nominal
1. (of a role or status) existing in name only: Thailand retained nominal independence under Japanese military occupation. • of, relating to, or consisting of names. • Grammar relating to, headed by, or having the function of a noun.
2. (of a price or amount of money) very small; far below the real value or cost: some firms charge only a nominal fee for the service.
3. (of a quantity or dimension, esp. of manufactured articles) stated or expressed but not necessarily corresponding exactly to the real value: legislation allowed variation around the nominal weight (that printed on each packet). • Economics (of a rate or other figure) expressed in terms of a certain amount, without making allowance for changes in real value over time: the nominal exchange rate.
4. informal (chiefly in the context of space travel) functioning normally or acceptably.
As so often happens, we were both right and our understanding of the term rested on the context within which we were most familiar with it. To a space geek like Mark, NASA staffers' use of the term made perfect sense whereas it sounded bizarre to me. Mark found some information suggesting that NASA's use of the term is borrowed from the term's usage in statistics. "Mission control-types are looking for unusual readings, so readings within an expected, or nominal, range are normal," he noted. This Wikipedia article on the term's various usage contexts provides further insights.
Fortunately, the shuttle experienced a nominal, full deployment of its chutes during its Sunday night landing, completing a safe and successful mission.