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I understand (I think) that a vehicle on or near a planet with greater mass - such as the Juno probe entering Jupiter's orbit soon- will experience time slightly slower relative to us on Earth. However, I'm having trouble wrapping my head around if and how that impacts the mission.

  • If the probe is set to take a measurement once per second in "Jupiter Time" and sends them to Earth, what will the interval between measurements be to an Earth observer?
  • How do such missions really operate in practice? For example, when Juno has to do a "30 minute burn" to enter orbit, is that in Jupiter minutes or Earth minutes? What do they set the timer to on the craft?
  • If you have a 100Mhz processor does it operate slower speed (from our perspective on Earth) when nearer massive objects such as Jupiter or the Sun?
  • Or is the difference so negligible that none of this matters until we send a probe to a black hole?
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  • $\begingroup$ There is definitely a significant effect for GPS satellites, but it's significant only because GPS satellites require extremely good timekeeping. They have atomic clocks aboard. The clocks are set to a frequency of 10.22999999543 MHz before launching them into orbit; on the average, this is perceived on the ground as 10.23 MHz. For probes, you basically see radio transmissions Doppler shifted. You can think of the Doppler shift as being partly gravitational time dilation and partly kinematic. This is the kind of thing seen in the observations that led to the Pioneer anomaly. $\endgroup$ – Ben Crowell Jul 2 '16 at 1:52
  • $\begingroup$ @ben: wow, that's obvious in retrospect but I didn't realize they have that adjustment. $\endgroup$ – SF. Jul 9 '16 at 7:59
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It's pretty small. This plot shows the example of Earth's orbit

enter image description here

Note that is from the surface of the. The difference is on the order of picoseconds/second, or parts per trillion. That small of a time is far less than the uncertainty in pressure, temperature, and even actuation time causing small amounts of thrust uncertainty.

The difference only matters if one needs a very accurate clock. GPS satellites famously take into account the time dialation, otherwise their location would drift considerably with time.

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    $\begingroup$ This doesn't really say anything about Earth vs. Jupiter. Jupiter is 95x more mass than Earth, is that massive enough to have a different effect? $\endgroup$ – FGreg Jun 30 '16 at 23:57
  • $\begingroup$ Yes, but still only maybe a part or two per billion. $\endgroup$ – PearsonArtPhoto Jul 1 '16 at 0:01

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