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 <[email protected]>
To: Meteorite List <[email protected]>; MexicoDoug
<[email protected]>
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" <[email protected]>
Sent: Monday, September 12, 2011 9:39 AM
To: <[email protected]>; <[email protected]>;
<[email protected]>
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 <[email protected]>
To: jim_brady611 <[email protected]>; meteorite-list
<[email protected]>
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 <[email protected]>
To: meteorite-list <[email protected]>
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
______________________________________________
Visit the Archives at
http://www.meteoritecentral.com/mailing-list-archives.html
Meteorite-list mailing list
[email protected]
http://six.pairlist.net/mailman/listinfo/meteorite-list
______________________________________________
Visit the Archives at
http://www.meteoritecentral.com/mailing-list-archives.html
Meteorite-list mailing list
[email protected]
http://six.pairlist.net/mailman/listinfo/meteorite-list
______________________________________________
Visit the Archives at
http://www.meteoritecentral.com/mailing-list-archives.html
Meteorite-list mailing list
[email protected]
http://six.pairlist.net/mailman/listinfo/meteorite-list
______________________________________________
Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html
Meteorite-list mailing list
[email protected]
http://six.pairlist.net/mailman/listinfo/meteorite-list
