• Calculations
• Observations

More than a year ago, I ran experiments that showed the GPS satellite movement as displayed by the Handheld Garmin Vista GPS unit and the Delorme Street Atlas program.

During that time I started experimenting with the NMEA data that comes from the Garmin GPS and put some of the data on this website for others to play with. This data can be found under Tracks, Waypoints and Photos.

Also during this time, I have been doing a little research in astronomy books and on the internet.

A summary of this research follows:

Definitions of orbits:

• Supersynchronous orbit - Above synchronous orbit and appears to drift westward.
      Source: http://en.wikipedia.org/wiki/Supersynchronous_orbit
• synchronous orbit - An orbit that has a period roughly the same as the rotation period of the planet.
      Source: Federal Standard 1037C - http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm
• geosynchronous orbit - An orbit around earth that has the same period as the earth's rotation period and going the same direction as the earth's rotation. May appear to move in a figure eight.
      Source: Federal Standard 1037C - http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm
• geostationary orbit - A circular orbit around the equator and is a geosynchronous orbit. The satellite will appear to remain in one place.
      Source: Federal Standard 1037C - http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm
• Subsynchronous orbit - An orbit below synchronous orbit and appears to drift eastward.
      Source: http://en.wikipedia.org/wiki/Subsynchronous_orbit
• semi-synchronous orbit - A 12 hour orbit around the earth in the same direction of the earth's rotation and is of course, a subsynchronous orbit.
      Source: Encyclopedia of Astrobiology, Astronomy, and Spaceflight - http://www.daviddarling.info/encyclopedia/S/semi-synchronous_orbit.html

• Satellite 21 (and others) appear to move from west to east. That is to say, drifts eastward.
• For any given time, the satellite will return the same spot at the same time every day.
• The maximum number of times any satellite is seen is twice.

Calculations:

First thing to do when approaching any calculations in this area is to define your units.

• Radius of the earth: 6378.136 km
• Lunar month: 27.322 days
• Distance to the Moon: 384,404 km
• Earth + Moon Mass in Earth masses: 1.0123

• 6076.1155 feet
• 1.852 km (exact)
• 1.150779 mile (statute)
• 2025.372 yard

The next thing to do is find equations which give reasonable accuracy for the purpose at hand. I found these in my college astronomy text book and on NASA's web site.

The page of calculations was scanned in and converted it to a PDF format so Adobe Reader will be needed to view my hen-scratches. Yes, I did show my work.