7. Global Positioning System GPSGlobal Positioning System GPS
العالمى المواقع تحديد نظامالعالمى المواقع تحديد نظام
من النظام يتكونمن النظام يتكون33:أجزاء:أجزاء
Space segment .1Space segment .1الفضائي الجزءالفضائي الجزء
Control Segment .2Control Segment .2التحكم جزءالتحكم جزء
User segment .3User segment .3المستخدم جزءالمستخدم جزء
8. الفضائي الجزءالفضائي الجزءSpace segmentSpace segment
24+ satellites24+ satellites
• 6 planes with 55° inclination6 planes with 55° inclination
• Each plane has 4-5 satellitesEach plane has 4-5 satellites
Very high orbitVery high orbit
• 20,200 km20,200 km
• 1 revolution in approximately 12 hrs1 revolution in approximately 12 hrs
9. GPS (Global Positioning SystemGPS (Global Positioning System((
GPS Satellites visible
Black = visible satellites,
Red = not visible,
Green = sight lines
10. 1010
Control SegmentControl Segment
Master Control Station
Monitor Station
Ground Antenna
Colorado
Springs
Hawaii Ascension
Islands
Diego
Garcia
Kwajalein
Monitor and Control
11. 1111
Control Segment: Maintaining the SystemControl Segment: Maintaining the System
(5) Monitor Stations
Correct Orbit
and clock
errors
Create new
navigation message
Observe
ephemeris
and clock
Falcon AFB
Upload Station
17. Garmin GPSmap60-C
Zoom In/Out
Find
(Cities, Waypoints)
Mark (Waypoints)
Quit
(close screen)
Power / Backlight
Rocker (navigation)
Pan map or select
options on a page
Page
Menu
Enter
Battery Life
The second segment we'll talk about is the Operational Control Segment. This segment consists of 5 Monitor Stations on islands near the equator (Hawaii, Ascension, Diego Garcia, and Kwajelin) and one Master Control Station located at Falcon AFB, CO. All of these stations track the GPS signals, and send them back to the Master Control Station at Falcon. A backup MCS exists at Loral Federal System in Gaithersburg, MD. The four stations track and monitor the where-abouts of each GPS satellite each day. Then land-based and space-based communications are used to connect the monitoring stations with MCS.
The MCS, at Falcon AFB, is responsible for the overall command and control, which includes maintaining the exact orbits of each satellite and determining any timing errors that may be present in the highly accurate atomic clocks. The errors are corrected by Falcon with updated orbits and clock corrections relayed once a day to each satellite via four ground antennas. In the future, more monitor stations will be added to further refine the system. Military customers get better than required accuracy as a result. It is important to note that even though the Air Force operates the constellation of satellites on a day-to-day basis, the overall GPS program is jointly managed. The unit that develops the hardware (both military receivers and the actual satellites) is the GPS Joint Program Office (JPO) at Los Angeles AFB. There are, among others, Army, Navy, DoT, and even DMA Deputy Program Managers.