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The Kessler syndrome (also called the Kessler effect, collisional cascading, or ablation cascade), proposed by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
scientist
Donald J. Kessler Donald J. Kessler (born 1940) is an American astrophysicist and former NASA scientist known for his studies regarding space debris. Early life and education Kessler grew up in Texas. He served in the US Army in the Air Defense Command. He at ...
in 1978, is a scenario in which the density of objects 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 m ...
(LEO) due to
space pollution Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacecr ...
is high enough that collisions between objects could cause a cascade in which each collision generates
space debris Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacec ...
that increases the likelihood of further collisions. In 2009 Kessler wrote that modeling results had concluded that the debris environment was already unstable, "such that any attempt to achieve a growth-free small debris environment by eliminating sources of past debris will likely fail because fragments from future collisions will be generated faster than atmospheric drag will remove them". One implication is that the distribution of debris in orbit could render space activities and the use of
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 radioiso ...
s in specific orbital ranges difficult for many generations.


History


NORAD, Gabbard and Kessler

Willy Ley Willy or Willie is a masculine, male given name, often a diminutive form of William (given name), William or Wilhelm (name), Wilhelm, and occasionally a nickname. It may refer to: People Given name or nickname * Willie Aames (born 1960), American ...
predicted in 1960 that "In time, a number of such accidentally too-lucky shots will accumulate in space and will have to be removed when the era of manned space flight arrives". After the launch of
Sputnik 1 Sputnik 1 (; see § Etymology) was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program. It sent a radio signal back to Earth for ...
in 1957, the
North American Aerospace Defense Command North American Aerospace Defense Command (NORAD ), known until March 1981 as the North American Air Defense Command, is a combined organization of the United States and Canada that provides aerospace warning, air sovereignty, and protection ...
(NORAD) began compiling a database (the Space Object Catalog) of all known rocket launches and objects reaching orbit: satellites, protective shields and upper- and lower-stage booster rockets.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
later published modified versions of the database in
two-line element set A two-line element set (TLE) is a data format encoding a list of orbital elements of an Earth-orbiting object for a given point in time, the ''epoch''. Using a suitable prediction formula, the state (position and velocity) at any point in the past ...
, and during the early 1980s the CelesTrak
bulletin board system A bulletin board system (BBS), also called computer bulletin board service (CBBS), is a computer server running software that allows users to connect to the system using a terminal program. Once logged in, the user can perform functions such ...
re-published them., 2-line elements dating to 1980. The trackers who fed the database were aware of other objects in orbit, many of which were the result of in-orbit explosions.Schefter, p. 48. Some were deliberately caused during the 1960s
anti-satellite weapon Anti-satellite weapons (ASAT) are space weapons designed to incapacitate or destroy satellites for strategic or tactical purposes. Several nations possess operational ASAT systems. Although no ASAT system has been utilised in warfare, a few ...
(ASAT) testing, and others were the result of rocket stages blowing up in orbit as leftover propellant expanded and ruptured their tanks. To improve tracking, NORAD employee John Gabbard kept a separate database. Studying the explosions, Gabbard developed a technique for predicting the orbital paths of their products, and Gabbard diagrams (or plots) are now widely used. These studies were used to improve the modeling of orbital evolution and decay. When the NORAD database became publicly available during the 1970s, NASA scientist Donald J. Kessler applied the technique developed for the asteroid-belt study to the database of known objects. In June 1978, Kessler and Burton Cour-Palais co-authored "Collision Frequency of Artificial Satellites: The Creation of a Debris Belt", demonstrating that the process controlling asteroid evolution would cause a similar collision process in LEO in decades rather than billions of years. They concluded that by about 2000, space debris would outpace micrometeoroids as the primary ablative risk to orbiting spacecraft. At the time, it was widely thought that drag from the
upper atmosphere Upper atmosphere is a collective term that refers to various layers of the atmosphere of the Earth above the troposphere and corresponding regions of the atmospheres of other planets, and includes: * The mesosphere, which on Earth lies between th ...
would de-orbit debris faster than it was created. However, Gabbard was aware that the number and type of objects in space were under-represented in the NORAD data and was familiar with its behavior. In an interview shortly after the publication of the 1978 paper, Gabbard coined the term ''Kessler syndrome'' to refer to the accumulation of debris; it became widely used after its appearance in a 1982 ''
Popular Science ''Popular Science'' (also known as ''PopSci'') is an American digital magazine carrying popular science content, which refers to articles for the general reader on science and technology subjects. ''Popular Science'' has won over 58 awards, incl ...
'' article,Schefter which won the Aviation-Space Writers Association 1982 National Journalism Award.


Follow-up studies

The lack of hard data about space debris prompted a series of studies to better characterize the LEO environment. In October 1979,
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
provided Kessler with funding for further studies. Several approaches were used by these studies. Optical telescopes and short-wavelength radar were used to measure the number and size of space objects, and these measurements demonstrated that the published population count was at least 50% too low.Kessler 1991, p. 65. Before this, it was believed that the NORAD database accounted for the majority of large objects in orbit. Some objects (typically, US military spacecraft) were found to be omitted from the NORAD list, and others were not included because they were considered unimportant. The list could not easily account for objects under in size—in particular, debris from exploding rocket stages and several 1960s anti-satellite tests. Returned spacecraft were microscopically examined for small impacts, and sections of
Skylab Skylab was the first United States space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three separate three-astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Major operations ...
and the
Apollo Command/Service Module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functioned as a mother sh ...
which were recovered were found to be pitted. Each study indicated that the debris flux was higher than expected and debris was the primary source of micrometeoroids and orbital debris collisions in space. LEO already demonstrated the Kessler syndrome. In 1978, Kessler found that 42 percent of cataloged debris was the result of 19 events, primarily explosions of spent rocket stages (especially US Delta rockets).Kessler 1981 He discovered this by first identifying those launches that were described as having a large number of objects associated with a payload, then researching the literature to determine the rockets used in the launch. In 1979, this finding resulted in establishment of the NASA Orbital Debris Program after a briefing to NASA senior management, overturning the previously held belief that most unknown debris was from old ASAT tests, not from US upper stage rocket explosions that could seemingly be easily managed by depleting the unused fuel from the upper stage Delta rocket following the payload injection. Beginning in 1986, when it was discovered that other international agencies were possibly experiencing the same type of problem, NASA expanded its program to include international agencies, the first being the European Space Agency. A number of other Delta components in orbit (Delta was a workhorse of the US space program) had not yet exploded.


A new Kessler syndrome

During the 1980s, the US Air Force (USAF) conducted an experimental program to determine what would happen if debris collided with satellites or other debris. The study demonstrated that the process differed from micrometeoroid collisions, with large chunks of debris created which would become collision threats. In 1991, Kessler published "Collisional cascading: The limits of population growth in low Earth orbit"Kessler 1991 with the best data then available. Citing the USAF conclusions about creation of debris, he wrote that although almost all debris objects (such as paint flecks) were lightweight, most of its mass was in debris about or heavier. This mass could destroy a spacecraft on impact, creating more debris in the critical-mass area.Kessler 1991, p. 63. According to the National Academy of Sciences:
A 1 kg object impacting at 10 km/s, for example, is probably capable of catastrophically breaking up a 1,000 kg spacecraft if it strikes a high-density element in the spacecraft. In such a breakup, numerous fragments larger than 1 kg would be created.
Kessler's analysis divided the problem into three parts. With a low-enough density, the addition of debris by impacts is slower than their decay rate and the problem is not significant. Beyond that is a critical density, where additional debris leads to additional collisions. At densities beyond this critical mass production exceeds decay, leading to a cascading
chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. Chain reactions are one way that sys ...
reducing the orbiting population to small objects (several centimeters in size) and increasing the hazard of space activity. This chain reaction is known as the Kessler syndrome. In an early 2009 historical overview, Kessler summed up the situation:
Aggressive space activities without adequate safeguards could significantly shorten the time between collisions and produce an intolerable hazard to future spacecraft. Some of the most environmentally dangerous activities in space include large constellations such as those initially proposed by the Strategic Defense Initiative in the mid-1980s, large structures such as those considered in the late-1970s for building solar power stations in Earth orbit, and anti-satellite warfare using systems tested by the USSR, the US, and China over the past 30 years. Such aggressive activities could set up a situation where a single satellite failure could lead to cascading failures of many satellites in a period much shorter than years.


Anti-satellite missile tests

In 1985, the first anti-satellite (ASAT) missile was used in the destruction of a satellite. The American 1985 ASM-135 ASAT test was carried out, in which the Solwind P78-1 satellite flying at an altitude of 555 kilometres was struck by the 14 kilogram payload at a velocity of 24,000 kilometres per hour (15,000 mph; 6.7 km/s). When NASA learned of U.S. Air Force plans for the Solwind ASAT test, they modeled the effects of the test and determined that debris produced by the collision would still be in orbit late into the 1990s. It would force NASA to enhance debris shielding for its planned space station. On 11 January 2007, China conducted an anti-satellite missile test in which one of their FY-1C weather satellites was chosen as the target. The collision occurred at an altitude of 865 kilometres, when the satellite with a mass of 750 kilograms was struck in a head-on-collision by a kinetic payload traveling with a speed of 8 km/s (18,000 mph) in the opposite direction. The resulting debris orbits the
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 sur ...
with a mean altitude above 850 kilometres, and will likely remain in orbit for decades or centuries. The destruction of the Kosmos 1408 satellite by a Russian ASAT missile on November 15, 2021, has created a large debris cloud, with 1500 pieces of debris being tracked and an estimated hundreds of thousands of pieces too small to track. Since the satellite was in a
polar orbit A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It has an inclination of about ...
, and its debris has spread out between the altitudes of 300 km and 1000 km, it could potentially collide with any LEO satellite, including the
International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...
and the Chinese Space Station (Tiangong).


Debris generation and destruction

Every satellite,
space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; o ...
, and
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 ...
has the potential to produce
space debris Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacec ...
. The theoretical cascading Kessler syndrome becomes more likely as satellites in orbit increase in number. As of 2014, there were about 2,000 commercial and government satellites orbiting the earth, and more than 4000. It is estimated that there are 600,000 pieces of space junk ranging from , and 23,000 larger than that. On average one satellite is destroyed by collision with space junk each year. there had been four collisions between catalogued objects, including a collision between two satellites in 2009.
Orbital decay Orbital decay is a gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods. These orbiting bodies can be a planet and its satellite, a star and any object orbiting it, or ...
is much slower at altitudes where atmospheric drag is insignificant. Slight
atmospheric drag In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding flu ...
, lunar
perturbation Perturbation or perturb may refer to: * Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly * Perturbation (geology), changes in the nature of alluvial deposits over time * Perturbat ...
, and
solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
drag can gradually bring debris down to lower altitudes where fragments finally re-enter, but this process can take millennia at very high altitudes.


Implications

The Kessler syndrome is troublesome because of the
domino effect A domino effect or chain reaction is the cumulative effect generated when a particular event triggers a chain of similar events. This term is best known as a mechanical effect and is used as an analogy to a falling row of dominoes. It typically ...
and feedback runaway wherein impacts between objects of sizable mass
spall Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...
off debris from the force of the collision. The fragments can then hit other objects, producing even more space debris: if a large enough collision or explosion were to occur, such as between a space station and a defunct satellite, or as the result of hostile actions in space, then the resulting debris cascade could make prospects for long-term viability of satellites in particular low Earth orbits extremely low. However, even a catastrophic Kessler scenario at LEO would pose minimal risk for launches continuing past LEO, or satellites travelling at
medium Earth orbit A medium Earth orbit (MEO) is an Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between above sea level.
(MEO) or
geosynchronous orbit A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbita ...
(GEO). The catastrophic scenarios predict an increase in the number of collisions per year, as opposed to a physically impassable barrier to space exploration that occurs in higher orbits.


Avoidance and reduction

Designers of a new vehicle or satellite are frequently required by the
ITU The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Union ...
to demonstrate that it can be safely disposed of at the end of its life, for example by use of a controlled
atmospheric reentry Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the ...
system or a boost into a
graveyard orbit A graveyard orbit, also called a junk orbit or disposal orbit, is an orbit that lies away from common operational orbits. One significant graveyard orbit is a supersynchronous orbit well beyond geosynchronous orbit. Some satellites are moved into ...
. For US launches or satellites that will have broadcast to US territories—in order to obtain a license to provide telecommunications services in the United States—the
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdicti ...
(FCC) required all geostationary satellites launched after 18 March 2002 to commit to moving to a graveyard orbit at the end of their operational life. US government regulations similarly require a plan to dispose of satellites after the end of their mission: atmospheric re-entry, movement to a storage orbit, or direct retrieval. A proposed energy-efficient means of
deorbit Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entr ...
ing a spacecraft from MEO is to shift it to an orbit in an unstable
resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscil ...
with the Sun or Moon that speeds up orbital decay. One technology proposed to help deal with fragments from in size is the laser broom, a proposed multimegawatt land-based laser that could deorbit debris: the side of the debris hit by the laser would
ablate Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft material for ...
and create a thrust that would change the eccentricity of the remains of the fragment until it would re-enter and be destroyed harmlessly.


Potential triggers

The
Envisat Envisat ("Environmental Satellite") is a large inactive Earth-observing satellite which is still in orbit and now considered space debris. Operated by the European Space Agency (ESA), it was the world's largest civilian Earth observation satell ...
satellite is a large, inactive satellite with a mass of that orbits at , an altitude where the debris environment is the greatest—two catalogued objects can be expected to pass within about of Envisat every year—and likely to increase. Don Kessler predicted in 2012 that it could easily become a major debris contributor from a collision during the next 150 years that it will remain in orbit.
SpaceX Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal o ...
's
Starlink Starlink is a satellite internet constellation operated by SpaceX, providing satellite Internet access coverage to 45 countries. It also aims for global mobile phone service after 2023. SpaceX started launching Starlink satellites in 2019. As ...
program raises concern among many experts about significantly worsening the possibility of Kessler Syndrome due to the large number of satellites the program aims to place in LEO, as the program's goal will more than double the satellites currently in LEO. In response to these concerns, SpaceX said that a large part of Starlink satellites are launched at a lower altitude of to achieve lower latency (versus as originally planned), and failed satellites or debris are thus expected to deorbit within five years even without propulsion, due to atmospheric drag.


In fiction

* The 2013 film ''
Gravity 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 stro ...
'' features a Kessler syndrome catastrophe as the inciting incident of the story, when Russia shoots down an old satellite. *
Neal Stephenson Neal Town Stephenson (born October 31, 1959) is an American writer known for his works of speculative fiction. His novels have been categorized as science fiction, historical fiction, cyberpunk, postcyberpunk, and baroque. Stephenson's work e ...
's 2015 novel '' Seveneves'' begins with the unexplained explosion of the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
into seven large pieces, the subsequent creation of a cloud of debris by Kessler syndrome collisions, and the eventual bombardment of Earth's surface by lunar meteoroids.


See also

* 1961 and 1963 * 1985 ASM-135 ASAT test – 1985 United States anti-satellite missile test * * * anti-satellite missile test * * * * * *


Citations


General and cited references

* Donald Kessler (Kessler 1991)
"Collisional Cascading: The Limits of Population Growth in Low Earth Orbit"
''Advances in Space Research'', Volume 11 Number 12 (December 1991), pp. 63–66. * Donald Kessler (Kessler 1971), "Estimate of Particle Densities and Collision Danger for Spacecraft Moving Through the Asteroid Belt", ''Physical Studies of Minor Planets'', NASA SP-267, 1971, pp. 595–605.
Bibcode The bibcode (also known as the refcode) is a compact identifier used by several astronomical data systems to uniquely specify literature references. Adoption The Bibliographic Reference Code (refcode) was originally developed to be used in SIM ...
br>1971NASSP.267..595K
* Donald Kessler (Kessler 2009)

8 March 2009. * Donald Kessler (Kessler 1981)
"Sources of Orbital Debris and the Projected Environment for Future Spacecraft"
''Journal of Spacecraft'', Volume 16 Number 4 (July–August 1981), pp. 357–60. * Donald Kessler and Burton Cour-Palais (Kessler 1978)
"Collision Frequency of Artificial Satellites: The Creation of a Debris Belt"
''Journal of Geophysical Research'', Volume 81, Number A6 (1 June 1978), pp. 2637–46. * Donald Kessler and Phillip Anz-Meador
"Critical Number of Spacecraft in Low Earth Orbit: Using Fragmentation Data to Evaluate the Stability of the Orbital Debris Environment"
Presented and the Third European Conference on Space Debris, March 2001. * (Technical), "Orbital Debris: A Technical Assessment" ''National Academy of Sciences'', 1995. . * Jim Schefter
"The Growing Peril of Space Debris"
''Popular Science'', July 1982, pp. 48–51.


Further reading

* * An article in the July 2009 issue of ''
Popular Mechanics ''Popular Mechanics'' (sometimes PM or PopMech) is a magazine of popular science and technology, featuring automotive, home, outdoor, electronics, science, do-it-yourself, and technology topics. Military topics, aviation and transportation o ...
'' by Glenn Harlan Reynolds discusses the Kessler syndrome in regards to the February
2009 satellite collision On February 10, 2009, two communications satellites—the active commercial Iridium 33 and the derelict Russian military Kosmos 2251—accidentally collided at a speed of and an altitude of above the Taymyr Peninsula in Siberia. It was the fi ...
and how international law may need to address the problem to help prevent future incidents: Reynolds, G. H. (2009, July). "Collision course". ''Popular Mechanics'', pp. 50–52. * Documentary: ''Collision point: The Race to Clean Up Space'' (length: 22 minutes 28 seconds), included in the extra material on the
Blu-ray Disc The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital optical disc data storage format. It was invented and developed in 2005 and released on June 20, 2006 worldwide. It is designed to supersede the DVD format, and capable of sto ...
for the film ''Gravity''.


External links


Donald Kessler's Web Page
at uwo.ca
Orbiting Satellites in real time
at stuffin.space *

at lasp.colorado.edu * * * *
Aggregated public information research on space debris, graveyard orbits, etc.
* {{cite news, url= http://hosted2.ap.org/txash/f7ded15e4d4846268a17b79c1c4b7cb8/Article_2011-09-01-Space%20Junk/id-a08163f140094ef8ab62a3cf4a6d0826 , title= Space junk littering orbit; might need cleaning up, publisher= Associated Press , date= 1 September 2011
"How space debris threatens modern life"
''Financial Times''. 8 June 2022. Meteorological hypotheses Pollution Space hazards Space warfare 1978 neologisms