Multifidelity design of low-thrust resonant captures for near-Earth asteroids

The design of a space trajectory is strongly linked to the gravitational and non-gravitational environment and the dynamical frameworks required to model it. These dynamical models may range from low to high fidelity, with corresponding computational costs. This paper proposes a multifidelity approach for the computation of nearly resonant trajectories with the Earth. This framework is used to compute trajectories for the capture of near-Earth asteroids into libration point orbits of the Sun – Earth system. The transfer is first computed in a suitable low-fidelity model, the Keplerian map, and a multifidelity approach is subsequently used to refine the solution from an impulsive approximation into a low-thrust transfer in the circular restricted three-bodyproblem. The entire trajectory follows a nearly resonant motion with the Earth, lasting less than two synodic periods; starting when the retrieval spacecraft attaches itself to the asteroid, they will encounter the Earth twice, being captured into the target orbit at the end of the second encounter. A velocity change maneuver is carried out at the beginning of the motion, so that the first encounter with the Earth provides a gravitational perturbation resulting on a reduction of overall propellant costs of the transfer. The developed framework is very flexible in terms of the desired accuracy and allows for the low computational cost exploration of a vast number of possible trajectories. The obtained low-thrust transfers yield, for six asteroids, a much higher retrievable mass in comparison with direct capture trajectories, which do not undertake Earth-resonant encounters

Landing in binary asteroids: A global map of feasible descend opportunities for unpowered spacecraft

Asteroid surface science provides the necessary “ground-truth” to validate and enhance remote sensing from orbiting spacecraft. Yet, due to uncertainties associated with the dynamical environment near asteroids, it is generally prudent for the main spacecraft to remain at a safe distance. Instead, small landers could be used much more daringly. This paper explores the potential for ballistic landing opportunities in binary asteroid systems. The dynamics near a binary asteroid are modelled by means of the Circular Restricted Three Body Problem, which provides a reasonable representation of a standard binary system. Natural landing trajectories are sought that allow for deployment from safe distances and touchdown with minimum local-vertical velocity. The necessary coefficient of restitution to ensure a successful landing and the effects of navigation and deployment errors are also analysed. Assuming deployment errors in the order of 10 meters and 1 cm/s (1-sigma), the results show that ballistic descent landing operations are likely to be successful if targeting near equatorial regions with longitude within 320o to 20o in the secondary of the binary system

Near rectilinear orbits around the moon as operational orbit for the future deep space gateway

The aim of this paper is to revise the suitability of Near- Rectilinear Halo Orbits (NRHOs) as long-term destinations for a new crew-tended space station; referred here as Deep Space Gateway (DSG). NRHOs are a subset of the halo families characterized by promising stability properties. The document presents the formal definition and identification of NRHOs, as in the CR3BP model. Dynamical substitutes of the NRHOs are also refined in the Bi-Circular Model (BCM) by means of a multiple shooting method. Key features such as lunar south-pole coverage, station keeping requirements and accessibility of the orbit are then analysed. Several maintenance strategies based on three different underlying principles are considered and, finally, the accessibility of NRHOs from the Earth and polar Moon orbits is investigated

Opportunities for ballistic soft landing in binary asteroids

Remote sensing instrumentation onboard missions to asteroids is paramount to address many of the fundamental questions in modern planetary science. Yet in situ surface measurements provide the “ground truth” necessary to validate and enhance the science return of these missions. Nevertheless, because of the dynamical uncertainties associated with the environment near these objects, most missions spend long periods of times stationed afar. Small landers can be used much more daringly, however, and thus have already been identified as valuable assets for in situ exploration. This paper explores the potential for ballistic landing opportunities enabled by the natural dynamics found in binary asteroid systems. The dynamics near a binary asteroid are modeled by means of the circular restricted three-body problem, which provides a reasonable representation of a standard binary system. Natural landing trajectories are then sought that allow for a deployment from the exterior region and touchdown with minimum local-vertical velocity. The results show that, although landing on the main body of the system would require an effective landing system capable to dissipate excess of energy and avoid bouncing off the asteroid, the smaller companion offers the prospect of simple ballistic landing opportunities

Opportunities for ballistic soft landing in binary asteroids

Remote sensing instrumentation onboard missions to asteroids is paramount to address many of the fundamental questions in modern planetary science. Yet in situ surface measurements provide the “ground truth” necessary to validate and enhance the science return of these missions. Nevertheless, because of the dynamical uncertainties associated with the environment near these objects, most missions spend long periods of times stationed afar. Small landers can be used much more daringly, however, and thus have already been identified as valuable assets for in situ exploration. This paper explores the potential for ballistic landing opportunities enabled by the natural dynamics found in binary asteroid systems. The dynamics near a binary asteroid are modeled by means of the circular restricted three-body problem, which provides a reasonable representation of a standard binary system. Natural landing trajectories are then sought that allow for a deployment from the exterior region and touchdown with minimum local-vertical velocity. The results show that, although landing on the main body of the system would require an effective landing system capable to dissipate excess of energy and avoid bouncing off the asteroid, the smaller companion offers the prospect of simple ballistic landing opportunities

Optimal Sunshade Configurations for Space-Based Geoengineering near the Sun-Earth L1 Point

Within the context of anthropogenic climate change, but also considering the Earth’s natural climate variability, this paper explores the speculative possibility of large-scale active control of the Earth’s radiative forcing. In particular, the paper revisits the concept of deploying a large sunshade or occulting disk at a static position near the Sun-Earth L1Lagrange equilibrium point. Among the solar radiation management methods that have been proposed thus far, space-based concepts are generally seen as the least timely, albeit also as one of the most efficient. Large occulting structures could potentially offset all of the global mean temperature increase due to greenhouse gas emissions. This paper investigates optimal configurations of orbiting occulting disks that not only offset a global temperature increase, but also mitigate regional differences such as latitudinal and seasonal difference of monthly mean temperature. A globally resolved energy balance model is used to provide insights into the coupling between the motion of the occulting disks and the Earth’s climate. This allows us to revise previous studies, but also, for the first time, to search for families of orbits that improve the efficiency of occulting disks at offsetting climate change on both global and regional scales. Although natural orbits exist near the L1equilibrium point, their period does not match that required for geoengineering purposes, thus forced orbits were designed that require small changes to the disk attitude in order to control its motion. Finally, configurations of two occulting disks are presented which provide the same shading area as previously published studies, but achieve reductions of residual latitudinal and seasonal temperature changes

Asteroid belt multiple flyby options for M-Class Missions

Addressing many of the fundamental questions in modern planetary science, as well as in ESA’s cosmic vision, requires a comprehensive knowledge of our Solar System’s asteroid belt. This paper investigates potential opportunities for medium-class asteroid belt survey missions in the timeframe of 2029-2030. The study has been developed in support to CASTAway Asteroid Spectroscopic Survey mission proposal, which is to be submitted to the latest ESA’s medium size mission call. CASTAway envisages the launch of a small telescope with relatively straightforward (i.e. high TRL) remote sensing instrumentation to observe asteroids at a long-range (i.e. point source), but also at a short-range, resolving them at ~10 m resolution. This paper presents a challenging multi-objective optimization problem and discusses the feasibility of such a mission concept. A baseline trajectory is presented that meets both ESA’s medium size mission constraints and the science requirements. The trajectory loops through the asteroid belt during 7 years, visiting 10 objects of a wide range of characteristics, providing sufficient survey time to obtain compositional information for 10,000s of objects and the serendipitous discovery of also 10,000s of 10-m class asteroids. The methodology developed has enabled the exploration of the entire design space for a conservative Soyuz-launch performance, and has found a total of 200 different tour opportunities of the asteroid belt; all compliant with ESA’s 5th call for medium size missions

Un modelo numérico para la simulación de la evolución del fondo marino en la zona cercana a la costa

En este artículo se presenta un modelo numérico que simula la evolución del fondo marino en la zona cercana a la costa. El modelo está dividido en tres módulos que calculan la propagación del oleaje, las corrientes inducidas por oleaje y viento y el transporte de sedimentos y los cambios morfodinámnicos asociados al mismo. Para calibrar y validar el modelo se han utilizado algunos ejemplos extraídos de la literatura, así como datos de campo. Los resultados del modelo muestran que éste estima adecuadamente tanto las magnitudes como las tendencias de la evolución del fondo marino bajo distintas condiciones hidrodinámicas, por lo que puede ser considerada una herramienta útil para propósitos ingenieriles.Peer Reviewe

Aproximació a les migracions històriques a través de l'estudi dels cognoms. Catalunya, 1497-1601

Treball de Recerca del Màster en Estudis Territorials i de la Població (UAB), codirigit per Anna Cabré i Joana M. Pujadas. Bellaterra, 5 de juliol 2011.L'estudi analitza els fluxos migratoris esdevinguts a Catalunya durant la primera meitat del segle XVI, a través d'un mètode d'estimació indirecta, l'anàlisi dels cognoms continguts en els fogatges de 1497 i 1553. La recerca es centra en l'anàlisi descriptiu de les dades, focalitzant-se especialment en els cognoms més comuns de l'època. Així mateix, s'ha analitzat la distribució espacial d'aquests, entre 1497 i 1553, cartografiant la seva evolució al llarg del temps. Finalment, el grau d'interrelació entre les distintes demarcacions territorials de la Catalunya moderna (col·lectes) ha estat establert mitjançant l'aplicació del coeficient de Chen i Cavalli-Sforza (1983).El artículo analiza los flujos migratorios acaecidos en Cataluña durante la primera mitad del siglo XVI a través de un método de estimación indirecta como es el análisis de los apellidos contenidos en los recuentos de fuegos u hogares (fogajes) de 1497 y 1553. El estudio se centra en el análisis descriptivo de los datos, focalizándose en los apellidos más comunes de la época. Así mismo, se ha analizado la distribución espacial de éstos entre 1497 y 1553, cartografiando su evolución a lo largo del tiempo. Finalmente, el grado de interrelación entre las distintas demarcaciones territoriales de la Cataluña moderna (col·lectes) ha sido establecido a través de la aplicación del coeficiente de Chen y CavalliSforza (1983).This paper aims to identify migration flows during the first half of the XVI century. To achieve this goal we analyze population movements using the distribution and emergence of family names. For that purpose the Catalan household tax counts (fogatges) of 1497 and 1553 are used. These counts were made for fiscal purposes and collect each family unit (household or fireplace) of the region by villages. Firstly we conduct a descriptive analysis of the data, focusing on the most common surnames of that period. Secondly, the spatial distribution of these surnames among the two aforementioned periods is analyzed, mapping their distribution throughout time. Finally, we concern on the degree of interrelation among different regions of Catalonia in that time (col·lectes) applying the coefficient of Chen and Cavalli-Sforza (1983)