The left stuff

I was given the opportunity to go to Mars and once selected I could not refuse. My body was not up to tolerating 20G and the radiation in space so they transplanted a new body which could have a 50% chance of being alive for a month after arrival. It was still a problem as I was not going to let myself be stuck in a tin can with tons of explosives under my ass and having a 2.5 year lifespan limit. So, they transplanted my head with one that would comply. They said "Now you have the Right Stuff!". I said, "Which head are you talking to?".