In 1958, when NASA began its search for America’s first group of astronauts, no one knew what an astronaut was or what he was expected to do. This made the selection process a crapshoot built on trial and error. What kind of man would have the ideal demeanor of an astronaut? What was the appropriate genetic background? And what mattered more in flight: physical or mental fitness? Physical fitness was certainly a part of it, and the fitness tests facing the Mercury astronauts were unconventional, not totally unexpected when you consider the astronauts were strapped in a capsule that prevented all movement. So how fit does a man need to be to fly in space if he can’t move?
As possible astronauts, NASA briefly considered acrobats, daredevils, and contortionists — all people familiar with cramped environments and dangerous jobs. But President Eisenhower had other ideas for the astronaut corps and stipulated that the candidate pool be limited to military test pilots. These men (because they were all men in the 1950s) had security clearance in a time of war and were comfortable with unknown environments in the air. A perfect mix.
In addition to this fairly common background was a set of limiting factors: candidates had to be under 40 years of age, hold a bachelor’s degree in engineering or something equivalent, be a graduate of a test pilot school, and be a qualified jet pilot with at least 1, 500 hours of flying time.
Physically, astronaut candidates had be “in excellent physical condition, ” under five feet eleven inches, and weigh less than 180 pounds. The height and weight limits, interestingly, had nothing to do with physical demands placed on the astronaut but the limited size and lift capacity of the Redstone and Atlas launch vehicles. If an astronaut weighed 185 pounds, forget it. He wasn’t going anywhere.
From the United States Air Force, the United States Navy, and the United States Marine Corps, only 110 men met these requirements. The first 69 to volunteer were interviewed. 32 of those interviewed were selected to proceed to the final round in the testing process – physical and mental fitness testing at the Lovelace Clinic in Albuquerque, New Mexico.
The psychological tests were essential to ensure the astronauts were the most even-keeled and balanced men able to reliably think clearly in dangerous situations. To this end, the psychological tests included Rorschach tests, isolation chamber tests, heat tests, cold tests, and a variety of other tests designed to see which candidates would crack under stress and which were able to keep their cool.
The physical tests, however, brought a different set of challenges. How would NASA determine the optimal fitness level of a man sitting in a confined space? He could barely move his legs and he certainly wasn’t about to do anything as physically demanding as a space walk. Overall fitness was a necessity; the Mercury program was the first in NASA’s long term plan and later missions would likely have the same astronauts in much more physically demanding roles. But what about the immediate missions?
Missions planners determined that overcoming stress was likely to be the most challenging aspect of a mission. As such, the one muscle that would really get a workout on a Mercury mission was the astronaut’s heart, a vital muscular organ extremely susceptible to stress.
Mercury astronaut candidates faced a battery of physical tests designed to measure the strength of the heart using two measurements: blood pressure and heart rate.
Blood pressure refers to the amount of blood pumped through the body in a single beat. It is expressed as two numbers, for example 120/80. The first number (120) refers to systolic pressure or the amount of blood the heart expels through the arteries per beat. The second number (80) refers to diastolic pressure or the amount of blood the heart receives as the muscle relaxes. Heart rate is expressed as beats per minute; between blood pressure and heart rate, a physician can get a good idea of your cardiac output and heart health.
These two very basic measurements also mean it’s possible to do some of the candidate tests at home and see how you measure up.
Some tests are impossible to replicate unless you have access to a full scale pressure chamber and space suits. But three tests are easy enough to do on your own and only require blood pressure and heart rate measurements: The Harvard Step Test, the Cold Pressor Test, and the Treadmill Test.
Measuring your heart rate is easily done on the radial pulse—the artery that runs down from your thumb on the inside of your wrist. With two fingers apply gentle pressure until you feel a rhythmic pulse. Count the pulses for 30 seconds then multiply by 2 and you have your beats per minute. Blood pressure can’t be measured as easily and is best done with an automatic pressure cuff—easy enough to find, especially if you know someone with high blood pressure who monitors themselves.
For the Harvard Step Test, you need a clock with a second hand, a 19.5-inch high step (a couch will be a fair substitute) and a metronome (optional, but will make pacing yourself easier). Start the clock and begin walking up the step—up for one second down for one second and so on such that you complete 30 steps in 60 seconds. Maintain this pace or as close are you can for five minutes and count your steps. When you’re done, restart the clock and take three measurements of your heart rate: count pulses for thirty seconds from 1 minute to 1 minute 30 seconds, from 2 minutes to 2 minutes 30 seconds, and again from 4 minutes to 4 minutes 30 seconds.
To score the Harvard Step Test, multiply each of your three heart rate measurements by two and add them together. Divide this number by the total number of steps climbed, and multiply this result by 150 to get your final score. The average score of candidates to be launched into space was 52.8 with a standard deviation of 5.3.
The second at-home test is the Cold Pressor Test and requires a bucket of ice water chilled to 4 degrees centigrade or 39.2 Fahrenheit and a towel. Sit in a chair and measure your blood pressure and heart rate once a minute for three minutes. Then, stick your feet in the bucket of ice water for seven minutes, measuring your blood pressure and heart rate once a minute.Remove your feet—either after the full seven minutes or when you just can’t stand the cold anymore—and place them on the dry towel. Again, measure your heart rate and blood pressure once a minute for three minutes.