Why each GPS satellite holds four atomic clocks?

In summary, each of the 24 GPS satellites holds four atomic clocks for redundancy, with a combination of rubidium and cesium clocks being used in earlier models. This is to ensure a fail-safe system, as fewer clocks may not produce a majority for decision-making and more clocks would be overkill. While the cost of these clocks may seem expensive, it is a necessary investment for the reliability of the satellite system.
  • #1
SciencePF
56
0
Each of the 24 GPS satellites holds four atomic clocks! Why four and not one or two? They are not cheap!
Thanks
 
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  • #2
Redundancy.

And compared to the cost of launching them into space, they probably are pretty cheap.
 
  • #3
Ok, redundancy, but ... why 4 and not 5 or 3 or ... XY?

Thanks.
 
  • #4
Perhaps for the same reason as the redundancy of space shuttle computers; they essentially 'vote' upon decisions. Three might not produce enough of a majority to be fail-safe, and five is overkill.
 
  • #5
The block 1 satelites used rubidium clocks and had three of them as the normal backup - 3 can vote and still have a backup if one fails.
Prototype ceasium clocks where developed and one clock was added alongside the existing 3 ( so the rubidium ones could be used if it didn't work).
In later model satelites 2 rubidium and 2 ceasium were used, so each had a backup.
Then when ceasium proved best they were switched to all ceasium, but since the design hardware and software was for four clocks it was as easy and safer to fit four of them.

(Not sure of exactly what changes where when and on what block numbers)
 
  • #6
Thanks for a great explanation, Mgb. :approve:
 
  • #7
It's also worth pointing out that "not cheap" is relative statement. Nothing in orbit is ever cheap. So the differential cost isn't always driven by the cost of the instrument.
 

1. Why does each GPS satellite need four atomic clocks?

Each GPS satellite needs four atomic clocks because it allows for accurate and reliable timekeeping. The atomic clocks are used to keep track of time and each satellite sends out signals that include the current time. Having four clocks ensures that even if one or two fail, the other clocks can still provide accurate time information.

2. How do the atomic clocks work in a GPS satellite?

The atomic clocks in a GPS satellite work by using the vibrations of atoms to keep track of time. The satellites use cesium or rubidium atoms, which are known to vibrate at a consistent rate. These vibrations are then used to generate an electrical signal that can be used to accurately measure time.

3. Can't one atomic clock be enough for a GPS satellite?

While technically one atomic clock could be enough for a GPS satellite, having four clocks ensures redundancy and improves the accuracy of the satellite's timing. With four clocks, any malfunction or drift in timekeeping of one clock can be detected and corrected by comparing it to the other three clocks.

4. How are the atomic clocks synchronized in a GPS satellite?

The atomic clocks in a GPS satellite are synchronized using a process called clock offset calibration. This involves comparing the time signals from the atomic clocks to a master clock on the ground. Any differences in time are then used to adjust and synchronize the clocks on the satellite.

5. What happens if one of the atomic clocks in a GPS satellite fails?

If one of the atomic clocks in a GPS satellite fails, the other three clocks can still provide accurate time information. However, the satellite's internal systems will detect the failure and compensate for it by adjusting the time signals from the remaining clocks. This ensures that the satellite continues to function properly and can still provide precise location and timing data.

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