Ask HN: What is a rocket launch moment in your engineering or startup career?

For engineers at companies like SpaceX or Rocket Labs, a rocket launch is an emotional event where, within just a few minutes, the work of many months or years is rewarded (if the rocket works). What is an equivalent in your field of work/field of engineering?

For a chip designer I could imagine it is the first chip being shipped from the fab for testing. For a civil engineer maybe the completion of a bridge? For a software engineer the launch of an app/a product? For an AI engineer evaluating the capabilities or a newly trained model?