# FW: AO40 velocity

• Subject: FW: [amsat-bb] AO40 velocity
• From: Robert McGwier <rwmcgwier@xxxxxxxxxxx>
• Date: Fri, 30 Aug 2002 07:14:21 -0400

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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
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  /
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---/   / | / |  _   _   _    `  _AOPA 925383/ order amid change and /
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-/ (_/   '  K3XS  .-/ .-/    ARRL 39280   /___ --A.N.Whitehead ___/
/____ICQ 7161096_(_/_(_/__AMSAT 32844____/ <maggie@voicenet.com>

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