Missing submersible

[Will]

Obviously I offer up my best wishes for a good outcome regarding the missing Titan submersible and its crew.

The technical dimensions are intriguing. From what I've read, the Titan descends without tether or umbilical, down to the ocean floor, communicating using sound bursts which are translated into text (like fancy Morse code?). Apparently radio waves that would carry voice and data don't penetrate far underwater, so two-way radio communication and GPS aren't available.

The craft can use accelerometers and pressure sensors to report on its orientation, speed, and depth. If you synch the submersible's navigation system with GPS before it descends, then like INS on an aircraft, it should be able to tell you where it is now by computing how it's moved.

This conflicts a bit with something I read that made it seem like the Titan does communicate with the surface ship using radio, with a simple navigation device that lets the ship know the position of the submersible relative to itself, and thus the ship provides steering commands to the Titan so it can find its target ("go farther west", or something like that).

My questions...

I guess the submersible won't get moved too far out of place by undersea currents, but this would seem like a danger, given the small thrusters on the Titan. Is getting carried far away from the target as much of a threat as it seems to me? If it just goes straight down and up again, what is the expected position error at the surface? Tens of feet? Thousands of feet? Given the way they were talking about the search on the surface, it seems like the Titan could come to the surface a very long way away from where it went down.

What can you guys tell me about using acoustic data packets for communicating with the surface? Is it like fancy Morse code?

What about navigation... do you suppose they use something like INS, or range-finding from the surface ship, or both?

Thanks, and fingers crossed for a good outcome.