Poopy Joe was the first (and the only fully trained) American Monkeynaut, who died in the crash of his rocket moments after launch. The rocket in question had been sabotaged by Mann Co. who had hosted its launch for the price of one dollar as a ploy to steal its Australium fuel source; the crash was subsequently covered up.
Mann Co. denies all responsibility for his death, and actually created commemorative plates in remembrance of Poopy Joe, and America's dream of conquering space. The plates depict a series of items that Poopy Joe would have used in space, which were: A Sword for fighting Vladimir Bananas, a Bugle to be blown to sound for help should he encounter trouble, and a Pick-axe for digging into Heaven's vault.
During the ARG leading up to the Pyromania Update, new information surrounding the death of Poopy Joe came to light. In leaked pages from the Senate Hearing of Mann Co. it is revealed that the rocket's Australium fuel had been switched for gravel water from defective suitcase explosives, and stolen by the Administrator. Once the rocket hit ignition the lack of fuel caused it to malfunction and crash, detonating the explosives on impact and killing Poopy Joe.