Which statement best describes the devices used to maintain accurate time for GPS positioning?

Which statement best describes the devices used to maintain accurate time for GPS positioning?

• A. Receivers use quartz oscillators, while satellites use four atomic oscillators
• B. Receivers use cesium clocks; satellites use rubidium clocks
• C. Receivers use rubidium clocks; satellites use quartz crystal oscillators
• D. Timekeeping is not critical for GPS

Answer: (A)

Timing in GPS hinges on accurate time references: satellites carry on-board atomic clocks that define GPS time, while receivers rely on a quartz crystal oscillator for their local time base. Satellites keep precise time with multiple atomic clocks (redundant units), ensuring a stable beacon time even if one clock drifts. When a receiver computes its position, it uses the timestamps from the satellites and the measured ranges, solving for the receiver’s clock error as part of the navigation solution. This is why the correct description is that receivers use quartz oscillators, and satellites use atomic clocks (often multiple for redundancy). The other statements misstate who keeps the time or the type of clock used on each side, and GPS timing is essential to determine accurate positions.

Timing in GPS hinges on accurate time references: satellites carry on-board atomic clocks that define GPS time, while receivers rely on a quartz crystal oscillator for their local time base. Satellites keep precise time with multiple atomic clocks (redundant units), ensuring a stable beacon time even if one clock drifts. When a receiver computes its position, it uses the timestamps from the satellites and the measured ranges, solving for the receiver’s clock error as part of the navigation solution. This is why the correct description is that receivers use quartz oscillators, and satellites use atomic clocks (often multiple for redundancy). The other statements misstate who keeps the time or the type of clock used on each side, and GPS timing is essential to determine accurate positions.