Definition
Small timing errors in the atomic clocks carried aboard GPS satellites. Because GPS position is calculated from how long a signal takes to travel from a satellite to the receiver, even tiny errors in the satellite's clock translate directly into errors in the calculated position. These clock drifts are monitored by ground control stations and corrected through updates uploaded to the satellites, but residual errors remain a recognized source of GPS position inaccuracy.
Plain English
GPS works by timing how long a signal takes to reach the receiver from a satellite, so the satellite's clock has to be extremely accurate. The clocks are very precise, but they drift slightly. Even a tiny timing error becomes a noticeable position error on the ground.
Context Anchor
Seen in GPS error discussions, especially when learning why GPS position can be inaccurate even when the receiver is working normally.
Derivation
Satellite comes from a word meaning an attendant or companion, which fits an object that travels with or around another body. Atomic clock means a clock that keeps time using the steady behavior of atoms. In GPS, that matters because position depends on extremely exact time measurement.
Why Pilots Care
These timing errors contribute several meters of position uncertainty that must be considered when using GPS for instrument approaches.
Analogy
It is like two people starting a stopwatch to time the same event, but one stopwatch starts a tiny fraction of a second late. The difference may look small, but if the timing is used to measure distance, the result can be off.
Grounding Statement
GPS position depends on timing, so a tiny timing error in a satellite can become a position error in the cockpit.
Intuition Check
Do not assume “atomic clock” means the clock can never be wrong. Here, “inaccuracies” means very small timing errors that can still affect GPS position.
Example Sentence 1
Satellite atomic clock inaccuracies are one of the small but unavoidable sources of error in any GPS position fix.
Example Sentence 2
Even with satellite atomic clock inaccuracies present, the GPS still met the required navigation performance for the approach.