How do radio waves transmissions work in space? How long does it take to send/receive signals ?
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Radio waves propagate at the speed of light in vacuum. ‘Radio’ is merely a range of wavelengths on the electromagnetic spectrum, so it acts like any other waves on the spectrum.
However, this doesn’t actually tell you how long it takes because while a radio wave can travel at the speed of light, *information* – the actual signal – cannot. To send information, you need to somehow encode it in the radio wave.
To encode information in a wave, we need to vary the wave’s amplitude (how ‘loud’ it is), frequency (how often it repeats) or phase (what portion of the wavelength it is offset from the zero position). Those variations encode information, but it takes time to transmit/detect them.
Moreover, you have to deal with the problem of noise. Think of trying to talk to someone across a crowded bar in a whisper. It’s not that you’re not generating sound or the sound isn’t reaching them – the problem is that all the other sound in the bar drowns it out so they can’t discern what you’re saying.
The most obvious solution is to simply talk louder – increase the amplitude. But waves normally expand spherically and attenuate as the square of distance from the source. At space distances, this means you’d need enormous amounts of power to solve your problem with pure amplitude – possible for an Earthbound station sending signals, impossible for your spacecraft that has limited power.
So what we actually do is use error correction. By encoding additional information into the signal, we can mitigate the impact of noise – some of the signal is lost amidst the noise, but we have enough redundancy to figure out the lost parts. However, all that additional encoding means taking additional time to send the signal.
This means that the answer to “how long” depends on distance, the amount of power you have and the type of encoding you use.
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