So, for example, if an astronaut is waken up out of sleep and there has to be a spacewalk for emergency purposes, you want that astronaut at their peak alertness.

打个比方说，若一个宇航员刚刚睡醒就因突发情况要求进行太空行走，当然大家都希望他处于最佳清醒机敏的状态。