I regret to inform you that waterfall planning is often considered a fail state in the toilet development world (and a messy one to clean up).

I can however recommend the Spiral Model [1] as a lesser known Waterfall variation, which carries a heavier focus on risk management. It resembles a conch shell, and may require up to three attempts [2] to get your toilet development process correct.

[1] https://en.m.wikipedia.org/wiki/Spiral_model

[2] https://en.m.wikipedia.org/wiki/Demolition_Man_(film)

Make sure there's plenty of space to output those logs.

Waterfall in a zero-g environment? I don't think so sir, Agile all the way.

Boooo :)