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Gravitationally bound geoengineering dust shade at the inner Lagrange point
Abstract
This paper presents a novel method of space-based geoengineering which uses the mass of a captured near Earth asteroid to gravitationally anchor a cloud of unprocessed dust in the vicinity of the L1L1 position to reduce the level of solar insolation at Earth. It has subsequently been shown that a cloud contained within the zero-velocity curve of the largest near Earth asteroid, Ganymed, can lead to an insolation reduction of 6.58% on Earth, which is significantly larger than the 1.7% required to offset a 2 °C increase in mean global temperature. The masses of the next largest near Earth asteroids are found to be too small to achieve the required level of insolation reduction, however, they are significant enough to be used as part of a portfolio of geoengineering schemes.
... Variations on the original proposals to shade Earth with artificial sun shields include the use of dust. Clouds of micron-size gains at the Earth-Sun L 1 point [15][16][17], at Lagrange points of the Moon-Earth system [11,18], and in orbit around Earth [19][20][21] have all shown some promise, albeit with limitations. The potential sources of dust include terrestrial and lunar mines and near-Earth asteroids. ...
... A swarm of purely absorbing dust particles could provide an effective sun shield [15,16,19]. However, with an attenuation of solar radiation by a factor of 10 −26 per micron-sized grain, climate-impacting reduction in solar radiance at Earth requires a large cloud of dust. ...
... Roughly 10 10 kg of material annually is needed for Earth-climate impact, depending on the dust properties and how the cloud is deployed. Sources of dust include Earth, the Moon [18], or possibly a deflected asteroid [15,16,19]. Because dust grains between Earth and the Sun tend to drift out of alignment, they must be replenished. ...
We revisit dust placed near the Earth–Sun L 1 Lagrange point as a possible climate-change mitigation measure. Our calculations include variations in grain properties and orbit solutions with lunar and planetary perturbations. To achieve sunlight attenuation of 1.8%, equivalent to about 6 days per year of an obscured Sun, the mass of dust in the scenarios we consider must exceed 10 ¹⁰ kg. The more promising approaches include using high-porosity, fluffy grains to increase the extinction efficiency per unit mass, and launching this material in directed jets from a platform orbiting at L 1 . A simpler approach is to ballistically eject dust grains from the Moon’s surface on a free trajectory toward L 1 , providing sun shade for several days or more. Advantages compared to an Earth launch include a ready reservoir of dust on the lunar surface and less kinetic energy required to achieve a sun-shielding orbit.
... The first takeaway from this literature (see Table 1) is the diversity of strategies (and attached metaphors) for diminishing the amount of solar radiation reaching the Earth. As a sampling, there is a 2000-km-wide, 10 μm-thick glass shield which could refract sunlight away from the Earth [17]; light-scattering clouds of dust, either from the Moon or a near-Earth asteroid which would be captured, towed, and gravitationally tethered in a useful position, to act as "sunscreen" for the Earth" [18][19][20]; a "heliotropic dust ring" that would endow Earth with its own Saturn-style ring [13,21]; a swarm of 800,000 solar-collecting devices ("Dyson dots") covering an area more than 1 million-square kilometers (i.e. about the size of Texas) that simultaneously functions as a "parasol" and captures energy from the Sun [4]; or a "flotilla" of upwards of 16 trillion feather-light, transparent flying disks, each weighing only 1 g, with tiny fins that gather solar energy and actively adjust their relative position to work in concert with the other disks [ [9,16], see also [22]]. There are no shortage of ideas vying with one another. ...
... Compares advantages and disadvantages of two main types of proposals, signaling overall potential of sunshade concept and how continued technical development can increase viability of macroscopic designs Bewick et al. [18] Cloud of dust particles of asteroid material SEL1 Calculates potential to capture a nearby asteroid and gravitationally anchor it in place at SEL1 to achieve reduction in solar insolation by upwards of 6.58% Bewick et al. [21] Saturn-style dust ring Equatorial ring in LEO Demonstrates potential of providing Earth with its own elliptical ring, but highlighting greater effect on tropical regions as well as the possibility of space-debris issues and seasonal variations Kennedy et al. [4] Swarm of 800,000 solar-energy collecting "Dyson dots" covering more than 1 million square kilometers SEL1 Lays out potential for swarm of Dyson dots about the size of Texas to both "transform the "solar constant" to a controlled solar variable" and capture energy from the Sun to then be beamed back to Earth Sánchez and McInnes [31] Space-based sunshade or occulting disk SEL1 Climate-modelling exercise illustrating how large-scale regional (or seasonal) variations can be mitigated through "out-of-plane sinusoidal motion", that is, letting orbit of the sunshade not be fully in sync with the Earth Salazar et al. [32] Space-based solar reflectors on polar orbits Near-circular orbits around polar regions Explores possibility of using solar reflectors as a way to mitigate future natural climate variability, i.e., global cooling Salazar and Winter [33] Space-based solar reflectors, orbiting around Mars Inclination of ≤90 • to the orbital plane of Mars Considers possibility of using space-based solar reflectors to heat up and prepare Mars for terraforming IRS and Airbus [34] Inter planetary sun shade (IPSS) with an area of 500,000 km SEL1 High-level concept description of IPSS that would be built using in-situ materials from the Moon and by Gigasail factories to be set up at SEL1, with an expected cost of around 1 trillion US dollars, which is aimed to be potentially offset by harvesting and beaming solar energy back to Earth Source: Compiled by the authors. ...
Space-based geoengineering is gaining attention, if not necessarily traction, as a possible "break the glass" solution to mitigate the worst impacts of climate change and facilitate the transition to a low-carbon future. Though still on the periphery of discussions around climate mitigation and geoengineering, space-based methods that would deflect or block incoming sunlight, and thereby diminish how much radiation ultimately reaches the Earth, could offer advantages, notably, by avoiding the need for difficult trade-offs and decisions in terms of land and resource use on Earth. Aside from a few specialist-oriented studies, the literature on space-based geo-engineering remains limited. In this study, we utilize a large and diverse expert-interview exercise (N = 125) to provide a first critical examination of the promise and relevance of space-based geoengineering for tackling climate change, including perhaps as a source of renewable energy, its feasibility and prospective risks, as well as key actors and issues related to commercialization and governance. To our knowledge, no other study has employed empirical data of any kind to examine perceptions of space-based geoengineering, let alone in relation to other kinds of climate-intervention technologies. Not only does the current research represent the first of its kind, it also provides a foundation for more informed, comprehensive deliberations around this interesting, possibly even necessary solution to climate change.
... However, cooling is to be expected if the amount of extraterrestrial dust in the atmosphere for several 100 ka or longer increases by more than three orders of magnitude. Following the LCPB breakup, not only Earth's atmosphere but also much of interplanetary space in the inner solar system became dusty, further shading Earth from sunlight [see e.g., 38,39]. Dust from the LCPB breakup may also have fertilized large areas of the ocean, which could have led to drawdown of CO 2 from the atmosphere (40). ...
... In an effort to mitigate ongoing global warming, it has been suggested to capture a large near-Earth asteroid and position it at the first Lagrange point as a source of dust that could help to reduce solar insolation on Earth (39). Gravitationally "anchoring" such a dust cloud at this point would reduce dust particle dispersion and create a prolonged cooling effect. ...
The breakup of the L-chondrite parent body in the asteroid belt 466 million years (Ma) ago still delivers almost a third of all meteorites falling on Earth. Our new extraterrestrial chromite and ³ He data for Ordovician sediments show that the breakup took place just at the onset of a major, eustatic sea level fall previously attributed to an Ordovician ice age. Shortly after the breakup, the flux to Earth of the most fine-grained, extraterrestrial material increased by three to four orders of magnitude. In the present stratosphere, extraterrestrial dust represents 1% of all the dust and has no climatic significance. Extraordinary amounts of dust in the entire inner solar system during >2 Ma following the L-chondrite breakup cooled Earth and triggered Ordovician icehouse conditions, sea level fall, and major faunal turnovers related to the Great Ordovician Biodiversification Event.
... A number of studies have suggested reducing the amount of sunlight reaching the Earth by placing solid or refractive disks, or dust particles, in outer space (Early, 1989;Mautner, 1991;Angel, 2006;Bewick et al., 2012). Although we do not assess the feasibility of these methods, they provide an easily described mechanism for reducing sunlight reaching the planet, and motivate the idealized studies discussed in Section 7.7.3. ...
... Settling the Solar System can be motivated by serving human needs. These can include: satellite solar power stations for permanent clean energy [17]; a space sunshade against global warming [18,19]; mining of asteroids metals and structural materials [11,20]; large space colonies for growth and survival [3]; high resolution lunar telescopes [21]; and lunar gene banks for saving and re-cloning endangered species, including endangered human ethnic groups [22]. The space infrastructure that develops for these purposes will then allow exponential human growth in the Solar System, and serve as a base for seeding new solar systems [23][24][25]. ...
Astroecology concerns the relations between life and space resources, and cosmo-ecology extrapolates these relations to cosmological scales. Experimental astroecology can quantify the amounts of life that can be derived from space resources. For this purpose, soluble carbon and electrolyte nutrients were measured in asteroid/meteorite materials. Microorganisms and plant cultures were observed to grow on these materials, whose fertilities are similar to productive agricultural soils. Based on measured nutrient contents, the 10^22 kg carbonaceous asteroids can yield 10^18 kg biomass with N and P as limiting nutrients (compared with the estimated 10^15 kg biomass on Earth). These data quantify the amounts of life that can be
derived from asteroids in terms of time-integrated biomass [BIOTAint = biomass (kg) × lifetime (years)], as 10^27 kg-years during the next billion years of the Solar System (a thousand times the 1024 kg-years to date). The 10^26 kg cometary materials can yield biota 10 000 times still larger.
In the galaxy, potential future life can be estimated based on stellar luminosities.
For example, the Sun will develop into a white dwarf star whose 1015 W luminosity can sustain a (BIOTAint) of 10^34 kg-years over 10^20 years. The 10^12 main sequence and white and red dwarf stars can sustain 10^46 kg-years of (BIOTAint) in the galaxy and 10^57 kg-years in the universe. Life has great potentials in space, but the probability of present extraterrestrial life may be incomputable because of biological and ecological complexities. However, we can establish and expand life in space with present technology, by seeding new young solar systems. Microbial representatives of our life-form can be launched by solar sails to new planetary systems, including extremophiles suited to diverse new environments, autotrophs and heterotrophs
to continually form and recycle biomolecules, and simple multicellulars to jump-start higher evolution.
These programs
can be motivated by life-centered biotic ethics that seek to secure and propagate life. In space, life can develop immense populations and diverse new branches. Some may develop into intelligent species that can expand life further in the galaxy, giving our human endeavors a cosmic purpose.
... Material extracted from a much larger (> 500 m diameter) captured asteroid could create a solar insulating dust ring around the Earth [Bewick et al., 2013[Bewick et al., , 2012bPearson et al., 2006;Stuck, 2007]. A cloud of ejected and unprocessed material would become gravitationally anchored at, or around, the L 1 point [Bewick et al., 2012a[Bewick et al., ,b, 2010. By preventing, and controlling how much sunlight is absorbed into the Earth's atmosphere, the effects of global warning could be reduced. ...
http://theses.gla.ac.uk/5219/
Laser ablation has been investigated as a possible technique for the contactless deflection of Near Earth Asteroids. It is achieved by irradiating the surface of an asteroid with a laser light source. The absorbed heat from the laser beam sublimates the surface, transforming the illuminated material directly from a solid to a gas. The ablated material then forms into a plume of ejecta. This acts against the asteroid, providing a controllable low thrust, which pushes the asteroid away from an Earth-threatening trajectory.
The potential of laser ablation is dependent on understanding the physical and chemical properties of the ablation process. The ablation model is based on the energy balance of sublimation and was developed from three fundamental assumptions. Experimental verification was used to assess the viability of the ablation model and its performance in inducing a deflection action. It was achieved by ablating a magnesium-iron silicate rock, under vacuum, with a 90 W continuous wave laser. The laser operated at a
wavelength of 808 nm and provided intensities that were below the threshold of plasma formation. The experiment measured the average mass flow rate, divergence geometry and temperature of the ejecta plume and the contaminating effects - absorptivity, height and density - of the deposited ejecta. Results were used to improve the ablation model. A critical discrepancy was in the variation between the previously predicted
and experimentally measured mass flow rate of the ablated ejecta. Other improvements have also included the energy absorption within the Knudsen layer, the variation of sublimation temperature with local pressure, the temperature of the target material and the partial re-condensation of the ablated material. These improvements have enabled the performance of the ablation process and the specifications of the laser to be revised.
Performance exceeded other forms of electric propulsion that provided an alternative contactless, low thrust deflection method. The experimental results also demonstrated the opportunistic potential of laser ablation.
Using existing technologies, with a high technology readiness level, a small and low-cost mission design could demonstrate the technologies, approaches and synergies of a laser ablation mission. The performance of the spacecraft was evaluated by its ability to deflect a small and irregular 4 m diameter asteroid by at least 1 m/s. It was found to be an achievable and measurable objective. The laser ablation system could be successfully sized and integrated into a conventional solar-power spacecraft. Mission
mass and complexity is saved by the direct ablation of the asteroid's surface. It also avoids any complex landing and surface operations. Analysis therefore supports the general diversity and durability of using space-based lasers and the applicability of the model's experimental verification.
... Material extracted from a much larger (> 500 m diameter) captured asteroid could create a solar insulating dust ring around the Earth [3,4,46,67]. A cloud of ejected and unprocessed material would become gravitationally anchored at, or around, the L 1 point [1][2][3]. By preventing, and controlling how much sunlight is absorbed into the Earth's atmosphere, the effects of global warning could be reduced. ...
Analysis gained from a series of experiments has demonstrated the effectiveness of laser ablation for the low thrust, contactless deflection and manipulation of Near Earth Asteroids. In vacuum, a 90 W continuous wave laser beam has been used to ablate a magnesium-iron silicate sample (olivine). The laser operated at a wavelength of 808 nm and provided intensities that were below the threshold of plasma formation. Olivine was use to represent a rocky and solid asteroidal body. Assessed parameters included the average mass flow rate, divergence, temperature and velocity of the ejecta plume, and the height, density and absorptivity of the deposited ejecta. Experimental data was used to verify an improved ablation model. The improved model combined the energy balance of sublimation with the energy absorption within the Knudsen layer, the variation of flow with local pressure, the temperature of the target material and the partial re-condensation of the ablated material. It also enabled the performance of a space-based laser system to be reassessed. The capability of a moderately sized, conventional solar powered spacecraft was evaluated by its ability to deflect a small and irregular 4 m diameter asteroid by at least 1 m/s. Deflection had to be achieved with a total mission lifetime of three years. It was found to be an achievable and measurable objective. The laser (and its associated optical control) was designed using a simple combined beam expansion and focusing telescope. The mission study therefore verified the laser's proof-of-concept, technology readiness and feasibility of its mission and subsystem design. It also explored the additional opportunistic potential of the ablation process. The same technique can be used for the removal of space debris.
The annual global greenhouse gas (GHGs) emissions have continued to grow since the industrial revolution. The dominant driving force for the anthropogenic GHGs emission include population growth, economic growth, fossil fuel consumption and land use change. Since the beginning of industrial revolution to 2015, cumulative anthropogenic carbon dioxide (CO2) emission of 600 ± 70 Pg C were released to the atmosphere, causing an increase in atmospheric CO2 relative abundance of 144% compared to pre-industrial era. The atmospheric concentrations of methane (CH4) and nitrous oxide (N2O) have also increased significantly. As a result, changes in climate has caused impacts on natural and human systems across the globe, and continued GHGs emission will cause further climate change impacts. Accurate assessment of anthropogenic CO2 emissions and their redistribution among the atmosphere, ocean and terrestrial biosphere provides better understanding of C cycling and also support the development of climate policies, and project future climate change. The mitigation options available combine measures to reduce energy use and CO2 intensity of the end use sectors, reduction of net GHG emissions, decarbonization of the energy supply, and capture and sequestration of C through enhancement of natural C sinks or by engineering techniques. There has also been emphasis on engineering of climate as an alternative mitigation option. Geoengineering
, a global large-scale manipulation of the environment, is considered as one of the effective means of mitigating global warming caused by anthropogenic greenhouse gases (GHGs) emission. Assessment of technical and theoretical aspects of solar radiation management (SRM) and carbon dioxide (CO2) removal methods (CRM) as well as their potential impacts on global climate and ecosystems will be reviewed. Most of the proposed geological engineering methods involving land or ocean will use physical, chemical, or biological approaches to remove atmospheric CO2, while those proposed for atmosphere or space will target radiation without affecting atmospheric CO2 concentration. The CRM schemes tend to be slower, and able to sequester an amount of atmospheric CO2 that is small compared to cumulative anthropogenic CO2 emissions. In contrast, SRM approaches have relatively short lead times and can act rapidly to reduce temperature anomaly caused by GHGs emission. Overall, current research on geoengineering is scanty and various international treaties may limit some geoengineering experiments in the real world due to concerns of an unintended consequences.
Currently, climate change is a significant threat to our way of life, with global mean temperatures predicted to increase by 1.1-6.4°C by the end of the century (IPCC 2007). This increase is driven by multiple factors, with the main contributors being the increasing concentrations of Greenhouse Gases (GHG), mainly CO2, CH4 and N2O, in the atmosphere, which is altering the Earth's current energy balance and therefore the present climate. The current consensus within the scientific community is that the dominant factor in the changing climate of the Earth is the anthropogenic emission of GHG's, with the probability of this being true termed "very likely" (90% probability) by the IPCC (IPCC 2007). Whilst the main effort within the global community should be to control climate change by reducing our emissions of GHG's, it is prudent to investigate other methods of managing the climate system. The field of deliberately manipulating the Earth's climate is called geoengineering, or climate engineering.
Most future concepts for the exploration and exploitation of space require a large initial mass in low Earth orbit. Delivering this required mass from the Earth's surface increases cost due to the large energy input necessary to move mass out of the Earth's gravity well. An alternative is to search for resources in-situ among the near-Earth asteroid population. The near-Earth asteroid resources that could be transferred to a bound Earth orbit are determined by integrating the probability of finding asteroids inside the Keplerian orbital element space of the set of transfers with an specific energy smaller than a given threshold. Transfers are defined by a series of impulsive maneuvers and computed using the patched-conic approximation. The results show that even moderately-low-energy transfers enable access to a large mass of resources.
The distribution of regolith on asteroid surfaces has only recently been measured directly by in situ observations from spacecraft. To the surprise of many researchers, most of the classical predictions for the distribution of asteroid impact ejecta have not rung true, with regoliths appearing to be geologically active at small scales on asteroid surfaces. This indicates that significant insight into geological processes on asteroids may be inferred by detailed studies of the distribution of impact ejecta on asteroids. This chapter has been written to support these future investigations, by trying to identify and clarify all the important elements for such a study, to point to the recent history of such studies, and to indicate the current gaps in our understanding. The chapter begins with a discussion of the initial conditions of ejecta fields generated from impacts on the asteroid surface. Then the relevant physical laws and forces affecting asteroid ejecta, in orbit and on the surface, are reviewed and the basic dynamical equations of motion for ejecta are stated. Some general results and constraints on the solutions to these equations are given, and a classification scheme for ejecta trajectories is given. Finally, recent studies of asteroid ejecta are reviewed, showing the application of these techniques to asteroid science.
The Active Cavity Radiometer Irradiance Monitor (ACRIM I) measured the sun's luminosity from early 1980 to late 1989. The first account of the complete ACRIM I data set is presented and evidence is given which confirms that solar luminosity varies with the 11-yr solar cycle. This slow variation closely follows statistical measures of the distribution of magnetic and photospheric features on the solar surface. An exception to this correlation occurred in the form of a remarkable irradiance excess during 1980, at about the time of the sunspot maximum of solar cycle 21. The linkage, over a whole cycle, of luminosity variation to photospheric activity suggests the existence of an unknown physical mechanism other than the thermal diffusion model that explains luminosity deficits due to sunspots. Luminosity models connecting total irradiance to global indicators of solar activity are consistent with the gross features of the variability but fail to account for the 1980 irradiance excess.
In this paper a method of geoengineering is proposed involving clouds of dust placed in the vicinity of the L1 point as an alternative to the use of thin film reflectors. The aim of this scheme is to reduce the manufacturing requirement for space-based geoengineering. It has been concluded that the mass requirement for a cloud placed at the classical L1 point, to create an average solar insolation reduction of 1.7%, is 7.60 × 1010 kg yr−1 whilst a cloud placed at a displaced equilibrium point created by the inclusion of the effect of solar radiation pressure is 1.87 × 1010 kg yr−1. These mass ejection rates are considerably less than the mass required in other unprocessed dust cloud methods proposed and are comparable to thin film reflector geoengineering requirements. Importantly, unprocessed dust sourced in-situ is seen as an attractive scheme compared to highly engineered thin film reflectors. It is envisaged that the required mass of dust can be extracted from captured near Earth asteroids, whilst stabilised in the required position using the impulse provided by solar collectors or mass drivers used to eject material from the asteroid surface.
To counteract anthropogenic climate change, several schemes have been proposed to diminish solar radiation incident on Earth's surface. These geoengineering schemes could reverse global annual mean warming; however, it is unclear to what extent they would mitigate regional and seasonal climate change, because radiative forcing from greenhouse gases such as CO2 differs from that of sunlight. No previous study has directly addressed this issue. In the NCAR CCM3 atmospheric general circulation model, we reduced the solar luminosity to balance the increased radiative forcing from doubling atmospheric CO2. Our results indicate that geoengineering schemes could markedly diminish regional and seasonal climate change from increased atmospheric CO2, despite differences in radiative forcing patterns. Nevertheless, geoengineering schemes could prove environmentally risky.
The radiation pressure force, that acts on dust in interplanetary space depends on size and composition of the particles. The knowledge of this effect is essential for the study of dust dynamics. Four models of “typical” interplanetary dust grains are constructed from common notions of their physical properties, and their possible parent bodies. The influence of radiation pressure forces on the particles is estimated by means of so-called β-values, that give the ratio of radiation pressure force to gravitation force in interplanetary space. The β-values and albedos are calculated using Mie theory for homogeneous and core-mantle spheres. The Maxwell-Garnett mixing rule is used to describe either the porosity of particle or the inclusion of another material. Derived albedos of mixed-material particles appear to be generally lower than those of grains consisting of pure, strongly absorbing substances, which has also influence on the radiation pressure forces. The calculations show that the assumption of extremely porous particles, often discussed as a description of cometary dust, leads to very high radiation pressure forces. Models applied for more compact particles, either of interstellar and asteroidal origin or produced by alteration of “fresh” cometary material show similar slopes of their beta values, which are lower than for the “young” cometary material. The study shows that only particles with masses m>10−10g can be assumed to behave dynamically (i.e. under influence of radiation pressure forces) like the “big” zodiacal particles (m>10−8g).
An artificial planetary ring about the Earth, composed of passive particles or controlled spacecraft with parasols, is proposed to reduce global warming. A flat ring from 1.2 to 1.6 Earth radii would shade mainly the tropics, moderating climate extremes, and counteract global warming. A preliminary design of the ring is developed, and a one-dimensional climate model is used to evaluate its performance. Earth, lunar, and asteroidal material sources are compared to determine the costs of the particle ring and the spacecraft ring. Environmental concerns and effects on existing satellites in Earth orbit are addressed. The particle ring endangers LEO satellites, is limited to cooling only, and lights the night many times as bright as the full moon. It would cost an estimated $6–200 trillion. The ring of controlled satellites with reflectors has other attractive uses, and would cost an estimated $125–500 billion.
The prospect of engineering the Earth's climate (geoengineering) raises a multitude of issues associated with climatology, engineering on macroscopic scales, and indeed the ethics of such ventures. Depending on personal views, such large-scale engineering is either an obvious necessity for the deep future, or yet another example of human conceit. In this article a simple climate model will be used to estimate requirements for engineering the Earth's climate, princi-pally using space-based geoengineering. Active cooling of the climate to mitigate anthropogenic climate change due to a doubling of the carbon dioxide concentration in the Earth's atmosphere is considered. This representative scenario will allow the scale of the engineering challenge to be determined. It will be argued that simple occulting discs at the interior Lagrange point may represent a less complex solution than concepts for highly engineered refracting discs proposed recently. While engineering on macroscopic scales can appear formidable, emerging capabili-ties may allow such ventures to be seriously considered in the long term. This article is not an exhaustive review of geoengineering, but aims to provide a foretaste of the future opportunities, challenges, and requirements for space-based geoengineering ventures.
We use a radar-derived physical model of 4179 Toutatis (975870) to investigate close-orbit dynamics around that irregularly shaped, non-principal-axis rotator. The orbital dynamics about this body are markedly different than the dynamics about uniformly rotating asteroids. The results of this paper are generally applicable to orbit dynamics about bodies in a non-principal-axis rotation state. The radar results support the hypothesis that Toutatis has a homogeneous density distribution, and we assume a density of 2.5 g/cc. The asteroid's gravity field is computed using a truncated harmonic expansion when outside of its circumscribing sphere and a closed-form expression for the potential field of an arbitrary polyhedron when inside that sphere. The complete equations of motion are time-periodic in the Toutatis-fixed frame due to the complex rotation of the asteroid. The system is Hamiltonian and has all the characteristics of such a system, including conservation of phase volume, but there is no Jacobi constant of the motion and zero velocity surfaces cannot be used to analyze the system's behavior. We also examine some of the close-orbit dynamics with the Lagrange planetary form of the equations of motion. Families of quasi-periodic “frozen orbits” that show minimal variations in orbital elements are found to exist very close to the asteroid; some of them are stable and hence can hold natural or artificial satellites. A retrograde family of frozen orbits is especially robust and persists down to semi-major axes of about 2.5 km, comparable to half of Toutatis' longest dimension. We identify families of periodic orbits, which repeat in the Toutatis-fixed frame. Due to the time-periodic nature of the equations of motion, all periodic orbits about Toutatis in its body-fixed frame must be commensurate with the 5.42-day period associated with those equations. Exact calculations of both stable and unstable periodic orbits are made. The sum of surface forces acting on a particle on Toutatis is time-varying, so particles on and in the asteroid are being continually shaken with a period of 5.42 days, perhaps enhancing the uniformity of the regolith distribution. A global map of the gravitational slope reveals that it is surprisingly shallow for such an elongated, irregularly shaped object, averaging 16° globally and less than 35° over 96% of the surface. A global map of tangential accelerations shows no values larger than 0.5 mm/s2, an average value of 0.2 mm/s2, and less than 0.25 mm/s2over 70% of the surface. A global map of the escape speed for launch normal to the surface shows that quantity to be between 1.2 and 1.8 m/s over most of the surface. Each of these mapped quantities has small periodic variations. We have found trajectories that leave the surface, persist in the region of phase space around a frozen orbit, and then impact the surface after a flight time of more than 100 days. Return orbit durations of years seem possible. Whereas a uniformly rotating asteroid preferentially accumulates non-escaping ejecta on its leading sides, Toutatis accumulates ejecta uniformly over its surface. We render a variety of close orbits in inertial and body-fixed frames.
Predictions of future potential Earth impacts by near-Earth objects (NEOs) have become commonplace in recent years, and the rate of these detections is likely to accelerate as asteroid survey efforts continue to mature. In order to conveniently compare and categorize the numerous potential impact solutions being discovered we propose a new hazard scale that will describe the risk posed by a particular potential impact in both absolute and relative terms. To this end, we measure each event in two ways, first without any consideration of the event's time proximity or its significance relative to the so-called background threat, and then in the context of the expected risk from other objects over the intervening years until the impact. This approach is designed principally to facilitate communication among astronomers, and it is not intended for public communication of impact risks. The scale characterizes impacts across all impact energies, probabilities and dates, and it is useful, in particular, when dealing with those cases which fall below the threshold of public interest. The scale also reflects the urgency of the situation in a natural way and thus can guide specialists in assessing the computational and observational effort appropriate for a given situation. In this paper we describe the metrics introduced, and we give numerous examples of their application. This enables us to establish in rough terms the levels at which events become interesting to various parties.
If it were to become apparent that dangerous changes in global climate were inevitable, despite greenhouse gas controls, active methods to cool the Earth on an emergency basis might be desirable. The concept considered here is to block 1.8% of the solar flux with a space sunshade orbited near the inner Lagrange point (L1), in-line between the Earth and sun. Following the work of J. Early [Early, JT (1989) J Br Interplanet Soc 42:567-569], transparent material would be used to deflect the sunlight, rather than to absorb it, to minimize the shift in balance out from L1 caused by radiation pressure. Three advances aimed at practical implementation are presented. First is an optical design for a very thin refractive screen with low reflectivity, leading to a total sunshade mass of approximately 20 million tons. Second is a concept aimed at reducing transportation cost to 50 dollars/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. Third is an implementation of the sunshade as a cloud of many spacecraft, autonomously stabilized by modulating solar radiation pressure. These meter-sized "flyers" would be assembled completely before launch, avoiding any need for construction or unfolding in space. They would weigh a gram each, be launched in stacks of 800,000, and remain for a projected lifetime of 50 years within a 100,000-km-long cloud. The concept builds on existing technologies. It seems feasible that it could be developed and deployed in approximately 25 years at a cost of a few trillion dollars, <0.5% of world gross domestic product (GDP) over that time.
There are many indications that anthropogenic global warming poses a serious threat to our civilization and its ecological support systems. Ideally this problem will be overcome by reducing greenhouse gas emissions. Various space-based methods, including large-scale solar shades, diffusers or atmospheric pollutants, have been considered to reduce the solar constant (input flux) and the warming in case emissions reductions are not achieved in a timely way. Here it is pointed out that proposed technologies for near-Earth orbiting comet deflection, suggest a different kind of space-based solar shade. This shade would be made up of micron-sized dust particles derived from comet fragments or lunar mining, and positioned in orbits near the triangular Lagrange points of the Earth-Moon system. Solar radiation pressure can render such orbits unstable, but a class of nearly resonant, and long-lived orbits is shown to exist, though the phase space volume of such orbits depends on dust grain size. Advantages and disadvantages of this scheme relative to others are considered.
Earth rings for planetary environment control Asteroid resource map for near-earth space Analytical Mechanics of Space Systems Dynamics of Orbits Close to Asteroid 4179 Toutatis The fate of asteroid ejecta
- J Pearson
- J Oldson
- E Levin
- J P Sanchez
- C Mcinnes
- H Schaub
- J L Junkins
- D J Scheeres
- S J Ostro
- R S Hudson
Pearson, J., Oldson, J., Levin, E. Earth rings for planetary environment control. Acta Astronautica 58, 44–57, 2006. Sanchez, J.P., McInnes, C. Asteroid resource map for near-earth space. Journal of Spacecraft and Rockets 48, 153–165, 2011. Schaub, H., Junkins, J.L. Analytical Mechanics of Space Systems. AIAA, 2003. Scheeres, D.J., Ostro, S.J., Hudson, R.S., et al. Dynamics of Orbits Close to Asteroid 4179 Toutatis. Icarus 132, 53–79, 1998. Scheeres, D.J., Durda, D.D., Geissler, P.E. The fate of asteroid ejecta, in: Bottke, W.F., Cellino, A., Paolicchi, P., et al. (Eds.), Asteroids III. University of Arizona Press, Tucson, pp. 527–544, 2002. Struck, C. The feasibility of shading the greenhouse with dust clouds at the stable lunar Lagrange points. JBIS 60, 82–89, 2007.
McInnes, C.R. Space-based geoengineering: challenges and requirements The league of extraordinary machines: a rapid and scalable approach to planetary defense against asteroid impactors
- Ipcc
- Switzerland Geneva
- J Olds
- A Charania
- M Graham
In: Core Writing Team, Pachauri, R.K., Reisinger, A. (Eds.), IPCC, Geneva, Switzerland, p. 104, 2007. McInnes, C.R. Space-based geoengineering: challenges and requirements. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, 571–580, 2010. Olds, J., Charania, A., Graham, M., et al., The league of extraordinary machines: a rapid and scalable approach to planetary defense against asteroid impactors, NASA Institute for Advanced Concepts, 30th April, 2004.