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There have been 22 extinction events of varying degrees on Earth, at least 10 of which have been caused by near-Earth asteroid impacts on Earth.
This article was preferentially published from the journal of the Chinese Academy of Engineering, China Engineering Science, No. 2, 2022
Author: Wu Weiren, Gong Zizheng, Tang Yuhua, Zhang Pinliang
Source: Research on the Risk Response Strategy of Near-Earth Asteroid Impact[J].Chinese Journal of Engineering Science,2022,24(2).
Editor's Note
A near-Earth asteroid (NEA) is an asteroid whose orbit intersects that of earth. There have been 22 extinction events of varying degrees on Earth, at least 10 of which have been caused by NEA impacts on Earth. The impact of a near-Earth asteroid on Earth is a major potential threat to humanity for a long time. Preventing the risk of near-Earth asteroid impacts is related to global security and the survival of human civilization, and the actual needs of related research are urgent and of far-reaching strategic significance.
Recently, the scientific research team of Academician Wu Weiren of the Chinese Academy of Engineering published the article "Research on the Risk Response Strategy of Near-Earth Asteroid Impact" in the journal of the Chinese Academy of Engineering, China Engineering Science, No. 2, 2022. This paper expounds the hazards of near-Earth asteroid impacts and the risk of impacts on the Earth, judges the significance of active response, systematically analyzes the current international research trend of near-Earth asteroid impact risk response, covering response processes, monitoring and early warning, impact disaster assessment, on-orbit disposal, etc., and comprehensively summarizes the basic progress and shortcomings of continental near-Earth asteroid impact risk response. On this basis, the research puts forward the development goals and system composition of the mainland to deal with the risk of near-Earth asteroid impact, and demonstrates the formation of key tasks such as monitoring and early warning, on-orbit disposal, disaster rescue, as well as basic research and international cooperation. The article suggests that we strengthen the top-level design and long-term planning of impact risk response capabilities, efficiently establish a "cohesive and outreach" impact risk response business system, quickly form impact risk response capabilities and innovation capabilities, and strive to build a community of human destiny in the field of planetary defense, so as to develop a planetary defense system that adapts to the characteristics of national conditions and is "accurate monitoring, reliable early warning, effective response, and strong rescue".
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I. Introduction
In astronomy, asteroids with orbital perihelion distances within 1.3 AU (1 AU = 1.496 ×108 km) are called near-Earth asteroids (NEAs). As of March 7, 2022, a total of 28 464 NEA have been discovered, of which 10 024 are larger than 140 m in diameter, 887 are larger than 1 km in diameter, and 2263 are potentially dangerous. NEA is dimly lit, widely distributed, difficult to detect, and its orbit is susceptible to change by the pull of large planets; it may intersect with Earth and have a certain suddenness of impact on Earth.
Historically, NEA impacts on Earth have occurred frequently. There have been 22 extinction events of varying degrees on Earth, at least 10 of which have been caused by NEA impacts on Earth. On February 15, 2013, a NEA with a diameter of about 18 m and a mass of about 7,000 t exploded at a height of about 30 km in the Chelyabinsk region of Russia at a speed of 18.6 km/s, causing personal injury and property damage. In 2021 alone, about 1,600 NEA flyby events occurred around the world, and 29 NEA were observed entering the Earth's atmosphere; fire meteor events also occurred in Zhumadian City, Henan Province, on the mainland.
NEA flies to the earth, there will be an air explosion in the atmosphere, the impact on the surface may cause earthquakes, tsunamis, volcanic eruptions, may also lead to global climate and environmental catastrophes, and even cause global extinction and civilization disappearance; as a major potential threat facing mankind for a long time, it needs to be jointly dealt with by all countries in the world; and it also brings major scientific and technological challenges to the international space community, the astronomical community and other fields. Regarding the NEA impact risk response, it is generally referred to internationally as planetary defense. The 1994 comet-wood impact event and the 2013 CHELYABINSK NEA impact in Russia have all contributed to the general attention of the international community, such as the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS), governmental and non-governmental levels have established planetary defense organizations to actively respond to them. In 1995, the United Nations convened for the first time the International Symposium on "Prevention of Neo-Earth Objects From Hitting the Earth". In 2014, the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG) were established under the framework of UNCOPUOS. In 2016, the United Nations General Assembly designated 30 June as International Minor Planet Day to guide the public to better understand the potential threat of the NEA to The Planet. Since 2009, the International Academy of Astronautics and the United Nations Department for Outer Space Affairs (UNSO) have regularly held the International Planetary Defense Congress (PDC). At the government level, the United States established the Office of Planetary Defense Coordination (PDCO) (2016), issued the National Neo-Object Response Strategy and Action Plan (2018), aimed at improving the NEA's ability to detect, track, characterize and develop NEA deflection and destruction technologies, and issued the "Report on the Emergency Agreement on the Threat of Near-Earth Object Impacts" (2021); Germany, the United Kingdom, Russia, Japan and other countries have established the Near-Earth Object Monitoring and Early Warning Defense Center.
In contrast, the mainland NEA impact risk response work started late, the research work is mostly spontaneous, sporadic, scattered, lack of comprehensive deployment planning and special support channels, resulting in a weak foundation, the bottom of the international contribution rate, and the small international discourse power; the gap with the dominant countries shows a widening trend, which is not conducive to national security, but also affects the independent decision-making and dominance in the face of the NEA impact threat, which is a major event of global security, and the image of a responsible and responsible big country, building a scientific and technological power, The international status of the space powers is not commensurate.
Since 2021, the China National Space Administration, together with relevant ministries and commissions, has launched the demonstration of the medium- and long-term development plan for the response to NEA impact risks in the mainland, aiming to systematically strengthen the NEA impact risk response and disposal capabilities. As the leading content of related research, this paper analyzes the response needs, sorts out the current situation trend, summarizes the gaps faced, puts forward development goals, demonstrates the composition of the system, and plans key tasks, in order to provide a basic reference for the formulation of national planning and overall research related to NEA impact risk response.
Second, it is important to actively respond to the risk of near-Earth asteroid impacts
significance
(i) Overview of the hazards of near-Earth asteroid impacts
The degree of harm caused by NEA impact on the Earth is directly related to the impact energy, and the corresponding process is divided into three stages: ultra-high-speed entry into the atmosphere, impact on the surface, and long-term environmental effects (see Figure 1). NEA enters the Earth's atmosphere at a very high speed (about 20 km/s), forming a high-temperature, high-pressure shock wave in the atmosphere; the shock wave propagates to the surface, causing ground overpressure damage. NEA undergoes violent ablation and disintegration under the coupling of aerothermal and aerodynamic forces, and even explodes in the air to form a fireball, which forms thermal radiation along with the ionization of atmospheric molecules, which in turn spreads to the surface causing thermal radiation damage and triggering forest fires. Disintegrated fragments with smaller diameters and larger structural looseness will be burned to ashes in the atmosphere; disintegrated fragments with larger diameters and less structural looseness will pass through the atmosphere and hit the earth's surface, sharply releasing the huge kinetic energy they carry in a short period of time. Usually stony meteorites larger than 60 m in diameter (type S) or iron meteorites larger than 20 m (type M) can cross the Earth's atmosphere and hit the Earth's surface.
Figure 1 Schematic diagram of the process and hazards of NEA impact on the Earth
After NEA hits the surface, the material in the impact area instantly undergoes an extreme state of temperature from 300 K to 105 K, pressure from 0.1 MPa to 10 TPa, and strain rate up to 108/s, and fragmentation, melting, gasification and even plasma phase transformation occur, resulting in impact craters. A NEA impact causes a chemical reaction (producing various gases) on surface rocks, which may throw parts of the surface material and dust into the air (creating a cloud of anti-splash debris), and the corresponding shock waves can induce strong earthquakes. These gases, dust and ashes will pervade the entire atmosphere (obscuring the sun), and in exceptional circumstances can reduce the average annual temperature of the surface by 2 to 5 °C, affecting it for millions of years. A direct impact of NEA on the ocean can trigger huge waves hundreds of meters high, triggering strong tsunamis and earthquakes, a large amount of seawater evaporation/sputtering; seafloor sediments and rock dust are ejected into the stratosphere and remain, and a large number of organisms in the ocean die.
NEA impact on Earth is a physical-mechanical-chemical strong coupling process. Ultra-high-speed entry and impact experiments, combined with numerical simulations and theoretical analysis, are needed to establish accurate models of the process and effects of entering the atmosphere and impacting the surface, which is a major frontier and difficult issue of international significance.
However, NEA diameter is more readily available than other parameters, and NEA mass can also be estimated by equivalent diameter, so equivalent diameters are commonly used internationally to characterize impact hazards. The corresponding degree of harm is mainly divided into 5 categories:
The equivalent diameter is in the kilometer range and can trigger global disasters, such as the K-T event 65 million years ago, which has a probability of occurring every 1×108 years;
The equivalent diameter is 140 meters and can trigger intercontinental disasters, such as the 2019 OK asteroid event, which has a probability of occurring once every 1000 years;
The equivalent diameter is 50 meters, which can trigger large city-level disasters, such as the Tunguska incident in Russia in 1908, which has a probability of occurring once every 100 years;
The equivalent diameter is 10 meters, which can trigger small town-level disasters, such as the Chelyabinsk incident in Russia in 2013, which has a probability of occurring every 30 to 50 years;
The equivalent diameter is in the meter range, and most of them produce air explosions and fire meteor phenomena, such as the 2021 Zhumadian City Fire Meteor Event in Henan Province, which occurs frequently. Statistics of impact events show that NEA's impact landing sites are evenly distributed across the Earth's surface.
(ii) Near-Earth asteroid impact risk analysis
Impact risk refers to the product of the probability of impacting the earth and the harm caused by the impact, and the assessment of NEA impact risk usually involves the Turin risk index and the Palermo risk index: the former uses 11 integers (0 to 10) to divide the risk level into 5 types, corresponding to different impact probabilities and hazards; the latter is calculated by the impact probability, the time of the impact, the impact energy, etc. In order to further clarify the physical significance of the relevant index, some studies have introduced casualty estimates into the NEA impact risk assessment, and a quantitative assessment index based on the probability of impact, the type of impact event and the warning time can be used to give the number of deaths caused by the impact.
Data analysis shows that the most threatening NEA in 100 years is the asteroid number 99942 with a diameter of about 370 m, which is predicted to fly over the Earth at a distance of 3.1×104 km from the surface on April 14, 2029 (at an altitude less than THE GEO orbit), and approach the Earth again in 2068 (the probability of impact is about 7 parts per million); the most threatening NEA in 10 years is the asteroid with a diameter of about 18 m, number 2016 NL39, which is expected to be 1.2 × from the Earth on June 30, 2030 Fly over the Earth at 105km (about 1/3 of the Earth-Moon distance).
It should be noted that more than 98% (in terms of quantity) of the NEA has not been inventoried by human discoveries and may pose a serious threat to the Earth; for example, about 70% of the NAAs with a diameter of more than 140 meters, about 97% of the naea with a diameter of 50 to 140 meters, and about 99% of the NEA with a diameter of 10 to 50 meters have not been discovered. These large numbers of undiscovered NEAs, whose movement processes are subject to the gravitational influence of other large celestial bodies, cause flight trajectory changes, and the impact threat is difficult to predict accurately, so the actual risk is much more serious than the already mastered situation; it is urgent to improve the level of NEA detection and develop more accurate impact risk estimation theories and models. From a historical point of view, the probability of nea impact events with a diameter of more than 1 km is low, and it is difficult to effectively implement on-orbit disposal defense in the short term; although impact events below 10 m in diameter are frequent, the actual harm is small; therefore, the NEA with a diameter of 10 to 1000 m should be the focus of the international community's attention and response, and the NEA with a diameter of 30 to 50 m is the "top priority".
Internationally, according to the NEA equivalent diameter, the impact risk and the corresponding warning and response are divided into 4 levels:
Level I risk (corresponding to red warning), particularly serious hazard event, focusing on NEA with a diameter of more than 140 m, and the hazard range is intercontinental to global;
Level II risk (corresponding to orange warning), serious hazard event, focusing on NEA with a diameter of 50 to 140 m, and the hazard range is large city level to intercontinental level;
Level III risk (corresponding to yellow warning), more serious hazard events, the focus object is NEA with a diameter of 20 to 50 m, and the hazard range is from small and medium-sized city level to large city level;
Level IV risk (corresponding to blue warning), general hazard event, the focus object is NEA with a diameter of less than 20 m, and the hazard range is from the urban level to the small and medium-sized city level.
(iii) The significance of coping with the risk of near-Earth asteroid impacts
Different from natural disasters such as earthquakes and floods, the harm of NEA impact on the earth has the following characteristics: first, the instantaneous global disaster, in the diameter of more than 50 m, especially more than 140 m NEA impact, no country and personnel can be spared; second, the impact threat is measurable, as long as the monitoring and early warning capabilities are continuously improved, and international cooperation is steadily enhanced, the NEA impact time, impact landing point, and degree of harm can be predicted in advance relatively accurately; third, the impact hazard is preventable. Actively develop multi-means on-orbit disposal technology to form a certain active defense capability, which can completely avoid or significantly reduce the losses caused by impact.
Strengthening the response to nea impact risks is of great practical significance and far-reaching historical significance.
The first is an important practice that is indispensable for implementing the overall national security concept. Although the risk probability of NEA hitting the earth is not high, it is extremely harmful, and it is closely related to the safety of almost all areas of the national security system; NEA impact on the earth directly threatens the safety of residents' lives and property, affecting economic and social development and security and stability. Properly responding to the neaxia impact risk is not only an inevitable requirement for the overall development of various undertakings, but also an important entry point for building a solid national security foundation and promoting deep integration and development.
The second is an important driving force leading the development of scientific and technological innovation. To cope with the nea impact risk, it is necessary to solve the basic science and key technical problems involved in the fields of astronomy, mathematics, physics, mechanics, geoscience, information science, control science, aeronautics and astronautics, and law, and the multidisciplinary intersection is remarkable. Improving the level of science and technology in related fields and forming system capabilities is an important way to advance the development and utilization of outer space resources and drive the development of new space technologies, and it is also the due meaning of radiation to drive the development of related industries and accelerate the construction of a scientific and technological power and a space power.
The third is an important measure to promote the construction of a community with a shared future for mankind in outer space. Once the NEA impact on the earth occurs, human beings are in it, and the effectiveness of the response measures is related to the survival of human civilization; therefore, it is the common responsibility of mankind and all countries to deal with the impact risk and protect the earth's homeland. The mainland's active response to the nea sea impact risk and working with the international community to protect human security will highlight the good image of a responsible space power, embody the consistent purpose of peaceful use of space and enhance human well-being, and support the construction of a new type of international relations and a community with a shared future for mankind.
Third, the international research situation of the risk response of near-Earth asteroid impacts
(1) Impact risk response process
Based on the international nea impact risk study, the response process can be summarized as follows (see Figure 2).
Monitoring and early warning, including search and discovery, tracking and fixing and data updates, physical property measurement, impact risk forecasting, etc., provide input for impact risk assessment.
Impact risk assessment, including impact probability calculation, impact risk corridor estimation, impact landing point forecast, impact effect analysis, etc. based on asteroid orbital and physicochemical characteristic parameters, to provide input for on-orbit disposal.
On-orbit disposal, under the premise of early warning of the dangerous NEA, change the NEA orbit to avoid impacting the earth, or split the NEA into fragments to avoid or reduce the harm to the earth; including disposal task planning, disposal plan design, disposal task implementation, disposal effect evaluation, to provide input for disaster relief work.
Disaster rescue, for impact events that fail to be warned in advance or are not successfully handled, establish an impact disaster emergency response mechanism, and carry out disaster rescue to reduce disaster losses and restore the environment.
Figure 2 General response process for NEA impact risk
(2) Monitor the progress of early warning research
NeA monitoring and early warning methods have a variety of methods, according to the location of the observation point can be divided into ground-based monitoring, space-based monitoring, from the perspective of technical principles can be subdivided into optical observation, infrared spectrum observation, radar detection. There are three main types of monitoring and early warning scenarios:
Daily cataloging scenes, through dedicated space-based and ground-based equipment, routine sky survey searches to discover new NEA, tracked by precision telescopes to obtain sufficient data and orbit cataloging;
Threat early warning scenario, for NEA with an impact probability greater than 1% in 20 years in the daily catalog, carry out precision tracking through special/part-time equipment such as ground-based and space-based, obtain precision orbits and refine the assessment of impact risks and hazards;
In the short-term forecast scenario, for the NEA that enters within 7.5 ×106 km of the earth and has an impact probability greater than 10%, the encrypted tracking and characteristic measurement are carried out, the physical and chemical characteristics are obtained, and the impact area (landing point) information is continuously predicted.
The NEA monitoring and early warning project of the United States began in 1992 ("SpaceGuard Sky Survey" project), which has relatively completely constructed a ground-based and space-based supplementary monitoring network, which is the forerunner of the world's near-Earth object monitoring technology and the main contributor to monitoring data; the monitoring and discovery system has the characteristics of different caliber collocations, optical and radar coordination, southern/northern hemisphere layout, and special/combined, and the international cataloguing contribution rate exceeds 98%. For example, in terms of daily cataloguing, there are 11 dedicated optical telescopes (aperture of 0.5 to 1.8 m) with a maximum aperture of 4.2 m for combined use; an average of about 1,500 NEAs are discovered each year, a database is being constructed and publicly released; space-based infrared telescopes (aperture of 0.5 m) and ground-based large field survey telescopes (aperture of 8.4 m) will form the ability to monitor 1 AU with a distance diameter of 30 m NEA.
The European Space Agency (ESA) established the Planetary Defense Office in 2013 to organize technical research work such as NEA monitoring, data processing, and disposal in orbit; there are 14 dual-use telescopes (aperture of 0.4 to 4.2 m), the contribution rate of international cataloguing is 0.88%, and a "compound eye" system of 1 m aperture is being built to significantly improve search efficiency.
Russia established the Planetary Defense Center in 2002, and there are 9 dedicated telescopes (aperture of 0.2 to 0.7 m), but there are few monitoring data for international sharing (the contribution rate of international cataloging is 0.08%); the maximum aperture of the combined telescope is 2.6 m, mainly used for NEA characteristic measurements; and the AZT-33VM large telescope (1.6 m diameter) put into use in 2016 can detect long-distance NEO.
On the basis of monitoring and cataloging, the United States uses ground-based optical equipment, arecibo radio telescope, Goldstone solar system radar, etc., to carry out research on precise orbit determination and characteristic measurements that threaten the NEA, and evaluate the impact risk in detail. The "Sentinel" impact monitoring system has been established to analyze and determine the precise orbit of the newly discovered NEA, calculate the probability of hitting the Earth, find nea that may be close to the Earth in the next 100 years, update and publicly publish the analysis results in a timely manner, and provide decision support for the PDCO. At the same time, for a large number of NEAs that cannot be cataloged in the short term and may suddenly approach the Earth, good short-term forecasting capabilities have been formed (such as several NEA impact events such as 2008 TC3, 2014 AA, 2018 LA, 2019 MO, etc.).
The construction of the foundation monitoring and early warning system started early, the technology is relatively mature, is the current backbone equipment, but in the accuracy, efficiency, ability has its inherent defects that are difficult to overcome, can not achieve the whole airspace, all-day monitoring and early warning, mainly reflected in: their own ability is subject to atmospheric conditions, station location constraints, there is a "dead corner" in the sunlight area, can only monitor about 30% of the sky domain; belongs to the "waiting for the rabbit" work mode, to reach the peak of the number of detection time is long, can not be completed in a given period of time. The space-based monitoring and early warning system has the technical advantages of wide monitoring range, diverse tracking means, and accurate orbit prediction, which can make up for the inherent defects of the ground-based monitoring system and become the key construction direction of the current countries, but it also faces constraints such as high cost, difficult maintenance on-orbit, and single payload configuration. Subsequently, the equipment and technology development direction of monitoring and early warning are manifested as follows: the foundation is mainly turned to the foundation / space-based coordination, the caliber is further increased, the field of view continues to be broadened, the visible light is transformed to infrared, single band to multi-band integration, and attention is paid to cutting-edge technology demonstration and verification and software and hardware upgrades; the formation of space-space integrated monitoring and early warning capabilities, the NEA with a diameter greater than 140 m is completed not less than 90% of the cataloguing, and the NEA monitoring and early warning and cataloging with a diameter of 50 meters are carried out.
(3) Research progress in impact disaster assessment
Nasa has applied the aerodynamic technology developed by the development of ultra-high-speed aircraft to the NEA entry process, established the NEA ultra-high-speed atmospheric high-temperature flow field, the coupling algorithm of shock layer radiation and ablation, the ground test method of NEA material ablation and radiation effect during the entry process, and the numerical simulation method of the shock wave effect of the NEA entry process, and deeply studied the aerothermal environment, ablation and shock wave propagation problems of NEA. The Lawrence Livermore National Laboratory in the United States has developed an impact dynamics method that simulates the nea entry and impact effects, and has studied the disintegration of the NEA entry, the explosion in the air, the impact into the crater, and the impact of the ocean causing tsunamis. In 2017, NASA established the NEA Entry and Impact Risk Analysis and Assessment System (PAIR), which can quantitatively analyze the process and effects of the NEA impact on the Earth and conduct quantitative assessment of the hazards of the ground population and facilities, and has become the main supporting tool for the implementation of the NEA Joint Emergency Tabletop Exercise/Exercise. Imperial College Of Technology, Von Carmen Institute of Fluid Mechanics in Belgium, University of Stuttgart in Germany, Czech Academy of Sciences and other institutions have studied the disintegration of the NEA ultra-high-speed entry process, air explosions, thermal radiation and impact surface craters, and developed corresponding impact dynamic simulation methods; British scientific research institutions have established NEA entry and impact effect models, developed NEA impact disaster assessment software, and provided open use services.
At present, the research hotspots and difficulties of NEA impact disasters include: accurately describing the whole process of NEA impact on the earth, revealing the mechanism of disaster causation and disaster evolution, and establishing a whole process response model and a disaster evolution model.
In terms of the atmospheric effect and mechanism of NEA's extremely high-speed entry, the lack of high-temperature gas models with velocities greater than 12 km/s, ground-based experimental techniques, NEA's porosity, cracks, anisotropy, and complex geometry further increase the difficulty of the problem, and the research progress has been slow for decades.
In terms of NEA extremely high-speed impact surface effect and modeling, due to the extremely high relative velocity (average 20 km/s), the impact on the surface of the earth to produce a solid-liquid-gas-plasma multiphase mixture and become a physical-mechanical-chemical strong coupling process, such extremely high-speed impact experiments cannot be carried out internationally; the impact zone material is in a solid-liquid-gas multiphase mixed state, and the theoretical modeling of the wide-area multiphase state equation describing such a state is not mature.
In terms of the disaster mechanism and long-term environmental effects of NEA impact on the earth, the work has been concentrated on single disaster species such as shock waves, earthquakes, fires, sputters, impact craters, tsunamis, volcanic eruptions, etc., while the coupling effects of various disaster types caused by impacts have not been carried out, and there is a gap in the study of the long-term evolution of disasters after impact.
(4) Research progress on on-orbit disposal
The research on on-orbit disposal began in the 1980s, has formed a relatively complete technical system, focusing on the development of two types of means: kinetic energy impact-based instantaneous mode of action, has been carried out on-orbit demonstration verification task; laser ablation, drag, gravitational traction and other long-term mode of action, is still in the stage of concept exploration.
In 2005, the United States successfully implemented the "Deep Impact" mission, and the copper impactor with a mass of 370 kg hit the nucleus of Comet Temple 1 at a relative speed of 10 km/s after flying 4.3 × 108 km, verifying the technical feasibility of kinetic impact defense asteroids. NASA and ESA jointly launched the Asteroid Impact Deflection Assessment Program (AIDA) to further validate kinetic impact defense technology in orbit. The Double Asteroid Redirection Test (DART) mission in the AIDA project, implemented by NASA and successfully launched on November 24, 2021, is scheduled to use a 550 kg impactor to hit the smaller B star (160 m in diameter) of the double asteroid (No. 65803) at a relative speed of 1.1× km/s at a relative velocity of 6.6 km/s, with an estimated speed change of about 0.4 mm/s from the B star, The orbital period is shortened by about 10 min, followed by joint observations using ground-based optical equipment and accompanying small satellites (released 10 days before impact) to demonstrate and verify key technologies such as approach detection, kinetic energy impact, and performance evaluation. ESA undertakes the task of approach measurement and evaluation of impact effects and effects, and the corresponding accompanying small satellites are scheduled to be launched in 2024 and orbit the impact asteroids in 2026, which can more accurately assess the kinetic impact effect and correct the kinetic impact deflection model.
The trends in on-orbit disposal research mainly include: further verifying the effectiveness of kinetic energy impact deflection technology on orbit, improving disposal- and evaluating integrated technologies; developing new technologies such as laser ablation deflection and towing, moving from concept research to key technology research; comprehensively analyzing and evaluating the applicability, efficiency and cost of single disposal technology to various targets, and carrying out multi-means coordinated efficient disposal scheme design; comprehensive on-orbit and ground demonstration verification to accelerate the practicalization process of asteroid defense capabilities.
Fourth, the basic situation of the risk response of continental near-Earth asteroid impact
(1) Overall progress
Since 2000, relying on the "space debris special scientific research" of the State Administration of Science, Technology and Industry for National Defense, common technologies and equipment such as space debris monitoring and early warning and clearance have been formed, which has provided a key foundation for the implementation of NEA impact risk response. In 2018, the 634th Xiangshan Science Conference was held with the theme of "Cutting-edge Scientific Issues and Key Technologies of Asteroid Monitoring and Early Warning, Security Defense and Resource Utilization", focusing on the issue of asteroid security defense. From 2018 to 2020, three "National Planetary Defense Seminars" were organized. In 2019, "Near-Earth Small Object Investigation, Defense and Development Issues" was selected as one of the 20 major frontier scientific and engineering problems released by the 21st Annual Conference of the China Association for Science and Technology that have a guiding role in scientific development and a key role in promoting technological and industrial innovation. In October 2021, the first National Planetary Defense Conference was successfully held, with more than 300 delegates attending.
In 2020, the China National Space Administration took the lead in setting up an expert group to carry out program demonstration work on the NEA impact risk response problem. In April 2021, the China National Space Administration said that China Aerospace will demonstrate the implementation of the fourth phase of the lunar exploration project, the planetary exploration project, the International Lunar Research Station, and the NEA defense system, thus launching a new prologue for the nine days of mainland exploration in the new era. In 2021, the China National Space Administration will take the lead in demonstrating and formulating a medium- and long-term development plan for the response to nea impact risks on the mainland. The "2021 China Aerospace" white paper proposes to demonstrate the construction of a near-Earth asteroid defense system. It can be considered that 2021 is the first year for the mainland to comprehensively carry out the capacity building of the planetary defense business structure, mechanism process and system.
(2) Technical research and foreign cooperation
In terms of ground-based observation, the 1 m aperture telescope of the Purple Mountain Observatory of the Chinese Academy of Sciences is the only NEA monitoring special equipment on the mainland (located in Xuyi County, Huai'an City, Jiangsu Province, station number D29), which has joined the International Survey Network and supports daily cataloguing work, which can monitor NEA with a diameter of more than 300 m; by 2021, a total of 33 NEAs have been discovered, and the international cataloguing contribution rate is 0.13%. Another 32 telescopes (more than 1 m aperture) on the mainland can also take into account the NEA monitoring.
In terms of space-based observation, the continent does not yet have space-based monitoring and early warning equipment in orbit. The NEA Census and Positioning System (CROWN) scheme proposed by the mainland to construct a space-based heterogeneous constellation is proposed to deploy several small satellites (including a mobile host satellite equipped with a narrow-field optics -infrared telescope and multiple tiny satellites equipped with wide-field optical band telescopes) in a Venus-like orbit 0.6 to 0.8 AU from the sun; satellite constellations, such as heterogeneous designs at multiple levels such as field of view, resolution, sensitivity, sky survey mode, and on-board computation, thus forming a space-based mission mode that combines census and detailed investigation. Mainland scholars have also proposed the concept of the Farscope Mission for Space-based Monitoring and Early Warning in the Earth's Pilot Orbit, which provides a feasible solution for making up for the blind spot of ground-based monitoring and warning from the NEA in the daytime direction by deploying space-based telescopes at about 1×107 km in front of or behind the Earth. To date, the continents have not established their own asteroid databases.
In terms of impact disaster assessment, the mainland has carried out research on the physical-chemical characteristics of NEA and its statistical distribution based on observational data, explored some key technologies and ground shrinkage test methods in advance, studied the aerothermal environment, ablation, shock wave, ground crater and anti-splash debris cloud problems of NEA entering the Earth's atmosphere, developed numerical simulation methods for NEA impacts on land and ocean, and preliminarily established an analysis and evaluation model of NEA entering the atmosphere and impacting the surface. The modeling and simulation of the momentum transmission law of kinetic energy impact deflection asteroids, the feasibility of laser deflection defense technology based on the ground test of laser ablation drive to remove space debris and the semiphysical simulation system have been carried out, and the basic performance evaluation ability in kinetic energy impact is carried out. The concept of enhanced kinetic energy impact defense schemes such as "stone hitting stone" and "final stone striking" is proposed, which provides a new option for defending against large-scale potential threats nea in addition to nuclear explosion; the numerical simulation of the mechanism of action of nuclear explosion defense NEA is carried out, the NEA deflection law under different nuclear explosion conditions is obtained, and the safety assessment and analysis of typical nuclear facilities under NEA impact conditions is carried out.
The mainland attaches great importance to international cooperation in NEA defense, and its participation in this field has steadily increased in recent years. In 2018, the Council of the Asia-Pacific Space Cooperation Organization approved the Asia-Pacific Space Science Observatory project to deploy a small-aperture telescope in each of the eight official member countries (including China) to carry out NEA monitoring and early warning research. In 2019, Xuyi Station, Changchun Station, Xinjiang Station and Weihai Station affiliated to the Chinese Academy of Sciences and universities participated in the 1999KW4 international joint observation of asteroids. In addition, for laws and regulations in the field of planetary defense, due to the broad content of the legality, responsibility, obligation, decision-making mechanism and other aspects of defense, mainland related research is still in its infancy.
(3) Urgent issues facing development
First, the top-level design of NEA impact risk response is lacking. The mainland has not yet formed a top-level planning and system design in this field, and the corresponding organizational system, process mechanism, and work responsibility subjects of each link have not yet been clarified.
Second, there is a lack of dedicated monitoring equipment and information platforms. At present, there is only one dedicated telescope, which can only monitor the NEA with a diameter of more than 300 m (brightness equivalent to absolute magnitude 20), and does not have the ability to catalog NEA orbits; it has not yet independently established the NEA information platform, cannot aggregate data and carry out early warning business, and monitoring and early warning data rely on international open platforms
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Third, relevant scientific research and technical reserves are insufficient. For the scientific and technical problems of NEA impact risk response, systematic sorting, system layout, and deepening research have yet to be carried out, and the current research tendency of heavy technology and light science is prominent; on-orbit disposal technology is basically in the conceptual research stage, the depth and breadth of impact disaster assessment and on-orbit disposal research are insufficient, and the simulation simulation platform for the whole process of impact disaster assessment and on-orbit disposal has not been established, which cannot support the development of whole-process exercises/drills.
Fourth, the international contribution rate in the field of planetary defense is low and the right to speak is small. Limited by the NEA's monitoring equipment and technical capabilities, domestic institutions provide less observational data to the international community and do not form an influence commensurate with the mainland's international status. Especially in the research and formulation of relevant international rules, it has failed to actively speak out, lacks the right to speak, and is inconsistent with the image of a responsible space power on the mainland.
Fifth, the continental near-Earth asteroid impact risk response
Disposal system and key tasks
(1) Respond to the development goals of the disposal system
Combined with the national conditions and commonalities, in accordance with the principle of "laying the foundation, making up for shortcomings, tapping potential, strengthening the system, and raising the level", we will steadily develop the mainland NEA impact risk response and disposal system. The international cutting-edge research level and the strong business ability to guarantee are equally important, and the construction of the disposal system is carried out with this as the core goal; and major projects such as the asteroid space-earth collaborative monitoring network, the on-orbit disposal demonstration and verification system, and the major disaster rescue system are implemented to form a planetary defense capability of "accurate monitoring, reliable early warning, effective disposal, and powerful rescue".
In the near future (before 2025), we will focus on building a NEA monitoring and early warning network, with a diameter of 140 meters NEA independent discovery and continuous cataloguing capabilities, improve the mainland's international cataloguing contribution rate; complete the research on key technologies for on-orbit disposal such as kinetic energy impact, and choose the opportunity to carry out demonstration and verification of on-orbit disposal technologies; initially establish a special disaster rescue force system to enhance the supply capacity of advanced and applicable equipment for disaster relief; and establish a domestic response mechanism and international cooperation mechanism.
In the medium term (before 2030), focus on improving the on-orbit disposal capability and establishing a monitoring and early warning network with a coordinated space-earth collaboration; have the ability to independently discover and continuously catalog the NEA with a diameter of 50 meters, build an NEA database based on independent data, and further increase the contribution rate of the mainland's international cataloguing; carry out on-orbit demonstration and verification of disposal technologies such as kinetic energy impact and disposal effect evaluation, and form a 50-meter-diameter NEA on-orbit disposal technology capability; and normalize joint exercises/drills to enhance the comprehensive capability of special disaster rescue.
In the long term (before 2035), comprehensively improve the system response capability, build a comprehensive and reliable monitoring and early warning network, have the ability of independent discovery and continuous cataloguing of NEA with a diameter of 30 meters, and the contribution rate of mainland cataloguing has reached the international advanced level; deepen the demonstration and verification of disposal technology on orbit, with the multi-means on-orbit disposal technology capability of NEA with a diameter of 50 meters; significantly enhance the comprehensive strength of composite catastrophe emergency rescue, and strive to build a community of human destiny in the field of planetary defense.
(2) Composition of the response disposal system
According to the response and disposal process of NEA impact risk, the response and disposal system is mainly divided into decision-making command layer, organization and coordination layer, and implementation layer (see Figure 3); an expert committee is established to support the technical work at all levels, formulate a working mechanism and standardize the process, and form a scientific hierarchical work procedure. The decision-making command is responsible for making decisions on major matters related to the prevention of NEA impacts. The organizational coordination layer is responsible for resource coordination and task planning, and routinely carries out routine work. The executive level is responsible for the specific implementation of preventive decision-making, involving monitoring and early warning, on-orbit disposal, disaster relief, international cooperation and other major aspects:
Carry out normalized monitoring, implement emergency monitoring after the discovery of NEA impact threats, timely identify risks, report early warning information, and provide early warning data and input for on-orbit disposal;
Assess NEA impact hazards, formulate disposal plans, implement on-orbit disposal tasks, and assess disposal effects;
Make emergency preparations in peacetime, initiate emergency rescue after obtaining early warning and hazard assessment information, and carry out emergency recovery after the impact event occurs;
Participate in international joint testing/joint defense/joint assistance and exchange and sharing data, formulate relevant international policies, regulations and standards, and propose an international research plan on NEA impact risk response that exerts continental influence.
Figure 3 Composition of the response and disposal system for nea impact risk in mainland China
(3) Respond to key construction tasks of the disposal system
1. Monitoring and early warning
The construction focuses on the integrated monitoring system and integrated service platform between heaven and earth. In accordance with the basic ideas of "heaven-earth collaboration, capability complementarity, scenario-driven, and business operation", we will build a space-earth integrated collaborative monitoring and early warning system with accurate early warning and normal operation.
Based on the basic conditions of the existing foundation equipment, the daily cataloguing capability of NEA with a diameter of 140 meters is added, and a multi-caliber collocation, multi-functional combination and efficient coordination of the foundation monitoring network is formed. In accordance with the technical route of "optimizing the layout in China, promoting overseas station construction, and comprehensive development of general measurement/ precision measurement", we will build a world-class foundation monitoring network. Construct a space-based monitoring network with "complementary visual sky areas, time-sharing collaborative cataloguing, short/near detection alarms, and wide-area sky survey", and have the ability to work efficiently and jointly with the ground-based monitoring network. In accordance with the technological evolution route of "carrying out verification tests, deploying monitoring systems, and upgrading and improving capabilities", we have comprehensively broken through key technologies such as the overall layout of space-based monitoring systems and advanced monitoring loads. Focus on space-based monitoring equipment that can be deployed in low-Earth orbit, Earth-Moon leveling point, moon, solar-earth leveling point, Earth orbit, Venus-like orbit, etc. (Figure 4), enrich space-based monitoring means, and strive to catch up with and surpass the first-mover countries and international advanced levels as soon as possible.
Figure 4 Schematic diagram of space-based monitoring and early warning system and equipment layout
The comprehensive service platform has various capabilities such as task planning, data integration, cataloging update, risk analysis, information release, decision-making command, resource scheduling, and rescue support. In accordance with the development route of "initially building a platform, carrying out demonstration applications, expanding upgraded applications, carrying out business operations, strengthening cohesion and outreach, and effectively supporting decision-making", advanced software has been developed and equipped with necessary hardware to provide comprehensive service guarantee for the coordinated operation of the tiandi monitoring network and the implementation of early warning services.
2. Disposal in orbit
The construction focuses on the development of an on-orbit disposal technology system based on kinetic energy impact, and carries out demonstration and verification tasks for on-orbit disposal with Chinese characteristics and international highlights. Take the on-orbit flight missions such as disposal - assessment combination, multi-objective/ multi-means synergy as the traction, carry out key technology research with the instantaneous effect of kinetic energy impact as the mainstay, the long-term role of drag and laser deflection as the supplement, taking into account the new concept disposal technology; develop and improve the disposal technology system covering instantaneous action, medium- and long-term role, and frontier exploration, comprehensively evaluate the efficiency (such as efficiency, maturity, cost), and clarify the scene adaptability; establish decision support and evaluation on orbit disposal, task whole process design simulation, Ground test verification and other systems support ground deduction and on-orbit verification. In accordance with the strategy of "colliding, colliding and moving, and being able to prevent", the on-orbit demonstration and verification task with international display and influence is implemented step by step, forming a 50-meter-diameter NEA multi-means collaborative on-orbit disposal task capability. Based on the physicochemical characteristics of NEA targets, various hazard effects of impacting the earth are studied, and a theoretical model of hazard effects is established. On the basis of the "lunar exploration project," the research, test, and construction of a "view-and-place" integrated system plan that takes into account space-based monitoring and early warning and on-orbit disposal capabilities is a breakthrough point for the mainland's planetary defense field to catch up with and surpass the international advanced level.
3. Disaster Relief
Based on the current national emergency rescue system, in view of the characteristics of the NEA disaster that hit the earth, focus on the development of complex catastrophe emergency rescue capabilities; in accordance with the development path of "improving institutional mechanisms, improving comprehensive capabilities, and significantly improving capabilities", step by step construction, and synchronously improving emergency command institutions at all levels. Establish a monitoring, evaluation and early warning system covering multiple disaster types and disaster chains, optimize the disaster evolution and rapid assessment model in complex scenarios, and realize the normalization of nea impact disaster rescue exercises/drills using the simulation platform. Strengthen the special disaster rescue forces required for NEA impact risk response, and improve the support capabilities in major scenarios.
4. Relevant frontier basic research
According to the basic principle of "leading the development of disciplines, leading and supporting major tasks in the future", focusing on the development trend of planetary defense in the next 5 to 10 years, we will carry out relevant basic research and conceptual/principle research, improve the ability of basic research and innovation in the field, and cultivate a team of specialized talents. Focusing on the orbital operation law, physical and chemical characteristics, impact effect and disaster mechanism, disposal response mechanism and other directions of NEA, the research of cutting-edge basic scientific issues is laid out, such as the origin and evolution of asteroids, the dynamic evolution mechanism of asteroid orbit, the composition/ structural characteristics / radiation characteristics of NEA, the orbital uncertainty of NEA under the influence of large body perturbation, the thermal-mechanical coupling / ablation / explosion disintegration mechanism of NEA entering the atmosphere, the transient effect of NEA impact on the surface and the mechanism of secondary disasters caused by NEA, NEA The long-term evolutionary effect of impact on the Earth's environment, the dynamic response and energy transfer law of NEA under kinetic energy impact, the mechanism and effect of close nuclear explosion on NEA, the mechanism of NEA deflection and orbital shift under non-contact action such as laser ablation, etc.
5. International cooperation
The characteristics of NEA impact hazards determine that effective defense is inseparable from international cooperation. Adopt the basic idea of "focusing on improving the degree of integration, focusing on the development of regional cooperation, and contributing more Chinese strength", deeply participate in international organizations and institutions (such as IAWAN, SMPAG, PDC) according to the actual conditions of the country, and actively carry out bilateral and multilateral international cooperation. In terms of bilateral international cooperation, we will make full use of the mainland's bilateral cooperation mechanism in space, carry out joint observation, joint disposal and joint rescue, improve the level of data sharing, promote the realization of "joint consultation" of response, "joint construction" of equipment, and "sharing" of data, and stimulate new vitality of space cooperation. In terms of multilateral international cooperation, we will deeply participate in the formulation and improvement of relevant international cooperation rules, and under the guidance of the concept of building a community with a shared future for mankind in outer space, put forward an international research plan, international negotiation rules, and international cooperation mechanism proposals for the neA impact risk response led by the mainland.
6. Countermeasures and suggestions
(1) Strengthen the top-level design and long-term planning of impact risk response capabilities
Give full play to the advantages of Our new national system, strengthen the construction of the organizational system and response process mechanism, and clarify the responsible subjects of each link. Strengthen the top-level design of the field, accelerate the formulation and timely release of the medium- and long-term development plan and roadmap for the NEA impact risk response. In accordance with the step arrangement of focusing on building a monitoring and early warning system by 2025, focusing on improving response and disposal capabilities by 2030, and comprehensively improving the response capacity of the system by 2035, the impact threat can be measured and prevented as soon as possible, and a NEA national response capability system matching the international status can be formed.
(2) Efficiently establish a "cohesive outreach" impact risk response business system
Establish the NEA Impact Risk Response Expert Committee to provide intellectual support for impact risk response. Relying on superior technical units, a national asteroid monitoring and early warning research center has been established. Establish an asteroid information platform, create a high-level, commercial, and open national research and development force, and carry out daily cataloguing, threat warning, short-term forecasting, information sharing and other business work on a regular basis. Enhance the security of planetary defense data, enhance the international discourse power, and ensure that the national level work coordination mechanism carries out NEA risk defense related work. Actively mobilize social forces to intervene, and part of the commercial development model can be adopted.
(3) Rapidly form impact risk response capabilities and innovation capabilities
It is proposed to set up the National Natural Science Foundation of China - the National Administration of Science, Technology and Industry for National Defense Planetary Defense Joint Fund to support the research of basic scientific problems involved in the NEA impact risk response in a major special manner, and provide a solid scientific foundation for planetary defense engineering. It is recommended to coordinate the channels of special scientific research on space debris and civil space scientific research of the State Administration of Science, Technology and Industry for National Defense, combined with the planetary exploration projects being demonstrated and implemented, to set up major nea impact risk response projects in the country, support key technologies for planetary defense and system capacity building, and establish a systematic NEA impact risk response capability as soon as possible. It is recommended to establish a national laboratory for deep space exploration as soon as possible, gather the advantages of relevant fields, build an innovative research and development system and mechanism that integrates science, technology and engineering, and support the construction of a national science and technology collaborative innovation platform for planetary defense.
(4) Strive to build a community with a shared future for mankind in the field of planetary defense
Thinking of danger in times of peace, taking precautions, starting from the concept of building a community with a shared future for mankind, participating in international affairs of planetary defense with an open, inclusive, cooperative and leading attitude, and jointly carrying out NEA impact risk response work. It has deeply participated in relevant United Nations organizations and taken the initiative to display the good image of a responsible space power on the mainland. Discuss the "joint defense" mechanism with the international community, share the "joint test" data, and jointly build the "joint aid" force, and actively contribute China's wisdom, Chinese solutions, and Chinese strength to the world's planetary defense.
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About the author
Wu Weiren is an expert in the overall design of aerospace measurement and control communications and deep space exploration projects, and an academician of the Chinese Academy of Engineering.
He has long been engaged in aerospace telemetry, measurement and control communications and deep space exploration engineering research. Responsible for the successful development of the mainland's first-generation computer telemetry system and remote aerospace measurement and control communication system, reaching the international advanced level. Presided over the realization of aerospace measurement and control communication from S-band near-Earth space to X-band deep space technology leap. Proposed and realized Chang'e-2 multi-objective exploration of the moon, solar-earth Lagrange L2 point and asteroid, opening up a new field of continental deep space exploration. Presided over the soft landing and inspection and exploration of the Chang'e-3 moon, setting a new milestone in China's aerospace. As the main proposer, the unmanned lunar sample return technology scheme was proposed, which has been approved by the state for implementation.