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| Artist's impression of Voyager 1. Credit: NASA/JPL-Caltech |
It takes 23 hours for a control signal to reach the spacecraft and another 23 hours for telemetry data to travel the 15 billion miles back to Earth. Deep space telephone calls using radio waves aren't exactly going to be possible unless we make some fundamental discovery in physics. Radio, just like light is part of the electromagnetic spectrum, limited to a speed of transmission of 300,000 km per second. That might sound fast, but Voyager 1 is almost a light day (24 light hours) away from Earth and that means it takes almost a day for a signal to travel the intervening distance. Our nearest star Proxima Centauri is 4.25 light years distant. It's a red dwarf type star with a mass 12.5% that of the Sun.