The first primate went into space in 1961 when a chimpanzee named Ham rocketed skyward. Fifteen primates followed until the last American monkey went into space in 1985. 

Now, NASA is reintroducing primates to the heavens. The space agency will expose 18 to 28 squirrel monkeys to low doses of daily radiation to study the effects of long-term radiation exposure outside Earth’s magnetic shield. 

With NASA’s sights set on traveling to Mars, scientists want to look at how radiation impacts the monkeys' central nervous systems and behaviors over time. Jack Bergman is a behavioral pharmacologist at Harvard Medical School's McLean Hospital in Boston. As he told Discovery News, "There's a long-standing commitment on the part of NASA to deep space travel and with that commitment comes a need for knowing what kinds of adverse effects deep space travel might have, what are the risks to astronauts."

The experiment, which will take place at NASA's Space Radiation Laboratory at the Department of Energy's Brookhaven National Laboratory in New York, involves the squirrel monkeys training on a variety of tasks. They will be tested to see how exposure to radiation impacts performance.

Bergman says this process enables scientists to assess the monkeys at different time points after radiation exposure. This way, they can get a sense of both immediate and long-term effects.

NASA has issued a statement that the animals will not be killed and will remain at McLean’s hospital for the duration of their lives.