Mars Clock Delay

[Raider5678]

Alright, say a rocket was sent towards Mars, at a point it's delay of radio signals was 12 minutes.

Every second it sent back a short radio signal signalling the second.

So:

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As it got farther away, I have a question.

Would the signals stop reaching earth every second and start having longer and longer periods of time between them? Or what exactly would happen?

Would it maintain every second signal, but the signal you're getting was sent 12 minutes ago?

[swansont]

 

As you move closer to Mars, the delay is reduced. So you've sent out 31.536 million pulses over the course of a year (365 days @ 86400 sec/day). At the end of that year let's say the delay is 6 minutes. In a year starting 24 minutes later (to account for the original delay), how long will it take you to get the 31.536 million pulses? It will be 6 minutes before the receiver's year ends. If you go in the opposite direction it will take longer — you don't get the last pulse until 1 year + 6 minutes. (We're ignoring relativity here.) That's only a part in 10^5, but there is a shift. It's the Doppler shift, which might be more obvious if you thought of this as a continuous signal with a frequency of 1 Hz. The source is moving, so the frequency of the signal must change.

 

[Raider5678]

1 hour ago, swansont said:

 

As you move closer to Mars, the delay is reduced. So you've sent out 31.536 million pulses over the course of a year (365 days @ 86400 sec/day). At the end of that year let's say the delay is 6 minutes. In a year starting 24 minutes later (to account for the original delay), how long will it take you to get the 31.536 million pulses? It will be 6 minutes before the receiver's year ends. If you go in the opposite direction it will take longer — you don't get the last pulse until 1 year + 6 minutes. (We're ignoring relativity here.) That's only a part in 10^5, but there is a shift. It's the Doppler shift, which might be more obvious if you thought of this as a continuous signal with a frequency of 1 Hz. The source is moving, so the frequency of the signal must change.

 

 

Makes sense.

 

So the receiving end would continue to receive the signals every second?

 

Edited January 4, 2018 by Raider5678

[swansont]

1 hour ago, Raider5678 said:

Makes sense.

 

So the receiving end would continue to receive the signals every second?

 

No. You move toward/away from the receiver, so the signal travel time is shifted. As long as there is relative motion, the frequency will change.

[Janus]

1 hour ago, Raider5678 said:

Makes sense.

 

So the receiving end would continue to receive the signals every second?

 

No.  Let's say that it takes a year for the rocket to reach Mars and it is 12 light min from the Mars receiver when it sends its first signal.  This means that the receiver gets the starting signal 12 min later.  The ship send 31557600 "blips", each a second apart during the year it takes to reach Mars (Using a Julian year of 365.25 days) The very last blip is sent when the ship is right on top of the receiver and there would be no delay.  Thus the 31557600th blip arrives exactly 1 year after the ship started and he first blip arrived 12 min after the ship started.  All 31557600 blips arrived at the receiver over a time period of 1 year - 12 min, or 31556880 sec.   To have received 31557600 blips in 31556880 sec they would have to have arrived ~0.999977 sec apart at the receiver.