High-g training

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The 20 g centrifuge at the NASA Ames Research Center 20G centrifuge.jpg
The 20 g centrifuge at the NASA Ames Research Center

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 (g-LOC), a situation when the action of g-forces moves 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 capable of sustaining high-g for considerable periods.

Contents

The value of training has been well established during the decades since the 1970s and has been the subject of much research and literature, and training has contributed to extending pilots' g tolerance in both magnitude and duration. [1] Training includes centrifuge, Anti-g Straining Maneuvers (AGSM), and acceleration physiology.

Overview

As g-forces increase, visual effects include loss of colour vision ("greyout"), 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. The reverse effect is experienced in advanced aerobatic maneuvers under negative g-forces, where excess blood moves towards the brain and eyes ("redout").

The human body has different tolerances for g-forces depending on the acceleration direction. Humans can withstand a positive acceleration forward at higher g-forces than they can withstand a positive acceleration upwards. This is because when the body accelerates up at such high rates the blood rushes from the brain which causes loss of vision.

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 the aircraft can dive into the ground. Dreams are reported to follow g-LOC which are brief and vivid. [2]

The g thresholds at which these effects occur depend on the training, age and fitness of the individual. An untrained individual not used to the g-straining maneuver 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 may not produce any obvious 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 maneuver can, with some difficulty, sustain up to 9 g without loss of consciousness.

The human body is considerably more able to survive g-forces that are perpendicular to the spine. This is not true in 0 g when you strafe up; that is an eyeballs-down maneuver, which is the same force as a blackout where blood rushes to the feet, and this force is parallel to the spine. In general, when the g-force pushes the body forwards (colloquially known as 'eyeballs in' [3] ) a much higher tolerance is shown than when g-force is pushing the body backwards ('eyeballs out') since blood vessels in the retina appear more sensitive to that direction. [4]

G-suits

A g-suit is worn by aviators and astronauts who are subject to high levels of acceleration and, hence, increasing positive g. It is designed to prevent a blackout and g-LOC, due to the blood pooling in the lower part of the body when under high-g, thus depriving the brain of blood.

Human centrifuge training

TsF-18 centrifuge at the Yuri Gagarin Cosmonauts Training Center RU270484.star city centriguge2.jpg
TsF-18 centrifuge at the Yuri Gagarin Cosmonauts Training Center

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.

In the UK High-G training is provided at the High-G Training and Test Facility, RAF Cranwell using an AMST built human centrifuge. The facility trains Royal Navy, Royal Air Force and international students. [5]

KBRwyle at Brooks City-Base in San Antonio, Texas, operates a human centrifuge. The centrifuge at Brooks is used to train USAF and USN aircrew for sustained high-g flight. [6]

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 free fall. [7] [8] An example of this can be seen aboard the Discovery spacecraft in the film 2001: A Space Odyssey .

Human-rated centrifuges are made by AMST Systemtechnik in Austria (Austria Metall SystemTechnik), Latécoère in France, Wyle Laboratories and ETC in the US.

See also

Related Research Articles

<span class="mw-page-title-main">Centrifuge</span> Device using centrifugal force to separate fluids

A centrifuge is a device that uses centrifugal force to subject a specimen to a specified constant force, for example to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby separating fluids of different densities or liquids from solids. It works by causing denser substances and particles to move outward in the radial direction. At the same time, objects that are less dense are displaced and moved to the centre. In a laboratory centrifuge that uses sample tubes, the radial acceleration causes denser particles to settle to the bottom of the tube, while low-density substances rise to the top. A centrifuge can be a very effective filter that separates contaminants from the main body of fluid.

<span class="mw-page-title-main">Tunnel vision</span> Medical condition

Tunnel vision is the loss of peripheral vision with retention of central vision, resulting in a constricted circular tunnel-like field of vision.

g-force Term for accelerations felt as weight in multiples of standard gravity

The g-force or gravitational force equivalent is mass-specific force, expressed in units of standard gravity. It is used for sustained accelerations, that cause a perception of weight. For example, an object at rest on Earth's surface is subject to 1 g, equaling the conventional value of gravitational acceleration on Earth, about 9.8 m/s2. More transient acceleration, accompanied with significant jerk, is called shock.

g-suit Flight suit which controls blood-flow during high acceleration

A g-suit, or anti-g suit, is a flight suit worn by aviators and astronauts who are subject to high levels of acceleration force (g). It is designed to prevent a black-out and g-LOC caused by the blood pooling in the lower part of the body when under acceleration, thus depriving the brain of blood. Black-out and g-LOC have caused a number of fatal aircraft accidents.

<span class="mw-page-title-main">STS-58</span> 1993 American crewed spaceflight

STS-58 was a NASA mission flown by Space Shuttle Columbia launched from Kennedy Space Center, Florida, on October 18, 1993. The missions was primarily devoted to experiments concerning the physiological effects in space. This was the first in-flight use of the "Portable In-flight Landing Operations Trainer" (PILOT) simulation software. It was also the last time Columbia would land at Edwards Air Force Base, California.

<span class="mw-page-title-main">Space adaptation syndrome</span> Condition caused by weightlessness

Space adaptation syndrome (SAS) or space sickness is a condition experienced by as many as half of all space travelers during their adaptation to weightlessness once in orbit. It is the opposite of terrestrial motion sickness since it occurs when the environment and the person appear visually to be in motion relative to one another even though there is no corresponding sensation of bodily movement originating from the vestibular system.

Spatial disorientation is the inability to determine position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibular system, and proprioceptive system collectively work to coordinate movement with balance, and can also create illusory nonvisual sensations, resulting in spatial disorientation in the absence of strong visual cues.

<span class="mw-page-title-main">Artificial gravity</span> Use of circular rotational force to mimic gravity

Artificial gravity is the creation of an inertial force that mimics the effects of a gravitational force, usually by rotation. Artificial gravity, or rotational gravity, is thus the appearance of a centrifugal force in a rotating frame of reference, as opposed to the force experienced in linear acceleration, which by the equivalence principle is indistinguishable from gravity. In a more general sense, "artificial gravity" may also refer to the effect of linear acceleration, e.g. by means of a rocket engine.

<span class="mw-page-title-main">Effect of spaceflight on the human body</span> Medical issues associated with spaceflight

The effects of spaceflight on the human body are complex and largely harmful over both short and long term. Significant adverse effects of long-term weightlessness include muscle atrophy and deterioration of the skeleton. Other significant effects include a slowing of cardiovascular system functions, decreased production of red blood cells, balance disorders, eyesight disorders and changes in the immune system. Additional symptoms include fluid redistribution, loss of body mass, nasal congestion, sleep disturbance, and excess flatulence. Overall, NASA refers to the various deleterious effects of spaceflight on the human body by the acronym RIDGE.

<span class="mw-page-title-main">Motion simulator</span> Type of mechanism

A motion simulator or motion platform is a mechanism that creates the feelings of being in a real motion environment. In a simulator, the movement is synchronised with a visual display of the outside world (OTW) scene. Motion platforms can provide movement in all of the six degrees of freedom (DOF) that can be experienced by an object that is free to move, such as an aircraft or spacecraft:. These are the three rotational degrees of freedom and three translational or linear degrees of freedom.

g-force induced loss of consciousness is a term generally used in aerospace physiology to describe a loss of consciousness occurring from excessive and sustained g-forces draining blood away from the brain causing cerebral hypoxia. The condition is most likely to affect pilots of high performance fighter and aerobatic aircraft or astronauts but is possible on some extreme amusement park rides. G-LOC incidents have caused fatal accidents in high performance aircraft capable of sustaining high g for extended periods. High-g training for pilots of high performance aircraft or spacecraft often includes ground training for G-LOC in special centrifuges, with some profiles exposing pilots to 9 gs for a sustained period.

<span class="mw-page-title-main">Environmental suit</span> Clothing worn to protect a person in a hostile environment

An environmental suit is a suit designed specifically for a particular environment, usually one otherwise hostile to humans. An environment suit is typically a one-piece garment, and many types also feature a helmet or other covering for the head. Where the surrounding environment is especially dangerous the suit is completely sealed.

<span class="mw-page-title-main">Mission: Space</span> Space simulator attraction at Epcot

Mission: Space is a space exploration-themed pavilion and attached centrifugal motion simulator attraction located in the World Discovery section of Epcot at Walt Disney World in Bay Lake, Florida. The attraction simulates what an astronaut might experience aboard a spacecraft on a mission to Mars, from the higher g-force of liftoff, to the speculative hypersleep. The pavilion also includes the Mission Space: Cargo Bay gift shop, the Advanced Training Lab interactive play area and Space 220 Restaurant.

<span class="mw-page-title-main">Space medicine</span> For health conditions encountered during spaceflight

Space medicine is an area in aerospace medicine that focuses on the medical care of astronauts and spaceflight participants. The spaceflight environment poses many unique stressors to the human body, including G forces, microgravity, unusual atmospheres such as low pressure or high carbon dioxide, and space radiation. Space medicine applies space physiology, preventive medicine, primary care, emergency medicine, acute care medicine, austere medicine, public health, and toxicology to prevent and treat medical problems in space. This expertise is additionally used to inform vehicle systems design to minimize the risk to human health and performance while meeting mission objectives.

A greyout is a transient loss of vision characterized by a perceived dimming of light and color, sometimes accompanied by a loss of peripheral vision. It is a precursor to fainting or a blackout and is caused by hypoxia, often due to a loss of blood pressure.

<span class="mw-page-title-main">David Clark Company</span>

David Clark Company, Inc. is an American manufacturing company. DCC designs and manufactures a wide variety of aerospace and industrial protective equipment, including pressure-space suit systems, anti-G suits, headsets, and several medical/safety products. DCC has been involved in the design and manufacture of air-space crew protective equipment since 1941, beginning with the design and development of the first standard anti-G suits and valves used by allied fighter pilots during World War II.

<span class="mw-page-title-main">Weightlessness</span> Zero apparent weight, microgravity

Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g or, incorrectly, zero gravity.

<span class="mw-page-title-main">RAF Centre of Aviation Medicine</span> Military unit

The RAF Centre of Aviation Medicine is a medical organisation run by the Royal Air Force and based at RAF Henlow in Bedfordshire. It is the main organisation conducting aviation medicine research in the UK.

Space neuroscience or astroneuroscience is the scientific study of the central nervous system (CNS) functions during spaceflight. Living systems can integrate the inputs from the senses to navigate in their environment and to coordinate posture, locomotion, and eye movements. Gravity has a fundamental role in controlling these functions. In weightlessness during spaceflight, integrating the sensory inputs and coordinating motor responses is harder to do because gravity is no longer sensed during free-fall. For example, the otolith organs of the vestibular system no longer signal head tilt relative to gravity when standing. However, they can still sense head translation during body motion. Ambiguities and changes in how the gravitational input is processed can lead to potential errors in perception, which affects spatial orientation and mental representation. Dysfunctions of the vestibular system are common during and immediately after spaceflight, such as space motion sickness in orbit and balance disorders after return to Earth.

<span class="mw-page-title-main">Locomotion in space</span> Movement of astronauts bodies in outer space

Locomotion in space includes all actions or methods used to move one's body in microgravity conditions through the outer space environment. Locomotion in these conditions is different from locomotion in a gravitational field. There are many factors that contribute to these differences, and they are crucial when researching long-term survival of humans in space.

References

  1. "Centrifuge Training". Archived from the original on 2007-08-02. Retrieved 2008-02-04.
  2. Forster, Estrella M. (June 20, 1993). A Database to Evaluate Acceleration (+Gz) Induced Loss of Consciousness (G-Loc) in the Human Centrifuge (PDF) (Report). Defense Technical Information Center. Retrieved December 3, 2022.
  3. NASA Physiological Acceleration Systems Archived May 19, 2008, at the Wayback Machine
  4. NASA Technical note D-337, Centrifuge Study of Pilot Tolerance to Acceleration and the Effects of Acceleration on Pilot Performance, by Brent Y. Creer, Captain Harald A. Smedal, USN (MC), and Rodney C. Wingrove
  5. "High G Training and Test Facility". Thales Group. 6 June 2019. Retrieved December 3, 2022.
  6. "KBRwyle Provides High-G Centrifuge Flight Training". KBRWyle. March 7, 2019. Retrieved December 3, 2022.
  7. "The Pull of HyperGravity - A NASA researcher is studying the strange effects of artificial gravity on humans". NASA. Archived from the original on 16 March 2012. Retrieved 11 March 2012.
  8. Hsu, Jeremy (12 May 2010). "New Artificial Gravity Tests in Space Could Help Astronauts". Space.com . Retrieved 11 March 2012.