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

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> ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

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