Active spacecraft attitude control by using a pumped fluid as the inertial mass has potential advantages over reaction wheels, including high torque, lower power consumption, reduced jitter and prolonged lifetime. Previous work addressed conceptual and mission-specific control aspects, and one fluid loop has flown on a demonstration mission. In this dissertation, a parametric sizing model is developed that can optimize a fluid loop for any mission, based on pump capabilities and customer requirements. The model can be applied to circular, square and helical fluid loops, and includes the power consumption due to viscous friction. A configurable prototype was developed to verify the model, as well as a spherical air bearing to verify the rotational aspects of the various fluid loop configurations. The model was applied to various hypothetical missions. In conclusion, the fluid loop has the fundamental potential to replace reaction wheels in a wide variety of satellites above approximately 20 kg, if mass is carefully optimized and efforts are made to develop a suitable pump. This is considered worthwhile, as the actuator comes with many potential advantages.

The Dream Chaser is a space vehicle currently under development by the Sierra Nevada Corporation for purposes of carrying humans and cargo to low Earth orbit. In 2016, the United Nations entered into an agreement with Sierra Nevada Corporation to fly experimental payloads on the Dream Chaser. The collaborative UNOOSA-SNC Dream Chaser mission will be approximately two to three weeks in duration, with the Dream Chaser orbiting Earth at an altitude of 500 km with an inclination of 0 − 35◦ . This will be the first space mission dedicated to attaining the Sustainable Development Goals. In this investigation the South African space and aerospace industry is placed under the microscope for the purpose of studying the feasibility of landing the Dream Chaser Space Vehicle on South African soil. The research dictates possibly having to establish a dualuse airport/spaceport recognised by the South African Space Council under supportive legislation to support this mission. Elements addressed in this investigation range from physical facilities such as the airports, workshops and laboratories through Dream Chaser specific requirements and specifications, right down to space and civil aviation regulations. This dissertation will assess all available infrastructure and supporting entities that will facilitate the safe landing of the Dream Chaser space vehicle in South Africa. However site visits and interviews were not part of this investigation. This investigation prefaces the University of Cape Town's Space Lab plans to submit a landing proposal for a possible alternative landing site(s) for the Dream Chaser outside of the USA. This report is the first major step in researching and documenting the potential for landing the Dream Chaser or any reusable space vehicle in South Africa and will therefore make the case for South Africa as a suitable and attractive landing destination, not just for the Dream Chaser, but for accompanying scientists and researchers from all over the world involved in the mission.

Satellite imagers, in contrast to commercial imagers, demand exceptional performance and operate under harsh conditions. The camera is an essential part of an Earth Observation Electro Optical (EO) payload that is designed in response to needs such as military demands, changes in world politics, inception of new technologies, operational requirements and experiments. As one of the key subsystems, the Imager Electronics Subsystem of a high-resolution EO payload plays very important role in the accomplishment of mission objectives and payload goals. Hence, these Electronics Subsystems require a special design approach optimised for their needs and meticulous characterizations of high-resolution space applications. This dissertation puts forward the argument that the system being studied is a subsystem of a larger system and that systems engineering principles can be applied to the subsystem design process also. The aim of this dissertation is to design the Imager Electronics Subsystem of a high-resolution Electro Optical Payload using a systems engineering approach to represent a logical integration and test flow using the space industry guidelines. The Imager Electronics Subsystem consists of group of elements forming the functional chain from the Image Sensors on the Focal Plane down to electrical interface to the Data Handling Unit and power interface of the satellite. This subsystem is responsible for collecting light in different spectral bands, converting this light to data of different spectral bands from image sensors for high-resolution imaging, performing operations for aligning, tagging and multiplexing along with incorporating internal and external interfaces.

Includes bibliographical references / Global Navigation Satellite Systems (GNSS) are used to provide information on position, time and velocity all over the world at any time of the day. Currently there are four operational GNSS and one of them is GPS (Global Positioning System) that is developed and maintained by U.S Department of Defence (DoD), which is widely used and accessible all over the world. The accuracy of the output or even the availability of the navigation system depends on current space weather conditions, which can cause random fluctuations of the phase and amplitude of the received signal, called scintillation. Interference of GNSS signals that are reflected and refracted from stationary objects on the ground, with signals that travel along a direct path via the ionosphere to the antenna, cause errors in the measured amplitude and phase. These errors are known as multipath errors and can lead to cycle slip and loss of lock on the satellite or degradation in the accuracy of position determination. High elevation cut off angles used for filtering GNSS signals, usually 15-30°, can reduce non-ionospheric interference due to multipath signals coming from the horizon. Since a fixed-elevation threshold does not take into consideration the surrounding physical environment of each GPS station, it can result in a significant loss of valuable data. Alternatively, if the fixed-elevation threshold is not high enough we run the risk of including multipath data in the analysis. In this project we characterized the multipath environment of the GPS Ionospheric Scintillation and TEC (Total Electron Content) Monitor (GISTM) receivers installed by SANSA (South African National Space Agency) at Gough Island (40:34oS and 9:88° W), Marion Island (46:87° S and 37:86° E), Hermanus (34:42° S and19:22° E) and SANAE IV (71:73° S and 2:2° W) by plotting azimuth-elevation maps of scintillation indices averaged over one year. The azimuth-elevation maps were used to identify objects that regularly scatter signals and cause high scintillation resulting from multipath effects. After identifying the multipath area from the azimuth-elevation map, an azimuth-dependent elevation threshold was developed using the MATLAB curve fitting tool. Using this method we are able to reduce the multi-path errors without losing important data. Using the azimuth-dependent elevation threshold typically gives 5 to 28% more useful data than using a 20° fixed-elevation threshold.

No description available.