Eli5: How is communication possible with remote machines on space missions but similar communication under sea is challenging?
In: Engineering
Radio/electronic waves don’t travel through water the same way they do through air. Water is much more dense than air so the waves can’t go nearly as far.
It’s the same idea as why you can shout across a huge open field and someone on the other side can hear you but if you shout in a room with thick concrete walls no one outside the room will hear you – stuff gets in the way.
Electromagnetic waves travel uninterrupted forever in empty space because there’s virtually nothing to block them. The only thing that makes the signal weaker is the waves spreading out as they move away from the source. The ocean on the other hand, is all stuff – specifically water. In the same way a thick wall absorbs the sound waves from your voice in the above analogy, water absorbs the energy from electromagnetic waves so the waves dissipate very quickly.
Sea water is especially good at blocking electromagnetic waves because sea water is full of salt and salt is a conductor. This means that the dissolved salt ions in sea water absorb the energy electromagnetic waves and turn it into a small amount of electrical current, which dissipates the electromagnetic waves even faster.
because in space, nothing is in the way.
But in the sea, all the water is in the way.
In space the only problem is when another planet gets in the way (use a relay satellite) and the latency (no way around, you just have to cope)
The denser something is, the harder it is to travel through it. Water is very dense compared to space.
A good visual example of water affecting what travels through it would be [Cherenkov Radiation](https://en.wikipedia.org/wiki/Cherenkov_radiation)
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