• Calculations
• Observations

A while ago, I ran experiments that showed the GPS satellite movement as displayed by the Handheld Garmin GPS unit and the Delorme Street Atlas program.

During this time, I was 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.