1,596 research outputs found
The Right Honourable Malcolm MacDonald : Angkor
No full textGroslier Bernard Philippe. The Right Honourable Malcolm MacDonald : Angkor. In: Bulletin de l'Ecole française d'Extrême-Orient. Tome 50 N°1, 1960. pp. 197-204
Introduction to pharmacokinetics and pharmacodynamics
No full textPreceded by Introduction to pharmacokinetics and pharmacodynamics : the quantitative basis of drug therapy / Thomas N. Tozer, Malcolm Rowland. c2006.Includes index.pharmacy bookfair2016xii, 386 pages :Preceded by Introduction to pharmacokinetics and pharmacodynamics: the quantitative basis of drug therapy / Thomas N. Tozer, Malcolm Rowland. c2006
Survey of highly non-Keplerian orbits with low-thrust propulsion
No full textCelestial mechanics has traditionally been concerned with orbital motion under the action of a conservative gravitational potential. In particular, the inverse square gravitational force due to the potential of a uniform, spherical mass leads to a family of conic section orbits, as determined by Isaac Newton, who showed that Kepler‟s laws were derivable from his theory of gravitation. While orbital motion under the action of a conservative gravitational potential leads to an array of problems with often complex and interesting solutions, the addition of non-conservative forces offers new avenues of investigation. In particular, non-conservative forces lead to a rich diversity of problems associated with the existence, stability and control of families of highly non-Keplerian orbits generated by a gravitational potential and a non-conservative force. Highly non-Keplerian orbits can potentially have a broad range of practical applications across a number of different disciplines. This review aims to summarize the combined wealth of literature concerned with the dynamics, stability and control of highly non-Keplerian orbits for various low thrust propulsion devices, and to demonstrate some of these potential applications
Solar Sailing: applications and technology advancement
Get PDFHarnessing the power of the Sun to propel a spacecraft may appear somewhat ambitious and the observation that light exerts a force contradicts everyday experiences. However, it is an accepted phenomenon that the quantum packets of energy which compose Sunlight, that is to say photons, perturb the orbit attitude of spacecraft through conservation of momentum; this perturbation is known as solar radiation pressure (SRP). To be exact, the momentum of the electromagnetic energy from the Sun pushes the spacecraft and from Newton’s second law momentum is transferred when the energy strikes and when it is reflected. The concept of solar sailing is thus the use of these quantum packets of energy, i.e. SRP, to propel a spacecraft, potentially providing a continuous acceleration limited only by the lifetime of the sail materials in the space environment. The momentum carried by individual photons is extremely small; at best a solar sail will experience 9 N of force per square kilometre of sail located in Earth orbit (McInnes, 1999), thus to provide a suitably large momentum transfer the sail is required to have a large surface area while maintaining as low a mass as possible. Adding the impulse due to incident and reflected photons it is found that the idealised thrust vector is directed normal to the surface of the sail, hence by controlling the orientation of the sail relative to the Sun orbital angular momentum can be gained or reduced. Using momentum change through reflecting such quantum packets of energy the sail slowly but continuously accelerates to accomplish a wide-range of potential missions
Malcolm Lowry - Detours and Dislocations - Douglas and Dollarton: Proposals for Artworks
Get PDFA 1/50 scale model of Malcolm Lowry’s 1944 shack at Dollarton, and a carousel, slide-projected, artwork of 80, 35 mm colour slides (Cates Park and Maplewood Mudflats) were exhibited at the Bluecoat, Liverpool as part of the conference proceedings, July 28 - 29, 2017. A conference paper of the same title discussed the research and making of these artworks.As a set of 'Proposals for Artworks' and associated writing this project builds on previous research, which retraces the footsteps of Wirral-born author of Under the Volcano, Malcolm Lowry. The work emerges from photography and moving image made on location in Vancouver in June 2017. A paper entitled ‘Malcolm Lowry – Detours and Dislocations – Douglas and Dollarton’ was presented at the LJMU conference: Under the Volcano – 70 Years On: An International Malcolm Lowry Conference. A 1/50 scale model of Malcolm Lowry’s 1944 shack at Dollarton, and a carousel, slide-projected, artwork of 80, 35 mm slides (Cates Park and Maplewood Mudflats) was exhibited at the Bluecoat, Liverpool as part of the conference proceedings, July 28 - 29, 2017
Non-Keplerian orbits using low thrust, high ISP propulsion systems
No full textThe technology of high ISP propulsion systems with long lifetime and low thrust is improving, and opens up numerous possibilities for future missions. The use of continuous thrust can be applied in all directions including prependicular to the flight direction to force the spacecraft out of a natural orbit (or A orbit) into a displaced orbit (a non-Keplerian or B orbit): such orbits could have a diverse range of potential applications. Using the equations of motion we generate a catalogue of these B orbits corresponding to displaced orbits about the Sun, Mercury, Venus, Earth, the Moon, Mars, Phobos and Deimos, the dwarf planet Ceres, and Saturn. For each system and a given thrust, contours both in and perpendicular to the plane of the ecliptic are produced in the rotating frame, in addition to an equithrust surface. Together these illustrate the possible domain of B orbits for low thrust values between 0 and 300mN. Further, the required thrust vector orientation for the B orbit is obtained and illustrated. The sub-category of solar sail enabled missions is also considered. Such a catalogue of B orbits enables an efficient method of indentifying regions of possible displaced orbits for potential use in future missions
Low-thrust enabled highly non-Keplerian orbits in support of future Mars exploration
No full textThe technology of high specific impulse propulsion systems with low thrust is improving, opening up numerous possibilities for future missions applying continuous thrust to force a spacecraft out of a natural Keplerian orbit into a displaced non-Keplerian orbit. A systematic analysis is presented as to the applicability of highly non-Keplerian orbits throughout the Solar System. Thereafter, two applications of such orbits in support of future high-value asset exploration of Mars are detailed: a novel concept for an Earth-Mars interplanetary communications relay, on which the paper largely focuses, and a solar storm warning mission. In the former the relay makes use of artificial equilibrium points, allowing a spacecraft to hover above the orbital plane of Mars and thus ensuring communications when the planet is occulted by the Sun with respect to the Earth. The spacecraft’s power requirements and communications band utilized are taken into account to determine the relay architecture. A detailed contingency analysis is considered for recovering the relay after increasing periods of spacecraft propulsion failure, combined with a consideration of how to deploy the relay spacecraft to maximise propellant reserves and mission duration. For such a relay, a combination of solar sail and solar electric propulsion may prove advantageous, but only under specific circumstances of the relay architecture suggested. For highly non-Keplerian orbits the dynamics of the spacecraft is also briefly extended to consider the elliptic restricted three-body problem and the effects of orbit eccentricity
Solar sail science mission applications and advancement : solar sailing: concepts, technology, missions
No full textSolar sailing has long been envisaged as an enabling or disruptive technology. The promise of open-ended missions allows consideration of radically new trajectories and the delivery of spacecraft to previously unreachable or unsustainable observation outposts. A mission catalogue is presented of an extensive range of potential solar sail applications, allowing identification of the key features of missions which are enabled, or significantly enhance, through solar sail propulsion. Through these considerations a solar sail application-pull technology development roadmap is established, using each mission as a technology stepping-stone to the next. Having identified and developed a solar sail application-pull technology development roadmap, this is incorporated into a new vision for solar sailing. The development of new technologies, especially for space applications, is high-risk. The advancement difficulty of low technology readiness level research is typically underestimated due to a lack of recognition of the advancement degree of difficulty scale. Recognising the currently low technology readiness level of traditional solar sailing concepts, along with their high advancement degree of difficulty and a lack of near-term applications a new vision for solar sailing is presented which increases the technology readiness level and reduces the advancement degree of difficulty of solar sailing. Just as the basic principles of solar sailing are not new, they have also been long proven and utilised in spacecraft as a low-risk, high-return limited-capability propulsion system. It is therefore proposed that this significant heritage be used to enable rapid, near-term solar sail future advancement through coupling currently mature solar sail, and other, technologies with current solar sail technology developments. As such the near-term technology readiness level of traditional solar sailing is increased, while simultaneously reducing the advancement degree of difficulty along the solar sail application-pull technology development roadmap
An analysis of dissipation functions in swarming systems
Get PDFSwarms of multiple, autonomous mobile agents have been shown to have advantages over single agent systems such as scalability, robustness and flexibility. This paper considers swarm pattern control using a generic artificial potential field and a range of dissipation control terms. An investigation of a number of dissipation terms to induce different swarm behaviours is undertaken. In addition, a novel dissipation control term is introduced based on time-delay feedback control. It is shown that a delayed dissipation term can induce vortex formations without knowledge of relative velocities. Finally, a stability analysis is undertaken that verifies swarm behaviour in a subset of these cases
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