The round-trip delay time is the minimum time between a probe signal reaching Earth, and the probe getting instructions from Earth. Given that information can travel no faster than the speed of light, this is for the Voyager 1 about 32 hours, near Proxima Centauri it would be 8 years. Faster reactions would have to be programmed to be carried out automatically. Of course, in the case of a manned flight the crew can respond immediately to their observations. However, the round-trip delay time makes them not only extremely distant but, in terms of communication, extremely isolated from Earth. Another factor is the energy needed for interstellar communications to arrive reliably. Obviously, gas and particles would degrade signals (interstellar extinction), and there would be limits to the energy available to send the signal.
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