Hugh G. Lewis

• Doctor of Philosophy
• Professor of Astronautics at University of Southampton

The collision risk posed to satellites is a key factor when assessing the long-term sustainability of activities in space. Additionally, advocates for the preservation of dark and quiet skies have raised concerns about the impacts of large satellite constellations in Low Earth Orbit (LEO) on astronomical observations due to satellite streaks and an...

Peatlands across the world are vital carbon stores. However, human activities have caused the degradation of many sites, increasing their greenhouse gas emissions and vulnerability to wildfires. Comprehensive monitoring of peatlands is essential for their protection, tracking degradation and restoration, but current techniques are limited by cost,...

Increasing carbon dioxide concentrations in the mesosphere and lower thermosphere are increasing radiative cooling in the upper atmosphere, leading to thermospheric contraction and decreased neutral mass densities at fixed altitudes. Previous studies of the historic neutral density trend have shown a dependence upon solar activity, with larger F10....

Increasing carbon dioxide concentrations in the mesosphere and lower thermosphere are increasing radiative cooling in the upper atmosphere, leading to thermospheric contraction and decreased neutral mass densities at fixed altitudes. Previous studies of the historic neutral density trend have shown a dependence upon solar activity, with larger F10....

In order to combat greenhouse gas emissions, the sources of these emissions must be understood. Environmental monitoring using low-cost wireless devices is one method of measuring emissions in crucial but remote settings, such as peatlands. The Figaro NGM2611-E13 is a low-cost methane detection module based around the TGS2611-E00 sensor. The manufa...

We introduce a methodology for estimating the risk posed to the space environment by a spacecraft over an arbitrary period of time following a risk mitigation strategy, in terms of aggregate collision probability. Our methodology enables estimation of residual risk and maneuver frequency, where residual risk is defined conceptually as the risk to a...

We introduce a methodology for estimating the risk posed to the space environment by a spacecraft over an arbitrary period of time following a risk mitigation strategy, in terms of aggregate collision probability. Our methodology enables estimation of residual risk and maneuver frequency, where residual risk is defined conceptually as the risk to a...

The objective of this paper is to identify the illumination conditions that maximise the differences that can be measured between light curves of an object resulting from its attitude state. This is relevant to attitude determination techniques using light curve data, and is valuable for the design of observation strategies that maximise the inform...

The mapping of all close approaches in low Earth orbit (LEO) by collision probability, consequence, and risk provides insight into both current and future collision hazards. Probability is determined using the miss distance, hard body radius, and covariance derived from the LeoLabs data platform. Consequence is calculated using the mass involved in...

Increasing carbon dioxide causes cooling in the upper atmosphere and a secular decrease in atmospheric density over time. With the use of the Whole Atmospheric Community Climate Model with thermosphere and ionosphere extension (WACCM‐X), neutral thermospheric densities up to 500 km have been modeled under increasing carbon dioxide concentrations. O...

A number of initiatives for quantifying the environmental impact of space missions, the sustainability of space activities and the so-called "carrying capacity" of Earth orbital regions, have emerged in the last few years. Most initiatives lack an awareness of the deep time issues that arise from the enduring nature of the space debris problem. We...

Simulations of the thermosphere under increasing carbon dioxide concentrations have been performed with the Whole Atmosphere Community Climate Model-extended (WACCM-X). These have been used to create a density scaling factor for thermospheric density, which is dependent upon altitude, ground-level carbon dioxide (CO 2) concentration, and solar acti...

Computational models of the space debris population are used to identify and evaluate mitigation guidelines aiming to prevent the generation of new space debris. Conventionally, these models evaluate different scenarios featuring variations of proposed interventions with respect to a reference scenario in which the intervention is not implemented....

The amount of orbital debris generated in low Earth orbit has been steadily increasing. Recently, deployments of large satellite constellations in low-Earth orbit (LEO) mean that the number of satellites in key orbits will increase at a much higher rate than seen historically, raising concerns over the sustainability of future space activities. Thi...

This paper describes a process for identifying the intact objects in orbit that (a) pose the greatest debris-generating potential risk to operational satellites or (b) would reduce the risk the most if they were removed or prevented from colliding with each other (i.e., remediated). To accomplish this, a number of diverse, international space organ...

In the past few years, the interest towards the implementation of design-for-demise measures has increased steadily. The majority of mid-sized satellites currently launched and already in orbit fail to comply with the casualty risk threshold of 10−4. Therefore, satellites manufacturers and mission operators need to perform a disposal through a cont...

In the past few years, the interest towards the implementation of design-for-demise measures has increased steadily. Most mid-sized satellites currently launched and already in orbit fail to comply with the casualty risk threshold of 0.0001. Therefore, satellites manufacturers and mission operators need to perform a disposal through a controlled re...

The ‘NewSpace’ era of the last two decades has seen increasing disruption and innovation in the space industry driven by a growing commercial element. A new investigation of spacecraft launched between 1980 and 2017 identified an increase in the number of spacecraft being deployed into similar target orbits. This has resulted in a shift from a more...

Until two decades ago, the dominance of the space industry by national governments shaped the key characteristics of the spacecraft population and hence the space debris models used to anticipate future orbital populations. The rise of `NewSpace’ with the growth of private sector involvement has brought innovations, disrupting the status quo and ch...

Linear growth of the orbital debris population is observed in the results of many evolutionary models when they are used to simulate the effects of the widespread adoption of the Inter-Agency Space Debris Coordination Committee (IADC) debris mitigation guidelines. Such linear growth seemingly confirms the belief that adopting these debris mitigatio...

Large constellations of satellites in Low Earth Orbit (LEO) may adversely impact the sustainable use of the space environment over the long-term unless appropriate plans for orbital debris mitigation measures are incorporated into the design and operation. In particular, recent computer modelling studies have shown that comprehensive observance of...

The space environment around the Earth is populated by more than 130 million objects of 1 mm in size and larger, and future predictions shows that this amount is destined to increase, even if mitigation measures are implemented at a far better rate than today. These objects can hit and damage a spacecraft or its components. It is thus necessary to...

The space environment around the Earth is populated by more than 130 million objects of 1 mm in size and larger, and future predictions shows that this amount is destined to increase, even if mitigation measures are implemented at a far better rate than today. These objects can hit and damage a spacecraft or its components. It is thus necessary to...

A new Hopfield neural network (HNN) model for downscaling a digital elevation model in grid form (gridded DEM) is proposed. The HNN downscaling model works by minimizing the local semivariance as a goal, and by matching the original coarse spatial resolution elevation value as a constraint. The HNN model is defined such that each pixel of the origi...

Due to the significant computational demands involved in the long-term projection of large debris populations, evolutionary models make use of fast and efficient algorithms for collision risk assessment. A commonly used algorithm for collision risk assessment is the cube method, introduced by Liou et al. in 2003. Relatively little research has been...

Among the mitigation measures introduced to cope with the space debris issue there is the de-orbiting of decommissioned satellites. Guidelines for re-entering objects call for a ground casualty risk no higher than 0.0001. To comply with this requirement, satellites can be designed through a design-for-demise philosophy. Still, a spacecraft designed...

The paper is concerned with examining the effects that design-for-demise solutions can have not only on the demisability of components, but also on their survivability that is their capability to withstand impacts from space debris. First two models are introduced. A demisability model to predict the behaviour of spacecraft components during the at...

Large constellations of satellites offering global communications services are being planned for Low Earth Orbit (LEO). The deployment of such constellations would transform space traffic in this important environment, leading to questions about the sustainability of this activity in the LEO region. This paper reports the results of a study using t...

Several private companies, including OneWeb, Boeing, SpaceX and Samsung, have recently shown interest in deploying constellations of hundreds or even thousands of spacecraft in the Low Earth Orbit (LEO) region. Their objective is to provide global telecommunications services and internet coverage with low latency. However, the constant growth of th...

Poster for the Aeronautic and Astronautic Poster challenge at University of Southampton, 2018.

Recently, several studies reported that the current level adoption of end-of-life mitigation guidelines should not be able to prevent the increase of the orbital population over a 200-year timeframe. Therefore, the active removal of debris has been seen as a possible solution to stabilise the population and reduce the collision risk with space debr...

This work aims to in­ves­ti­gate the re­sponse of the low Earth orbit en­vi­ron­ment to the change in num­ber and dis­tri­b­u­tion of new launches and to un­der­stand the ef­fects of the size and post-mis­sion life­time of a large con­stel­la­tion of space­craft. The analy­sis pre­sented in this pa­per were car­ried out us­ing MISSD, Model for In­v...

Environmental indices for space objects have been proposed to identify good candidates for active debris removal missions and to deal with the licensing process of space objects before their launch. A way to rank the environmental impact of spacecraft may be based on the assessment of how their fragmentations would affect operational satellites. In...

The aim of this work is to investigate a new approach that can increase the Active Debris Removal (ADR) effectiveness regardless of the boundary conditions and the evolution of the Low Earth Orbit (LEO) population. This study use the Model to Investigate control Strategies for Space Debris (MISSD), developed at Southampton University. This statisti...

The paper presents the development of a multi-objective optimisation framework to study the effects that preliminary design choices have on the demisability and the survivability of a spacecraft. Building a spacecraft such that most of it will demise during the re-entry through design-for-demise strategies may lead to design that are more vulnerabl...

In space debris models, even a small change in the simulation variables can profoundly influence the evolution of the orbital population. The focus of this paper is to investigate the response of the LEO environment to the change in number and distribution of new object launched. The results of the performed sensitivity analysis suggest that the mo...

A sensitivity study on the launch rate and profile on the Low Earth Orbit environment. PPT presentation of the EUCASS 2017 conference paper with the same title.

Environmental indices for space objects have been proposed to identify good candidates for active debris removal missions and to deal with the licensing process of space objects before their launch. A way to rank the environmental impact of spacecraft may be based on the assessment of how their fragmentations would affect operational satellites. In...

In a period where the evolution of the space environment is causing increasing concerns for the future of space exploitation and sustainability, the design for demise philosophy has gained an increased interest. However, satellites designed for demise still have to survive the space environment polluted by space debris. Within this context we are d...

The uncertainty region associated with short arcs is typically large, making the initialization of orbit estimators a challenging task. In this work we propose a method to reduce the size of the uncertainty region using automatic domain pruning. The initial orbit and its confidence region are obtained by using a differential algebra-based initial o...

In the framework of space debris remediation and mitigation and eco-design of space systems, a design indicator is proposed to measure the management of end-of-life options and to compare different design options of a space mission from the perspective of the impacts of space debris. Such an indicator measures the orbital space occupied by missions...

In recent years several formulations of debris indices have been proposed to provide a fast assessment of the criticality of a space object in terms of its impact on the debris environment. In a previous work, we proposed a formulation (ECOB, Environmental Consequences of Orbital Breakups) based on the evaluation of the consequences of the fragment...

Several strategies have been implemented or proposed to tackle the space debris problem. However, there is still debate on the feasibility, cost, and effectiveness of these mitigation measures, especially in light of the increasing use of small satellites in low Earth orbit (LEO) and the drive towards space debris remediation. This work presents a...

Several strategies have been implemented or proposed to tackle the space debris problem. However, there is still debate on the feasibility, cost and effectiveness of these mitigation measures, especially in light of the increasing use of small satellites in low Earth orbit (LEO) and the drive towards space debris remediation. This work presents a s...

In a period where the evolution of the space environment is causing increasing concerns for the future of space exploitation and sustainability, the design-for-demise philosophy has gained an increased interest. However, building a spacecraft such that most of it will demise through design-for-demise strategies may lead to designs that are more vul...

Presentation of the model, validation and preliminary results.

A set of 50,000 artificial Earth impacting asteroids was used to obtain, for the first time, information about the dominance of individual impact effects such as wind blast, overpressure shock, thermal radiation, cratering, seismic shaking, ejecta deposition and tsunami for the loss of human life during an impact event for impactor sizes between 15...

A set of 50,000 artificial Earth impacting asteroids was used to obtain, for the first time, information about the dominance of individual impact effects such as wind blast, overpressure shock, thermal radiation, cratering, seismic shaking, ejecta deposition and tsunami for the loss of human life during an impact event for impactor sizes between 15...

An asteroid impact is a low probability event with potentially devastating consequences. The Asteroid Risk Mitigation Optimization and Research (ARMOR) software tool calculates whether a colliding asteroid experiences an airburst or surface impact and calculates effect severity as well as reach on the global map. To calculate the consequences of an...

Efficient long-term propagation of orbits is needed for e.g. the design of disposal orbits and analysis of their stability. Semi-analytical methods are suited for this as they combine accuracy and efficiency. However, the semi-analytical modelling of non-conservative forces is challenging and in general numerical quadrature is required to accuratel...

An asteroid impact is a low probability event with potentially devastating consequences. The Asteroid Risk Mitigation Optimization and Research (ARMOR) software tool calculates whether a colliding asteroid experiences an airburst or surface impact and calculates effect severity as well as reach on the global map. To calculate the consequences of an...

Space debris simulations, e.g. those performed by the Inter-Agency Debris Coordination Committee (Liou et al., 2013), showed that the number of objects in orbit is likely to increase. This study analyses the uncertainty in the results of space debris simulations performed using semi-stochastic models that necessitate the use of Monte Carlo simulati...

Opportunities provided by small satellites in low Earth orbit (LEO) are anticipated to make a significant impact on the space economy through the delivery of important and innovative services. However, with plans by some companies to operate large constellations of small satellites in LEO, and with many small satellite launches forecast in coming d...

Among the mitigation measures introduced to cope with the space debris issue there is the de-orbiting of decommissioned satellites. Guidelines for re-entering objects call for a ground casualty risk no higher than 10⁻⁴. To comply with this requirement, satellites can be designed through a design-for-demise philosophy. Still, a spacecraft designed t...

The paper is concerned with examining the effects that design-for-demise solutions can have not only on the demisability of components, but also on their survivability that is their capability to withstand impacts from space debris. First two models are introduced. A demisability model to predict the behaviour of spacecraft components during the at...

In space debris models, even a small change in the simulation variables can profoundly influence the evolution of the orbital population. The focus of this paper is to investigate the response of the LEO environment to the change in number and distribution of new object launched. The results of the performed sensitivity analysis suggest that the mo...

Active Debris Removal (ADR) methods are being developed due to a growing concern about the congestion on-orbit and sustainability of spaceflight. This study examined the probability of an on-orbit collision between an ADR target, whilst being de-orbited, and all the objects in the public catalogue published by the US Strategic Command. Such a colli...

The total number of active satellites, rocket bodies, and debris larger than 10 cm is currently about 20,000. Considering all resident space objects larger than 1 cm this rises to an estimated minimum of 500,000 objects. Latest generation sensor networks will be able to detect small-size objects, producing millions of observations per day. Due to o...

This work presents a source-sink debris evolutionary model of the Low Earth Orbit (LEO) with a proportional control on Active Debris Removal (ADR). The model is based on a set of first order differential equations, which describe the injection and removal rates in several altitude bands within the LEO. Explosions and collisions generate fragments v...

Adaptive Remediation of the Space Debris Environment using Feedback Control

The number of artificial objects in orbit continues to increase and, with it, a key threat to space sustainability. In response, space agencies have identified a set of mitigation guidelines aimed at enabling space users to reduce the generation of space debris by, for example, limiting the orbital lifetime of their spacecraft and launcher stages a...

In a period where the evolution of the space environment is causing increasing concerns for the future of space exploitation and sustainability, the design-for-demise philosophy has gained an increased interest. However, satellites designed for demise still have to survive the space environment, polluted by space debris, for many years. Within this...

ESA and NASA maintain asteroid hazard lists that contain all known asteroids with a non zero chance of colliding with the Earth in the future. Some software tools exist that are, either, capable of calculating the impact points of those asteroids, or that can estimate the impact effects of a given impact incident. However, no single tool is availab...

ESA internal presentation about asteroid risk quantification.

Adaptive Remediation of the Space Debris Environment Using Feedback Control

In the past years, several methods have been proposed to rank spacecraft and space debris objects depending on their effect on the space environment. The interest in this kind of indices is primarily motivated by the need of prioritising potential candidates of active debris removal missions and to decide on the required reliability for disposal ac...

Presentation to the United Nations Space Mission Planning Advisory Group (SMPAG) who are leading the effort to implement asteroid threat response procedures and set up a framework to facilitate international collaboration to answer the hazard. The presentation introduces the method of asteroid risk assessment to SMPAG.

Predicting the re-entry of space objects enables the risk they pose to the ground population to be managed. The more accurate the re-entry forecast, the more cost-efficient risk mitigation measures can be put in place. However, at present, the only publicly available ephemerides (two line element sets, TLEs) should not be used for accurate re-entry...

The presentation is about the human population vulnerability models that are a component for asteroid risk assessment.

Asteroids that could collide with the Earth are listed on the publicly available Near Earth Object (NEO) hazard web sites maintained by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). The risk of 69 potentially threatening NEOs that produce 261 dynamically distinct impact instances, or Virtual Impactors...

ESA and NASA maintain asteroid hazard lists that contain all known asteroids with a non zero chance of colliding with the Earth in the future. Some software tools exist that are, either, capable of calculating the impact points of those asteroids, or that can estimate the impact effects of a given impact incident. However, no single tool is availab...

This article proposes a continuum density approach for space debris modelling. The debris population in Low Earth Orbit (LEO) is represented through its density in semi-major axis, eccentricity and inclination. The time evolution of the density in orbital elements is modelled through the continuity equation. The perturbing effect of aerodynamic dra...

Earth orbits are becoming increasingly congested. This will not only impact future space operations but also become a concern for the population on the ground; with more spacecraft being flown, more objects will re-enter the atmosphere in an uncontrolled fashion. Parts of these satellites can reach Earth surface and endanger the ground population (...

As the debris spatial density increases due to recent collisions and inoperative spacecraft, the probability of collisions in space grows. Even a collision involving small objects may produce thousands of fragments due to the high orbital velocity and the high energy released. The propagation of the trajectories of all the objects produced by a bre...

Asteroids that could collide with the Earth are listed on the publicly available Near-Earth object (NEO) hazard web sites maintained by the US and European space agencies (NASA and ESA). The impact probability distribution of 69 potentially threatening NEOs from these lists that produce 261 dynamically distinct impact instances, or Virtual Impactor...

In February 2015 the satellite DMSP-F13 exploded in orbit producing 160 new trackable pieces of space debris. In the following days, operators assessed how the explosion affects the risk for their spacecraft, considering only debris objects larger than 10 cm. However, also smaller fragments are an important part of the debris population as any coll...

On the influence of increased asteroid risk modelling fidelity on nation specific risk results.

ESA’s asteroid risk list contains all known asteroids that have a non-zero chance of colliding with the Earth in the future. The possible impact locations of the asteroids in the list with a minimum diameter of 30 m were calculated. To this end, the freely available software OrbFit was utilized to find orbit solutions for each asteroid that result...

As the debris population increases, the probability of collisions in space grows. Because of the high level of released energy, even collisions with small objects may produce thousands of fragments. Propagating the trajectories of all the objects produced by a breakup could be computationally expensive. Therefore, in this work, debris clouds are mo...

Space debris simulations show that if current space launches continue unchanged, spacecraft operations might become difficult in the congested space environment. It has been suggested that Active Debris Removal (ADR) might be necessary in order to prevent such a situation. Selection of objects to be targeted by ADR is considered important because...

Logistic regression studies which assess landslide susceptibility are widely available in the literature. However, a global review of these studies to synthesise and compare the results does not exist. There are currently no guidelines for the selection of covariates to be used in logistic regression analysis, and as such, the covariates selected v...

The present distribution of intact objects is a good proxy to quantify the catastrophic collision risk and consequences in the coming decades. The results of a large number of long term simulations of the LEO environment perturbed by the collisional fragmentation of massive objects are used to identify the main driving parameters of the long term c...

Which nations should be concerned about asteroid impacts? 261 impact corridors were calculated based on orbital data and impact probabilities of observed asteroids that could impact the Earth before 2100. The corridors, in the form of impact probability distributions were projected onto the Earth map. The cumulative impact probability distribution...

Current debris evolutionary models usually neglect fragments smaller than 10 cm because of the high computational effort they add to the simulation. However, small-debris objects can also be dangerous to operational satellites. This work proposes an analytical approach to describe the evolution of a cloud of small fragments generated by a collision...

Small fragments are rarely included in the evolution of the debris population as their number is so large that the computational time would become prohibitive. However, they also can be dangerous to operational satellites, so it is important to study their contribution to the collision probability. This work proposes an analytical method to propaga...

Quantitative modelling of landslide hazard, as opposed to landslide susceptibility, as a function of the earthquake trigger is vital in understanding and assessing future potential exposure to landsliding. Logistic regression analysis is a method commonly used to assess susceptibility to landsliding; however, estimating probability of landslide haz...

Around the Earth there are more than ten million objects larger than 1 mm that can interfere with other orbiting spacecraft. In particular, objects larger than 1 cm are considered massive enough to seriously damage or even destroy a satellite in case of collision. The traditional piece-by-piece approach to study the evolution of debris objects cann...

As the debris population increases, the probability of collisions in space grows. Even a collision involving small objects may produce thousands of fragments due to high orbital velocity and the high energy released in the collision. The propagation of the trajectories of all the objects would be prohibitive in terms of computational time, so simpl...

In their 2011 paper, Oltrogge and Leveque encouraged the CubeSat community to take leadership roles in space debris assessment, ensuring that debris guidelines and standards are met and by implementing effective debris mitigation strategies. However, common misconceptions about the role of CubeSats in the evolution of the space debris environment r...