OpenUCT :: Browsing by Author "Martinez, Peter"

Browsing by Author "Martinez, Peter"

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Open Access
A fluid loop actuator for active spacecraft attitude control - A Parametric Sizing Model and the Design, Verification, Validation and Test with a Prototype on an Air Bearing
(2019) Martens, Bas; Martinez, Peter
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.
Open Access
African perspective on integrated space and air traffic management
(2019) Gairiseb, Alexander; Martinez, Peter
Space Traffic Management (STM) is an emerging area of interest in the space sector because States and private actors are collaborating on ways to manage the growing congestion in orbit and to mitigate the impact of space debris and space weather as part of sustainable use and exploration of outer space. Further, the pace at which commercial space operations is mushrooming and the potential for growth that the suborbital space flight market presents has led to talks about integrating space and air traffic management, through technological interfaces and harmonised regulatory regimes. But, the current global challenge is the lack of a legal framework, either in the existing space-related treaties or the adoption of a new treaty regulating STM similar to the other traffic regimes, namely aviation and maritime, and advancement in technology to seamlessly integrate Space Traffic Management (STM) and Air Traffic Management (ATM). Therefore, the proposed integration of space and air traffic management necessitates an analysis of African perspectives when it comes to consolidating the two traffic regimes, taking into account the fact that ATM in Africa is fragmented. Hence, this study analyses the legal aspects of integrating Space and Air Traffic Management from the African perspective.
Open Access
Assessment of the potential for developing a micro-launcher industry in South Africa
(2019) Campbell, Victoria; Martinez, Peter
Small satellites have dramatically lowered the barriers to participating in space activities for many emerging countries, including South Africa. The rapid up-take of this facet of space technology has spurred the development of several micro-launchers dedicated to lofting small satellites to low Earth orbit. However, the majority of these micro-launcher initiatives and the majority of spaceports in use are located in the northern hemisphere, and there are currently no operational spaceports in Africa. In this study the potential for developing a micro-launcher industry in South Africa is explored, building on the launch facilities established for the previous space programme of the 1980s and early 1990s, and existing capabilities in present-day academic institutions and industry. Potential markets, financial requirements, technical feasibility, available infrastructure, and regulatory and policy aspects of such a venture are reviewed with respect to South Africa’s current political situation and attitude towards space activities. Several possible options for establishing small satellite launch capabilities in South Africa are used as a framework to assess the feasibility of a micro-launcher industry in South Africa. These range from a simple “ship and shoot” scenario with no indigenously developed technology to more complex cooperative arrangements which would, to varying degrees, require technology transfers and cooperation with potential international partners.
Open Access
The Cape rapidly oscillating Ap star survey
(1993) Martinez, Peter; Kurtz, D W
This thesis describes a survey, the Cape Survey, which was started with the intention of discovering more roAp stars suitable for asteroseismological studies and also to identify the limits of the roAp phenomenon in temperature and luminosity. This is the most extensive survey of the roAp phenomenon to date. Prior to the start of the Cape Survey, only 14 roAp stars, discovered over a period of 12 years, were known. The Cape Survey has yielded another 10 new roAp stars in the past three years. The candidates for the Cape Survey were mostly drawn from the Ap SrCrEu stars in the Michigan Spectral Catalogue.
Open Access
Characterization of the Multipath Environment of Ionospheric Scintillation Receivers
(2015) Atilaw, Tsige Yared; Cilliers, Pierre; Martinez, Peter
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.
Open Access
Design and analysis of highspeed electronics for electro optical payload of small satellites
(2022) Naveed, Mohammad; Martinez, Peter
With the increase in the resolution of the Earth observation satellites, the cameras on these satellites require more detectors to fulfil the swath need and also the image sensors have to operate at a very high-speed with the sensor electronics requiring faster clock rates and larger bandwidth. The sensor data handler has to transfer a large amount of data to the spacecraft in real time incorporating the outcomes of the signal integrity and power integrity analysis in the design. High-speed analysis is an important consideration for high resolution cameras and is often performed on the satellites. This research work aims towards presenting the design and analysis of high-speed electronics for small Earth observation satellites. A methodology will be defined for the designing of high-speed electronics that will involve both the pre-layout and post-layout designs for signal and power integrity analysis. The proposed research work also provides the pre-layout and post-layout signal integrity analysis of the high-speed electronics and interfaces and it will also validate the signal integrity performance of the module by comparing it with standard performance parameters. Similarly, we will perform a pre-layout and post-layout power integrity analysis of the high-speed electronics and interfaces and its effects on the power lines and power planes.
Open Access
Design consideration, trade-off and performance analysis of a high-resolution optical telescope design for a satellite
(2023) Raza, Asim; Martinez, Peter
High resolution satellite imagery serves a more and more important role in applications ranging from environmental protection, disaster response and precision farming to defence and security. The design of high resolution payload requires relevant technical expertise, expensive equipment and software. Different aspects of telescopes have been researched separately but process of translation of system requirements into actual optical design of high resolution payload is unique and challenging work for this dissertation. This research will help to understand system level approach to design complex system. The scope of this research to identify optics requirements from system requirements, explore optical design concept and trade-off of concepts based on system requirements of high resolution optical payload. Basically, this research will follow SMAD process to explore design engineering of optical payload from objective, requirement to detail design. This research will also include different optical layout and their performance analysis in terms of MTF and tolerances. This research does not include opto-mechanical design, thermal design, focal plane array assembly, manufacturing and detailed AIT procedure.
Open Access
Design of the Electronics Subsystem for a High-Resolution Electro-Optical Payload Using Systems Engineering Approach
(2022) Mehmood, Nasir; Martinez, Peter
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.
Open Access
Designing of a solar panel deployment mechanism for small satellite
(2021) Kabir, Saqib; Martinez, Peter
In the last few years, there has been a considerable increase of low cost space mission. Almost every small satellite has appendages like Solar Panels OR Antennas. These appendages have large inertial forces with low structural rigidity and mass to size ratio. These appendages are in stowed position in launcher to accommodate the whole satellite in the Launcher. However after launching these appendages are deployed to obtain the required power and the pointing of antennas. Their power producing capability is directly related to their area of exposure to sun, that is why these panels are available in different sizes and configurations. The requirement for the deployment mechanism for these appendages need to be cost effective, compact, lighter in weight and simple. It is entirely dependent on the structural designer to create such a robust mechanism that conforms to the requirements of the mission. In order to deploy the solar panels, it is mandatory that some sort of actuating system is employed. In this regard, we are aiming to use the torsional spring to induce the required torque for the deployment. There has been a considerable amount of research work [1-4] for a robust deployment mechanism to deploy the solar panel reliably without compromising on the overall cost and strength of the system. To realize the practical utility of Torsion Springs [5] for solar panel deployment, with the deficiency of locking after deployment and hold down mechanism when stowed. We propose a simple actuation scheme of designing the mechanism using Spiral Torsional spring for small satellite with its Zero 'g' testing and mitigation of expected Risks.
Open Access
Firmware Design and Testing for Data Handling and Control of Time Delay Integration Image Sensors in an Earth Observation Payload
(2022) Ahmed, Muhammad Ebtisam; Martinez, Peter
Earth observation is becoming more and more important in this age of information. It provides critical information in every field of work be it military, scientific research, disaster management, urban planning and many others. Better planning in all these fields is possible with more detailed information which translates to a requirement of high-resolution Earth observation data. These high-resolution images tend to generate a lot of data which needs to be processed in a very short time. This high data rate problem is the focus of this work. This work tries to tackle this problem in two ways. Firstly, a Time Delay Integration (TDI) image Sensor is used which drastically improves image Signal to Noise Ratio (SNR) and decreases the amount of data generated. Secondly, an FPGA is used for data handling and processing of this generated data. The large number and high bandwidth of FPGA inputs/outputs enables it to handle huge data generated. Functional analysis and requirements of firmware design will be analyzed based on previous works addressing a similar problem. Based on that, requirements will be proposed. The firmware design of the FPGA is proposed, which drives firmware architecture. This architecture serves as a guideline for detailed firmware design which will be done in VHDL. This firmware design will be tested as per requirements and presented in this work.
Open Access
A frequency analysis of the rapidly oscillating Ap star HD 101065
(1989) Martinez, Peter; Kurtz, D W
The study of pulsating stars is a mature and important field of stellar astrophysics. The recent discovery that main sequence stars such as the Sun and the cool Ap stars oscillate with a large number of normal modes has given rise to asteroseismology, a new approach which promises to yield accurate knowledge of the interior structure and dynamics of these stars. Although the techniques of asteroseismology have yet to be perfected, they will provide us with extremely powerful tools to test theories of stellar structure and evolution and to provide detailed knowledge of stellar mass, age, internal rotation, magnetism and convection. They may also provide information on the elemental abundances and mixing and indicate the presence of low-mass companions. In asteroseismological studies, the primary data are the frequencies of the normal modes present in the object of interest. This thesis describes an attempt to perform a definitive frequency analysis of the rapidly oscillating Ap star HD 101065. The results of the intense observing program and the subsequent frequency analysis have been published and we reproduce them here in their entirety. The disadvantage in this approach is that the terseness expected by the editor of a scientific journal is sometimes a stumbling block for the reader not fully acquainted with the field. It is thus the purpose of Part l of this thesis to supplement the papers presented in Part II and the Appendix and to provide a more general background against which they can be read and understood.
Open Access
Guidance and control of sounding rockets
(2013) Wright, David Andrew; Martinez, Peter; Inggs, Michael
This dissertation presents the design, fabrication and testing of a sounding rocket flight computer for the South African Astronomical Observatory (SAAO). Sounding rockets carry instruments with which to take measurements in the Earth’s atmosphere in sub-orbital flight. The South African Astronomical Observatory (SAAO) requires a flight computer for their sounding rockets. This flight computer is to replace the current commercial flight computer currently in use improving on its functionality and expandability.
Open Access
Identification and monitoring of oil pipeline spill fire using space applications
(2018) Gbenga, Ogungbuyi Michael; Martinez, Peter; Eckardt, Frank
Oil pipeline spills in the Niger Delta cause a great deal of environmental damage to sensitive ecosystems and losses of many millions of dollars to the Nigerian economy every year. These spills occur along the routes of pipeline infrastructure and other oil facilities like flowlines, trunk lines, flow stations, barges, well heads etc. The causes of these spill events include: operational or maintenance error, ageing oil facilities, as well as acts of deliberate sabotage of the pipeline equipment which often result in explosions and fire outbreaks. In this project, we have investigated whether satellite observations could be used to detect these oil pipeline fires. The Nigerian National Oil Spill Detection and Response Agency (NOSDRA) database contains a total of 10 072 oil spill reports from 2007 to 2015. The space-based approach we considered in this dissertation included the use of data gathered by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites, which recorded 85 129 active fire hotspots in the Niger Delta from 2007 to 2015. Since the oil spill reports serve as validation data for these oil spill fires, we explored the capability of the MODIS instrument to study the spatio-temporal correlation between spills and fire events by attempting to investigate whether the largest spills by volume that resulted in fires could be detected from space in near-real time. Although the NOSDRA oil spill reports are plagued with several irregularities from the Joint Investigation Visits by the joint task force who visit spill sites, our approach in this dissertation automated the filtering process of the raw database to meet our research goal and objective. This study confirms that, indeed, fires resulting from oil spills are detectable using the MODIS fire products. For 43 of the largest spill events, we were able to establish a spatio-temporal correlation of spill incident reports with MODIS fires clearly associated with the oil pipeline infrastructure. Our study also shed light on the spatial and temporal characteristics of non-pipeline fires in the study area.
Open Access
Identifying Ionospheric Scintillation in the South Atlantic Magnetic Anomaly using motion-affected GPS data from a ship-based receiver
(2019) Vermeulen, Annelie; Cilliers, Pierre; Martinez, Peter
his dissertation serves to report on the novel use of a geodetic-grade, dual-frequency Global Positioning System (GPS) Ionospheric Scintillation and Total Electron Content Monitor (GISTM), in an attempt to identify instances of ionospheric scintillation over the South Atlantic Magnetic Anomaly (SAMA) while located aboard the moving polar research vessel SA Agulhas II. The SAMA is a region in the South Atlantic Ocean where the Earth’s magnetic field is weakest in relation to other regions at comparable latitudes, resulting in the precipitation of high-energy particles into the ionosphere during geomagnetic storms. Ionospheric scintillations are rapid fluctuations in the phase and amplitude of trans-ionospheric radio signals resulting from electron density variations along the ray path. As a result, spacebased navigation systems can encounter increased errors in position accuracy or complete loss of lock. These are risk factors for modern aircraft and ocean vessels which rely on access to accurate Position, Navigation and Timing (PNT) services to operate safely. In this research, only the radio signals from GPS satellites are specifically used to measure these fluctuations. Traditional scintillation measurements are done using dedicated dual-frequency GPS receivers at fixed terrestrial locations. Most of the SAMA lies beyond the reach of the land-based sensors. The South African National Space Agency (SANSA) operates several GISTM stations in Southern Africa, at Marion Island, Gough Island, and the SANAE-IV base in Antarctica. The NovAtel GSV4004B GPS Ionospheric Scintillation and Total Electron Content Monitor (GISTM) installed on board the SA Agulhas II in 2012 has enabled for the first time the terrestrial measurement of scintillation from within the SAMA region. In this project, the amplitude scintillation (S4) and phase scintillation (σφ) indices from 50 Hz L1 GPS signals recorded during the 2014 and 2015 voyages of the SA Agulhas II were analysed for the first time. The scintillation effects are characterised in terms of position and motion data, carrierto-noise-density ratio, number of satellites, and satellite lock time. The goal is to develop an understanding of the effect of motion on the quality of data recorded by the receiver. The roll angle thresholds for the SA Agulhas II are calculated and it is shown that multipath errors are unlikely to be experienced. Significant data challenges were identified stemming from the incorrect setup of the SA Agulhas II GISTM. Data from elevations below 10° were missing because of hard-coded limitations within the GISTM on-board software. The data underwent significant reprocessing before being used. Comparisons were done in-harbour and out at sea with data from the nearest stationary GISTM receivers. It was shown that the movement of the receiver induces significant noise in the data. The noise levels are proportional to the velocity of the ship. An attempt to filter out the noise was unsuccessful. The motion-induced noise in the ship data masked the presence of any potential scintillations. With the ability to detect scintillation compromised, it was decided that a comparison with a land-based receiver within the SAMA would be necessary. Only one identical GISTM receiver met these requirements, located on Gough Island, at 40°20’ 58.90" S, 9°52’ 49.35" W. Data was isolated from both the SA Agulhas II GISTM and Gough Island GISTM for a period where the separation between the two receiver locations was less than 100 km. The Symmetric-Horizontal disturbance index (SYM-H) was used to identify geomagnetic storm conditions. GPS visibility maps were used to identify any potential signal obstructions. No correlation could be seen between position error and the number of satellites locked due to the high number of GPS satellites available at all times. It was discovered that the high noise levels had no effect on the position accuracy of the moving receiver, but that rapid changes in the instantaneous velocity coincided with peaks in the position error. No scintillation events were identified using the SA Agulhas II GISTM as a result of masking by the noise, however, the Gough Island GISTM data showed that no scintillation events occurred during the period in question anyway. Wind was identified as a potential contributing factor to the motion noise effect. This study provided justification for the purchase and installation of a newly developed motion-compensated GISTM receiver on board the SA Agulhas II, running off the same antenna and thus the same received signals. These data sets can be used for a direct receiver comparison in future work.
Open Access
International space law and norms: an approach for assessing compliance
(2019) Lindgren, David; Martinez, Peter
The number and types of space activities and space actors continue to increase, posing new and unique challenges for space governance and policy. Presently, a comprehensive, periodic, and systematic measure of states’ efforts to comply with existing international space law and norms does not exist, suggesting a critical need to ensure robust and informed policymaking as space activities and actors increase. The evidence-based policymaking and programming movement, alongside the rise of ratings and rankings research, suggest the utility of such an assessment to informing policymaking and identifying compliance or partial or noncompliance of spacefaring countries. Numerous ratings and rankings assessments measure country-level trends across various sectors, including but not limited to business, democracy, economics, human rights, governance, and prosperity. However, none currently measure the behaviour and policies of countries regarding the exploration and use of outer space. An annual space report, published by the Space Security Index, does provide an overview of space activities and trends according to various thematic areas, but neither provides a historical nor baseline comparison of states’ behaviour. This dissertation endeavours to propose a set of criteria, grounded in international space treaties and United Nations-level principles, resolutions, and guidelines, for which space policy stakeholders can apply to countries and develop a comparative understanding of their levels of compliance with binding international space law and non-binding space norms.
Open Access
Investigation Of Material Properties Of Sintered Black Point-1 Lunar Regolith Simulant
(2019) Ogunyinka, Adebayo Olutumbi; Martinez, Peter
The quest for establishing a human presence and development beyond the Earth, especially on the moon has opened up opportunities for future plans for lunar bases and settlements. However, the cost of using resources outside the lunar environment can inhibit this form of expansion, therefore the need for In Situ Resource Utilization (ISRU). The aim of this research was to investigate the possible usage of in situ resources for lunar construction and other economic development. The study evaluated different methods of material preparation using lunar regolith simulant for structural applications on the moon. The research employed the use of the regolith simulant known as Black Point-1 (BP-1). This research work presents the methodology used in developing lunar simulant and compares the properties of BP-1 regolith simulant to those of lunar soil, in terms of geotechnical and mechanical properties. Various laboratory analyses were carried out to determine these properties with the aid of thermal and analysis, particle size distribution, and XRD experiments. Our findings show that the particle size distribution and porosity of BP-1 are similar to that of the lunar regolith. The simulant was then sieved to produce four grades of powder (38 µmm, 106 µm, 212 µm and unsieved). The graded powders were then compressed to form a series of disc-shaped green compacts for sintering. The sintered samples were then subjected to compression testing. There were four different values of average compressive strength of the porosity materials ranging from lowest to highest porosity corresponding to the smallest to largest average grain sizes of 38 µm, 106 µm, unsieved and 212µm and they were 66.14MPa, 60.47MPa, 58.52MPa, 42.74 MPa, respectively. The particle size distribution was investigated on Black Point-1 simulant to determine the effect of the porosity while the bulk properties of the material were also examined for each of the four porosity grades, and this includes toughness, Poisson ratio, bulk modulus, Young’s modulus of elasticity and compressive strength. When compared with other ISRU structural materials and published data for real lunar regolith it was observed that sintered BP-1 is sufficiently strong for lunar structural applications.
Open Access
Investigation of the potential applications of shape memory alloys for space debris remediation applications
(2018) Feng, Louis Wei-Yu; Martinez, Peter
Active debris removal is becoming an important area of research due to the rapid growth of space debris and the need for some form of debris remediation. Debris remediation concepts fall into two general categories: contactbased and contactless. Contact-based schemes for debris capture have to overcome the challenge of capturing a noncooperating object in space with no pre-designed attachment points. Various schemes involving, inter alia, nets and harpoons have been proposed. In this paper we explore the potential to use shape-memory alloys as a technological basis for a debris capturing solution that can be used multiple times. A proof-of-concept prototype was developed at the University of Cape Town, named MEDUSA (Mechanism for Entrapment of Debris Using Shape memory Alloy). This has been designed as a validation payload for a CubeSat test platform to perform a small debris capture proofof-concept demonstration. MEDUSA uses the shape-memory alloy ninitol, which gives it the ability to assume preprogrammed “open” and “closed” shapes after distortion. Each of the five arms of MEDUSA can attain both preprogrammed shapes to allow reversible operations. This paper presents the design and development process from the conceptual design to the current Mk-III prototype, this work is an improvement based on the prototype Mk-II. The device has completed thermal and vacuum testing at the Institute for Space Systems in Stuttgart Germany to assess its performance under various environmental conditions.
Open Access
Low cost and portable software defined radio ground station
(2019) Ojur, Barbara Apili; Martinez, Peter
Small satellites are being launched by a multitude of private and public organizations around the world. They are innately cheaper than their large counterparts. This attribute, and additional ones, such as their easy-to-assemble nature and the convenience of using commercially available off-the-shelf parts to build them has enhanced their popularity. Now that getting into space has become more accessible there is an influx of information available from small satellites, however the information is not being utilized too efficiently on Earth. One reason as to why this is evident is because traditional ground stations, which are largely hardware dependent, are expensive to develop. However, with the introduction of Software Defined Radios (SDRs) many of the operations formerly done using hardware can now be implemented in software. Using a SDR can substantially reduce the cost of a traditionally hardware-based ground station. A number of universities and other organizations have or are developing SDR ground stations to communicate with satellites in different orbits. The ability to receive or transmit signals is important because it displays the capability to develop and operate satellites to various stakeholders. This dissertation attempted to enhance the movement towards satellite communication using SDR technology by developing a low cost, portable, easy to assemble and extendable ground station at the University of Cape Town in order to make contact with one or more small satellites in Low Earth Orbit (LEO), to encourage data usage, national and international collaboration and education. The ground station was constructed and tested based on its objectives, requirements and constraints. The commissioning tests were conducted in the SpaceLab at the University of Cape Town. The ground station was able to make contact with two small satellites in LEO successfully. Packets were received from two satellites that clearly stated who they were. The information contained in the packets was decoded into ASCII text and Hex code. They were compared with other successful amateur ground station results from all over the world to verify their authenticity. The main conclusion was that the SDR ground station was able to make contact with small satellites in LEO operating in the 70-cm band.
Open Access
Mechanical Structure Design and Analysis of Focal Plane Unit (Fpu) for Earth Observation (Eo) Payload
(2022) Anwar, Muhammad Mubeen; Martinez, Peter
The focal plane unit plays a vital role in an earth observation payload to meet its highly demanding optical performance requirements. Focal plane unit mechanics consist of a sensor module mounting and planar optics. An image is formed on the image plane and mechanics is used to hold sensors and planar optics in place. The mechanical design of this unit is has two functions. Firstly, it ensures optical focus and alignment of the image plane in the temperature extremes of the space environment. Secondly, the mechanics also needs to handle harsh launching loads to get the satellite in space. The important constraints of this design are the mass and volume which need to be considered during the design. Optical performance depends a lot on the design of the mechanics used to support and align optical elements and image sensors. In this dissertation we perform the design of a focal plane unit using Solid Works 3D CAD modelling software. To validate the mechanical performance of our design Finite Element Analysis (FEM) analysis needs to be performed on every mechanical element with application of launch and environmental loads. Assembly and integration of the focal plane unit is also an important consideration, which if not properly done may deteriorate the performance. Therefore, the assembly and integration procedure is also highlighted in this work. These processes are presented in this work with future recommendations for future work.
Open Access
Modelling and testing the effects of space radiation on space-borne electronic components
(2018) Snell, Holly; Martinez, Peter; Barbard, Arno
Outer space is a hazardous environment for satellites as they are continuously exposed to harsh space radiation in the form of cosmic rays and high-energy electrically charged particles (protons, electrons and alpha particles). Mission-critical electronic components are especially susceptible to space radiation as high-velocity charged particle impacts on molecular-sized circuitry can cause significant device upsets or permanent damage, compromising a satellite's functional integrity. In order to mitigate this radiation hazard, electronic components are carefully selected and tested prior to deployment. Part of this process involves consulting a space radiation model in order to be able to estimate the type of radiation environment the electronics will be exposed to. There are many different environmental models to choose from and the output from the models will influence whether a certain device will be selected or not. Due to this, the model selection process should be very well understood and all parameters carefully chosen. This project aims to describe the radiation environment in low Earth orbit, and to provide guidelines for using the space radiation models found on the Space ENVironment Information System (SPENVIS). By going through the modelling process in detail, we have found that the trapped radiation models are completely independent of the date specified when describing the orbit of interest. We found that all long-term solar proton models (except King) assume a zero flux for solar minimum dates. The accuracy of the model output for a specific orbit depends on the duration of the model's time span. For instance, we found that for certain low Earth orbits, the accuracy of the model output could be easily improved by increasing the number of days in the orbit generator from one to three. For the low Earth orbits we selected to analyse, we found that a one-year mission delay at any point on the solar cycle will not have great enough an effect on the output to warrant a re-calculation. It is important to consider both trapped and non-trapped radiation when calculating an upset rate and, lastly, the upset rate calculation could be altered by a factor of 1000 simply by selecting different models for the exact same device and orbit. We conclude this study with some guidelines for the use of SPENVIS for radiation modelling during mission planning.