Search

In recent years the space industry has seen significant growth in numbers of sub 10kg satellite platforms now known more broadly in the industry as nanosatellites. Nanosatellites potential applicability is driven by flourishing technologies miniaturisation in the consumer electronics market and commercialisation of space. Currently nanosatellite mission operations are limited in both lifetime and manoeuvrability due to limitations in on board propulsion technologies. Further enhancement of mission operations relies on more effective integration of current reaction-mass-based propulsion technologies and further development of miniaturised propulsion systems. Paradoxically, the compact spacecraft size and mass that facilitate nanosatellite access to space is presently a drawback in terms of acceptable systems performance and propulsion systems capacity. Moreover characteristic power density and vulnerability to the space environment is already high in nanosatellites in contrast to major satellites, rendering the design, inclusion, and optimisation of propulsion technologies a challenging task. This thesis focuses on techniques to support mission planning and characterisation of propulsion technologies for nanosatellites. Acknowledging the outweighing significance of solar activity modulating space environment perturbations and particularly atmospheric drag, a robust solar forecast method is proposed to support lifetime estimations. Complementing the pivotal framework information for propulsion system design and management, the vulnerability to atmospheric drag is assessed to identify the profile of the current vaguely defined drag coefficient of standard nanosatellites. Finally, addressing a crucial task on emerging propulsion technologies for nanosatellite systems, a method to improve low thrust characterisation via in-orbit manoeuvres using standard elementary attitude determination resources is devised. The robust solar activity forecast is carried out using observed historic and reconstructed Sun’s polar magnetic field, to define the initial state of an up-to-date solar magnetohydrodynamics computational model; the method successfully reproduces recent solar cycles activity, anticipating moderate-to-low activity during the next 25th cycle. The identification of the drag coefficient profile in standard nanosatellites is enabled by the statistical assessment of observed orbital decay through an iterative fitting process of propagated orbits; the profile is physically consistent and descriptive mostly in orbits below 350km during moderate-to-high solar activity. Finally, the devised thrust characterisation method exploits the regular geometry and mass distribution of standard nanosatellites to identify low thrust actuation via actuated body angular rotation rates in an intermediate axis spinner; precise computer simulations show that it is possible to improve low thrust estimations from weak and noisy sensor signals using the proposed method against typical methods using body angular acceleration.

This thesis combines both practice-based research, in the form of acousmatic composition, and theoretical research, addressing voice and poetry both as inspiration and material. It includes a portfolio of original compositions and a written text with aesthetic ideas that informed the compositional process. The aim of the research was to propose a particular creative strategy, based on Chilean poet Vicente Huidobro's aesthetic theory; a system which aims to create artistic works independent of real world by taking materials from reality and combining them in unexpected ways through an equilibrium between rationality and intuition. This theory, alongside various other theoretical and artistic sources informing the creative process, is explained in a section entitled Compositional Rationale. The broader thesis is divided into two parts, each starting with a methodology relating to the compositions described within: Part 1: Octophonic cycle La lumière artificielle and Part 2: Three acousmatic tributes. In order to examine how the Compositional Rationale operates within the portfolio's pieces, an analytical methodology has been proposed. This is described in an Analytical methodology section and considers the use of two parts of the tripartite model proposed by Nattiez (1990) and developed for electroacoustic music by Roy (2004). The two parts of the tripartite model are poietic analysis and neutral analysis. The first describes the creative process and compositional considerations of the author, and the second details the constitutive elements of each piece within five areas; Pierre Schaeffer's notion of sound objects (1966), Denis Smalley's notion of spectromorphological functions (1997), levels of spatial function by Annette Vande Gorne (2010), and finally two more types of analyses developed by the author: voice type and speech-sound type. Taken as a whole, the analysis demonstrates the structural constitution of each piece, and thus shows how Huidobro's creative system, called creacionismo, has been applied successfully to acousmatic composition, generating the notion of acousmatic-creationist as nomenclature for the process. This is the main outcome of this thesis, a new artistic strategy which balances rationality and intuition within acousmatic composition and places poetry as a driven force in the use of voice, merging artistic practice and theory in a recursive action.

The sorption and air drying characteristics of fresh and osmotically concentrated diced sweet potato were studied. Diced sweet potato (l-cm cubes) were concentrated in 50 and 60% (w/w) corn syrup solutions of 42 DE at 25°C for 2 and 5 h. Fresh and osmotically concentrated diced sweet potato were air dried in a laboratory tray dryer at 55°C with an air velocity of 1.5 m/s for approximately 12 h. The sorption characteristics of osmotically concentrated diced sweet potato in the aw range of 0.9 to 0.97 were found to be different from that of fresh diced sweet potato. Considerable overlapping of the sorption data of fresh and osmotically concentrated diced sweet potato was observed outside the aw range of 0.9 to 0.97. The Oswin equation was found to fit sorption isotherms well. Parameters of the Oswin equation were estimated in the aw range of 0.6 to 0.99 with R2 values of 0.89 and 0.91 for osmotically concentrated and fresh diced sweet potatoes, respectively. The drying rate curves of fresh and osmotically concentrated diced sweet potato exhibited non-linear falling rate periods with no constant rate drying period. Moisture transport during the falling rate drying period was modeled using Pick's second law. The effective moisture diffusivities for osmotically concentrated diced sweet potato were slightly greater than that of fresh diced sweet potato (3.88x10-10 m2/s for fresh and between 3.69x10-10 m2/s to 4.35x10-10 m2 for osmotically concentrated diced sweet potato). Although some differences were observed between the drying rates of fresh and osmotically concentrated diced sweet potato, the differences among the diffusivities were not significant. The sorption data and moisture diffusivities obtained through this study provide useful information for the design and development of a sweet potato dehydration process.