Pattern transition in spacecraft formation flying using bifurcating potential field

Many new and exciting space mission concepts have developed around spacecraft formation flying, allowing for autonomous distributed systems that can be robust, scalable and flexible. This paper considers the development of a new methodology for the control of multiple spacecraft. Based on the artificial potential function method, research in this area is extended by considering the new approach of using bifurcation theory as a means of controlling the transition between different formations. For real, safety or mission critical applications it is important to ensure that desired behaviours will occur. Through dynamical systems theory, this paper also aims to provide a step in replacing traditional algorithm validation with mathematical proof, supported through simulation. This is achieved by determining the non-linear stability properties of the system, thus proving the existence or not of desired behaviours. Practical considerations such as the issue of actuator saturation and communication limitations are addressed, with the development of a new bounded control law based on bifurcating potential fields providing the key contribution of this paper. To illustrate spacecraft formation flying using the new methodology formation patterns are considered in low-Earth-orbit utilising the Clohessy-Wiltshire relative linearised equations of motion. It is shown that a formation of spacecraft can be driven safely onto equally spaced projected circular orbits, autonomously reconfiguring between them, whilst satisfying constraints made regarding each spacecraft

Passive orbit control for space-based geo-engineering

In this Note we consider using solar sail propulsion to stabilize a spacecraft about an artificial libration point. It has been demonstrated that the constant acceleration from a solar sail can be used to generate artificial libration points in the Earth-Sun three-body problem. This is achieved by directing the thrust due to the sail such that it adds to the centripetal and gravitational forces. These libration points have the potential for future space physics and Earth observation missions. Of particular interest is the possibility of placing solar reflectors at the L1 artificial libration point to offset natural and human driven climate change. One engineering challenge that presents itself is that these artificial libration points are highly unstable and require active control for station-keeping. Previous work has shown that it is possible to stabilize a solar sail about artificial libration points using variations in both pitch and yaw angles. However, in a practical sense, solar sails are large structures and active control of the sail's attitude is a challenging engineering problem. Passive stabilization of such reflectors is to be investigated here to reduce the complexity of space-based geo-engineering schemes

Mining electron density for functionally relevant protein polysterism in crystal structures.

This review focuses on conceptual and methodological advances in our understanding and characterization of the conformational heterogeneity of proteins. Focusing on X-ray crystallography, we describe how polysterism, the interconversion of pre-existing conformational substates, has traditionally been analyzed by comparing independent crystal structures or multiple chains within a single crystal asymmetric unit. In contrast, recent studies have focused on mining electron density maps to reveal previously 'hidden' minor conformational substates. Functional tests of the importance of minor states suggest that evolutionary selection shapes the entire conformational landscape, including uniquely configured conformational substates, the relative distribution of these substates, and the speed at which the protein can interconvert between them. An increased focus on polysterism may shape the way protein structure and function is studied in the coming years

The indicators of pupil opinion and teacher interactivity for inquiry-based science teaching

In order to establish those practices which underpin a science teaching performance that combines pupil enthusiasm and creative classrooms, it will be necessary to uncover evidence of inquiry-based learning experiences in science that can provide a warrant for theory and practice that will assist new science teachers in recognising and developing opportunities for investigative activity. Remaining aware, however, of the recurring theme in contemporary educational research which suggests that learning to teach has an important affective dimension associated with developing relationships and the formation of a teaching identity – a model of development which thus transcends atheoretical checklists of professional standards or pedagogical steps – the nature of that evidence will necessarily be in the area of the formative development of new teachers’ professional knowledge and understanding

Becoming an effective science teacher at the Department of Curricular Studies, University of Strathclyde

In an article for the International section, Allan Blake, Colin Smith and Jim McNally from Strathclyde report on the start of a very important EU-funded project, involving 15 countries, which looks at how ‘inquiry-based science’ can be promoted in science teaching and the significance for teacher education. In their view, inquiry-based science is more about open-endedness and uncertainty of outcome than routine (prescribed) practical work. STE will keep track of this important project and we will report on its progress and outcomes in future issues

Venus: A search for clues to early biological possibilities

The extensive evidence that there is no extant life on Venus is summarized. The current atmospheric environment, which is far too hostile by terrestrial standards to support life, is described. However, exobiologists are interested in the possibility of extinct life on Venus. The early history of Venus is discussed in terms of its ability to sustain life that may now be extinct

Neutron irradiation of Linde sieve 13-X

Imperial Users onl

Mode-matching analysis of a shielded rectangular dielectric-rod waveguide

Rectangular cross-section dielectric waveguides are widely used at millimeter wavelengths. In addition, shielded dielectric resonators having a square cross-section are often used as filter elements, however there is almost no information available on the effect of the shield. Rectangular or square dielectric waveguide is notoriously difficult to analyze, because of the singular behaviour of the fields at the corners. Most published analyses are for materials with a low dielectric constant, and do not include the effects of a shield. This paper describes a numerically efficient mode matching method for the analysis of shielded dielectric rod waveguide, which is applicable to both low and high dielectric constant materials. The effect of the shield on the propagation behaviour is studied. The shield dimensions may be selected such that the shield has a negligible effect, so that results can be compared with free space data. The results are verified by comparison with several sets of published data, and have been confirmed by measurement for a nominal 'e' r of 37.4

STOVL aircraft simulation for integrated flight and propulsion control research

The United States is in the initial stages of committing to a national program to develop a supersonic short takeoff and vertical landing (STOVL) aircraft. The goal of the propulsion community in this effort is to have the enabling propulsion technologies for this type aircraft in place to permit a low risk decision regarding the initiation of a research STOVL supersonic attack/fighter aircraft in the late mid-90's. This technology will effectively integrate, enhance, and extend the supersonic cruise, STOVL and fighter/attack programs to enable U.S. industry to develop a revolutionary supersonic short takeoff and vertical landing fighter/attack aircraft in the post-ATF period. A joint NASA Lewis and NASA Ames research program, with the objective of developing and validating technology for integrated-flight propulsion control design methodologies for short takeoff and vertical landing (STOVL) aircraft, was planned and is underway. This program, the NASA Supersonic STOVL Integrated Flight-Propulsion Controls Program, is a major element of the overall NASA-Lewis Supersonic STOVL Propulsion Technology Program. It uses an integrated approach to develop an integrated program to achieve integrated flight-propulsion control technology. Essential elements of the integrated controls research program are realtime simulations of the integrated aircraft and propulsion systems which will be used in integrated control concept development and evaluations. This paper describes pertinent parts of the research program leading up to the related realtime simulation development and remarks on the simulation structure to accommodate propulsion system hardware drop-in for real system evaluation