OTOH, I've been in that situation too, and it was successful. The International Space Station has not yet fallen out of the sky. There are situations where waterfall is appropriate.
I am curious if this is usually argued. I thought it that was generally held that agile and similar methodologies at least in the sense that sprints are defined in days/weeks and not months/years is for use cases where the product doesn't have well defined specifications.
And yet the ISS has still had many bits added on, replaced, upgraded and modified. They just work to far, far higher standards than almost any company will pay for because they know if it goes wrong some very high profile people get dead.
