For what it's worth, I am an active developer of space flight software. This might be true somewhere, but it's not true anywhere I've ever encountered. The contortions required to avoid using the stack would be insane and cause far more bugs than it could ever prevent. I'm pretty confident asserting that this is simply not a thing. Even heap allocation is very often allowed, but restricted to program initialization only. Furthermore, these rules are relaxing all the time. I am aware of at least one mission currently in space that is flying the C++14 STL with no restrictions on heap allocation and exceptions enabled. Unmodified `std::map` is currently flying in space with no ill effects.

I'm guessing that you work for SpaceX.