[vincent-manis]

I was puzzled by this claim, too. I think that the article is wrong, and that the code is written in HAL/S, a NASA-only language that sort of started off as a preprocessor to Fortran, though it has some PL/I-like features. If it really was written in Fortran, it probably was in a vendor-extended Fortran IV, which a lot of old guys like us know. But NASA used HAL/S for a number of projects, including the Shuttle. (And, by the way, thanks to perplexity.ai, here's a link to the HAL/S language manual: https://archive.org/details/nasa_techdoc_19750002029.)

The parent comment is apt. Of course, languages have their own quirks. But, as Christopher Strachey is once claimed to have said, “I use the same language no matter what compiler I run.”

Now what is more likely to be true is that the code is strangely structured (both because structured programming was new then, and because of memory and processor limitations), and also that much of the internal documentation has been lost. I wish the article had been clearer on that.

[pklausler]

I think that the Voyager software is in assembly languages (there are several distinct computers on board), and that it is the program preparation software is written in a “Fortran V” extension.

[vincent-manis]

That could well be, the article is still wrong.