However, the most extreme G-forces mankind has ever generated have actually been created here on Earth. For example, in the immediate post-WWII era, Air Force physician John Stapp set about researching how to improve cockpit designs to make them safer and better protect pilots against not just the G-forces experienced during a crash (which were thought to be the main cause of pilot deaths back in WWI) but also the mangling effects of the airplane as it disintegrated upon impact (which is what was really killing pilots).


To prove this was the case and that the human body could withstand much higher Gs than conventional wisdom dictated, Stapp developed the "Gee Whiz", a rocket-powered, track-mounted acceleration sled, to see just how many Gs the human body could really handle.

By 1948, Stapp had stopped using test dummies aboard the Gee Whiz and had begun using himself instead. Through these experiments—in which the sled was violently accelerated then stopped just as abruptly—Stapp showed that the body could withstand up to 35 Gs and survive.


In the 1950's, Stapp built and tested the Gee Whiz' successor, the Sonic Wind, which accelerated him to 632 mph in less than 5 seconds, then stopped in just one second. This generated a staggering 46.2 g (which means his 168 pound framed felt like it weighed just over 7,700 pounds) and exposed Stapp to 2 full tons of air pressure during the ride. Surprisingly, he walked away from the ride without a scratch—proving that the human body is fully capable of massive G loads, albeit only for a short time.


This rocket-sled record was then broken again in the 1970s aboard the Daisy Decelerator, which was built to test the effects of -Gx forces. Major John Beeding, an Air Force volunteer, endured a whopping 83g (albeit for .04 seconds) during the sled's nearly instantaneous stop. He too walked away from the experiments none the worse for wear.

Both of these experiments only focused on the effects of exceedingly large G-forces over extremely short time periods largely because that's what the human body can handle. This has important implications, not just here on Earth, but for our space exploration aspirations as well. As Bruce Thompson of NASA Quest explains:

The human body can tolerate violent accelerations for short periods, i ncluding the prolonged high-g acceleration necessary to reach Earth orbit. However very prolonged periods of high-g acceleration during travel between planets would be very harmful to the body, and therefore out of the question.

Imagine traveling to Mars, accelerating all the way at 3 gravities. You would weight three times your normal weight for the duration of the trip and would barely be able to move, but what would the unrelenting acceleration be doing to your body? Heavy acceleration is a speeded-up aging process. Tissues break down, capillaries break down and the heart has to do many times its proper work. You could not count on being in good shape when you arrived.


It's an interesting paradox. The closer to light we travel, the slower we age (relatively); yet the faster we accelerate to reach those speeds, the faster our bodies break down. Hopefully future advances in cryogenics, or at least fluid-filled pods which would help absorb the force of sustained high-G acceleration, will allow us to shorten that duration significantly.

[ FAA - NASA - NOVA - University of Ohio - GForces - AV Stop - Soaring Safety]