It definitely doesn’t happen on the ISS. In very short, the physics don’t work. Even if you could find the straps to have some stable position, a position away from the cameras that cover every inch of the station besides the bathrooms that barely fit one person, if you’re a man you’re simply not getting an erection, or you’re getting an erection that is too painful to use, and pretty much no in between; and that mostly depends on how healthy your heart was before you went up. The longer you spend in space, the less capable your cardiovascular system becomes.

On top of this, if, say, you didn’t need penetration or a male partner to get off, you’d still run into pretty intense headaches. People tend to strain and move and increase blood pressure, which is already higher in space. Best case scenario you get a bad headache from the extra strain, worst case you pop a blood vessel somewhere.

Also, you’re in space, under intense physical, emotional, and psychological stress, working 16 hour days, getting 1 day off a week, and acutely aware, more so than any other being at the time, how close you constantly come to dying painfully. Now Astronauts are currently chosen specifically to resist the effects of stress on the human body and mind; but that doesn’t mean they’re invincible™. We need only look at the astronaut that drove cross country while shitting in her diapers to confront her ex for getting a new girlfriend to see the line between ‘toughest brightest mind on earth,’ and ‘batshit insane psychotic break,’ is far thinner than we’d like to believe.