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  WAAS Satellite Move Affects Extreme Eastern US

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Author Topic:   WAAS Satellite Move Affects Extreme Eastern US
jimh posted 06-02-2006 08:47 AM ET (US)   Profile for jimh   Send Email to jimh  
According to an article from the Federal Aviation Administration (FAA), a move of a satellite used to provide Wide Area Augmentation System (WAAS) data may affect signals to users of GPS receivers in the extreme eastern United States.

The position of the WAAS satellite INMARSAT-3 AOR began to change in February, 2006, from its original location at 54°W. By May this INMARSAT-3 satellite should be located at 142°W.

This move will cause the satellite to appear lower on the horizon than previously seen in many eastern U.S. locations. This could affect reception if the antenna of a GPS receiver has difficulty receiving the satellite from its new location.

By the fall of 2006 a new satellite (PanAmSat) should be in orbit at 133°W and providing WAAS service.


See:

Current News
http://gps.faa.gov/programs/waas/for_pilots.htm

Wide Area Augmentation System
http://gps.faa.gov/FAQ/faq-waas-text.htm

GPS Basics
http://gps.faa.gov/gpsbasics/index.htm

and
Wandering WAAS — Satellite to relocate
http://www.aopa.org/whatsnew/newsitems/2006/060130waas.html

for more details.

jimh posted 06-02-2006 09:10 AM ET (US)     Profile for jimh  Send Email to jimh     
You can compute the azimuth and elevation to IMARSAT 3 F4 now located at 142°W from your location using the nice JAVA applet available at

http://www.lyngsat.com/tracker/inmar3f4.html

Using this applet I calculate that the elevation angle to IMARSAT 3 F4 at 142°W from the eastern Great Lakes will be about 12 to 13 degrees. This is fairly low on the horizon. As a receiver moves farther east and north, the elevation angle to this satellite will decrease.

If the antenna on your GPS has problems with receiving low elevation angles, this could affect your WAAS signal acquisition.

Chuck Tribolet posted 06-02-2006 10:05 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
We on the west coast dealt with low angles to the WAAS birds
for several years. Net: On open water it's not a problem.
On land, or on water surrounded by hills, it can be.


Chuck

jimh posted 06-03-2006 09:51 AM ET (US)     Profile for jimh  Send Email to jimh     
The replacement WAAS satellite for the eastern U.S. is PanAmSat's GALAXY-15 at 133° West. This satellite was launched in October of 2005 and is in position. Its primary customers are C-band high-definition television distribution clients such as MS-NBC and Disney.

According to PanAmSat:

"Galaxy 15 also features a unique hybrid payload configuration which allows it to also broadcast Global Positioning System (GPS) navigation data using L-band frequencies. This payload is part of the Geostationary Communications and Control Segment (GCCS) being implemented by Lockheed Martin for the United Stated Federal Aviation Administration (FAA). GCCS is a GPS-based navigation and landing system for aviation use to provide precision guidance to aircraft at thousands of airports and airstrips where there is currently no precision landing capability."

The current status of the WAAS operation on GALAXY 15 can be obtained from:

http://www.nstb.tc.faa.gov/incoming/New_WAAS_Geo_Status.pdf

As of today, Saturday, June 3, 206, the satellite was operating in test mode, and the integrity of the GEO ranging data is not known.

More information:

PanAmSat's GALAXY 15
http://www.panamsat.com/global_network/galaxy_15.asp

Calculate your LOOK ANGLE to this satellite:
http://www.panamsat.com/global_network/calc_look_angle.asp

From the Great Lakes the elevation angle is about 20-degrees.

See a coverage map:
http://www.panamsat.com/global_network/map_flash.asp

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