Assessment on the feasibility of future shepherding of asteroid resources

Most plausible futures for space exploration and exploitation require a large mass in Earth orbit. Delivering this mass requires overcoming the Earth's natural gravity well, which imposes a distinct obstacle to any future space venture. An alternative solution is to search for more accessible resources elsewhere. In particular, this paper examines the possibility of future utilisation of near Earth asteroid resources. The accessibility of asteroid material can be estimated by analysing the volume of Keplerian orbital element space from which Earth can be reached under a certain energy threshold and then by mapping this analysis onto an existing statistical near Earth asteroid (NEA) model. Earth is reached through orbital transfers defined by a series of impulsive manoeuvres and computed using the patched-conic approximation. The NEA model allows an estimation of the probability of finding an object that could be transferred with a given Δv budget. For the first time, a resource map provides a realistic assessment of the mass of material resources in near Earth space as a function of energy investment. The results show that there is a considerable mass of resources that can be accessed and exploited at relatively low levels of energy. More importantly, asteroid resources can be accessed with a entire spectrum of levels of energy, unlike other more massive bodies such as the Earth or Moon, which require a minimum energy threshold implicit in their gravity well. With this resource map, the total change of velocity required to capture an asteroid, or transfer its resources to Earth, can be estimated as a function of object size. Thus, realistic examples of asteroid resource utilisation can be provided

Orbit control of asteroids in libration point orbits for resource exploitation

The fascinating idea of shepherding asteroids for science and resource utilisation is being considered as a very credible concept in a not too distant future. Past studies have identified asteroids which could be injected into manifolds which wind onto periodic orbits around collinear Lagrangian points of the Sun-Earth system, by means of a low-cost manoeuvre. However, the periodic orbits as well as the manifolds are highly unstable, and small errors in the capture manoeuvre would bring to complete mission failure, with potential danger of collision with the Earth itself. The main source of injection error in position and velocity is the epistemic uncertainty of the asteroid mass, which cannot be measured directly. For this reason, asteroid orbit control will be a strict requirement for such mission. This paper investigates the controllability of some asteroids during the transfer and along the period orbits, assuming the use of a solar-electric low-thrust engine. The control scheme is based on a linear quadratic regulator. A stochastic simulation with a Monte Carlo approach is used to simulate a range of different perturbed initial conditions. Results show that only a small subset of the considered combinations of trajectories/asteroids are reliably controllable, and therefore controllability must be taken into account in the selection of potential targets

On the ballistic capture of asteroids for resource utilisation

This paper investigates the concept of capturing in the Earth’s neighbourhood Earth-approaching objects such as asteroids and comets. These objects may provide access to potential resources, as well as be potential scientific mission opportunities. A statistical approach is used to assess the fraction of the near-Earth object population with a given set of Keplerian elements. This is used to estimate the number of objects with the potential to fly-by the Earth with low relative velocities. The circular restricted three-body problem is then used to show that objects approaching Earth at low hyperbolic excess velocities can potentially be gravitationally captured at Earth. The Tisserand parameter, used as an approximation of the Jacobi constant, can be used to delimit the orbital regions from were low-energy transfers should be expected to exist and asteroids could possibly be transported at a minimum expenditure of energy. Finally, a semi-analytical approximation of the gravitational perturbation in the CR3BP is used to assess the feasible asteroid transport fluxes of capturable material that could be achieved by judicious use of Earth gravitational perturbations

An L1 positioned dust cloud as an effective method of space-based geoengineering

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 2.93x109 kg yr-1 whilst a cloud placed at a displaced equilibrium point created by the inclusion of the effect of solar radiation pressure is 8.87x108 kg yr-1. These mass ejection rates are considerably less than the mass required in other unprocessed dust cloud methods proposed and, for a geoengineering period of 10 years, they are comparable to thin film reflector geoengineering requirements. 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

On the consequences of a fragmentation due to a NEO mitigation strategy

The fragmentation of an Earth threatening asteroid as a result of a hazard mitigation mission is examined in this paper. The minimum required energy for a successful impulsive deflection of a threatening object is computed and compared with the energy required to break-up a small size asteroid. The fragmentation of an asteroid that underwent an impulsive deflection such as a kinetic impact or a nuclear explosion is a very plausible outcome in the light of this work. Thus a model describing the stochastic evolution of the cloud of fragments is described. The stochasticity of the fragmentation is given by a Gaussian probability distribution that describes the initial relative velocities of each fragment of the asteroid, while the size distribution is expressed through a power law function. The fragmentation model is applied to Apophis as illustrative example. If a barely catastrophic disruption (i.e. the largest fragment is half the size the original asteroid) occurs 10 to 20 years prior to the Earth encounter only a reduction from 50% to 80% of the potential damage is achieve for the Apophis test case

Asteroid hazard mitigation: deflection models and mission analysis

Small celestial bodies such as Near Earth Objects (NEOs) have become a common subject of study because of their importance in uncovering the mysteries of the composition, formation and evolution of the solar system. Among all asteroids, NEOs have stepped into prominence because of two important aspects: they are among the easiest celestial bodies to reach from Earth, in some cases with less demanding trajectories than a simple Earth-Moon trajectory and, even more meaningful, they may pose a threat to our planet. The purpose of this thesis is to provide a comprehensive insight into the asteroid hazard problem and particularly to its mitigation. Six different concepts are fully described; specifically models for nuclear interceptor, kinetic impactor, low-thrust propulsion, mass driver, solar collector and gravity tug are developed and their efficiency is assessed for a complete set of different types of hazardous celestial objects. A multi-criteria optimization is then used to construct a set of Pareto-optimal asteroid deflection missions. The Pareto-optimality is here achieved not only by maximizing the deflection of the threatening object, but also by minimizing the total mass of the deflection mission at launch and the warning time required to deflect the asteroid. A dominance criterion is also defined and used to compare all the Pareto sets for all the various mitigation strategies. The Technology Readiness Level for each strategy is also accounted for in the comparison. Finally, this thesis will also show that impulsive deflection methods may easily catastrophically disrupt an asteroid if the required energy for a deflection reaches a certain limit threshold. A statistical model is presented to approximate both the number and size of the fragments and their initial dispersion of velocity and then used to assess the potential risk to Earth posed by the fragmentation of an asteroid as a possible outcome of a hazard mitigation mission

Magnetic properties of the ternary oxide glasses, Li2O-B2 O3-Fe2O3 from 57Fe Mössbauer spectroscopy

57Fe Mössbauer spectroscopy has been combined with bulk magnetic measurements to determine the valence state and coordination of iron as well as the magnetic properties of the ternary oxide glasses, Li2O-B 2O3-Fe 2O3. In all investigated glasses (≤ 8.4 at % Fe), the Fe3+ ions coexist in tetrahedral and octahedral coordinations ; the presence of Fe2+ ions ( < 15 %), which is observed in some glasses, is related to preparation conditions. The magnetic properties of the glasses are governed by the iron content. At low iron concentration (< 3 at %), isolated Fe3+ ions coexist with antiferromagnetic dimers and trimers. At large iron content (3.8 to 8.4 at %) the glasses undergo a mictomagnetic transition to a speromagnetic ordered state. The freezing temperature (Tf), which is frequency dependent, is found to follow a Fulcher law in one sample (5.8 at % Fe) investigated in detail

Micro-to-macro: astrodynamics at extremes of lengths-scale

This paper investigates astrodynamics at extremes of length-scale, ranging from swarms of future `smart dust' devices to the capture and utilisation of small near Earth asteroids. At the smallest length-scales families of orbits are found which balance the energy gain from solar radiation pressure with energy dissipation due to air drag. This results in long orbit lifetimes for high area-to-mass ratio `smart dust' devices. High area-to-mass hybrid spacecraft, using both solar sail and electric propulsion, are then considered to enable `pole-sitter' orbits providing a polar-stationary vantage point for Earth observation. These spacecraft are also considered to enable displaced geostationary orbits. Finally, the potential material resource available from captured near Earth asteroids is considered which can underpin future large-scale space engineering ventures. The use of such material for geo-engineering is investigated using a cloud of unprocessed dust in the vicinity of the Earth-Sun $L_1$ point to fractionally reduce solar insolation

INTERACTIONS AND PRECIPITATIONS IN DILUTE TERNARY Fe Sb M ALLOYS (M = Ti, V, Cr, Mn, Co, AND Ni)

No abstract availabl

57Fe ABSORPTION AND EMISSION SPECTROSCOPY IN SOME COBALT ACETYLACETONATE COMPLEXES [Co (acac)3, Co (acac)2, Co (acac)2·2H2O]

No abstract availabl