Jack Harrhy
Linkblog /2025/04/26

How We Diagnosed And Fixed Voyager 1, Stop overbuilding evals.

David Cummings - How We Diagnosed and Fixed the 2023 Voyager 1 Anomaly from 15 Billion Miles Away

Voyager 1 is flaking out, but folks like David are the goats pulling dark magic to ‘debug’ it, under these challenges:

Challenges

  • JPL designed processor with custom instruction set
    • A document that may or may not be accurate
  • No source code files
    • Source code listing in Microsoft Word with errors
    • May or may not match the version on the spacecraft
  • No assembler
  • No simulator
  • No testbed
  • Telemetry must be restored as soon as possible!!!
    • No visibility into an aging and delicate spacecraft
  • AND: We were unable to find 256 contiguous words of memory that were unused!

And sometimes I can’t figure out where padding is coming from on my divs, we both have it rough.

Doug Turnbull - Stop overbuilding evals

Every startup ponders over-scaling risks. Vibe code a dumb app and be OK with a fail whale? Or build 50 microservices auto scaled in Kubernetes with a full devops team load balancing every layer?

You’re probably better off with the former as long as you can tolerate it.

Same thing can happen for evals in AI apps. The smartest teams can over invest before experiencing any success.

Evals seem to be the best way to wrangle and understand your LLM workflows, but also so full of fluff.

I’d like to know exactly how I’d integrate them into my work, but honestly I have no idea where I’d even start.

What should you do?

After 12 years of failing (and sometimes succeeding) at search, I trust this proven process™️ as the starting upoint

  1. Test in prod
  2. (With Feature flags!)
  3. Focus on systematic qualitative eval
  4. ‘Unit testing’ algorithmic behavior is a good thing
  5. Evolve to qualitative the quantiative

Feature flags are chefs-kiss.