11/05/2010 05:24:00 PM
This week's Flashback Friday is by Dr. Wernher von Braun, written in 1968 for Popular Science after he took a space suit for a test drive (dive?). He explains some of the difficulties of working in a pressurized suit, and how the Neutral Buoyancy pools help engineers and astronauts prepare for space missions. Enjoy!
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Engineers preparing these new missions, in close cooperation with the astronauts that will fly them, must see that every piece of equipment is designed to suit the conditions of its use; that a mission's plan gives the astronauts ample time for what they are to do; and that they do not overexert themselves to perform their tasks.
Aircraft flights through "ballistic parabolas" have long been used to study human-engineering problems under zero gravity, and will continue to be tremendously useful. But weightlessness during ballistic aircraft flights is limited to less than a minute -- too short for many of the complex tasks planned for the Apollo Applications Program.
All tasks requiring more time are therefore being studied in underwater tests -- an idea pioneered by the astronauts themselves. Astronaut M. Scott Carpenter, the second American to orbit the earth, first pointed out the great potential of this way to study human factors problems under zero gravity. Astronaut Eugene A. Cernan first tried it in a spacesuit. And Astronaut Edwin E. ("Buzz") Aldrin Jr., who rehearsed in a swimming pool for his successful space rigger's feats outside the orbiting Gemini 12 spacecraft, gave the final proof that underwater time, work, and motion studies in "inner space" really paid off handsomely in outer space.
Test tanks for space centers
To reduce water resistance in narrow passages, the mockup is an open-grid structure that permits water to pass freely through its walls. The upper side of a mockup has escape hatches that, pushed open from beneath, give free access to the water's surface in an emergency.
Trying it out.
To familiarize myself with some of the astronauts' tasks and get a feel for their difficulties, I recently spent about an hour in the Neutral Buoyancy Tank at Marshall. I tried my hand at relatively simple jobs, such as placing a cover over a vent outlet, that are involved in "activating" the Orbital Workshop (which, prior to human occupancy, will have served as a hydrogen tank).
After I was zipped up in the spacesuit and topped by the space helmet, a lead-weighted belt was thrown over my shoulders, and lead-weighted straps were fastened to my ankles. As I got up from my dress-up chair, I felt as if I had landed on the 2.5g surface of the planet Jupiter. But the load lightened when I entered the tank, where I first stood on a platform that kept me shoulder-deep in the water.
Now the pressurization of the suit began. They had strapped a dual pressure gauge to my wrist. The test controller, whose voice I heard over the helmet earphones, asked me to call out the suit pressure through my helmet mike. At a suit overpressure of 3.5 pounds per square inch, I was ready for underwater action.
Two scuba divers, who for safety always stay close to a test subject, gently inched me off the platform. They rotated me in a horizontal position, submerged and free-floating, to make sure I was properly weighted down to neutral buoyancy. I was. (They must have gotten my exact vital statistics from the Center doctor -- or a fine retrim would undoubtedly have been necessary.)
My awkward attempts to perform the assigned tasks must have been as amusing to onlookers, below and above the waterline, as they were educational to me. I was particularly impressed by the "straitjacket" effect our spacesuits still have. It takes physical force to bed your arm, because the internal pressure of your spacesuit wants your arm to be straight. The pressure also pushes your arm up around the shoulder joint, and it takes a certain effort to bring it down to your ribs.
A wrestle with a valve cap.
One of my tasks was to push a hubcap-size cover over a valve, and secure it by a turn to the right -- just as you would tighten the cap of your car's gas tank. As I tried to push and twist the cap into place, the reaction force turned me around instead. I anchored myself, with one hand, to a handhold provided near the work station -- but found it awfully difficult to do the pushing and the turning with the other hand alone. After a minute of real hard physical effort, I was panting heavily and had to rest a bit. Undoubtedly a few more hours of practicing this particular task would have enabled me to lick it. But I decided right then and there that the designers of that darn cap might as well take a course in basic physics, or try it in the tank themselves -- and come up with a design better suited for zero-gravity operations in a spacesuit.
With scuba gear, its another story
After exposing all my clumsiness in the spacesuit test, I tried performing the identical tasks in swimming trunks and scuba gear. The job in the spacesuit had made me perspire so profusely that I really longed for a refreshing swim -- for physical contact with the water from which the spacesuit had separated me.
The space rigger's tasks that were so difficult in a pressurized spacesuit turned out to be a cinch in swimming trunks and scuba gear. There was no spacesuit pressure to fight as I moved my limbs. My flippered feet gave all the maneuverability that I wanted. But, of course, kicking your feet won't get you anywhere in an air-filled environment, let alone an airless one! It is the first thing a skin diver has to unlearn when he turns to neutral buoyancy work, for it would lead to wrong results.
What trial tanks have shown
Underwater tests have already taught us valuable lessons. We have found out what can and cannot reasonably be expected from an astronaut under zero gravity: how much time and effort it takes; where foot and hand holds should be placed; how toggle switches should be reconfigured for easy operation; what corners should be padded, so a man won't get hung up or tear a hole in his suit. Most importantly, we have learned that whatever zero-gravity work can be done in shirtsleeves is many times simpler than the same work in a pressurized spacesuit that "fights back."
