A group of psychiatrists are deciding how to decide what candidates to pick for the Mars mission. Michel Duval half-joking says they should pick insane candidates in the first place because the trip will probably make them so.
Since the committee can't do that, they choose to send a psychologist to observe the candidates during their Antarctica training; Michel Duval's joke gets him a one-way ticket to the land down under the Down Under.
The Mars mission candidates include experts in a wide range of fields, not just astronauts. They know they are being tested both for their expertise and their mental makeup—the test for mental makeup causes some to crack under the pressure.
When it's over, fifty men and fifty women are chosen. Of that hundred, thirty-five are Americans, thirty-five are Russian, and thirty are, let's say, miscellaneous.
Michel's evaluation says that the selection process has embedded in this space-bound community a sense of competition and cliquey-ness. The committee believes it would best if they send a qualified psychiatrist.