Re: [amsat-bb] strange orbit

[David Rush <david@xxxxxxxxxxxxxx>]

A normal geostationary orbit is perfectly circular and in the plane of the 
equator.  If you slightly tilt that plane but still keep geostationary 
distance and orbital speed (one revolution per earth day), then from a 
fixed spot on the ground the satellite would appear to move up and down, 
one cycle per orbit.  So most of the time it would be out of the 
geostationary "belt", but would crash into other satellites that were in 
the belt, twice a day.
If you make an orbit that's slightly oval (an ellipse with it's center at 
the earth's center) then it'll move fast past the earth when it's closer, 
and slower when it's farther (but on the average maintain the same 
rotational speed as the earth), so it'll appear to move back and forth in 
the sky, two cycles with every earth rotation (one "slow" section on each 
"long" end of the ellipse, one "fast" section on the short sides of the 
ellipse).
So, if you do both, the bird moves up and down once a day and back and 
forth twice a day, making a figure eight as seen from the ground.
Doing both means you'll be running "inside" of the geostationary belt when 
you cross the plane of the equator, so you're not taking up a valuable true 
geostationary parking space, nor will you crash into any geostationary bird 
that is parked there.
Since the Sirius ground stations (consumer receivers) are not  directional 
anyway, they can get away with such an orbit and not need an expensive, 
limited resource true geosync parking space.

David, KY7DR

At 04:00 PM 11/19/2004, G8IFF/KC8NHF wrote:
> >>> And we're doing it with satellites. Every second of the day, SIRIUS 
> is shooting *over 120 channels of amazing radio* straight into the 
> heavens to our three state-of-the-art satellites that rotate in figure 
> eight, geo-synchronous orbits around the earth. <<<
>
>Would someone care to explain a figure of eight geo-synchronous orbit 
>around the earth that doesn't crash twice every orbit?
>
>
>--
><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
>Nigel A. Gunn. 59 Beadlemead, Milton Keynes, MK6 4HF, England. Tel +44 
>(0)1908 604004
>e-mail nigel@ngunn.net   http://www.ngunn.net
>or       nigel@ngunn.demon.co.uk   http://www.ngunn.demon.co.uk
>Amateur radio stations  G8IFF, KC8NHF
>Member of  AMSAT-UK #182, ARRL, GQRP Club, QRPARCI, SOC #548
>           Flying Pig #385, Dayton ARA #2128, AMSAT-NA  LM-1691, RAYNET
><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
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