).  They
> wouldn't have blasted it out very far considering it weighs 12,500
> pounds. Just because you have cleared the atmosphere with a heavy duty
> launch vehicle doesn't mean you can just kick a little out of orbit
> with the limited onboard fuel tank.
>
> It is a misconception that there is no gravity in lower earth orbits.
> This is because of the weightlessness.  The weightlessness is caused 
by
> the orbit being a continuous free fall where roughly no energy is
> required to maintain the orbit... just like being on a ride at an
> amusement park you feel reduced gravity:
> http://www.youtube.com/watch?v=4_YycEG4IkA&feature=related.
>
> If the satellite tried to stand still, it would burn its fuel out
> maintaining its altitude almost immediately.
>
> Of course, they could have done as you said and used it to raise the
> orbit until the fuel ran out.  Then there would be no risk from fuel
> since it would be all gone.  But it would still be there as space 
junk,
> intelligence information, and depending on how much propellant maybe
> decaying sooner rather than later anyway.
>
> Kindest wishes
> Doug
>
>
>
> -----Original Message-----
> From: jim_brady611 <jim_brady611 at o2.co.uk>
> To: meteorite-list <meteorite-list at meteoritecentral.com>
> Sent: Mon, Sep 12, 2011 10:31 am
> Subject: [meteorite-list] Why did they not use the leftover propellant
> to heighten the orbit and push the rogue satellite into space?
>
>
> from Rons original posting
>
> "...When NASA
> decommissioned the 12,500-pound satellite in 2005, controllers used
> leftover propellant to lower its orbit from 340 miles to expedite its
> re-entry. "
>
> Surely if they are already in orbit it would only take a tiny amount
> of fuel to push it completely out of orbit?
>
>
> can someone enlighten me please? The only thing I can guess is that it
> would endanger other satellites or possibly the ISS if they had
> propelled it away instead of towards the Earth.
>
> 2424
>
>
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