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*Subject*: RE: [amsat-bb] Osculating element sets and secular effects*From*: "Tom Clark, W3IWI" <w3iwi@xxxxxxxx>*Date*: Fri, 21 Feb 2003 21:21:09 -0500*In-Reply-To*: <200302212201.h1LM1nFY057045@bsd4.WPI.EDU>

Some good humorous answers -- let me try to be factual > I have seen the terms "osculating elements" and "secular effects" > mentioned in orbital mechanics texts, but can't for the life > of me figure > out how kissing can possibly have anything to do with > satellite tracking. > And if there are secular effects, are there also religious effects? > > Where do these terms come from? > > Joe KM1P In celestial mechanics the "two-body" problem can be solved exactly -- the orbit of a satellite around a single, isolated object is completely predictable. Except for effects like atmospheric drag, the orbital elements from "now" can forecast where a satellite will be into the distant future. But when three or more objects are involved in the system, the orbital properties cannot be perfectly predicted. If you have perfect knowledge of the state of the "N-body" system, then the future can be calculated only by numerical integration of the equations of motion. An example of this problem that we all remember is that AO-13 was launched into what was thought to be a stable orbit (AO-13 and earth = two bodies), but the combination of the AO-13 inclination and eccentricity and the gravitational tugs of the sun and moon (making for an N=4 body system) caused the satellite to crash in 10 years. The ancient astronomers (i.e., those in the era after Newton but before Cray computers) worked out a "patch" on the 2-body problem that allowed for an approximation to the N-body problem. It involved having the proper orbit "kissed" by the other planets. This resulted in orbits that change with time reflecting the effects of the other bodies in the system. Therefore osculating orbits change with time. To get more detail than you ever wanted to know, do a Google search on "osculating elements". The first hit you get will be a pointer to http://www.xylem.f2s.com/kepler/osculate.html which will give you more detail than you ever wanted to know! 73, Tom ---- Sent via amsat-bb@amsat.org. Opinions expressed are those of the author. Not an AMSAT member? Join now to support the amateur satellite program! To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**Osculating element sets and secular effects***From:*Joseph B. Fitzgerald

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