Expert: Marc Ebelini - 8/28/2009

Question
Hi, I was wondering what are the comparisons of the pressure an astronaut experiences in space to that of the pressure a deep sea diver experiences in water? How are they similar?
Thank you.

Answer
The pressures are opposite. At sea level an open gage reads "0" pressure when actually the pressure is 14.7 pounds per square inch depending on weather conditions. As you descend in water the pressure goes up as depth is increased. That is what limits divers without protective gear. As you ascend the pressure goes down until it become a vacuum in space. Using my experience on the Apollo project I can tell you that since the USA did not have a rocket powerful enough to launch a space craft strong to sustain the 14.7 PSI for the crew NASA used 5 PSI that was pure oxygen. Simply put, at 20% oxygen in the air at 14.7 PSI dropping to 5 PSI would not supply enough oxygen for the crew to survive so it was established that at 5 PSI of pure oxygen they could. I do not have any data available to give you pressures at various depths or pressures going up handy. The numbers are effected by temperature. That is why altimeters have a window to set the local barometric pressure to use as reference. Hope this will satisfy you curiosity.