Autonomous attitude using potential function method under control input saturation

The potential function method has been used extensively in nonlinear control for the development of feedback laws which result in global asymptotic stability for a certain prescribed operating point of the closed-loop system. It is a variation of the Lyapunov direct method in the sense that here the Lyapunov function, also called potential function, is constructed in such a way that the undesired points of the system state space are avoided. The method has been considered for the space applications where the systems involved are usually composed of the cascaded subsystems of kinematics and dynamics and the kinematic states are mapped onto an appropriate potential function which is augmented for the overall system by the use of the method of integrator backstepping. The conventional backstepping controls, however, may result in an excessive control effort that may be beyond the saturation bound of the actuators. The present paper, while remaining within the framework of conventional backstepping control design, proposes analytical formulation for the control torque bound being a function of the tracking error and the control gains. The said formulation can be used to tune to the control gains to bound the control torque to a prescribed saturation bound of the control actuators

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

Cargo compartment fire extinguishing system

In all large passenger transport airplanes, halon fire bottles are used to extinguish fire in the cargo compartments. Halon as a fire-extinguishing agent, contributes to the destruction of stratospheric ozone in the atmosphere and it is banned in many countries. FAA considers halon 1301 as an effective firefighting agent due to its low toxicity and noncorrosive properties but because it damages the ozone layer, it has been phased out of production. However, it is still widely used on commercial aircraft until a suitable replacement is found. In this paper we will present an alternative approach to using halon 1301 as a fire fighting paradigm. In the proposed method, nitrogen is first extracted from the atmosphere by using the onboard air separator module it is then cooled, and pressurized into the cargo compartments to suppress any fire. Several methodologies can be used to increase the flow rate from the air separator module, to extinguish fire in cargo compartment

Fuel leak detection on large transport airplanes

Fuel leakage has the risk of being ignited by external ignition sources, and therefore it is important to detect any fuel leakage before the departure of the aircraft. Currently, there are no fuel leak detection systems installed on commercial aircrafts, to detect fuel tank leakage, while only a small number of more recent aircraft, have a fuel monitoring system, that generates a fuel leak-warning message in cockpit in the case of fuel imbalance between the tanks. The approach proposed in this paper requires the fuel vent ports on the wings to be replaced with fuel vent valves, which can be controlled to be in open or close position. The fuel vent valve will be in close position, when certain conditions are fulfilled (all the related fuel valves closed, pumps not operating, etc.), the fuel tank ullage area is then pressurized to 4 psi and the rate of change of the pressure is measured over a period. Several experiments have been conducted and, the result show that a continuous fuel leak of one liter per minute can be detected. Further experiments show that if the fuel tank is pressurized to higher pressures, a fuel leak can be detected sooner

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

Large angle reorientation manoeuvre of spacecraft using robust backstepping control

The nonlinear control design problem for large angle reorientation manoeuvre of spacecraft has a proper structure for the direct application of backstepping design as its dynamics and kinematics are naturally in a cascade form. In this paper, the robustness of the backstepping control against the uncertainties in the moment of inertia matrix is investigated and a sufficient condition for the robust stability is derived. Numerical simulations show the validity of the condition

Space activities in Glasgow; advanced microspacecraft from Scotland

The City of Glasgow is renowned for its engineering and technological innovation; famous Glaswegian inventors and academics include James Watt (Steam Engine) and John Logie Baird (television), amongst many others. Contemporary Glasgow continues to pioneer and invent in a multitude of areas of science and technology and has become a centre of excellence in many fields of engineering; including spacecraft engineering. This paper will discuss how Clyde Space Ltd and the space groups at both Glasgow and Strathclyde Universities are combining their knowledge and expertise to develop an advanced microspacecraft platform that will enable a step change in the utility value of miniature spacecraft. The paper will also explore how the relationship between the academic and industrial partners works in practice and the steps that have been taken to harness resulting innovation to create space industry jobs within a city that was, until recently, void of any commercial space activity

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

A semiparametric bivariate probit model for joint modeling of outcomes in STEMI patients

In this work we analyse the relationship among in-hospital mortality and a treatment effectiveness outcome in patients affected by ST-Elevation myocardial infarction. The main idea is to carry out a joint modeling of the two outcomes applying a Semiparametric Bivariate Probit Model to data arising from a clinical registry called STEMI Archive. A realistic quantification of the relationship between outcomes can be problematic for several reasons. First, latent factors associated with hospitals organization can affect the treatment efficacy and/or interact with patient’s condition at admission time. Moreover, they can also directly influence the mortality outcome. Such factors can be hardly measurable. Thus, the use of classical estimation methods will clearly result in inconsistent or biased parameter estimates. Secondly, covariate-outcomes relationships can exhibit nonlinear patterns. Provided that proper statistical methods for model fitting in such framework are available, it is possible to employ a simultaneous estimation approach to account for unobservable confounders. Such a framework can also provide flexible covariate structures and model the whole conditional distribution of the response