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FW: AO40 velocity




Maggie:

The speed is related to center of mass in that the orbit is located
"around" the center of mass.  The speed in the vis-viva is tangential
velocity along the orbit,  not the velocity vector relative to the center
of the earth.  Thus I think the vis-viva equation is exactly the
answer he wanted unless Bob tells us Stacey and I both misunderstood
his question.

Converting mean anomaly to speed would require the complete solution
of the tracking problem in that the radius involved in the vis-viva
equation required TRUE anomaly to calculate.  True anomaly is derivable
from eccentric anomaly and eccentric anomaly is found by solving
Kepler's equation for eccentric anomaly given mean anomaly.  I think
Stacey and I both left this last detail but Bob can look at almost
any tracking program and derive the R distance (satellite from geocenter).

Bob


-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Margaret Leber
Sent: Thursday, August 29, 2002 7:42 PM
To: amsat-bb@AMSAT.Org
Subject: Re: [amsat-bb] AO40 velocity


Bob V Johnson wrote:

> I was asked how fast "those things" go.  I took a guess and probably was
> fairly correct.  That got me thinking how fast really is it.  Given the
> MA, at that part of the orbit is there a formula that would yield the
> velocity at that point?  

Oh, dear.

Whle W4SM and N4HY have given good answers, am I being my usual pedantic 
  self to point out that "what is the velocity of AO-40" is not a very 
meaningful question without selecting a frame of reference?

Stacy chose an LEO in circular orbit at AO-40's perigee altitude to 
generate an answer, and I'm thinking that vis-viva gives an answer 
relative to the center-of-mass of the primary (which in this case is the 
Earth), and that's what one would use in dealing with stuff like "escape 
velocity".

Robert's probably right that this is closest to what your friend  was 
asking, even though nobody is actually at the center of mass of the 
Earth. Reminds me of George Carlin mocking broadcast weather reports 
that give the temperature at the airport because "I don't know *anybody* 
who lives at the airport, man". :-)

Of course, neither of those answers is the "range rate" that you'd use 
to calculate Doppler...

  73 de Maggie K3XS

-- 
-----/___.   _)   Margaret Stephanie Leber    / "The art of progress  /
----/(, /|  /| http://voicenet.com/~maggie   / consists of preserving/
---/   / | / |  _   _   _    `  _AOPA 925383/ order amid change and /
--/ ) /  |/  |_(_(_(_/_(_/__(__(/_  FN20hd / change amid order."   /
-/ (_/   '  K3XS  .-/ .-/    ARRL 39280   /___ --A.N.Whitehead ___/
/____ICQ 7161096_(_/_(_/__AMSAT 32844____/ <maggie@voicenet.com>


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