Design of a Formation of Solar Pumped Lasers for Asteroid Deflection

This paper presents the design of a multi-spacecraft system for the deflection of asteroids. Each spacecraft is equipped with a fibre laser and a solar concentrator. The laser induces the sublimation of a portion of the surface of the asteroid. The jet of gas and debris thrusts the asteroid off its natural course. The main idea is to have a swarm of spacecraft flying in the proximity of the asteroid with all the spacecraft beaming to the same location to achieve the required deflection thrust. The paper presents the design of the formation orbits and the multi-objective optimization of the swarm in order to minimize the total mass in space and maximize the deflection of the asteroid. The paper demonstrates how significant deflections can be obtained with relatively small sized, easy-to-control spacecraft.Comment: Advances in Space Research, 201

Survey on studies about model uncertainties in small body explorations

Currently, the explorations of small solar system bodies (asteroids and comets) have become more and more popular. Due to the limited measurement capability and irregular shape and diverse spin status of the small body, uncertainties on the parameters of the system and s/c executions are a practical and troublesome problem for mission design and operations. The sample-based Monte Carlo simulation is primarily used to propagate and analyze the effects of these uncertainties on the surrounding orbital motion. However, it is generally time-consuming because of large samples required by the highly nonlinear dynamics. New methods need to be applied for balancing computational efficiency and accuracy. To motivate this research area and facilitate the mission design process, this review firstly discusses the dynamical models and the different methods of modeling the mostly related gravitational and non-gravitational forces. Then the main uncertainties in these force models are classified and analyzed, including approaching, orbiting and landing. Then the linear and nonlinear uncertainty propagation methods are described, together with their advantages and drawbacks. Typical mission examples and the associated uncertainty analysis, in terms of methods and outcomes, are summarized. Future research efforts are emphasized in terms of complete modelling, new mission scenarios, and application of (semi-) analytical methods in small body explorations

E-Glider: Active Electrostatic Flight for Airless Body Exploration

The environment near the surface of asteroids, comets, and the Moon is electrically charged due to the Sun's photoelectric bombardment and lofting dust, which follows the Sun illumination as the body spins. Chargeddust is ever present, in the form of dusty plasma, even at high altitudes, following the solar illumination. If abody with high surface resistivity is exposed to the solar wind and solar radiation, sun-exposed areas andshadowed areas become differentially charged. The E-Glider (Electrostatic Glider) is an enabling capability foroperation at airless bodies, a solution applicable to many types of in-situ mission concepts, which leverages thenatural environment. With the E-Glider, we transform a problem (spacecraft charging) into an enablingtechnology, i.e. a new form of mobility in microgravity environments using new mechanisms and maneuveringbased on the interaction of the vehicle with the environment. Consequently, the vision of the E-Glider is toenable global scale airless body exploration with a vehicle that uses, instead of avoids, the local electricallycharged environment. This platform directly addresses the "All Access Mobility" Challenge, one of the NASA'sSpace Technology Grand Challenges. Exploration of comets, asteroids, moons and planetary bodies is limitedby mobility on those bodies. The lack of an atmosphere, the low gravity levels, and the unknown surface soilproperties pose a very difficult challenge for all forms of know locomotion at airless bodies. This E-Gliderlevitates by extending thin, charged, appendages, which are also articulated to direct the levitation force in themost convenient direction for propulsion and maneuvering. The charging is maintained through continuouscharge emission. It lands, wherever it is most convenient, by retracting the appendages or by firing a cold-gasthruster, or by deploying an anchor. The wings could be made of very thin Au-coated Mylar film, which areelectrostatically inflated, and would provide the lift due to electrostatic repulsion with the naturally chargedasteroid surface. Since the E-glider would follow the Sun's illumination, the solar panels on the vehicle wouldconstantly charge a battery. Further articulation at the root of the lateral strands or inflated membrane wings,would generate a component of lift depending on the articulation angle, hence a selective maneuveringcapability which, to all effects, would lead to electrostatic (rather than aerodynamic) flight. Preliminarycalculations indicate that a 1 kg mass can be electrostatically levitated in a microgravity field with a 2 mdiameter electrostatically inflated ribbon structure at 19kV, hence the need for a "balloon-like" system. Due tothe high density and the photo-electron sheath and associate small Debye length, significant power is requiredto levitate even a few kilograms. The power required is in the kilo-Watt range to maintain a constant chargelevel

Design and optimisation of solar sail orbits in proximity of asteroids

A solar sail is a large reflective membrane which is capable of producing thrust for a spacecraft by the reflection of sunlight. Such a propellant-less propulsion system can offer solutions to high-energy missions which would be impossible for conventional propulsion systems. As a result, this technology has been proposed by many authors as the ideal candidate for a multiple asteroid rendezvous mission. At the time of writing, there are more than 30,000 known near-Earth asteroids (NEAs) alone. Adding to this those contained in the main belt and elsewhere in the solar system, the abundance of these small rocky worlds becomes apparent. Focusing only on the NEAs, there are many reasons for interest in missions to these bodies. In the first instance, they represent the earliest building blocks of the rocky worlds of the solar system, and are often still in pristine condition, similar to how they would have been since these earliest moments. As such, there is massive scientific interest in visiting and extracting samples of their constituent materials. There is another community which is also interested in the extraction of these materials: the future asteroid miners. This mining could provide propellant for deep space missions, materials for in-space infrastructure and potentially also in the return of minerals which are rare on Earth, and so of great value. However, although these bodies provide many opportunities, they are not without threat. Although the frequency of impacts of large bodies capable of causing considerable damage to Earth-based infrastructure is relatively low, there are still recent examples of just such events. With the potential for large scale loss of life due to an asteroid impacting populated areas, the science of planetary defence requires greater knowledge of the make-up of these bodies. Yet another reason for mission designers to examine further options in achieving efficient missions to these bodies. It would be beneficial, in terms of cost, for a single spacecraft to be able to carry out a mission to multiple asteroids. Such a high-energy mission is ideally suited to the solar sail. Although the literature has provided many works on orbital transfers to multiple bodies, the operation of the sail when in proximity of the asteroid has not received quite as much attention. It is in this phase of the mission, where the science objectives would be carried out, that this thesis focuses. There are numerous challenges which the sail faces in the near-asteroid environment. These include the irregular gravity field, the strength of the acceleration provided by the sail in a relatively weak gravitational field, the often fast rotational velocities of the asteroid and higher demands on slew rates for the sail due to the shorter period of low-altitude orbits. The work will consider three main proximity phases. The first operation is in the control of an orbit using the solar sail in an irregular gravity field. In this operation, the sail must counter the perturbative effects of a non-spherical body. This manifests in the rotation of the orbit node line, referred to as nodal regression. A new tool, referred to as the Control Transition Matrix (CTM), which aids in forcing a periodic orbit solution over multiple orbits is then presented. The second operation deals with the control of a sail at the point of and subsequent to the deployment of a lander and during the deployment of a series of small ChipSat probes. The landing conditions for deployments from various locations around the asteroid are analysed before the deployment is presented from a low-asteroid orbit. The control of the sail along a nominal orbit while the lander is still on-board is presented before the sail control subsequent to the lander deployment is considered. Given the high velocity impacts for a ballistic lander deployed at large distances from the surface, an alternative mission scenario of the deployment of small ChipSat probes is presented. These probes are envisaged to carry out their science goals during the descent and so the landing conditions are less important. The final operation is in the gravitational capture of the sail around the asteroid. This work provides a preliminary analysis of the capability of the sail in achieving this by using a simple on/off control law. Following this, a more detailed two-phase approach is presented. In the first “initial capture” phase, the sail uses the value of Jacobi constant in the 3 body system as a guide to reduce the orbit radius to within a defined region. After this, the “orbit shaping” phase aims to circularise the orbit at this radius. Subsequently, preliminary investigations into an optimal approach are presented. In controlling the effects due to the non-spherical asteroid shape, an optimally controlled solution, where a minimum effort control law is sought, is presented. Following this, a novel method of updating a control law was successfully applied to force a periodic orbit. In the work carried out on lander deployment, it was found that the sail was capable of maintaining a periodic orbit after the point of lander separation by application of time-delay feedback control. For the deployment of a series of small probes, it was found that maintaining a fixed attitude for the sail during the deployment was not considerably different in station-keeping performance compared with LQR control, and performed this with no effort required of the sail. Finally, in the work on capture, the two-phase approach provided successful capture trajectories down to the desired orbit radius. The work showed that, for reducing size of asteroid, there was a reduction in the time to capture. This is due to the fact that the same size of sail is used in the weakening gravity field of each asteroid. This makes the sail relatively more powerful and so able to affect quicker capture. It was also seen that long period capture trajectories are compounded by the need for the sail to spend periods of time waiting for the position of the Sun relative to the orbit to be in such a way as to permit the capture operations to proceed. There was also the successful demonstration of an optimally controlled capture which minimised the orbit semi-parameter over one orbit revolution. The work contained in this thesis provides preliminary analysis for the consideration of future solar sail mission designers in the proximity operations of a sail near an asteroid. The findings presented here have shown that the sail can be of considerable utility in these proximity operations. They also present challenges to the mission designer given the continuous thrust that they may provide. Where a powerful sail may benefit the interplanetary phase of a mission in reaching many more asteroids further from the Earth, this can also present a challenge in the relatively weak asteroid gravitational field. However, these challenges are not insurmountable and so the sail remains a promising option for these high-energy missions

Multi-fidelity modelling of low-energy trajectories for space mission design.

The proposal of increasingly complex and innovative space endeavours poses growing demands for mission designers. In order to meet the established requirements and constraints while maintaining a low fuel cost, the use of low-energy trajectories is particularly interesting. These paths in space allow spacecraft to change orbits and move with little to no fuel, but they are computed using motion models of a higher fidelity than the commonly used two-body problem. For this purpose, perturbation methods that explore the third-body effect are especially attractive, since they can accurately convey the system dynamics of a three-body configuration with a lower computational cost, by employing mapping techniques or exploring analytical approximations. The focus of this work is to broaden the knowledge of low-energy trajectories by developing new mathematical tools to assist in mission design applications. In particular, novel models of motion based on the third-body effect are conceived and classified by the forces they account for (conservative or non-conservative). The necessary numerical tools to complement the trajectory design are developed: this includes differential correction methods and targeting schemes, which take advantage of the Jacobian matrices derived from the presented models to generate full low-thrust control laws. One application of this analysis focuses on the trajectory design for missions to near- Earth asteroids. Two different projects are explored: one is based on the preliminary design of separate rendezvous and capture missions to the invariant manifolds of libration point L₂. This is achieved by studying two specific, recently discovered bodies and determining dates, fuel cost and final control history for each trajectory. The other covers a larger study on asteroid capture missions, where several asteroids are regarded as potential targets. The candidates are considered using a multi-fidelity design framework. Its purpose is to filter through the trajectory options using models of motion of increasing accuracy, so that a final refined, low-thrust solution is obtained. The trajectory design hinges on harnessing Earth’s gravity by exploiting encounters outside its sphere of influence, the named Earth-resonant encounters. An additional application explored in this investigation is the search and computation of periodic orbits for different planetary systems, following the current interest for missions involving distant retrograde and prograde orbits. In summary, this thesis presents four novel methods to model the third-body perturbation, distinct in their suitability for applications from real-time computations to long-term orbital predictions. These, together with the additionally developed tools for trajectory design, are applied in two asteroid mission cases. The developed Earth-resonant encounters allow for a very large increase in retrievable mass with respect to the state-of-the-art, namely for the cases of six near-Earth asteroids presented.PhD in Aerospac

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

Abstracts for the International Conference on Asteroids, Comets, Meteors 1991

Topics addressed include: chemical abundances; asteroidal belt evolution; sources of meteors and meteorites; cometary spectroscopy; gas diffusion; mathematical models; cometary nuclei; cratering records; imaging techniques; cometary composition; asteroid classification; radio telescopes and spectroscopy; magnetic fields; cosmogony; IUE observations; orbital distribution of asteroids, comets, and meteors; solar wind effects; computerized simulation; infrared remote sensing; optical properties; and orbital evolution

Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System

Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System Abstract of the Ph.D. thesis \s David Capek It has been shown, that the thermal effects are very important in the dynamics of small Solar System bodies. A phenomenon which is known as the Yarkovsky effect is able to secularly change the semimajor axis of an orbit, while the YORP effect affects the rotation state of a body. The Yarkovsky effect and the YORP effect were previously calculated with many constraining assumptions like spherical shapes of asteroids, circular orbits, small variations of the surface temperature, principal axis rotation, constant thermal parameters, etc. We developed a sophisticated numerical model of the Yarkovsky/YORP effect without such simplifications. With this model, we have been able to describe the shape, the orbit, the rotation and the thermal behaviour of an asteroid in a very precise way. The YORP effect was studied on a sample of artificially generated shapes, roughly resembling Main Belt asteroids, and also on several shapes of real asteroids. The depen- dence of YORP on the obliquity and the thermal parameters of the surface were studied (Vokrouhlicky and Capek, 2002; Capek and Vokrouhlicky, 2004). A wide variety of pos- sible YORP evolution paths of the spin state was found. The possibility of...Tepelne jevy ve fyzice a dynamice malych teles slunecm soustavy Abstrakt dizertacnf prace David Capek Behem posledni doby se ukazalo, ze tepelne jevy jsou velmi vyznamne v dynamice malych teles slunecni soustavy. Intenzivne studovan byl predevslm jev zvany Jarkovskeho efekt, ktery je schopen dlouhodobe menit velkou poloosn drahy a YORP efekt, jez ovlivnuje rotacni stav telesa. Jarkovskeho a YORP efekt byly drive pocitany s mnoha omezujicimi predpoklady. Napnklad byly uvazovany kulove tvary asteroidu, kruhove drahy, male variace povrchove teploty, rotace okolo hlavni osy tenzoru setrvacnosti, konstantni tepelne parametry a podobne. Proto jsme vyvinnli numericky model pro vypocet Jarkovskeho/YORP jevu, ktery neni omezen temito predpoklady. S timto modelem jsme byli schopni velmi pfesne popsat tvar, drahu, rotaci a tepelne vlastnosti studovaneho telesa. YORP efekt byl studovan na vzorku umele vytvofenych tvaru} ktere odpovidaji aste- roidum hlavniho pasu, a take na tvarech skutecnych asteroidu. Zkoumali jsme zejmena savislost YORP jevu na obliquite a na tepelnych parametrech povrchu. Byla zjistena a diskutovana siroka skala moznosti v)'voje rotacniho stavu asteroidu (Vokrouhlickj'- and Capek, 2002; Capek and Vokrouhlickyj 2004). Pro nektere asteroidy bylo predpovezeno, ze Ize v budoucnosti ocekavat uspesnou...Institute of Theoretical PhysicsÚstav teoretické fyzikyFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult