Re: how is assembler outdated and by what?
AFAIK, the Voyagers use old CPUs designs and thereby the related assembly code could look quite outdated compared to today standards - and probably the toolset to work with as well.
There's no a single "assembler", each assembly language is strictly tied to the CPU architecture it is designed for (being, after all, just a human representation of CPU opcodes), and they can be quite different from each other, although some basic instructions may be quite similar. If you learned assembly on an x86 today, and one day try to program a 6502, you'll find it outdated, and you'll have to learn not only the mnemonics, but how they need to be used on that particular architecture and hardware implementation.
And remember, they are not allowed a trial&error approach like most developers on Earth... sure, they can simulate, but once the instruction sequence is finalized, it has to work, and those old system have very few or none safety belts.