Modafinil indeed does what it says on the tin but routine use could come back to bite you if anything bad happens,
I didn't mention it as a happy option. Since it doesn't look that FTL, Duty time is being changed in a hurry What are the options for survival? Go to sleep and may be never get up? Or may be half asleep and land with disastrous consequences. Or occasionally when it gets real bad use a crutch to ride over the moment? It can happen even when proper rest was given but you couldn't rest.