You can't represent 26 possibilities with a single hex digit. So it'll require 2 hex digits.
If you're going to require 2 digits, then that can be done with 2 decimal digits as well. So there's no need for hex, and no need for ascii tables.
However, if you need more than just the 26 letters, e.g. if you also need numbers and/or punctuation, then ascii might be useful, and hex might be useful to encode ascii into 2 digits.
He later painstakingly translates machine code transmitted via the camera to the rover which patches the software to allow him to chat via text, so hex came in handy
I didn't say it needs to be sent 2 digits at a time.
The points of my previous comment:
* Ascii is only needed if we need to encode things other than just letters (or if case matters).
* Hex is only better than decimal if hex allows the number of digits to be reduced. If we need to only encode 26 elements, then hex doesn't reduce the number of digits compared to decimal, so hex has no advantage over decimal in the 26-element case.
Using just 0 or 1 will increase the number of digits needed, so has a clear disadvantage compared to hex or decimal.
> Hex is only better than decimal if hex allows the number of digits to be reduced. If we need to only encode 26 elements, then hex doesn't reduce the number of digits compared to decimal, so hex has no advantage over decimal in the 26-element case
He had more than 26 things to encode, I believe he started with numbers, letters and a question mark.
> Using just 0 or 1 will increase the number of digits needed, so has a clear disadvantage compared to hex or decimal
Using 0 or 1 decreases that to only 3 cards (including question mark), and increasing the safety margin to 120° on the setup he had. It'd take longer but be more robust.
If you're going to require 2 digits, then that can be done with 2 decimal digits as well. So there's no need for hex, and no need for ascii tables.
However, if you need more than just the 26 letters, e.g. if you also need numbers and/or punctuation, then ascii might be useful, and hex might be useful to encode ascii into 2 digits.