Thermospheric Heating Modes and their Effects on Satellites

The thermosphere is the uppermost layer of our atmosphere at the edge of space (85 to 1000 km altitude). Within this region orbit thousands of satellites worth billions of pounds that provide essential modern services including satnav, satcomms, and remote sensing. There are also many thousands more orbiting pieces of man-made space debris which present a significant risk to operational satellites because of the chance of collision.

We have now passed a tipping point where the increase in debris from collisions exceeds losses, leading to a net growth of the space debris population and thus ever-increasing risk of collisions.

Short- and long-term predictions of satellite and debris trajectories are vital to avoid the destruction of satellites in low-Earth orbit. A major factor limiting factor is knowing the density of the thermosphere, which can vary by up to 800% during extreme times. The variability is due to effects in near-Earth space from disturbances on the Sun, collectively called space weather.

In the polar regions, where there is the greatest concentration of satellites, the largest uncertainties in thermospheric density arise from "Joule" heating. This is caused by collisions between electrically-charged and neutral particles in the thermosphere, driven by space weather. Crucially, we have yet to properly understand when and where Joule heating will occur and how predictable it is. Accurate models and prediction of Joule heating are vital to safeguard the space assets on which modern society depends.

In this project we will develop a better understanding of Joule heating by analysing more than a decade of data from two major international polar instrument networks. We will use a statistical method developed in meteorology called Empirical Orthogonal Function (EOF) analysis, which is capable of uncovering the underlying patterns in a large, noisy data set.

In this way we will both resolve the Joule heating in unprecedented detail and separate it into patterns which depend to greater or lesser degrees on the solar sources of space weather. Since these sources can be observed before they cause space weather at Earth, this will allow us to quantify the limits of predictability of the Joule heating. By then assessing the relationship between the Joule heating and satellite trajectories, this will allow us to describe which orbital paths are most at risk from space weather.

Who:
The realisation of this study will contribute the socio-economic benefits of an improved understanding of satellite drag and its relationship to space weather events. The commercial sector is increasingly reliant on a vast and expanding network of satellites in many different orbits, and hence, is commensurately reliant on the accuracy of hazard-mitigation strategies aimed at protecting this space infrastructure. The growing importance of space weather hazards is reflected in their inclusion in the Cabinet Office's National Risk Register of Civil Emergencies (2015). Space weather will remain a matter of long-term importance as the UK's economical growth becomes increasingly technology-led. Near-Earth space is a shared resource, recognised by the United Nations Committee on the Peaceful Uses of Outer Space (UN COPUOS). Moreover, orbits safe from space debris are a depletable resource. Our results will therefore impact the decision-making processes of policy writers and insurance-risk assessors with regards to the continued development of low-Earth orbits.

Since the 2013 solar maximum and the associated increase in auroral displays at UK latitudes from geomagnetic storms, there is presently high public interest in the dynamic nature of the Earth's near space environment. We will capitalise on this interest to distribute the benefits of our new insights to the wider public.

How:
The hazards to satellites from space debris will increase in the upcoming solar minimum, where the average thermospheric density will decrease by an order of magnitude, reducing the natural tendency for space debris to de-orbit due to atmospheric drag. At the same time, the likelihood of an extreme space weather event is not decreased, and these events will have a proportionally greater impact on satellite and debris orbital deflection than the same event would at solar maximum. Our research will contribute to a better predictive capacity of the Joule heating given the input from space weather events, and will establish the extent to which the associated atmospheric drag can be forecast. These findings will be of great importance to the effectiveness of hazard mitigation strategies in near-Earth space. Our results will have further impact in the determination of space infrastructure insurance risk from scenarios such as space debris- or inter-satellite collisions, since we will be able to establish which particular orbital paths are most at risk from space weather-related fluctuations in satellite drag.

The public sector will benefit from the planned outreach efforts to improve general awareness of the dynamic nature of the near-Earth space environment. The budgeted production of outreach materials, and the planned outreach activities will each be instrumental in forming an active dialogue with public beneficiaries and communicating the importance of our science. The British Antarctic Survey has a high media profile and we are well-placed to provide outreach activities with the assistance of its Communications team.

In a wider sense, our research will help the UK to capitalise on its ESA investment in Earth observation, through the development and supply of data products which will aid both the research of the scientific community and the functioning of the UK economy.