31 Years of the Digest ... founded August 21, 1981Add this Digest to your personal or   The Telecom Digest for February 8, 2013
====== 31 years of TELECOM Digest -- Founded August 21, 1981 ====== | ||||
Telecom and VOIP (Voice over Internet Protocol) Digest for the
Internet. All contents here are copyrighted by Bill Horne and
the individual writers/correspondents. Articles may be used in other
journals or newsgroups, provided the writer's name and the Digest are
included in the fair use quote. By using any name or email address
included herein for any reason other than responding to an article
herein, you agree to pay a hundred dollars to that person, or email address
owner.
Addresses herein are not to be added to any mailing list, nor to be sold or given away without the explicit written consent of the owner of that address. Chain letters, viruses, porn, spam, and miscellaneous junk are definitely unwelcome. We must fight spam for the same reason we fight crime: not because we are naive enough to believe that we will ever stamp it out, but because we do not want the kind of world that results when no one stands against crime. - Geoffrey Welsh See the bottom of this issue for subscription and archive details and the name of our lawyer, and other stuff of interest. |
Date: Thu, 07 Feb 2013 18:18:00 -0600 From: Neal McLain <nmclain@annsgarden.com> To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org. Subject: Re: Closer than the satellites that guide your GPS Message-ID: <51144438.1090504@annsgarden.com> Barry Margolin <barmar@alum.mit.edu wrote: > More likely, they assumed GPS satellites were in > geosynchronous orbits (22,000 miles), like most > communication satellites. I was actually surprised > to see that they aren't. Most communication satellites are indeed in geosynchronous orbits. Furthermore, most of them are in the geostationary orbit; i.e., the Clarke Belt. The term "geosynchronous" means only that the satellite orbit equals one sidereal day. It says nothing about the inclination of the orbital plane or the eccentricity of the orbit. To be geostationary, an orbit must meet three criteria: - It must be geosynchronous. - The inclination of the orbital plane must be zero (i.e., it must lie in the earth's equatorial plane). - The eccentricity of the orbit must be zero (i.e., the orbit must be a circle). There's an infinite number of geosynchronous orbits but only one of them is geostationary. While most communications satellites move in geostationary orbits, a notable exception is the Sirius Satellite Radio fleet. These satellites lie in Tundra orbits, a highly-eccentric geosynchronous orbit lying at an orbital inclination of 63.4 degrees. At this angle, certain "secular perturbations" cancel out, resulting in a stable orbit. XM Satellite Radio's satellites move in geostationary orbits. The merged company, now known as SiriusXM, maintains both fleets in order to continue service to legacy customers. References: - Tundra orbit. Wikipedia http://en.wikipedia.org/w/index.php?title=Tundra_orbit - Orbital perturbation analysis (spacecraft). Wikipedia. http://en.wikipedia.org/wiki/Orbital_perturbation_analysis_%28spacecraft%29 - Tundra. Castor. http://www.castor2.ca/02_Basics/03_Orbits/05_Tundra/index.html - Sirius Tundra Orbit Animation. Verizon. http://tinyurl.com/siriusorbits Neal McLain ***** Moderator's Note ***** What's the third criteria? Bill Horne Moderator
TELECOM Digest is an electronic journal devoted mostly to telecom- munications topics. It is circulated anywhere there is email, in addition to Usenet, where it appears as the moderated newsgroup 'comp.dcom.telecom'. TELECOM Digest is a not-for-profit, mostly non-commercial educational service offered to the Internet by Bill Horne. All the contents of the Digest are compilation-copyrighted. You may reprint articles in some other media on an occasional basis, but please attribute my work and that of the original author. The Telecom Digest is moderated by Bill Horne.
Contact information: |
Bill Horne Telecom Digest 43 Deerfield Road Sharon MA 02067-2301 339-364-8487 bill at horne dot net |
Subscribe: | telecom-request@telecom-digest.org?body=subscribe telecom |
Unsubscribe: | telecom-request@telecom-digest.org?body=unsubscribe telecom |
This Digest is the oldest continuing e-journal about telecomm- unications on the Internet, having been founded in August, 1981 and published continuously since then. Our archives are available for your review/research. We believe we are the oldest e-zine/mailing list on the internet in any category! URL information: http://telecom-digest.org Copyright (C) 2013 TELECOM Digest. All rights reserved. Our attorney is Bill Levant, of Blue Bell, PA.
Finally, the Digest is funded by gifts from generous readers such as yourself who provide funding in amounts deemed appropriate. Your help is important and appreciated. A suggested donation of fifty dollars per year per reader is considered appropriate. See our address above. Please make at least a single donation to cover the cost of processing your name to the mailing list. All opinions expressed herein are deemed to be those of the author. Any organizations listed are for identification purposes only and messages should not be considered any official expression by the organization.