A new analysis of debris mitigation and removal using networks

Modelling studies have shown that the implementation of mitigation guidelines, which aim to reduce the amount of new debris generated on-orbit, is an important requirement of future space activities but may be insufficient to stabilise the near-Earth debris environment. The role of a variety of mitigation practices in stabilising the environment has been investigated over the last decade, as has the potential of active debris removal (ADR) methods in recent work. We present a theoretical approach to the analysis of the debris environment that is based on the study of networks, composed of vertices and edges, which describe the dynamic relationships between Earth satellites in the debris system. Future projections of the 10 cm and larger satellite population in a non-mitigation scenario, conducted with the DAMAGE model, are used to illustrate key aspects of this approach. Information from the DAMAGE projections are used to reconstruct a network in which vertices represent satellites and edges encapsulate conjunctions between collision pairs. The network structure is then quantified using statistical measures, providing a numerical baseline for this future projection scenario. Finally, the impact of mitigation strategies and active debris removal, which can be mapped onto the network by altering or removing edges and vertices, can be assessed in terms of the changes from this baseline. The paper introduces the network methodology, highlights the ways in which this approach can be used to formalise criteria for debris mitigation and removal. It then summarises changes to the adopted network that correspond to an increasing stability and changes that represent a decreasing stability of the future debris environment

A sensitivity analysis of breakup models

Four of the leading breakup models, IDES, SDM, MASTER and EVOLVE 4 were compared in terms of their distributions of the cumulative number of fragments, fragment delta-vs and mass-to-area ratios with respect to fragment mass. These comparisons were made for a number of fragmentation scenarios including high and low intensity explosions and catastrophic and non-catastrophic collisions. It has been found that the IDES, SDM and MASTER models are generally in fairly good agreement for all these distributions in all scenarios, although there are slight differences to be found in certain cases. the EVOLVE 4 model produces generally different results for all scenarios, most notably in its delta-v and mass-tp-area distributions. the major differences between all the models in terms of their equations are discussed herein. An example scenario of a low intensity explosion in GEO was chosen and the resulting debris cloud for all models was propagated using the same high-fidelity orbital propagator. The differences in the propagated clouds for each model were compared. Generally the debris clouds produced by the IDES, SDM and MASTER models were in fairly good agreement for most scenarios, whilst the debris cloud produced by EVOLVE 4 shows some significant differences

Global vulnerability to near-Earth object impact

A clear appreciation of the consequences resulting from an asteroid impact is required in order to understand the near Earth object (NEO) hazard. Three main processes require modelling to analyse the entire impact event. These are the atmospheric entry phase, land impact events and ocean impact events. A range of impact generated effects (IGEs) are produced by different impact scenarios. It is these IGEs that present the threat to human populations world wide, and the infrastructure they utilise. A software system for analysing the NEO threat has been developed, entitled NEOimpactor, to examine the social and economic consequences from land and ocean impacts. Existing mathematical models for the three principal impact processes have been integrated into one complete system, which has the capability to model the various effects of a terrestrial asteroid impact and, critically, predict the consequences for the global population and infrastructure. Analysis of multiple impact simulations provides a robust method for the provision of an integrated, global vulnerability assessment of the NEO hazard. The primary graphical outputs from NEOimpactor are in the form of ‘relative consequence’ maps, and these have been designed to be comprehensible to a non-specialist audience. By the use of a series of multiple-impact simulations, the system has identified the five countries most at risk from the impact hazard, as well as indicating the various factors influencing vulnerability