[dahart]

> Most of the numerical code they're going to use is in Fortran, and interlanguage calling convention and the runtime might pose a problem.

The rationale they used for these rules was written down. It has nothing to do with Fortran. I've offered links that you can read. You're making more assumptions. If there's C-to-Fortran calling at all, then recursion presents zero extra difficulty. Once you can make any function call, you can make all function calls.

> This is in addition to not using recursive functions being pretty standard in anything embedded.

It's true that for small embedded devices, recursion is not used often. It's also true that function pointers and heap allocations and unbounded loops are generally avoided too. Though, often main() in an embed is a white(true){} loop. I wouldn't be surprised to see that at NASA.

One could argue that all of these 10 NASA rules represent some standard practice in embedded code and/or some degree of common sense. They're not claiming to be new or non-standard or unintuitive or innovative; they simply wrote down what people agreed are best practices.