The United States and the U.S.S.R. had been putting animals atop rockets since 1947. In the early days of rocket science, no one knew what the effects of weightlessness would be. Animals — mainly dogs, monkeys and chimps — were used to test the safety and feasibility of launching a living being into space and bringing it back unharmed. Able, a Rhesus monkey, and Baker, a squirrel monkey, were launched together on May 28, 1959. They flew 300 miles high and returned unharmed. However, Able died during an operation to remove an electrode from under her skin. Baker lived until 1984, dying of kidney failure at age 27.