Compared to NASA's astronaut corps, getting into Harvard is a walk in the park. A mere 12 people were accepted from a pool of more than 18,353 applicants to this year's astronaut training program, making NASA's acceptance rate, effectively, 0.065 percent, or less than 1 out of 1,500. For comparison, the most difficult university to get into, Stanford, has an admittance rate of 4.65 percent, followed by Harvard at 5.2 percent. The seven men and five women will begin a two-year training at Johnson Air Space Center in Houston in August, where they'll study spacecraft systems, spacewalking skills and team building and learn Russian. After that, they will be assigned to work on the International Space Station, explore deep space through missions on NASA's Orion spacecraft, or work on one of two American-made commercial crew spacecraft currently being developed – Boeing's CST-100 Starliner or the SpaceX Crew Dragon.

What it takes to get in

To get into NASA's astronaut corps, candidates have to have a bachelor's degree in engineering, biological science, physical science or mathematics. The degrees accepted are specific — one in aviation technology, geography or nursing won't cut it, and an advanced degree is preferred. Candidates also must have at least three years of "related, progressively responsible professional experience, or at least 1,000 hours of pilot-in-command time in jet aircraft," according to NASA. Candidates also have to have 20/20 vision, though glasses, contacts and laser surgery are permitted. On top of all that, would-be astronauts must be exceptionally fit and able to withstand many uncomfortable physical situations associated with space travel.

Source: NASA

Take, for example, the NASA swim test, which must be completed while wearing a flight suit. A flight suit weighs approximately 280 pounds on earth. "[Candidates] must swim three lengths of a 25-meter pool without stopping, and then swim three lengths of the pool in a flight suit and tennis shoes with no time limit," a NASA manual reads. "They must also tread water continuously for 10 minutes wearing a flight suit." Worse than the pool athletic tests are the weightlessness simulations, where candidates are put into "modified jet aircrafts" as they perform "parabolic maneuvers that produce periods of weightlessness for about 20 seconds." Trainees are then returned to a normal altitude, at which point the sequence resumes. Feeling sick yet? This exercise is performed "up to 40 times a day."

Who got accepted

The selected candidates are: Kayla Barron, Submarine Warfare Officer, U.S. Navy Raja Chari, Lieutenant Colonel, U.S. Airforce Loral O'Hara, aerospace and aeronautics engineer and sea-going mechanical technician

NASA's 2017 astronaut candidates stop to take a group photo while getting fitted for flight suits at Ellington Field near NASA's Johnson Space Center in Houston.