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Re: Visual satellite position fix
From: Richard B. Langley
Date: 2013 Aug 25, 23:44 +0000

Nothing better during a wet afternoon in the desert than to respond to Frank's message. ;-) Quite right about the eccentricity of geosynchronous satellites (we prefer that term for satellites with inclined orbits whose period matches that of the Earth's rotation rather than geostationary as they aren't -- really). We use the abbreviation IGSO (inclined geosynchronous orbit) as opposed to GEO for such orbits. Attached is a plot of the orbit of Michibiki or QZS-1, the first satellite (so far) of the Japanese Quasi-Zenith Satellite System. Its inclination is about 40.6° and its inclination is about 0.0754. The apogee of the orbit is positioned over Japan where the satellite is high in the sky for an extended period of time, supplementing the measurements from the GPS satellites. My tables on the GPS World website (http://gpsworld.com/the-almanac/) mention several GNSS IGSO satellites.

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| Richard B. Langley                            E-mail: lang@unb.ca         |
| Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/ |
| Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142   |
| University of New Brunswick                   Fax:      +1 506 453-4943   |
| Fredericton, N.B., Canada E3B 5A3                                        |
|        Fredericton? Where's that? See: http://www.fredericton.ca/       |
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From: NavList@fer3.com [NavList@fer3.com] on behalf of Frank Reed [FrankReed@HistoricalAtlas.com]
Sent: Sunday, August 25, 2013 8:20 PM
To: Richard Langley
Subject: [NavList] Re: Visual satellite position fix

Richard Langley wrote: "Nothing to do with the Earth's precession. The figure-of-eight occurs if the orbit inclination is not exactly zero degrees. It becomes more pronounced the higher the inclination." Yes. In fact, the ground track of a geostationary satellite in a slightly elliptical orbit inclined 23.45° to the Earth's equator should look awfully familiar. It's identical to the Sun's analemma. And the "figure eight" shape has the same geometric origin. If the orbital eccentricity of a geostationary satellite is zero, the north and south lobes of the analemma are symmetrical. If the orbit has non-zero eccentricity, then one lobe will be larger than the other, much like the Sun's analemma. -FER ---------------------------------------------------------------- NavList message boards and member settings: www.fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3.com ----------------------------------------------------------------

: http://fer3.com/arc/m2.aspx?i=124974

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