Weight Loss in Space Suit

Project Mercury astronaut Virgil I. Grissom, during a dress rehearsal for his suborbital flight. Pressure suit specialist Joseph W. Schmitt can be seen adjusting a helmet respirometer that measures breathing rate.


The effect of spaceflight on human physiology has been tracked intensively from the dawn of the space age to current ongoing studies aboard the International Space Station. Revisiting data from Project Mercury—America’s first manned spaceflights—has yielded findings that may be of high interest to a new class of space travelers: tourists aboard commercial space flights that will be offered in the coming years.

For each of the six Mercury missions, which occurred between May 1961 and May 1963, NASA measured the vital signs of their astronauts before, during, and after each flight. The first two flights were suborbital, lasting around fifteen minutes each, with weightlessness limited to five minutes. The four orbital missions ranged from five hours to over thirty-four hours, with weightless time varying between four and a half hours to thirty-four hours. During their missions, the astronauts wore pressurized spacesuits for protection, even though the Mercury cabins were pressurized.

Although data were published after each mission, only now have scientists assembled and analyzed them on a comparative basis. Several physiological effects were common to all missions, according to the summary report by a team of researchers from NASA, Johns Hopkins University, and Baylor College of Medicine. It was generally concluded that humans could indeed function in the space environment for more than a day. This is common knowledge now but was a key concern more than five decades ago. Heart and respiration rates were consistently higher in all spaceflights than during training simulations, while blood pressure remained the same. All astronauts reported normal sensory functions and normal urination during weightlessness, but their appetites were reduced, as was water intake for most of the flights.

One unexpected finding was the cause of modest weight loss: it was more correlated with the time astronauts spent in their spacesuits during pre-launch, flight time, and post-flight recovery, than with their time in actual weightlessness. More negative physiological effects seemed to result from being in an uncomfortable, pressurized spacesuit rather than from the stressors of being in space. Modern spacesuits have evolved considerably from those of the Mercury flights. Still, the researchers suggest that, based on their analyses, reduced time spent in spacesuits will provide space travelers improved health, comfort, and performance during their short flights. (npj Microgravity)