Ground Segment

The Ground Segment provides an interface with GNSS satellites. They provide the ability to control, check their operational health, monitor the shape as well as the velocity of the orbit.

The accuracy of GNSS data depends on knowing satellite positioning at any point in time, considering that the satellites orbit can sometimes be disturbed by external factors, such as the gravitational pull of the Earth and Moon.

The ground segment also enables management of a satellite, and the distribution of payload data and telemetry amongst the interested parties on the ground.

Ground Stations can consist of one or more of the following;

Master Control Station

The Master Station/Section has the task to transmit corrections for the satellite’s clock offsets and ephemeris data, uploading it directly to each of the satellites.

The satellites will then use these updates in the signals they send to GPS devices.

From the Master Control Station adjustments to the satellites orbit can also be made, through commands that are emitted by the ground antennas.

Below is an overview of tasks carried out:

  • Provides control over GPS constellation via commands
  • Global Monitor Station data is used to compute exact location of satellites
  • Creates navigational messages which are transmitted to the satellites
  • Ensures constellation health and accuracy through monitoring of system integrity of the satellite broadcasts
  • Anomaly resolution & Satellite maintenance, correcting satellite orbit to maintain optimal constellation health
  • Backed up by a fully operational Alternate Master Control station

Monitor Stations

Monitor Stations are very precise GNSS receivers which record discrepancies between known and calculated positions, caused by variation in the satellite orbit.

They are installed at specific locations, with appropriate positioning required as they help maintain a wider coverage of the constellation.

This information is then relayed back to the Master Control Station to be processed and used for any necessary orbital adjustments.

Monitor Station tasks:

  • Track GPS satellites as they pass overhead
  • Collect navigation signals, range/carrier measurements, and atmospheric data
  • Feed observations to the master control station
  • Utilize sophisticated GPS receivers
  • Provide global coverage via 16 sites: 6 from the Air Force

Ground Antennas

The Ground Antennas main functions are:

  • Command transmission
  • Navigation data uploads
  • Loading processor program to the satellites.
  • Telemetry collection
  • S-band tasks
    • Communication
    • S-Band ranging for early orbit support andanomaly resolution

Every 8 hours this information can be uploaded to each satellite within the constellation.
However, it generally is updated only once per day.

Ground Antennas are usually paired within Monitor Stations.