Μg
   HOME

TheInfoList



OR:

The term micro-g environment (also μg, often referred to by the term microgravity) is more or less synonymous with the terms ''
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight. It is also termed zero gravity, zero G-force, or zero-G. Weight is a measurement of the force on an object at rest in a relatively strong gravitational fi ...
'' and ''zero-g'', but emphasising that
g-force The gravitational force equivalent, or, more commonly, g-force, is a measurement of the type of force per unit mass – typically acceleration – that causes a perception of weight, with a g-force of 1 g (not gram in mass measure ...
s are never exactly zero—just very small (on the International Space Station (ISS), for example, the small g-forces come from tidal effects, gravity from objects other than the Earth, such as astronauts, the spacecraft, and the Sun, air resistance, and astronaut movements that impart
momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass an ...
to the space station). The symbol for microgravity, ''μg'', was used on the insignias of
Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
flights
STS-87 STS-87 was a Space Shuttle mission launched from Launch Complex 39B of the Kennedy Space Center on 19 November 1997. It was the 88th flight of the Space Shuttle and the 24th flight of '' Columbia''. The mission goals were to conduct experiments u ...
and STS-107, because these flights were devoted to microgravity research in
low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
. The most commonly known microgravity environment can be found aboard the ISS which is located in
low-earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
at an altitude of around 400 km, orbiting Earth approximately 15 times per day in what is considered free fall. The effects of free fall also enable the creation of short-duration microgravity environments on Earth. This is accomplished by using droptube, parabolic flights and Random-positioning machines (RPMs).


Absence of gravity

A "stationary" micro-g environment would require travelling far enough into deep space so as to reduce the effect of gravity by
attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable att ...
to almost zero. This is simple in conception but requires travelling a very large distance, rendering it highly impractical. For example, to reduce the gravity of the Earth by a factor of one million, one needs to be at a distance of 6 million kilometres from the Earth, but to reduce the gravity of the Sun to this amount, one has to be at a distance of 3.7 billion kilometres. This is not impossible, but it has only been achieved thus far by four interstellar probes: (
Voyager 1 ''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin ''Voyager 2'', ''Voya ...
and 2 of the
Voyager program The Voyager program is an American scientific program that employs two robotic interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to Flyby (spacef ...
, and
Pioneer 10 ''Pioneer 10'' (originally designated Pioneer F) is an American space probe, launched in 1972 and weighing , that completed the first mission to the planet Jupiter. Thereafter, ''Pioneer 10'' became the first of five artificial objects to ach ...
and 11 of the
Pioneer program The Pioneer programs were two series of United States lunar and planetary space probes exploration. The first program, which ran from 1958 to 1960, unsuccessfully attempted to send spacecraft to orbit the Moon, successfully sent one spacecraft to ...
.) At the
speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
it would take roughly three and a half hours to reach this micro-gravity environment (a region of space where the acceleration due to gravity is one-millionth of that experienced on the Earth's surface). To reduce the gravity to one-thousandth of that on Earth's surface, however, one needs only to be at a distance of 200,000 km. At a distance relatively close to Earth (less than 3000 km), gravity is only slightly reduced. As an object orbits a body such as the Earth, gravity is still attracting objects towards the Earth and the object is accelerated downward at almost 1g. Because the objects are typically moving laterally with respect to the surface at such immense speeds, the object will not lose altitude because of the curvature of the Earth. When viewed from an orbiting observer, other close objects in space appear to be floating because everything is being pulled towards Earth at the same speed, but also moving forward as the Earth's surface "falls" away below. All these objects are in free fall, not zero gravity. Compare the gravitational potential at some of these locations.


Free fall

Free fall occurs when an object is in a gravitational field with no other forces acting on it. Although the force of gravity extends throughout all space, it is possible to experience "zero gravity" in free fall. That is, an object in free fall will accelerate. In the
frame of reference In physics and astronomy, a frame of reference (or reference frame) is an abstract coordinate system whose origin, orientation, and scale are specified by a set of reference points― geometric points whose position is identified both mathema ...
or
coordinate system In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is sig ...
moving with the object the gravitational force would be zero. This doesn't mean that the force has somehow been "turned off" or that gravity disappears, only that when viewed in the accelerated reference frame the force is zero. From the perspective of an observer not moving with the object (i.e. in an inertial reference frame) the force of gravity is exactly the same as usual. A classic example is an elevator car where the cable has been cut and it plummets toward Earth, accelerating at a rate equal to the 9.8 meters per second per second. In this scenario, the gravitational force is mostly, but not entirely, diminished; anyone in the elevator would experience an absence of the usual gravitational pull, however the force is not ''exactly'' zero. Since gravity is a force directed towards the center of the Earth, two balls a horizontal distance apart would by pulled in slightly different directions and would come closer together as the elevator dropped. Also, if they were some vertical distance apart the lower one would experience a higher gravitational force than the upper one since gravity diminishes according to the
inverse square law In science, an inverse-square law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity. The fundamental cause for this can be understoo ...
. These two second-order effects are examples of micro gravity.


Orbits

Orbital motion In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
is a form of free fall. Objects in orbit are not perfectly weightless due to several effects: *Effects depending on relative position in the spacecraft: **Because the force of gravity decreases with distance, objects with non-zero size will be subjected to a tidal force, or a differential pull, between the ends of the object nearest and furthest from the Earth. (An extreme version of this effect is
spaghettification In astrophysics, spaghettification (sometimes referred to as the noodle effect) is the vertical stretching and horizontal compression of objects into long thin shapes (rather like spaghetti) in a very strong, non-homogeneous gravitational field ...
.) In a spacecraft in
low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
(LEO), the
centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...
is also greater on the side of the spacecraft furthest from the Earth. At a 400 km LEO altitude, the overall differential in g-force is approximately 0.384 μ''g''/m. **Gravity between the spacecraft and an object within it may make the object slowly "fall" toward a more massive part of it. The acceleration is 0.007 μ''g'' for 1000 kg at 1 m distance. *Uniform effects (which could be compensated): **Though extremely thin, there is some air at orbital altitudes of 185 to 1,000 km. This atmosphere causes minuscule deceleration due to friction. This could be compensated by a small continuous thrust, but in practice the deceleration is only compensated from time to time, so the tiny g-force of this effect is not eliminated. **The effects of the solar wind and radiation pressure are similar, but directed away from the Sun. Unlike the effect of the atmosphere, it does not reduce with altitude. *Other Effects: **Routine crew activity: Due to the conservation of momentum, any crew member aboard a spacecraft pushing off a wall causes the spacecraft to move in the opposite direction. **Structural Vibration: Stress enacted on the hull of the spacecraft results in the spacecraft bending, causing apparent acceleration.


Commercial applications


Metal spheres


High-quality crystals

While not yet a commercial application, there has been interest in growing
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s in micro-g, as in a
space station A space station is a spacecraft capable of supporting a human crew in orbit for an extended period of time, and is therefore a type of space habitat. It lacks major propulsion or landing systems. An orbital station or an orbital space station i ...
or automated artificial
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
, in an attempt to reduce crystal lattice defects. Such defect-free crystals may prove useful for certain microelectronic applications and also to produce crystals for subsequent
X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. File:Comparison2.jpg, Comparison of boiling of water under earth's gravity (1 g, left) and microgravity (right). The source of heat is in the lower part of the photograph. File:Space Fire.jpg, A comparison between the combustion of a candle on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
(left) and in a microgravity environment, such as that found on the ISS (right). File:Crystals grown in microgravity.jpg, Protein crystals grown by American scientists on the Russian Space Station '' Mir'' in 1995. File:Insulin crystals comparison.jpg, Comparison of
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...
crystals growth in outer space (left) and on Earth (right). File:ScienceCasts- The Zero Gravity Coffee Cup.webm, Liquids may also behave differently than on earth, as demonstrated in this video


Health effects of the micro-g environment


Space motion sickness

Space motion sickness 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 ...
(SMS) is thought to be a subtype of motion sickness that plagues nearly half of all astronauts who venture into space. SMS, along with facial stuffiness from headward shifts of fluids, headaches, and back pain, is part of a broader complex of symptoms that comprise ''space adaptation syndrome'' (SAS). SMS was first described in 1961 during the second orbit of the fourth manned spaceflight when the cosmonaut Gherman Titov aboard the
Vostok 2 Vostok 2 (russian: Восток-2, ''Orient 2'' or ''East 2'') was a Soviet space mission which carried cosmonaut Gherman Titov into orbit for a full day on August 6, 1961, to study the effects of a more prolonged period of weightlessness on the ...
, described feeling disoriented with physical complaints mostly consistent with motion sickness. It is one of the most studied physiological problems of spaceflight but continues to pose a significant difficulty for many astronauts. In some instances, it can be so debilitating that astronauts must sit out from their scheduled occupational duties in space – including missing out on a spacewalk they have spent months training to perform. In most cases, however, astronauts will work through the symptoms even with degradation in their performance. Despite their experiences in some of the most rigorous and demanding physical maneuvers on earth, even the most seasoned astronauts may be affected by SMS, resulting in symptoms of severe
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
, projectile
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose. Vomiting can be the result of ailments like Food-poisoning, foo ...
,
fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
, malaise (feeling sick), and
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
. These symptoms may occur so abruptly and without any warning that space travelers may vomit suddenly without time to contain the emesis, resulting in strong odors and liquid within the cabin which may affect other astronauts. Some changes to eye movement behaviors might also occur as a result of SMS. Symptoms typically last anywhere from one to three days upon entering weightlessness, but may recur upon reentry to Earth's gravity or even shortly after landing. SMS differs from terrestrial motion sickness in that sweating and pallor are typically minimal or absent and gastrointestinal findings usually demonstrate absent bowel sounds indicating reduced
gastrointestinal motility Gastrointestinal physiology is the branch of human physiology that addresses the physical function of the gastrointestinal (GI) tract. The function of the GI tract is to process ingested food by mechanical and chemical means, extract nutrients and ...
. Even when the nausea and vomiting resolve, some central nervous system symptoms may persist which may degrade the astronaut's performance. Graybiel and Knepton proposed the term "
sopite syndrome The sopite syndrome (; Latin: sopire, "to lay to rest, to put to sleep") is a neurological disorder that relates symptoms of fatigue, drowsiness, and mood changes to prolonged periods of motion. raybiel, A., & Knepton, J. (1976), "Sopite Syndrome - ...
" to describe symptoms of lethargy and drowsiness associated with motion sickness in 1976. Since then, their definition has been revised to include "...a symptom complex that develops as a result of exposure to real or apparent motion and is characterized by excessive drowsiness, lassitude, lethargy, mild depression, and reduced ability to focus on an assigned task." Together, these symptoms may pose a substantial threat (albeit temporary) to the astronaut who must remain attentive to life and death issues at all times. SMS is most commonly thought to be a disorder of the vestibular system that occurs when sensory information from the visual system (sight) and the proprioceptive system (posture, position of the body) conflicts with misperceived information from the semicircular canals and the otoliths within the inner ear. This is known as the 'neural mismatch theory' and was first suggested in 1975 by Reason and Brand. Alternatively, the fluid shift hypothesis suggests that weightlessness reduces the hydrostatic pressure on the lower body causing fluids to shift toward the head from the rest of the body. These fluid shifts are thought to increase cerebrospinal fluid pressure (causing back aches), intracranial pressure (causing headaches), and inner ear fluid pressure (causing vestibular dysfunction). Despite a multitude of studies searching for a solution to the problem of SMS, it remains an ongoing problem for space travel. Most non-pharmacological countermeasures such as training and other physical maneuvers have offered minimal benefit. Thornton and Bonato noted, "Pre- and inflight adaptive efforts, some of them mandatory and most of them onerous, have been, for the most part, operational failures." To date, the most common intervention is promethazine, an injectable antihistamine with antiemetic properties, but sedation can be a problematic side effect. Other common pharmacological options include metoclopramide, as well as oral and transdermal application of
scopolamine Scopolamine, also known as hyoscine, or Devil's Breath, is a natural or synthetically produced tropane alkaloid and anticholinergic drug that is formally used as a medication for treating motion sickness and postoperative nausea and vomiting ...
, but drowsiness and sedation are common side effects for these medications as well.


Musculoskeletal effects

In the space (or microgravity) environment the effects of unloading varies significantly among individuals, with sex differences compounding the variability. Differences in mission duration, and the small sample size of astronauts participating in the same mission also adds to the variability to the
musculoskeletal disorder Musculoskeletal disorders (MSDs) are injuries or pain in the human musculoskeletal system, including the joints, ligaments, muscles, nerves, tendons, and structures that support limbs, neck and back. MSDs can arise from a sudden exertion (e.g., li ...
s that are seen in space. In addition to muscle loss, microgravity leads to increased bone resorption, decreased
bone mineral density Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although clinically it is measured by proxy according to optica ...
, and increased fracture risks. Bone resorption leads to increased urinary levels of
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
, which can subsequently lead to an increased risk of
nephrolithiasis Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
. In the first two weeks that the muscles are unloaded from carrying the weight of the human frame during space flight, whole muscle atrophy begins. Postural muscles contain more slow fibers, and are more prone to atrophy than non-postural muscle groups. The loss of muscle mass occurs because of imbalances in protein synthesis and breakdown. The loss of muscle mass is also accompanied by a loss of muscle strength, which was observed after only 2–5 days of spaceflight during the Soyuz-3 and Soyuz-8 missions. Decreases in the generation of contractile forces and whole muscle power have also been found in response to microgravity. To counter the effects of microgravity on the musculoskeletal system, aerobic exercise is recommended. This often takes the form of in-flight cycling. A more effective regimen includes resistive exercises or the use of a penguin suit (contains sewn-in elastic bands to maintain a stretch load on antigravity muscles), centrifugation, and vibration. Centrifugation recreates Earth's gravitational force on the space station, in order to prevent
muscle atrophy Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy leads to muscle weakness ...
. Centrifugation can be performed with centrifuges or by cycling along the inner wall of the space station. Whole body vibration has been found to reduce bone resorption through mechanisms that are unclear. Vibration can be delivered using exercise devices that use vertical displacements juxtaposed to a fulcrum, or by using a plate that oscillates on a vertical axis. The use of beta-2 adrenergic agonists to increase muscle mass, and the use of essential amino acids in conjunction with resistive exercises have been proposed as pharmacologic means of combating muscle atrophy in space.


Cardiovascular effects

Next to the skeletal and muscular system, the cardiovascular system is less strained in weightlessness than on Earth and is de-conditioned during longer periods spent in space. In a regular environment, gravity exerts a downward force, setting up a vertical hydrostatic gradient. When standing, some 'excess' fluid resides in vessels and tissues of the legs. In a micro-g environment, with the loss of a hydrostatic gradient, some fluid quickly redistributes toward the chest and upper body; sensed as 'overload' of circulating blood volume. In the micro-g environment, the newly sensed excess blood volume is adjusted by expelling excess fluid into tissues and cells (12-15% volume reduction) and
red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
s are adjusted downward to maintain a normal concentration (relative
anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...
). In the absence of gravity, venous blood will rush to the right atrium because the force of gravity is no longer pulling the blood down into the vessels of the legs and abdomen, resulting in increased
stroke volume In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the left ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood i ...
. These fluid shifts become more dangerous upon returning to a regular gravity environment as the body will attempt to adapt to the reintroduction of gravity. The reintroduction of gravity again will pull the fluid downward, but now there would be a deficit in both circulating fluid and red blood cells. The decrease in cardiac filling pressure and stroke volume during the orthostatic stress due to a decreased blood volume is what causes orthostatic intolerance. Orthostatic intolerance can result in temporary loss of consciousness and posture, due to the lack of pressure and stroke volume. Some animal species have evolved physiological and anatomical features (such as high hydrostatic blood pressure and closer heart place to head) which enable them to counteract orthostatic blood pressure. More chronic orthostatic intolerance can result in additional symptoms such as
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
,
sleep problems A sleep disorder, or somnipathy, is a medical disorder of an individual's sleep patterns. Some sleep disorders are severe enough to interfere with normal physical, mental, social and emotional functioning. Polysomnography and actigraphy are test ...
, and other vasomotor symptoms as well. Many studies on the physiological effects of weightlessness on the cardiovascular system are done in parabolic flights. It is one of the only feasible options to combine with human experiments, making parabolic flights the only way to investigate the true effects of the micro-g environment on a body without traveling into space. Parabolic flight studies have provided a broad range of results regarding changes in the cardiovascular system in a micro-g environment. Parabolic flight studies have increased the understanding of orthostatic intolerance and decreased peripheral blood flow suffered by Astronauts returning to Earth. Due to the loss of blood to pump, the heart can atrophy in a micro-g environment. A weakened heart can result in low blood volume, low blood pressure and affect the body's ability to send oxygen to the brain without the individual becoming dizzy. Heart rhythm disturbances have also been seen among astronauts, but it is not clear whether this was due to pre-existing conditions of effects of a micro-g environment. One current countermeasure includes drinking a salt solution, which increases the viscosity of blood and would subsequently increase blood pressure which would mitigate post micro-g environment orthostatic intolerance. Another countermeasure includes administration of
midodrine Midodrine is a vasopressor/antihypotensive agent (it raises the blood pressure). Midodrine was approved in the United States by the Food and Drug Administration (FDA) in 1996 for the treatment of dysautonomia and orthostatic hypotension. In A ...
, which is a selective alpha-1 adrenergic agonist. Midodrine produces arterial and venous constriction resulting in an increase in blood pressure by baroreceptor reflexes.


See also

*
Astronaut training Astronaut training describes the complex process of preparing astronauts in regions around the world for their space missions before, during and after the flight, which includes medical tests, physical training, extra-vehicular activity (EVA) tra ...
*
Astronaut An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
s * Commercial astronauts * Commercial use of space *
ESA Scientific Research on the International Space Station The following page is a list of scientific research that is currently underway or has been previously studied on the International Space Station by the European Space Agency. ESA reported ISS Research and Science Activity ESA's scientific progra ...
*
European Low Gravity Research Association The European Low Gravity Research Association (ELGRA) is a non-profit international society devoted to the promotion of scientific research under various gravity conditions in Europe. The organization, established in 1979, provides a networking ...
*
G-jitter G-jitter references forms of periodic or quasisteady residual acceleration encountered in a spacecraft floating through the micro-gravity confines of space. Such variations slightly change the orientation and magnitude of a body force in a low- ...
* Reduced-gravity aircraft *
Scientific research on the International Space Station The International Space Station is a platform for scientific research that requires one or more of the unusual conditions present in low Earth orbit (for example microgravity, ( cosmic) -radiation and extreme temperatures). The primary fields ...
*
Space manufacturing Space manufacturing is the production of tangible goods beyond Earth. Since most production capabilities are limited to low Earth orbit, the term in-orbit manufacturing is also frequently used. There are several rationales supporting in-space ...
*
Space medicine Space medicine is the practice of medicine on astronauts in outer space whereas astronautical hygiene is the application of science and technology to the prevention or control of exposure to the hazards that may cause astronaut ill health. Both ...
*
Weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight. It is also termed zero gravity, zero G-force, or zero-G. Weight is a measurement of the force on an object at rest in a relatively strong gravitational fi ...


References


External links


Overview of microgravity applications and methods

Criticism of the terms "Zero Gravity" and "Microgravity"
a persuasion to use terminology that reflects accurate physics (sci.space post).
Microgravity Collection, The University of Alabama in Huntsville Archives and Special Collections


* * {{cite journal , last1=Tirumalai , first1=Madhan R. , last2=Karouia , first2=Fathi , last3=Tran , first3=Quyen , last4=Stepanov , first4=Victor G. , last5=Bruce , first5=Rebekah J. , last6=Ott , first6=C. Mark , last7=Pierson , first7=Duane L. , last8=Fox , first8=George E. , title=The adaptation of Escherichia coli cells grown in simulated microgravity for an extended period is both phenotypic and genomic , journal=NPJ Microgravity , date=December 2017 , volume=3 , issue=1 , pages=15 , doi=10.1038/s41526-017-0020-1 , pmid=28649637 , pmc=5460176 Gravity Weightlessness Occupational safety and health