Early on an astronaut in a bar is asked: “What’s it like to fly to Mars on a rocket?”
His answer: “There’s six men, see? In a space the size of a Buick, and that’s all the room there is. Two of us in the bunks all the time, four of us on watch…”
In fact, the only way for them to last the two year journey is for psychological conditioning to make it impossible for them to kill each other; because after a few weeks of confinement there’s nothing else they dream about. So the astronaut is sitting in this bar, and occasionally someone nearby will sneeze just like one of his crewmates did, or will laugh in just the right way, and it’s all the astronaut can do to stop himself from taking his urge to kill his crewmates on their proxies…
A wonderfully excruciating story that makes the reader feel what the astronaut’s going through, as well as being a not implausible exploration for how the crew of such long journeys could psychologically survive.
The Hated by Frederik Pohl
Availability: free online
Word count: 4,100
First published: Galaxy, Jan 1958
Where to find it: It’s on Gutenberg here, and an audio recording on Librivox here.
For print, your best bet is The Best of Frederik Pohl, collection, 1975, Ballantine
Ten to Infinity 
“Early on an astronaut in a bar is asked: “What’s it like to fly to Mars on a rocket?”
His answer: “There’s six men, see? In a space the size of a Buick, and that’s all the room there is. Two of us in the bunks all the time, four of us on watch…”
In fact, the only way for them to last the two year journey is for psychological conditioning to make it impossible for them to kill each other; because after a few weeks of confinement there’s nothing else they dream about.”
This is such a gorgeous piece of writing – it works for me as a piece of micro-fiction just like this. Might well go and check out the longer work!
Yes, Frederik Pohl’s written a lot of wonderfully high concept stories, which I’ll have to talk about at a later date. And his ‘The Space Merchants’ is one of my favorite SF novels of the 20th century.