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Lisp code was live-debugged and fixed with REPL on a spacecraft 100 million miles away

“An even more impressive instance of remote debugging occurred on NASA's 1998 Deep Space 1 mission. A half year after the space craft launched, a bit of Lisp code was going to control the spacecraft for two days while conducting a sequence of experiments. Unfortunately, a subtle race condition in the code had escaped detection during ground testing and was already in space. When the bug manifested in the wild--100 million miles away from Earth--the team was able to diagnose and fix the running code, allowing the experiments to complete. One of the programmers described it as follows:

Debugging a program running on a $100M piece of hardware that is 100 million miles away is an interesting experience. Having a read-eval-print loop running on the spacecraft proved invaluable in finding and fixing the problem.”

https://gigamonkeys.com/book/...

Comments
  • 8
    I never found any use for a REPL other than experimenting a bit with library functions in the early stages of learning a tool if I found the examples inadequate, but I guess if NASA uses them this prevalently I should give them a better chance.
  • 1
    @bigmonsterlover same!
  • 2
    And it took like 24 hours to see results of changes.
  • 3
    @Demolishun I hope your favourite language does faster-than-light signal travel, unlike lisp. I guess C code would've need around five minutes round-trip, C goes fasta. And don't even get me started on Rust. Rust code would've appeared at the spacecraft even before it was written, this is how fast Rust is. Easy.
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