It was the basis of your training, the statement you clung to during your hushed up divorce, the money quote of every journalist covering the project. The human mind isn't built for deep space, but the human mind can be upgraded.
You bested dozens of other candidates for the right to have neurosurgeons gamble away their reputation and licenses in the soft puzzle of your grey matter for money and fame and perhaps history. For very wealthy people to become more so. For a country to beat another one in a symbolic race instead of the other way around. For you to gain a dozen different things, none of which mattered to you when you got them.
Only planetary orbits being surer than megaproject delays you were sent out before anybody fully understood what they had done to you, least of all yourself. But what they had set out to do, they had. They had cut away loneliness and fear, they had cauterized the parts of the brain that expected a biosphere somewhere near, they had kept the ability to do mathematics but removed the parts that could freeze in awe at what it meant. They made you not need people at all; not their touch, not their voices, not the memory of their breath.
Once they knew you would not go crazy in a place unfathomably far away from sanity's ecological niche they put you on a ship smaller and cheaper than any social primate could psychologically survive and they sent you away.
The first human going to Jupiter. They had to deepfake emotional reactions in your interviews; they had planned to anyway.
There were half a dozen potential disasters as you traveled, only two of which the public knew about. It would have been impossible to know of any by looking at your stress readings. Quietly, the Pentagon began talking about applying the process to Special Ops soldiers.
When you got past the asteroid belt there was humankind and their works on one side of the Solar System, and a few deep space probes and you on the other side, the one that included the rest of the universe. Simulations had shown 90% of trained but unmodified candidates broke down at this point.
You slept better than ever.
Jupiter was glory. For company and country, too, but for you it was reaching home.
You had your first anxiety attack as the ship started the return half of the trip. By the time you passed Mars orbit you were desperately trying to make it overshoot and go back somehow, but its designers had not been in the habit of thinking of pilots as people owed control.
After not much deliberation it was decided it would be best if you suffered an accident when approaching the Moon base and died doing something heroic to save somebody or something else. This, however, could not be remotely arranged.
They hadn't finished explaining it to you when you said yes.
You saw a light when you died, faint voices coming from it, but you blissfully floated away.