Professor Massimiliano Vasile explains how the Stardust training and research network is placing the Strathclyde Aerospace Centre of Excellence (ACE) at the cutting edge of aerospace research.
The Strathclyde Aerospace Centre of Excellence is a multidisciplinary research group within the University of Strathclyde, Scotland, developing advanced research on innovative concepts and solutions for present and future space systems, aerospace transport, space exploration, satellite applications and the sustainable exploitation and exploration of space. Some of the factors that put ACE at the cutting edge of aerospace research are the multi-disciplinary nature of their activities, the global outlook and partnerships, and the embracing of advanced methodologies at the interface between physics, applied math, engineering and computer science. As part of these multi-disciplinary activities, the Director of ACE, Professor Massimilano Vasile, started a stream of research on asteroids and space debris in 2011 supported by the European Space Agency (ESA) and the European Commission. At the centre of this stream of research is the Pan-European Stardust programme.
The European Commission-funded Stardust training and research network is studying space objects in the solar system, at two extremes of the length and time scales, to protect our planet and the space environment around it. Stardust put together, for the first time, the scientific community studying space debris and the one studying asteroids to develop effective solutions to prevent an impact of a Near Earth Object (NEO) with the Earth and make the use of space sustainable (see Fig 1).
The motivation for the creation of Stardust is twofold. The Kessler syndrome (where the density of objects in orbit is high enough that collisions could set off a cascade) is more real than when it was first formulated in 1978. In the intervening years, the situation has developed as more objects have been put into orbit. Although statistically less likely to occur, an asteroid impact would have devastating consequences for our planet and should be regarded as a low probability but high risk catastrophic event. While an impact with a large (~10km) to medium (~300m) sized asteroid is unlikely, still it is not negligible. Furthermore, close encounters and impacts with smaller size objects, between 10-100m in diameter, occur more frequently. Our knowledge of asteroids in that range of sizes is, however, limited at the moment. The unforeseen Chelyabinsk super-bolide event in February 2013 provides an excellent example. Approximatively 1,500 individuals were injured due to the air burst’s blast wave that hit an area around a hundred of kilometres wide.
Stardust began working in 2013, with a first network comprising 14 partners from around Europe and over the years has grown to over 20 partners by establishing connections and collaborations with institutions in the USA and Japan. After a break of two years, Stardust will restart working in January 2019, still under the co-ordination of Vasile, focusing on the sustainability and resilience of the space environment through the emerging concept of space traffic management. It will work at the interface between computer science and mathematical physics to develop new concepts marrying artificial intelligence and chaos theory. In parallel Stardust will give an answer to the ever compelling issue of learning more about NEOs at an affordable cost by using nanosatellites for the exploration of space.
A question of sustainability and resilience
The publication of the IAA Cosmic Study on STM 2006defined Space traffic management (STM) as ‘the set of technical and regulatory provisions for promoting safe access into outer space, operations in outer space and return from outer space to Earth free from physical or radio-frequency interference.’1 The ever-increasing number and variety of orbiting objects ranging in size from a few microns to several meters and the number of future mega constellations are posing a serious question on the future sustainability and resilience of the space environment around the Earth. In order to ensure that the space environment is resilient to anomalies and catastrophic events and its exploitation is sustainable, Stardust is studying solutions for a comprehensive STM system, integrating improved space situational awareness and new tools to support space operators.
Artificial intelligence for space traffic management2
In the context of STM, the prediction of rare and catastrophic events is key to improve the resilience of the space environment. Stardust will use a combination of computational and artificial intelligence techniques to study the global behavior of space objects, predict high risk events and quantify the associate uncertainty. This will require processing multiple sources of information to learn from past data about patterns and early warning signals that can predict rare events and plan recovery measures. Data fusion techniques able to deal with imprecise, incomplete and spurious data have been lately subject of an intense research and techniques coming from the field of fuzzy set theories, probabilistic methods and evidence theory have been applied also in this context.3
Unlocking the secrets of chaos
The Stardust programme, and following studies by some of the Stardust members, has shown the occurrence of a plethora of dynamical phenomena:
- The overlapping of resonances and the onset of chaos4;5
- The existence of a web-like structure of luni-solar resonances6
- The chaotic variation of the orbital elements
- The occurrence of bifurcations of equilibria
- The existence of libration regions which lead to excursions in the eccentricity
- The chaotic transport in the phase space
These intricate dynamics exists, for examples, in the neighbourhood of GNSS constellations. Despite the fact that the Medium Erath Orbit (MEO) region will be populated by four complete constellations, namely GPS, GLONASS, Galileo and BeiDou, there are no internationally agreed mitigation guidelines, as for LEO and GEO. Although, it is mandatory to completely understand the dynamics of these objects, past studies have not been able to completely characterise the chaotic nature of their orbital dynamics. Stardust aims at a complete investigation of the chaotic dynamics of every Earth orbital region, as well as its consequences for the long term diffusion of populations of space debris, with particular attention to highly inclined orbits, which are affected by strong luni-solar resonances.
The art of demise
On average, over the past decade, a space object above 800kg has been re-entering every week. Most of these objects do not totally demise during atmospheric re-entry. Fragments may survive and reach the ground where they pose a risk to people and things.7 Space agencies are currently enforcing constraints on the casualty risk for re-entry events. The re-entry process is extremely uncertain due to the interaction with the different layers of the atmosphere and the plethora of physical phenomena simultaneously dictating the demise of spacecraft. Stardust for the first time introduced elements of uncertainty quantification to better assess the casualty risk.8 Stardust will embed uncertainty quantification into the design of space objects to resolve the tension between demisability and the survivability of space objects during their mission lifetime.
Manipulating asteroids and comets
Various technologies have been proposed for the deflection of asteroids. Some deflection techniques imply an instantaneous transfer of momentum (explosive techniques, impact techniques) along with a low level of control but a sizeable effect, whereas others imply a controlled but fainter effect on the asteroid trajectory (gravity tractor, ion beam shepherd, laser ablation). Stardust has investigated and evaluated different techniques, old and new, to deflect or change the rotation motion of asteroids and developed new methods to assess the risk of an impact with the Earth pre and post deflection.9 Although some of these techniques are at very advanced stage of development the high degree of uncertainty on the physical nature of NEOs makes some conclusions on the impact risk questionable and require further investigation on the physical characteristics of minor bodies.
Miniaturising the exploration of near earth objects
The exploration of minor bodies can substantially contribute to our knowledge of the solar system and to plan for the exploitation and manipulation of comets and asteroids. A potential low-cost exploration and prospection technology is offered by CubeSats. A variety of CubeSat platforms are available for applications around the Earth. Proposals exist to extend these capabilities to interplanetary space including asteroids.10 This extension requires the development of guidance, navigation and control (GNC), power and propulsion systems for deep space missions that account for the limited resources on board small spacecraft and on ground. A further key exploration technology is offered by micro-landers. The information from the prospection of asteroids is essential to improve our ability to manipulate the rotational and orbital dynamics of NEOs.
1 Contant- Jorgenson, Lála, Schrogl, ‘The IAA Cosmic Study on Space Traffic Management’, 2006
2 Vasile, M., Rodriguez-Fernandez, V., Serra, R., Camacho, D., Ricardi, A. ‘Artificial Intelligence in Support to Space Traffic Management’, IAC2017, IAC-17-A6,7,1×41479, Adelaide, Australia, 2017
3 Bahador Khaleghi et al., ‘Multisensor data fusion: A review of the state-of-the-art’, Information Fusion 14(1): 28-44, 2013
4 Celletti, Gales, ‘On the dynamics of space debris: 1:1, and 2:1 resonances’, J. Nonlinear Science 24(6): 1231-1262, 2014
5 Gkolias et al, ‘From order to chaos in Earth sattelite orbits’, Astronomical Journal 152(5), 2016
6 Rosengren et al. ‘Chaos in navigation sattelite orbits caused by the peturbed motion of the Moon’, Mon. Not. R. Astron. Soc., 449: 3522-3526, 2015
7 Lemmens et al. ‘On-ground casualty risk reduction by structural design for demise’, Advances in Space Research, 55(11):2592-2606, 2001
8 Benedetti et al., ‘Low-fidelity modelling for aerodynamic characteristics of re-entry objects’, Stardust Final Conference 2016
9 Thiry, N., Vasile, M. ‘Statistical Multi-Criteria Evaluation of Non-Nuclear Asteroid Deflection Methods’, Acta Astronautica, Volume 140, November 2017, Pages 293-307, https://doi.org/10/2016/j.actaastro.2017.08.021.
10 Greco, C, Di Carlo, M, Walker, L, & Vasile, M 2018, ‘Analysis of NEOs reachability with nano-sattallites and low thrust propulsion’, paper presented at 4S Symposium 2018 – Small Sattellites Systems and Services, Sorrento, Italy, 28/05/18 – 1/06/18
Professor Massimiliano Vasile
Aerospace Centre of Excellence
University of Strathclyde
+44 (0) 141 574 5168