Outright refuse

"I'm not doing that!" Halley crossed her arms, thinking this was practically bullying at this point. "I refuse. That's outrageous."

Tim didn't seem at all reproached however in the face of Halley's sudden surge of self-righteous assertiveness. Instead, the only effect seemed to be to make him double down.

"Then you're done," he shrugged dismissively, already turning away from her. "If you can't meet even the most basic expectations, you're no good to us up here."

Halley blanched, suddenly sensing that he was absolutely serious. As her mentor, Tim absolutely was in a position to get Halley a ticket home. Urgently, she tried again, this time with her voice taking a more plaintive tone.

"You can't expect me to wear diapers, much less use them," she protested. "Not unless it's completely unavoidable, like an accident!"

"What about if it compromises safety and performance not to?" Tim turned back to face her down. "You're an astronaut. Astronauts wear diapers. How you ever got this far without coming to terms with that, I've no idea, but you're going no further if you can't."

"I just don't understand," Halley shook her head defiantly, still thinking there must be some way out of this. "Surely it doesn't come down to this?"

"You'll have plenty of time to understand on your ride back down," Tim responded coldly. "Go get your things together. I'll have your drop forms ready by the time you're done. No point dragging this out."

Halley gaped in disbelief, but this really was it. She was being fired?! For not using diapers?!

"I'll... I'll go to HR..." she threatened, but that attempt fell flat as well.

"Feel free," Tim shrugged. "They're not going to argue, if you can't even meet the basic requirements. We don't mess around up here."

Sure enough, not even six hours later, Halley found herself in a seat dropping back to earth down the space-elevator.

Who would have known you had to crap yourself to be an astronaut?