Context: https://www.bbc.com/news/world-us-canada-65953872
The above titanic submersible that went missing can only send short text messages from the ship to the submersible. From my understanding there is no GPS underwater and radio communication is impossible. How can Navy submarines communicate and navigate while submerged in the ocean but the missing submersible can’t?
In: 121
Submerged navy submarines communicate using VLF radio waves because they can penetrate seawater to some extent. VLF radio waves only work with giant antennas. Navy submarines carry extremely long wire antennas (hundreds of meters) that trail behind the submarine to pick up signals from massive military land-based antennas. Small commercial submersibles do not have these antennas. They don’t even have enough space to carry these antennas. Also, communication via VLF is only one-way (land to sub) so the submarine still has to surface to periscope depth or float an antenna buoy attached to a cable to transmit anything back.
Water is a really, really effective EM shield so most radio signals can’t penetrate very far at all. Higher frequencies are most affected so submarines often use [Extremely Low Frequency radio](https://en.wikipedia.org/wiki/Extremely_low_frequency) (ELF) for communications.
The catch is that this requires very long antennas to transmit so the submarines can only receive the message – they have to use other means to transmit a signal.
[VLF](https://en.wikipedia.org/wiki/Communication_with_submarines) can penetrate a few 10s of meters so a submarine can receive and transmit with an antenna on a buoy (float) without needing to surface.
The other thing that works well is sound – just like sonar uses sound to locate objects underwater because radar can’t penetrate, you can use sound to communicate directly.
I can’t find anything that says what this sub uses for comms but I’d guess [acoustic](https://en.wikipedia.org/wiki/Underwater_acoustic_communication#Applications)
Submarines can always receive information off hull via extremely low frequency radio waves (ELF and UHF). These signals require extremely large antennas that only nation states can afford. ELF and UHF are also extremely low bandwidth, so think only a few words or sentences a minute. But that’s enough to receive a fire order so it’s enough for the submarine’s purpose.
Submarines also cannot respond in ELF or UHF frequencies so they would come to the surface to quickly send/receive via VHF or satellite before submerging again. A submarine’s greatest asset is stealth so they are vulnerable if they are surfaced for too long.
Since this is a private company, it’s unlikely that this capsule had ELF or UHF receiving capabilities.
When they’re underwater, they don’t… normally. When they’re close to the surface, there’s antennas that can go out to communicate.
There is an underwater “telephone” that can be used for communication, but that can only communicate with a ship directly above it. Its normally only used for special testing, and the messages can break up.
Source: former submariner.
You’ve gotten some detailed answers that explain a lot one thing I haven’t seen mentioned yet. The Titanic came to rest on the ocean floor in just over 12,000 feet of water. The vessel that went down there is small and specifically designed for very deep dives.
A military submarines are much larger. Several hundred feet in length- how deep they can go is classified but the number the US Navy will publicly admit to is that they can go down more than 300 meters.
There would be very little reason for any Navy to build a submarine that can go down 10,000 -12000 feet.
I’m confused by this missing submersible. As I understand it, it is a tourist vehicle. The last time I was on a tourist submarine, it was designed with positive buoyancy. In other words, it had to push itself down to submerge. In the event of a power failure, the sub would automatically float to the surface. In addition, there were ballast weights that could be released manually that would accomplish the same thing. Was this submersible not equipped with the same features?
also, it serves to mention that OceanGate, the private company who’s sub is missing, has the only model of this submersible and was designed by the company founder. It’s literally one guys dream machine created for Titanic tourism. The only communication it has available is rudimentary text messages to the ship, plus sonic pings every 15 minutes.
Radio communication is impossible, but acoustic communication isn’t. There are types of “underwater telephone” that basically playthe sound into the water that is then picked up by a receiver in the sub. A fancy version of this using quick beeps to send ASCII / text is what the sub already uses for positional data.
[Underwater Acoustic Communication / UQC Underwater Telephone](https://en.m.wikipedia.org/wiki/Underwater_acoustic_communication)
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Because the navy has invested a few trillion dollars and centuries of technological advancement.
This guy stuck a bunch of people in a ton can and sunk it with a trolling motor. From the descriptions…
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