1,995 research outputs found
Activities of the Space Advanced Research Team at the University of Glasgow
A wide range of technologies and methodologies for space systems engineering are currently being developed at the University of Glasgow. Much of the work is centred on mission analysis and trajectory optimisation, complemented by research activities in autonomous and multi-agent systems. This paper will summarise these activities to provide a broad overview of the current research interests of the Space Advanced Research Team (SpaceART). It will be seen that although much of the work is mission driven and focussed on possible future applications, some activities represent basic research in space systems engineering
Collision and evaporation avoidance for spacecraft formation
<p>Formation flying is an extremely promising approach to space operations with the potential to enable new types of missions and providing substantial increase in the performance of future space science and Earth observation applications. To successfully validate formation flying however requires the development of specific technologies and methodologies, which are beyond current state-of-the art in a wide range of diverse fields such as metrology and spacecraft guidance, navigation and control. A number of missions are currently under different stages of development to implement some of these stringent requirements.</p>
<p>The paper develops and compares collision avoidance algorithms, demonstrating them within a 6 degrees of freedom, multi-spacecraft environment. At first a number of different collision avoidance scenarios will be identified alongside the triggers that will cause the algorithms to be activated. Once activated the collision avoidance algorithm must ensure corrective action to avoid catastrophic consequences to the mission.</p>
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
Preliminary space mission design under uncertainty
This paper proposes a way to model uncertainties and to introduce them explicitly in the design process of a preliminary space mission. Traditionally, a system margin approach is used in order to take them into account. In this paper, Evidence Theory is proposed to crystallise the inherent uncertainties. The design process is then formulated as an Optimisation Under Uncertainties (OUU). Three techniques are proposed to solve the OUU problem: (a) an evolutionary multi-objective approach, (b) a step technique consisting of maximising the belief for different levels of performance, and (c) a clustering method that
firstly identifes feasible regions. The three methods are applied to the BepiColombo mission and their
effectiveness at solving the OUU problem are compared
Implicit large eddy simulations of anisotropic weakly compressible turbulence with application to core-collapse supernovae
(Abridged) In the implicit large eddy simulation (ILES) paradigm, the
dissipative nature of high-resolution shock-capturing schemes is exploited to
provide an implicit model of turbulence. Recent 3D simulations suggest that
turbulence might play a crucial role in core-collapse supernova explosions,
however the fidelity with which turbulence is simulated in these studies is
unclear. Especially considering that the accuracy of ILES for the regime of
interest in CCSN, weakly compressible and strongly anisotropic, has not been
systematically assessed before. In this paper we assess the accuracy of ILES
using numerical methods most commonly employed in computational astrophysics by
means of a number of local simulations of driven, weakly compressible,
anisotropic turbulence. We report a detailed analysis of the way in which the
turbulent cascade is influenced by the numerics. Our results suggest that
anisotropy and compressibility in CCSN turbulence have little effect on the
turbulent kinetic energy spectrum and a Kolmogorov scaling is
obtained in the inertial range. We find that, on the one hand, the kinetic
energy dissipation rate at large scales is correctly captured even at
relatively low resolutions, suggesting that very high effective Reynolds number
can be achieved at the largest scales of the simulation. On the other hand, the
dynamics at intermediate scales appears to be completely dominated by the
so-called bottleneck effect, \ie the pile up of kinetic energy close to the
dissipation range due to the partial suppression of the energy cascade by
numerical viscosity. An inertial range is not recovered until the point where
relatively high resolution , which would be difficult to realize in
global simulations, is reached. We discuss the consequences for CCSN
simulations.Comment: 17 pages, 9 figures, matches published versio
Positrons and 511 keV radiation as tracers of recent binary neutron star mergers
Neutron-rich material ejected from neutron star-neutron star (NS-NS) and
neutron star-black hole (NS-BH) binary mergers is heated by nuclear processes
to temperatures of a few hundred keV, resulting in a population of
electron-positron pairs. Some of the positrons escape from the outer layers of
the ejecta. We show that the population of low-energy positrons produced by
NS-NS and NS-BH mergers in the Milky Way can account for the observed 511-keV
line from the Galactic center (GC). Moreover, we suggest how positrons and the
associated 511-keV emission can be used as tracers of recent mergers. Recent
discovery of 511 keV emission from the ultra-faint dwarf galaxy Reticulum II,
consistent with a rare NS-NS merger event, provides a smoking-gun signature of
our proposal.Comment: 5 pages + 2 page supplement, 4 figures; v3: minor modifications,
published versio
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