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Weightlessness is the complete or near-complete absence of the sensation of
weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar qua ...
. 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 field (such as on the surface of the Earth). These weight-sensations originate from contact with supporting floors, seats, beds, scales, and the like. A sensation of weight is also produced, even when the gravitational field is zero, when contact forces act upon and overcome a body's
inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...
by mechanical, non-
gravitational In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...
forces- such as in a
centrifuge A centrifuge is a device that uses centrifugal force 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 (e.g. cream from milk) or ...
, a rotating space station, or within an accelerating vehicle. When the gravitational field is non-uniform, a body in
free fall In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on ...
experiences tidal effects and is not stress-free. Near a black hole, such tidal effects can be very strong. In the case of the Earth, the effects are minor, especially on objects of relatively small dimensions (such as the human body or a spacecraft) and the overall sensation of weightlessness in these cases is preserved. This condition is known as microgravity, and it prevails in orbiting spacecraft.


Weightlessness in Newtonian mechanics

In Newtonian physics, the sensation of weightlessness experienced by astronauts is not the result of there being zero gravitational acceleration (as seen from the Earth), but of there being no g-force that an astronaut can feel because of the free-fall condition, and also there being zero difference between the acceleration of the spacecraft and the acceleration of the astronaut. Space journalist
James Oberg James Edward Oberg (born November 7, 1944) is an American space journalist and historian, regarded as an expert on the Russian and Chinese space programs. He had a 22-year career as a space engineer in NASA specializing in orbital rendezvous. Ob ...
explains the phenomenon this way:


Weightless and reduced weight environments


Reduced weight in aircraft

Airplanes have been used since 1959 to provide a nearly weightless environment in which to train astronauts, conduct research, and film motion pictures. Such aircraft are commonly referred by the nickname "
Vomit Comet A reduced-gravity aircraft is a type of fixed-wing aircraft that provides brief near-weightless environments for training astronauts, conducting research and making gravity-free movie shots. Versions of such airplanes were operated by the NAS ...
". To create a weightless environment, the airplane flies in a parabolic arc, first climbing, then entering a powered dive. During the arc, the propulsion and steering of the aircraft are controlled to cancel the drag (air resistance) on the plane out, leaving the plane to behave as if it were free-falling in a vacuum.


NASA's Reduced Gravity Aircraft

Versions of such airplanes have been operated by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
's Reduced Gravity Research Program since 1973, where the unofficial nickname originated. NASA later adopted the official nickname 'Weightless Wonder' for publication. NASA's current Reduced Gravity Aircraft, "Weightless Wonder VI", a
McDonnell Douglas C-9 The McDonnell Douglas C-9 was a military version of the McDonnell Douglas DC-9 airliner. It was produced as the C-9A Nightingale for the United States Air Force, and the C-9B Skytrain II for the U.S. Navy and Marine Corps. The final flight of t ...
, is based at
Ellington Field Ellington Field Joint Reserve Base is a joint installation shared by various active component and reserve component military units, as well as aircraft flight operations of the National Aeronautics and Space Administration (NASA) under the aegis ...
(KEFD), near Lyndon B. Johnson Space Center. NASA's
Microgravity University {{primary sources, date=December 2011 Microgravity University, also known as the Reduced Gravity Student Flight Opportunities Program (RGSFOP) was a program run by NASA which enables undergraduate university students to perform microgravity experi ...
- Reduced Gravity Flight Opportunities Plan, also known as the Reduced Gravity Student Flight Opportunities Program, allows teams of undergraduates to submit a microgravity experiment proposal. If selected, the teams design and implement their experiment, and students are invited to fly on NASA's Vomit Comet.


European Space Agency A310 Zero-G

The European Space Agency (ESA) flies parabolic flights on a specially modified
Airbus A310-300 The Airbus A310 is a wide-body aircraft, designed and manufactured by Airbus Industrie, then a consortium of European aerospace manufacturers. Airbus had identified a demand for an aircraft smaller than the A300, the first twin-jet wide-bod ...
aircraft to perform research in microgravity. Along with the French
CNES The (CNES; French: ''Centre national d'études spatiales'') is the French government space agency (administratively, a "public administration with industrial and commercial purpose"). Its headquarters are located in central Paris and it is und ...
and the German DLR, they conduct ''campaigns'' of three flights over consecutive days, with each flight’s about 30 parabolae totalling about 10 minutes of weightlessness. These campaigns are currently operated from
Bordeaux - Mérignac Airport Bordeaux ( , ; Gascon oc, Bordèu ; eu, Bordele; it, Bordò; es, Burdeos) is a port city on the river Garonne in the Gironde department, Southwestern France. It is the capital of the Nouvelle-Aquitaine region, as well as the prefecture ...
b
Novespace
a subsidiary of
CNES The (CNES; French: ''Centre national d'études spatiales'') is the French government space agency (administratively, a "public administration with industrial and commercial purpose"). Its headquarters are located in central Paris and it is und ...
; the aircraft is flown by test pilots from DGA Essais en Vol. , the ESA has flown 52 scientific campaigns and also 9 student parabolic flight campaigns. Their first Zero-G flights were in 1984 using a NASA KC-135 aircraft in
Houston Houston (; ) is the most populous city in Texas, the most populous city in the Southern United States, the fourth-most populous city in the United States, and the sixth-most populous city in North America, with a population of 2,304,580 i ...
, Texas. Other aircraft used include the
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
n Ilyushin Il-76 MDK before founding Novespace, then a French Caravelle and an Airbus A300 Zero-G.


Commercial flights for public passengers

Novespace created Air Zero G in 2012 to share the experience of weightlessness with 40 public passengers per flight, using the same A310 ZERO-G as for scientific experiences. These flights are sold by Avico, are mainly operated from Bordeaux-Merignac,
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
, and intend to promote European space research, allowing public passengers to feel weightlessness.
Jean-François Clervoy Jean-François André Clervoy (born 19 November 1958) is a French engineer and a CNES and ESA astronaut. He is a veteran of three NASA Space Shuttle missions. Early life and education Clervoy was born 19 November 1958 in Longeville-lès-Metz, ...
, Chairman of Novespace and
ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (120 ...
astronaut, flies with these one-day astronauts on board A310 Zero-G. After the flight, he explains the quest of space and talks about the 3 space travels he did along his career. The aircraft has also been used for cinema purposes, with
Tom Cruise Thomas Cruise Mapother IV (born July 3, 1962), known professionally as Tom Cruise, is an American actor and producer. One of the world's highest-paid actors, he has received various accolades, including an Honorary Palme d'Or and three Go ...
and Annabelle Wallis for
the Mummy A mummy is an unusually well preserved corpse. Mummy or The Mummy may also refer to: Places *Mummy Range, a mountain range in the Rocky Mountains of northern Colorado in the United States *Mummy Cave, a rock shelter and archeological site in Par ...
in 2017. The
Zero Gravity Corporation Zero Gravity Corporation (also known as Zero-G, stylized as ''zero G'') is an American company based in Exploration Park, Florida, formerly of Fort Lauderdale, Florida, which operates weightless flights from United States airports. Unlike NASA ...
operates a modified
Boeing 727 The Boeing 727 is an American narrow-body airliner that was developed and produced by Boeing Commercial Airplanes. After the heavy 707 quad-jet was introduced in 1958, Boeing addressed the demand for shorter flight lengths from smaller airpo ...
which flies parabolic arcs to create 25–30 seconds of weightlessness.


Ground-based drop facilities

Ground-based facilities that produce weightless conditions for research purposes are typically referred to as
drop tube In physics and materials science, a drop tower or drop tube is a structure used to produce a controlled period of weightlessness for an object under study. Air bags, polystyrene pellets, and magnetic or mechanical brakes are sometimes used to a ...
s or drop towers. NASA's
Zero Gravity Research Facility The Zero Gravity Research Facility at the NASA Glenn Research Center in Cleveland, Ohio is a unique facility designed to perform tests in a reduced gravity environment. It has successfully supported research for the United States crewed spacecraft ...
, located at the
Glenn Research Center NASA John H. Glenn Research Center at Lewis Field is a NASA center within the cities of Brook Park and Cleveland between Cleveland Hopkins International Airport and the Rocky River Reservation of Cleveland Metroparks, with a subsidiary facilit ...
in Cleveland, Ohio, is a 145 m vertical shaft, largely below the ground, with an integral vacuum drop chamber, in which an experiment vehicle can have a free fall for a duration of 5.18 seconds, falling a distance of 132 m. The experiment vehicle is stopped in approximately 4.5 m of pellets of expanded polystyrene, experiencing a peak
deceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by t ...
rate of 65 ''g''. Also at NASA Glenn is the 2.2 Second Drop Tower, which has a drop distance of 24.1 m. Experiments are dropped in a drag shield in order to reduce the effects of air drag. The entire package is stopped in a 3.3 m tall air bag, at a peak deceleration rate of approximately 20 ''g''. While the Zero Gravity Facility conducts one or two drops per day, the 2.2 Second Drop Tower can conduct up to twelve drops per day. NASA's Marshall Space Flight Center hosts another drop tube facility that is 105 m tall and provides a 4.6 s free fall under near-
vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...
conditions. Other drop facilities worldwide include: *
Micro-Gravity Laboratory of Japan The term micro-g environment (also μg, often referred to by the term microgravity) is more or less synonymous with the terms ''weightlessness'' and ''zero-g'', but emphasising that g-forces are never exactly zero—just very small (on the ...
(MGLAB) – 4.5 s free fall * Experimental drop tube of the metallurgy department of
Grenoble lat, Gratianopolis , commune status = Prefecture and commune , image = Panorama grenoble.png , image size = , caption = From upper left: Panorama of the city, Grenoble’s cable cars, place Saint- ...
– 3.1 s free fall *
Fallturm Bremen Fallturm Bremen is a drop tower at the Center of Applied Space Technology and Microgravity at the University of Bremen in Bremen. It was built between 1988 and 1990, and includes a 122-metre-high drop tube (actual drop distance is 110 m), in whic ...
University of Bremen The University of Bremen (German: ''Universität Bremen'') is a public university in Bremen, Germany, with approximately 23,500 people from 115 countries. It is one of 11 institutions which were successful in the category "Institutional Strategi ...
in Bremen – 4.74 s free fall * Queensland University of Technology Drop Tower - 2.0 s free fall


Neutral buoyancy


Weightlessness in a spacecraft


Weightlessness at the center of a planet


Human health effects

Following the advent of space stations that can be inhabited for long periods, exposure to weightlessness has been demonstrated to have some deleterious effects on human health. Humans are well-adapted to the physical conditions at the surface of the Earth. In response to an extended period of weightlessness, various physiological systems begin to change and atrophy. Though these changes are usually temporary, long term health issues can result. The most common problem experienced by humans in the initial hours of weightlessness is known as space adaptation syndrome or SAS, commonly referred to as space sickness. Symptoms of SAS include
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 ...
and
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 nose. Vomiting can be the result of ailments like food poisoning, gastroenteri ...
,
vertigo Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...
, headaches,
lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...
, and overall malaise. The first case of SAS was reported by
cosmonaut 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 ...
Gherman Titov Gherman Stepanovich Titov (russian: Герман Степанович Титов; 11 September 1935 – 20 September 2000) was a Soviet cosmonaut who, on 6 August 1961, became the second human to orbit the Earth, aboard Vostok 2, preceded by Y ...
in 1961. Since then, roughly 45% of all people who have flown in space have suffered from this condition. The duration of space sickness varies, but in no case has it lasted for more than 72 hours, after which the body adjusts to the new environment.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
jokingly measures SAS using the "Garn scale", named for
United States Senator The United States Senate is the upper chamber of the United States Congress, with the House of Representatives being the lower chamber. Together they compose the national bicameral legislature of the United States. The composition and powe ...
Jake Garn Edwin Jacob "Jake" Garn (born October 12, 1932) is an American politician and member of the Republican Party who served as a United States senator representing Utah from 1974 to 1993. Garn became the first sitting member of Congress to fly in sp ...
, whose SAS during
STS-51-D STS-51-D was the 16th flight of NASA's Space Shuttle program, and the fourth flight of Space Shuttle ''Discovery''. The launch of STS-51-D from Kennedy Space Center (KSC), Florida, on April 12, 1985, was delayed by 55 minutes, after a boat st ...
was the worst on record. Accordingly, one "Garn" is equivalent to the most severe possible case of SAS. The most significant adverse effects of long-term weightlessness are muscle atrophy (see
Reduced muscle mass, strength and performance in space Even before the very beginning of human space exploration, serious and reasonable concerns were expressed about exposure of humans to the microgravity of space due to the potential systemic effects on terrestrially-evolved life forms adapted to G ...
for more information) and deterioration of the skeleton, or
spaceflight osteopenia Spaceflight osteopenia refers to the characteristic bone loss that occurs during spaceflight. Astronauts lose an average of more than 1% bone mass per month spent in space. There is concern that during long-duration flights, excessive bone loss ...
. These effects can be minimized through a regimen of exercise, such as cycling for example. Astronauts subject to long periods of weightlessness wear pants with elastic bands attached between waistband and cuffs to compress the leg bones and reduce osteopenia.Health Fitness
", Space Future
Other significant effects include fluid redistribution (causing the "moon-face" appearance typical of pictures of astronauts in weightlessness), a slowing of the cardiovascular system as blood flow decreases in response to a lack of gravity, a decreased production of
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, balance disorders, and a weakening of the
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...
. Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, excess flatulence, and puffiness of the face. These effects begin to reverse quickly upon return to the Earth. In addition, after long
space flight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in ...
missions, astronauts may experience severe
eyesight Visual perception is the ability to interpret the surrounding environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum reflect ...
problems. Such eyesight problems may be a major concern for future deep space flight missions, including a
crewed mission Human spaceflight (also referred to as manned spaceflight or crewed spaceflight) is spaceflight with a crew or passengers aboard a spacecraft, often with the spacecraft being operated directly by the onboard human crew. Spacecraft can also be ...
to the planet
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. Exposure to high levels of radiation may influence the development of atherosclerosis also. On December 31, 2012, a
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
-supported study reported that human spaceflight may harm the
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...
s of
astronauts 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 ...
and accelerate the onset of Alzheimer's disease. In October 2015, the
NASA Office of Inspector General The NASA Office of Inspector General (NASA OIG or OIG) is the inspector general office in the National Aeronautics and Space Administration, the space agency of the United States. The OIG's stated mission is to "prevent and detect crime, fraud, wa ...
issued a health hazards report related to human spaceflight, including a human mission to
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
.


Effects on non-human organisms

Russian scientists have observed differences between cockroaches conceived in space and their terrestrial counterparts. The space-conceived cockroaches grew more quickly, and also grew up to be faster and tougher. Chicken eggs that are put in microgravity two days after fertilization appear not to develop properly, whereas eggs put in microgravity more than a week after fertilization develop normally. A 2006 Space Shuttle experiment found that ''
Salmonella typhimurium ''Salmonella enterica'' subsp. ''enterica'' is a subspecies of ''Salmonella enterica'', the rod-shaped, flagellated, aerobic, Gram-negative bacterium. Many of the pathogenic serovars of the ''S. enterica'' species are in this subspecies, includin ...
'', a bacterium that can cause food poisoning, became more virulent when cultivated in space. On April 29, 2013, scientists in Rensselaer Polytechnic Institute, funded by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
, reported that, during
spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in o ...
on the
International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ( ...
, microbes seem to adapt to the
space environment Space environment is a branch of astronautics, aerospace engineering and space physics that seeks to understand and address conditions existing in space that affect the design and operation of spacecraft. A related subject, space weather, deals ...
in ways "not observed on Earth" and in ways that "can lead to increases in growth and
virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...
". Under certain test conditions, microbes have been observed to thrive in the near-weightlessness of space and to survive in the vacuum of outer space.


Technical adaptation in zero gravity


See also

*
Artificial 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 re ...
*
Clinostat A clinostat is a device which uses rotation to negate the effects of gravitational pull on plant growth (gravitropism) and development ( gravimorphism). It has also been used to study the effects of microgravity on cell cultures, animal embryo ...
*
Effect of spaceflight on the human body Venturing into the environment of space can have negative effects on the human body. Significant adverse effects of long-term weightlessness include muscle atrophy and deterioration of the skeleton ( spaceflight osteopenia). Other significant ef ...
* European Low Gravity Research Association (ELGRA) * Micro-g environment *
Microgravity University {{primary sources, date=December 2011 Microgravity University, also known as the Reduced Gravity Student Flight Opportunities Program (RGSFOP) was a program run by NASA which enables undergraduate university students to perform microgravity experi ...
* Space adaptation syndrome *
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 ...
*
Vomit Comet A reduced-gravity aircraft is a type of fixed-wing aircraft that provides brief near-weightless environments for training astronauts, conducting research and making gravity-free movie shots. Versions of such airplanes were operated by the NAS ...


Notes


References


External links


Weightlessness Flight with Zero-Gravity airplane

Microgravity Centre




at
HowStuffWorks HowStuffWorks is an American commercial infotainment website founded by professor and author Marshall Brain, to provide its target audience an insight into the way many things work. The site uses various media to explain complex concepts, termin ...

NASA - SpaceResearch - Human Physiology Research and the ISS: Staying Fit Along the Journey

Zero gravity chair use the concept of weightlessness
*
Why are astronauts weightless?
Video explanation of the fallacy of "zero gravity". {{Authority control Gravity Space medicine