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Let's take this baby out for a spin!

20G centrifuge
For a larger view, right click on the picture and select "view image", then click on the picture again.

A centrifuge is a machine that spins around while containing something in compartments at its outer ends. Usually, this is used to separate chemicals or particles. The centrifugal force causes heaver things to separate to the outside and lighter things to separate to the inside.

But there is a special centrifuge, located at Holloman Air Force Base, which holds people in its outer chambers. It is not for separating their parts, although it may feel like it at high speeds. It is for training pilots how to deal with "high-G" forces. That is, forces which are higher than the pull of the Earth's gravitation.

Human Centrifuges are exceptionally large centrifuges that test the reactions and tolerance of pilots and astronauts to acceleration above those experienced in the Earth's gravity. The US Air Force at Holloman Air Force Base, NM operates a human centrifuge. It is operated by the aerospace physiology department for the purpose of training and evaluating prospective fighter pilots for high-g flight in Air Force fighter aircraft.

The use of large centrifuges to simulate a feeling of gravity has been proposed for future long-duration space missions. Exposure to this simulated gravity would prevent or reduce the bone decalcification and muscle atrophy that affect individuals exposed to long periods of freefall. An example of this can be seen in the film 2001: A Space Odyssey.

High-G training is done by aviators and astronauts who are subject to high levels of acceleration ('G'). It is designed to prevent a g-induced Loss Of Consciousness (abbreviated g-LOC), a situation when g-forces move the blood away from the brain to the extent that consciousness is lost. Incidents of acceleration-induced loss of consciousness have caused fatal accidents in aircraft.

Basically, when you are in the centrifuge, you sit inside a box at the end of one of the arms.

Cab B
For a larger view, right click on the picture and select "view image", then click on the picture again.

Don't worry, though. You sit in a comfortable seat inside the box. (If you didn't, your own weight could crush your body.) You are also in there with lots of monitors and other equipment to measure your body's reactions, and to make sure you are still OK.

As g-forces increase, visual effects include loss of colour vision (grey-out), followed by tunnel vision (where peripheral vision is lost, retaining only the centre vision). If g-forces increase further, complete loss of vision will occur, while consciousness remains. These effects are due to a reduction of blood flow to the eyes before blood flow to the brain is lost, because the extra pressure within the eye (intraocular pressure) counters the blood pressure.

A further increase in g-forces will cause g-LOC where consciousness is lost. This is doubly dangerous because, on recovery as g is reduced, a period of several seconds of disorientation occurs, during which a pilot's aircraft can dive into the ground. Brief and vivid dreams are also reported to follow G-LOC.

The g thresholds at which these effects occur depend on the training, age and fitness of the individual. An un-trained individual not used to the g-straining manoevre, can black out between 4 and 6 g, particularly if this is pulled suddenly. Roller coasters typically do not expose the occupants to much more than about 3 g. A hard slap on the face may impose hundreds of g-s locally but not produce any real damage: a constant 15 g-s for a minute, however, may be deadly. A trained, fit individual wearing a g suit and practising the straining manoeuvre (tightening of lower body muscles) can, with some difficulty, sustain up to 9g without loss of consciousness. The centrifuge at Holloman goes up to 20 G's - an amount which would be fatal for any human, but which allows for the testing and development of advanced G-suit design.

For a look at a movie of the actual process of an airman being tested in the human centrifuge at 4, 5, and 6 G's, click here

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