# How do radio waves transmissions work in space? How long does it take to send/receive signals ?

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How do radio waves transmissions work in space? How long does it take to send/receive signals ?

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Radio is on the electromagnetic spectrum with light, UV, infrared, etc. They all travel the same speed, the speed of light. Roughly 300000km/186000mi per second. So that’s why radio transmission to the moon and back takes just under 3 seconds.

They work the same way radio wave transmissions work on Earth, only without an atmosphere they’re subject to a hell of a lot less interference (mostly due to atmosphereic ionization). Radio waves are on the electromagnetic spectrum, like visible light. As such, they move at the speed of light.

Radio waves, like light waves, move at (approximately, or “~”) 186,000 miles per second, or ~11,160,000 miles per minute. When we’re getting into distances that great, we often just convert them to light speed measurements. For example, ~186,000 miles is one light second, ~11,160,000 miles is a light minute, etc. A light year is ~5.878 *trillion* miles in case you’re curious.

So, to answer the question about how long it takes to send and receive signals, you have to know how far away things are. The moon, for example, is ~283,900 miles away from Earth, or a *touch* over 1.5 light seconds. There’s your answer. It takes a signal a *touch* over a second and a half to get from Earth to the moon, and any answer takes another second and a half to get back. Mars (right now, at least) is 106,973,891 miles away, or ~9.58 light minutes. It would take a transmission 9 minutes and 34(ish) seconds for a signal to get from Earth to Mars, and another 9 minutes and 34(ish) seconds to get a response.

1.Radio waves can travel in space

2. It travels at the speed of light, so the required time to receive a radio signal depends on how far the source is from you

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.

Radio is basically the same thing as light.

You know how on a rainbow you can go from blue to green to yellow and red. Our eyes can’t see beyond that, but the spectrum goes much father in both directions. Beyond red we have infra-red and then microwaves and then radio waves. In the other direction you get ultra-violet and x-ray and gamma rays.

The difference between the light you can see with your eyes and radio waves is the same sort of difference as the one between blue and red only much more so.

Light/Radio/microwaves etc work in space the same way they work on earth. In fact they work a bit better, because in space there is nothing that gets in the way.

In ages past people mistakenly thought that light would need a medium like sound waves travel through air. They thought there would be some sort of “ether” out there for radio waves to travel through. That was wrong. Light/radio does not need a medium. It can travel through nothingness.

Radio travels at the speed of light, just like light does, since it really is a sort of light.

On earth we can usually treat the speed of light as instanteous it is received when it gets sent.

If you try to sent radio waves to the moon and back, the time it takes is long enough that even humans notice the delay. Other planets like Mars are so far away that it will take minutes or hours for radionsignals to travel there and be sent back.

Other stars are light years away and radionwaves that reach us from distant natural radio sources are ancient by human standards.

Right now we only really have radio communications with a small number of robots and probes that are far away enough for the light speed delay to matter. All humans in space since the end of the Apollo program have staid close by earth.

Another 8ssue with radio communications in spaces is that things in orbitbtend to move really fast compared to the ground and that space stations and space ships tend to spend half their time in places where the earth is between you and them and radio signals don’t travel through rock all that well. Relays are necessary to radio with humans in space for more than a very short while.

Fun fact:

When Ham Radio was still a big thing, people who used it as a hobby tried to compete to reach other operators as far away as they could and send postcards to each other to confirm long distance contacts.

Some manged to reach the ISS or other manned NASA vehicles via Ham Radio and got postcards from NASA to prove that they 5alke with someone in space via Radio.