Asteroid deviation strategies – Wikipedia

The mission of NASA DART launched at the end of 2021 is the first to experiment with a deviation method of a geocroiser asteroid by kinetic impact (view of artist of the spatial machine in approach to the asteroid on which it will crash) .

THE Asteroid deviation strategies are the methods that could potentially be used to divert an asteroid or a comet which would be on a collision trajectory with the earth (geocroisters objects) and whose size could produce damage deemed too important. Geocroisors are struggling at regular intervals our planet. If the smallest of these objects do not cause any damage, those whose size exceeds a few tens of meters can make many victims but their frequency is very low. Beyond a diameter of one kilometer, the impact can have planetary repercussions.

Since the end of the 1990s, this threat has been taken into account by certain government organizations, in particular by the American space agency, NASA which, as the European space agency, has set up a planetary defense program whose first objective was to launch observation programs intended to identify the geocroisters asteroids whose diameter is greater than a kilometer and then to 140 meters . Strategies to avoid a disaster have been developed. To prevent the impact must be deflected their trajectory. Several methods, which require being tested, have been identified: impactor, gravitational tractor, modification of the Yarkovsky effect, etc. NASA develops the DART mission which should make it possible to assess the effect of an impact on a small asteroid that has been launched the November 23, 2021 And who struck the September 26, 2022 The surface of the small dimorphos asteroid ( 160 meters of diameter), which orbit around the asteroid (65803) Didymos.

Geocroisters [ modifier | Modifier and code ]

The orbit of these asteroids or comets – also designated by their English acronym ( Near-Earth object ) – presents the particularity of cutting that of the earth or approaching it very closely.

A geocroiser object – also designated by their English acronym NEO ( Near-Earth object ) – is an asteroid or a comet of the solar system that its orbit around the sun brings at a distance from the terrestrial orbit, and therefore potentially near the earth. Given their mass and speed, geocroisters can cause a major human disaster – possibly planetary – even if the probability of such an impact is extremely low.

The threat constituted by these celestial objects began to be taken into account in the United States in the late 1990s. Observation campaigns carried out using terrestrial-based telescopes have been carried out since that time. In addition, NASA develops two space missions responsible for limiting the risk: Neosm is a space observatory devoted for the first time to the detection of these objects (launch date around 2025) while DART (launch in 2021) must test the method of The impactor to divert an asteroid from a collision trajectory with the earth.

Observation programs detect more than 2,000 new geocroisters objects: in September 2019 , the total number of these objects reached the figure of 21,000 including a hundred comets (NEC, Near Earth Comets ) the balance being made up of geocroisters asteroids (NEA, Near Earth Asteroids ). The census of the largest objects (more than a kilometer in diameter) is practically completed but only 40% of asteroids of more than 140 meters were discovered.

Consequences of an impact [ modifier | Modifier and code ]

Artist’s illustration of a major impact between an asteroid and the earth.

A sufficiently massive, asteroid or comet impactor, when he collides with the earth, can cause gigantic tsunamis or raise huge amounts of dust in the atmosphere, blocking solar rays and causing an artificial winter. There is 65 millions years, a collision between the earth and an object of approximately 10 km of diameter would have led to the extinction of the Cretaceous.

In theory, the probability of such an event is weak, but recent events, such as the collision of the comet Shoemaker- Levy 9 with Jupiter or the threat of the geocroiser asteroid (99942) Apophis (at a time classified in Level 4 On the Turin scale), drew the attention of scientists – and the public – to this threat. Technological advances make it possible to imagine certain defense options.

Diviation methods of geocroisters objects [ modifier | Modifier and code ]

Several methods have been imagined to divert a geocroiser object in order to prevent it from crashing on earth but none of them, in 2021, has been the subject of real experimentation. All these methods aims to slightly modify the orbit of the geocroiser object by applying a punctual thrust on the celestial body. It is enough that the geocroiser object is modified in order to cut the terrestrial orbit 7 minutes (Time put by the earth to cover a distance equal to its diameter) earlier or later to avoid impact. We distinguish impulsive techniques which use a kinetic impactor moving at high speed or a nuclear bomb, traction techniques or slow pushing. If the thrust is punctual (impulsive technique), it is preferable to apply it when the body is near its aphelia (apogee) because it is then more effective. If, on the contrary, we choose to exercise a lower but continuous push, it must be applied long before the early collision. The more the trajectory correction begins early, the less it needs to be important. The field of application of a method depends on the diameter/mass of the geocroiser and the time available: certain methods make it possible to move larger objects (energy transfer of the table on the right). Slow methods require having several years or decades to make the effect produced sufficient. In addition, slow -in -law methods have an average to low technical maturity unlike impulsive techniques based on proven techniques ^{[ 2 ] , [ 3 ]} .

The main methods studied are as follows:

The first method of deviation, tested by the NASA Dart mission launched in 2021 and which has already been implemented with a completely different objective (analysis of the structure and the composition of a comet) by the space probe Deep Impact of the NASA, consists in launching a spacecraft against the geocroiser object. The speed of the asteroid is modified due to the law of the conservation of the movement:

${DisplayStyle m_ {1} Times {thing {v_ {1}}}+m_ {2} Times {thing {v_ {2}}} = (m_ {1}+m_ {2}) }}}}$

with

${displaystyle M_{1}}$

The Masse de l’en Engin Spatial,

${displaystyle M_{2}}$

the mass of the celestial body,

${DisplayStyle {thing {v_ {1}}}}$

the speed vector of the space machine,

${DisplayStyle {thing {v_ {2}}}}$

the vector speed of the celestial body before impact and

${DisplayStyle {thing {v_ {3}}}}$

The vector speed of the celestial body (with the spacecraft crushed on it) after the impact.

The results of the impact method have several unknowns. The main thing stems from our limited knowledge of the structure and composition of asteroids and the incidence of these characteristics on the transmission of kinetic energy. Spatial missions Hayabusa 2 And Osiris-Rex, who studied carbon asteroids, discovered that these worlds were very porous with a density close to that of water. The energy of an impactor hitting this type of asteroid will be partly dissipated by the crushing of the porous parts. The role of this factor on the effectiveness of an impact is poorly modeled ^{[ 4 ]} . Below a notice period of a few months (depends on the mass of the geocroiser), there is no enough time to modify the trajectory using this method because it is necessary to have an impact of a mass incompatible with the capabilities of a launcher (to defly a geocroiser of 130 meters of diameter having a density of 1.5 by producing the impact three months in advance, the impactor must have a mass of 294 tonnes ) ^{[ 5 ]} .

DART: First mission testing a deviation method [ modifier | Modifier and code ]

The American space agency, NASA launched end November 2021 The DART mission which must test for the first time a method allowing to deviate an asteroid capable of crashing on the earth (geocroiser asteroid). The objective is to assess the use of the kinetic impact of a spacecraft to modify the trajectory of the asteroid so that it avoids the earth. The mission is part of the planetary defense program of the American space agency set up from the late 1990s and which also includes the exhaustive census of geocroisters asteroids presenting a significant risk by their size using Land and spatial observatories.

To assess the kinetic impact method, 550 kilograms Dart space probe will be launched at the speed of 23 700 km/h on the surface of the small dimorphos asteroid ( 160 meters of diameter), which orbit around the asteroid (65803) Didymos. The modification of the orbital period of dimorphos around Didymos resulting from the impact must make it possible to refine the existing models by specifying the incidence today poorly mastered parameters such as the structure of the hit object (porosity), the Nature of the materials of which it is formed as well as the value of the additional thrust provided by the ejectas projected in space. None of the two asteroids is on an impact trajectory with the earth before as after this test.

Dart is a spacecraft of 610 kilograms At the launch equipped with a camera and an ion engine. It is developed by the APL laboratory. It is placed on a heliocentric orbit the November 23, 2021 and must hit Dimorphos fine September 2022 . Terrestrial observatories as well as the liciacube nano-satellite accompanying the main space machine will collect images and data allowing to measure the result of the impact which takes place September 26, 2022 To 23 h  14 (UTC) .

Additional observations must be made on site by Hera , mission developed by the European space agency which must take off in 2024 and must be placed in orbit around Didymos around 2026.

• Method of the kinetic impactor
• 

  Procedure of the DART mission intended to test a method of modifying the orbit of a geocroiser object.

Chinese projects [ modifier | Modifier and code ]

China plans in 2022 to develop a mission allowing it to master the technologies of the kinetic impact by developing a mission similar to the DART/ Hera . Developed by the Chinese CASC aerospace conglomerate, the mission, temporarily baptized Near-Earth Asteroid Defence System Experimental Test , would include two separate spacecrafts, the first being responsible for crashing on the 2020 PN1 asteroid (ATEN type geocroiser) whose diameter is between 10 and 50 meters, the second being responsible for observing the course of the ‘ impact and its consequences. The mission will be launched in 2026 ^{[ 6 ]} .

To achieve asteroids really dangerous for human civilization, those whose diameter exceeds 400 meters, it is necessary to strongly increase the mass of the kinetic impactor. The National Center for Spatial Sciences (NSSC) and two other Chinese research centers presented in 2021 a concept called Aki ( Assembled Kinetic Impactor ): For this mission the second floor of the long walking rocket 5 remains united with that of the kinetic impactor which adds 8.75 tonnes to the 2.5 tonnes of the impactor. However, between 10 and 20 AKI impactors would be necessary to deflect the Bénou asteroid 500 meters in diameter. Another project proposed by the same institutions and baptized Eki ( Enhanced Kinetic Impactor ) would be spatial which would take a rock of 200 tonnes on the surface of an asteroid using a capture device similar to that provided for the American mission Asteroid Redirect Mission (canceled). The rock would then be placed on a collision trajectory with the asteroid to deviate. The Eki space probe would have a total mass of 8 tonnes and would use ion engines. According to the calculations of its designers, the EKI mission lasting 4 years would be capable of deviating an asteroid of the Apophis size but would require a lot of time before the date of the impact ^{[ 6 ]} .

Another very futuristic Chinese study is to build a line of defense against geocroisters asteroids at the level of the moon. A telescope would be installed at each pole of the moon and three interceptors would be pre-positioned at the points of Lagrange L3, L4 and L5 of the Earth-Moon system. Such a system would deviate from asteroids (small) with a notice of only a week ^{[ 6 ]} .

A method popularized by cinema (Armageddon) is to cause a nuclear explosion intended to fragment the asteroid. This solution is technically achievable but it has major drawbacks. Its effects are uncontrollable and its effectiveness remains to be demonstrated. It would be a solution to consider as a last resort ^{[ 7 ]} .

A more effective method would consist in exploding a nuclear load on the surface or at low distance from the geocroiser so as to transmit an impulse without fragment it. This technique raises two problems: on the one hand, it is necessary to control the vector of the impulse generated and on the other hand the explosion of a nuclear charge can raise political problems. This is a solution to consider when the notice period is very low.

Several methods based on a slow thrust exercised over long periods (years/decades) are envisaged. They can only be implemented on small geocroisors provided that they have a significant period. The maturity of the technologies used is low:

• The gravitational tractor is a method that uses mutual gravitational attraction between the geocroiser and a spacecraft. The latter is maintained at a constant distance from the geocroiseur using an electric propulsion. By its mass it exerts a very light force on the asteroid which in the duration sufficiently modifies the orbit. A spacecraft 20 tonnes by this method could sufficiently deflect an asteroid from 200 meters by staying for a year near it provided that it is 20 years Before the planned impact ^{[ 8 ]} .
• The use of the Yarkovsky effect, which is a force produced by the gap between solar absorption and thermal emission by radiation. This force which constantly contributes to shaping the orbit of the geocroiseur can be modified for example by interposing a screen between the sun and the asteroid or by modifying the albedo of it (for example by depositing a black or white coating on its surface). The intensity of this force is very low but it can over time allow you to obtain the desired deviation.
• Another method would be to install a propulsive system on a small asteroid to modify its trajectory and hit the geocroiser threatening the earth. This method is however complex to implement and its effects are not controllable.
• Suffering deviation consists in positioning a small distance spatial machine of the asteroid and directing an ion engine towards the surface of the asteroid. The ejected ions rebound on the surface of the asteroid and exert a push on it. The spacecraft has another propulsion directed in the opposite direction to neutralize the movement produced by the first engine. With an ion engine having a specific pulse of 3,000 seconds, a deviation can be obtained after a year with a space machine of 2 tonnes . If the engine has a specific pulse of 10,000 seconds, the mass of the space machine can be divided by two ^{[ 8 ]} .

As a last resort, if none of the deviation methods can operate (mainly because we do not have the necessary time), we can try to destroy the geocroiser object using a nuclear bomb so that debris are small enough not to present a threat to the earth in turn.

• (in) Committee to Review Near-Earth-Object Surveys and Hazard Mitigation Strategies Space Studies Board, Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies , THE NATIONAL ACADEMIES PRESS, 2010 , 152 p. (ISBN  978-0-309-15721-6 , read online ) – very detailed report of 2010 produced by the Academy of American Sciences evaluating the risks of geocroisters and means allowing them to be treated.
• (in) NASA, Office of Science and Technology Policy, Federal Emergency Management Agency,…, The National Near-Earth Object Preparedness Strategy and Action Plan (Strategy and Action Plan) , White House, 2018 , 23 p. ( read online ) -Strategic plan of the United States in the field of planetary defense for the next 10 years.
• (in) Committee on Science, Space, and Technology (House of Representatives), Threats from Space: A Review of U.S. Government Efforts to Track and Mitigate Asteroids and Meteors (Part I & Part II) , US Congress, two thousand and thirteen , 195 p. ( read online ) – Auditions on the theme of identifying the threats of the geocroisors and the implementation of against measures.
• (in) In Near-Earth Object Survey and Deflection Analysis of Alternatives (rapport au Congrès) , In, in, 2007 , 28 p. ( read online ) – Report established by NASA for the American Congress identifying the various scenarios of detecting geocroisters and the methods allowing to divert them.

• Planetary defense
• Potentially dangerous object (pha)
• Geocroiser object (neo), potentially dangerous object (pha), geocroiser asteroid
• Neowise, Neosm Spatial Missions devoted to the detection of geocroisors
• Catalina Sky Survey, Pan-Starrs, LSST Terrestrial Observatory devoted to the detection of geocroisors
• Don Quixote, Aida, Hera, Dart Missions intended to test the deflection of geocroisters objects
• Turin scale, Palermus scale risk assessment
• Chicxulub (extinction of Cretaceous), Meteor Crater, Toungouska, Tcheliabinsk geocroisters having struck the earth
• List of geocroisters asteroids
• Impactor, impact crater, list of impact craters on earth

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