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Re: Question about satellite orbit classification



Gilberto,

At 01:47 PM 01/13/2000 -0500, Gilberto_Campos@email.whirlpool.com wrote:
>Someone asked me this question I could not answer, nor had I ever thought
>of that:
>          -when is a sat called a Low Earth Orbit sat?
>
>More generally: what are the orbit classifications in function of
>perigee/apogee (apart from the obvious geostationary)?


According to algorithms used in SGP4/SDP4 propagation calculations, low 
earth orbits have a period of less than 225 minutes. This calculates to a 
little less than 6000 km for a circular orbit.

Personally, I think the definition is subjective, and could vary depending 
on state of the art at the present.

We can't forget the Russian Comsat birds, which wing around at 1600 
km.  Are they LEO birds?  I think so.

Typically, an amateur LEO satellite of the phase 2 variety will "see" less 
than 10% of the earth at any given moment.  A phase 3 bird will "see" more 
than 25% of the earth, except at perigee, if the orbit is eccentric.

Would you like to know how the Federal Communications Commission defines LEO?


FEDERAL COMMUNICATIONS COMMISSION
47 CFR Part 1
[MD Docket No. 98-36; FCC 98-40]
Assessment and Collection of Regulatory Fees For Fiscal Year 1998

...

33. "Non-Geostationary" satellite orbits were first introduced in the early 
90's with the filing of applications for non-voice, non-geostationary 
satellite service operating below 1 GHz. These satellites proposed to 
operate satellites in a "low earth" orbit, or a non-geostationary orbit The 
term, "low earth orbit" was then synonomous with "non-geostationary". As 
new technologies have evolved, we have received applications proposing to 
operate in "medium" and "high" earth orbit technologies, also 
non-geostationary orbits[, have been filed with the FCC]. Thus, we propose 
to change the name of the "Low Earth Orbit Satellite Systems" fee category 
to the "Non-Geostationary Satellite Systems" fee category in order to 
clarify that non-geostationary satellites, whether operating in low, medium 
or high orbits, are covered under this regulatory fee. This is consistent 
with current industry use, as well as with Commission rules, which refer to 
non-geostationary, not low earth, orbits and satellites. This name change 
will have no adverse impact on any entity covered by regulatory fees in FY 
1998.
...

So in essence, the FCC terms anything non-geostationary to be LEO.

Check 
out:  http://www.geocities.com/~saltillocib/sizepgs/geodef.html#anchor121819

This web site, maintained by Ricardo? has a good primer on sat orbits, the 
distinction between LEO, MEO, and geostationary  satellites.  They claim: 
"LEOs are either elliptical or (more usual) circular orbits at a height of 
less than 2,000 km above the surface of the earth."

They define a MEO thusly: "Intermediate Circular Orbits (ICO), or Medium 
Earth Orbits (MEO): ICOs are circular orbits at an altitude of around 
10,000 km."

And a HEO as: "HEOs typically have a perigee at about 500 km above the 
surface of the earth and an apogee as high as 50,000 km."



I don't really think this helps clarify much, but perhaps will allow you to 
tender a better response!

73, Mike



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