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&gt

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 $k^{-5/3}$ 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 $\sim 512^3$, 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