Model Based Systems Engineering (MBSE) is an interesting alternative to traditional systems engineering methods. Instead of using electronic documents to record system information, MBSE uses a unified and coherent system model. Trade-offs are a major element of a space systems engineer's role in early system design. This can be a particularly challenging process in the domain of spacecraft, as the system designs are often very complex and the constraints can be difficult to characterize. There has been little previous research on the use of MBSE as a design space exploration tool or in support of trade-offs. This paper investigates the potential to use MBSE for design exploration and to understand trade-offs, through the creation of a new toolset including a SysML profile. The tool draws on generative design (allowing automatic guided generation of a multitude of design alternatives) and system optimization to rapidly generate and assess new designs using interactive analysis and visualizations. Techniques such as surrogate modelling, genetic algorithms and robustness measurements will be available in the toolset. The toolset was applied to a design scenario aiming to improve the trade off and design selection process for LEO Earth observation satellites. The upcoming ESA TRUTHS space mission was used as a case study and the design process was recorded and compared to a manual design exploration approach. The toolset was found to reduce the design exploration time by 38% to 96% , allow exploration of more designs in an equivalent time and provide better quantification of the relationships present in the design space, all without drops in selected design quality. For now, the toolset can only perform parameter variation in the design exploration and future work is expected to extend this to higher levels of variability. The study also discusses how the MBSE toolset could be applied to other missions, offering the same advantages to all early phase spacecraft designers. TABLE OF CONTENTS 1. INTRODUCTION .

<p>Volcanic ash presents a challenge for the aviation industry. Volcanic ash is semi-transparent, absorbing in the 8-12 micron window. 3D information is needed to be able to back-calculate dose – this is a key parameter in managing airspace. To recreate the ash cloud, multiangle observations are required – making a nadir-pointing satellite ideal to perform observations for this purpose. Other mission objectives using the same instruments can also be realised, for example, as volcanic ash clouds are the primary target, there is the possibility to map new magma extrusions, lava and pyroclastic flow movements. Thermal infrared data has also previously been used to observe volcanic cycles and better understand their behaviour. There is also the possibility of including forest fires as targets of opportunity. The images required for 3D construction of ash clouds can also be used to create digital elevation models of terrain around volcanos which have application in disaster management and planning.</p><p>A CubeSat mission - Pointable Radiometer for Observing Volcanic Emissions (PROVE) - is proposed to monitor the ash cloud using both thermal infrared and visual cameras. All requirements and components were determined by students through trade-off studies. Each work package was undertaken by undergraduate and postgraduate students (both as part of research projects and on a voluntary extracurricular basis) supervised by academics. The resulting 1U+ payload consists of a thermal infrared camera (FLIR Tau 2 with a 50mm lens), and 2 visual cameras (a narrow field of view Basler ace ac5472-5gc with a Kowa LM75HC lens, and a 5MP Arducam with a 40 degree lens as a wide field of view instrument). Alongside this, a payload computer to communicate with the cameras and store data was selected (the Beaglebone Black Industrial) with a custom PCB providing connections to the instruments and bus. The software to operate the payload takes the form of a custom scheduler for an imaging pass, sending commands to the camera systems (and to the bus) to take the required multiangle images for ash cloud reconstruction.</p><p>The payload is currently in the final design and testing stage, with vibration and vacuum testing, as well as FlatSat testing before the final manufacture and integration of the payload. There is the possibility of a UK launch later this year.</p>

The University of Bristol is developing the PROVE (Pointable Radiometer for Observation of Volcanic Emissions) Pathfinder payload, a part of a 6U CubeSat hoped to launch in the next year. PROVE Pathfinder's aim is to image volcanic ash plumes from several different locations and aspects along its orbital trajectory. These images will be used to gain more knowledge of the ash cloud, useful in protecting civil aviation in the case of large-scale volcanic eruptions with ash associated. As CubeSats have historically suffered from a high failure rate, a thorough understanding of the reliability of the PROVE Pathfinder system is essential to mitigating the mission risk. This paper presents the analysis, results and recommended failure mitigation strategies from a reliability study carried out on the PROVE Pathfinder payload system. Several different analysis approaches were used to study the reliability of the system. These included Failure Mode Effects and Criticality Analysis (FMECA), Fault Tree Analysis (FTA), Monte Carlo simulation and a reliability model of PROVE Pathfinder devised using Model Based Systems Engineering (MBSE). Various estimates of system reliability were produced, with a final figure of 80% reliability. This estimate took account of the numerous mitigation strategies identified during the study, including cold redundancy in payload controllers and aluminum radiation shielding. While some discrepancies in qualitative reliability estimates were found, the insight gained during the study greatly assisted with identifying mitigation strategies and generally improved system reliability. A framework for reliability analysis approaches and mitigation strategy identification for general use on spacecraft systems is proposed, with opportunity for future development.