As a result of the U.S. space shuttle ‘Challenger’ disaster in 1986, how many fleet members aboard died?

Weird wording. What is a "fleet member"? Does it include guest crew members? The description was worded better.

No one ever seems to remember the seven lives lost aboard the Columbia as they re-entered Earth's atmosphere. All courageous, dying too young.

so sad, cuz I lived in NH and we lost our teacher.