This question originally appeared on Quora: Is it true that NASA continued to use 1960s and 1970s software technology during the space shuttle era into the 2000s because the software was bulletproof?

Answer by Robert Frost, NASA instructor/engineer in the Mission Operations Directorate, and previously the founder of Quigo, on Quora

There are multiple reasons why NASA continued to use 1960s-1970s software technology.

NASA is under-budgeted for its objectives. Our facilities arent all gleaming high tech. Every day, I use the same urinal that Neil Armstrong used and I keep my SpaceX Dragon Systems Manual in an Apollo 10 binder. We still have lead paint on our staircase banisters and asbestos in our ceilings. We still have white walls yellowed by 60s-70s cigarette smoke. If we cant afford to replace our toilets, we arent going to make big expensive changes elsewhere unless there is a mission need to do so.

Based on the experiences of the earlier programs, NASA decided to not use a machine language. They decided to use a high-level language. They created their own. It was called HAL/S (High-order Assembly Language/Shuttle). And for people like me, thank goodness they did. NASAs flight controllers and instructors are trained to be experts on space systems and operations, not programming. But we need to be able to examine the software to troubleshoot and script simulations.

HAL/S was specifically designed to accomplish the types of tasks we needed the Space Shuttle flight software to accomplish. The hardware on the Space Shuttle was specifically designed to run that software.

So, there was really no need to change. As Clay explained, it was well understood. It worked.

In the general world, we see software technologies change frequently. We see that because requirements change. A new need isnt well done by the existing technology, so a new technology is developed. Its chaotic and exciting. But in any very specialized use of technology, that evolution is much, more slower because it isnt required and any significant changes would be expensive to implement.

As for bulletproof the Shuttle software development team has a very well deserved reputation for producing almost bug free code, but that isnt all because of the technology being used. Their processes and documentation are designed to prioritize being error free and their customers have very specific requirements.

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NASA Used 1960s-1970s Software Into The 2000s, Here's Why