Why is nominal used instead of normal? I was watching the Antares livestream and the announcer kept saying “…power nominal, altitude nominal…” etc.
Is there a reason for using nominal instead of normal? (like niner instead of nine)
Nominal doesn’t mean normal and isn’t used to mean normal.
In technical parlance, nominal just means “equal to the value in the methodology/manual”. So when an astronaut says that power or altitude are nominal, it means that they are the same as the manual says they should be, not that they are normal.
While that may seem like a trivial distinction, it’s vitally important in technical fields. Normal is is a subjective figure that varies depending on the speaker and the circumstances. In a fast headwind with one engine not working, a pilot would consider it perfectly normal to be travelling at less than half the desired speed, and to be losing altitude as a result. So altitude and speed are normal. But altitude and speed aren’t anything like what is required for the project to success, so they are definitely not nominal. It can vitally important for anybody listening to know that.
Similarly, in a project designed to test the performance of a vehicle outside of specs, the rate of ascent could be way above normal, but exactly what the project demands. SO while the rate is anything but normal, it is nominal.
IOW what is normal is often not what is nominal and vice versa.