How many atomic clocks are on board each GPS satellite?

How many atomic clocks are on board each GPS satellite?

• A. 3
• B. 2
• C. 4
• D. 5

Answer: (C)

The main idea is that GPS timing depends on ultra-stable on-board atomic clocks, and the system uses more than one clock per satellite to keep time accurate and reliable. Each satellite carries multiple clocks so that the time reference it provides to the overall constellation remains continuous even if one clock drifts or fails. With four clocks aboard, there are enough references to keep GPS time stable, allow cross-checks between clocks, and provide backups in case of a malfunction. This redundancy is crucial because the navigation solution shipped to receivers relies on knowing the precise time offset between the satellite clocks and GPS time. Ground control monitors and uploads corrections, but the hardware setup must tolerate clock faults without disrupting service. That’s why the correct setup uses four atomic clocks on each satellite.

The main idea is that GPS timing depends on ultra-stable on-board atomic clocks, and the system uses more than one clock per satellite to keep time accurate and reliable. Each satellite carries multiple clocks so that the time reference it provides to the overall constellation remains continuous even if one clock drifts or fails. With four clocks aboard, there are enough references to keep GPS time stable, allow cross-checks between clocks, and provide backups in case of a malfunction. This redundancy is crucial because the navigation solution shipped to receivers relies on knowing the precise time offset between the satellite clocks and GPS time. Ground control monitors and uploads corrections, but the hardware setup must tolerate clock faults without disrupting service. That’s why the correct setup uses four atomic clocks on each satellite.