Contribution: This article presents a comprehensive overview of characteristics of educational designs of collaborative engineering design activities found in literature and how these characteristics mediate students' collaboration. Background: Engineers have to solve complex problems that require collaboration. In education, various collaborative engineering design activities have been implemented to prepare students for these professional practices. According to cultural historical activity theory (CHAT), educational activities can be described in terms of interrelated elements, i.e., subject, object, tools, rules, division of labor, and community, that influence learning outcomes. A key issue is how these elements mediate students' collaborative efforts and how they contribute to learning. Research Questions: 1) How is collaborative learning implemented in engineering design education? 2) How do the elements of CHAT and their interrelations mediate collaborative learning? and 3) What is the evidence that the implementation of collaborative learning contributed to the achievement of desired learning outcomes? Methodology: A systematic literature review following preferred reporting items for systematic review and meta-analyses protocols guidelines was conducted, including 111 articles published between 2011 and 2021. CHAT was used as analytical framework. Findings: Collaborative learning was implemented in engineering design activities to develop technical as well as nontechnical skills. For the CHAT elements, it was found that establishing a common object, rules for collaboration, and division of labor are essential for effective collaboration and can be enhanced through digital technologies (tools) and support from a community, for example, educators. Finally, results showed that there is evidence that described implementations contribute to learning. However, this evidence needs to be interpreted with care, due to methodological issues in some included articles.

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Higher educational institutions have broadly adopted Collaborative Engineering Design (CED) activities to prepare students for complex problem-solving in multidisciplinary settings. These activities are non-linear and mediated by various social practices and tools. Therefore educators might struggle in facilitating the achievement of specific learning goals. Embodied cognition is an approach that explains non-linear behaviour through orgamism-environment interactions and might therefore provide educators with insights on how to prompt students towards desired actions in CED activities. According to embodied cognition, we learn through actions that emerge as a response to a problem (task) and environmental constraints. Educators can guide students’ behaviour by proposing tasks and adapting the environmental constraints of a learning situation, thus creating a field of promoted action. In this paper, we outline the progress of a design-based research in which insights from embodied cognition are implemented to promote desired student behaviour in CED activities. We report on the results of our problem-exploration phase. A systematic literature review and focus groups with students revealed that students are often hesitant to adopt new practices and tools that could potentially improve their collaborative design process. Next, we propose three theory-based design principles in which the task and environmental constraints are leveraged to foster the adoption of practices and tools and apply them to CED activities. Finally, we will share preliminary observations of the learning processes triggered by the designed activities and outline the directions for future research.@en

To adequately prepare engineering students for their professional career, educational institutions offer projects in which students collaboratively solve engineering design problems. It is known from research these projects can lead to a variety of learning outcomes and student experiences. However, studies that provide insights in the influence of different features of an educational design are rare. In the current study we use Cultural Historical Activity Theory (CHAT) as analytical framework to understand how different elements of an educational design affect students’ experience. Additionally, we use the notion of contradictions to identify opportunities for structural course improvement. Focus groups were conducted with 12 Master students in Aerospace Engineering, that participated in a collaborative engineering design course. During the course, students applied Systems Engineering (SE) and Concurrent Engineering (CE) and worked in the Collaborative Design Laboratory (CDL), which is a state-of-the-art facility that holds a variety of industry relevant tools. It was found that students valued the guidance of their coach and experts, co-located collaboration and the freedom to structure their own process. However, they perceived challenges with regard to adoption of tools in the CDL, sharing their progress with their supervisor, coordination of collaborative efforts and scheduling issues. An analysis using CHAT revealed what contradictions caused these challenges. Finally, recommendations are given on how course structure can be structurally improved. @en

This study investigates the potential of a newly released multi-phase solver to simulate atomisation in an air-blast type atomiser. The 'VOF-to-DPM' solver was used to simulate primary and secondary atomisation in an atomiser with a coaxial injector-like geometry. The solver uses a hybrid Eulerian/Eulerian-Lagrangian formulation with geometric transition criteria between the two models. In this study isothermal, non-reacting flow at room temperature was assumed. The primary focus was predicting Sauter mean diameter and droplet velocity data at a sampling plane downstream of the injector. The solver produces the expected data and predicts trends similar to those found in experimental measurements. The accuracy of the produced droplet diameters was roughly a factor 2 off compared to experiment. This is attributed primarily to mesh resolution. It was concluded that the solver has the potential to predict atomisation at a reasonable computational cost, but further study is needed to confirm its full capabilities.@en

A subscale, research rocket thrust chamber operating with cryogenic oxygen and hydrogen exhibits self-excited transverse-mode instabilities with amplitudes of more than 80% of the steady combustion chamber pressure (peak-to-peak) for some operating conditions. During unstable combustion, an increase in the integral heat flux into the water-cooled combustion chamber walls of 20–40% with respect to stable conditions was experienced. A model was derived to predict changes in the axial heat flux profile considering only the dependence of flame length on the amplitude of transverse acoustic oscillations. The model predicts an increase in heat flux in the upstream part of the chamber by up to a factor of 7. This drastic increase is in agreement with past observations of rocket engine failures due to instabilities, in which the structural damage is commonly observed on the faceplate and the walls adjacent to the injection plane. The model also predicts a peak increase in integral heat flux of up to about 25%. While falling short of the peak experimental value of 40%, it nevertheless suggests that flame length is the dominant influence on the distribution of thermal loads in this study.

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Since there is a high interest in the use of green propellants, hydrogen peroxide is coming back after once making place for the rise of Hydrazine in monopropellant propulsion systems. Typically, these thrusters are outfitted with catalyst beds. A fully modular 1N thruster is designed to provide the capability of testing and comparing the performance of different concentrations of hydrogen peroxide, different catalysts as well as new technologies in an attempt to resolve the disadvantages associated with the use of catalyst beds. A preliminary baseline design of a catalytic thruster has been created. This will be followed by the design of a secondary decomposition chamber for new technologies, a propellant feed system, a test setup and a test plan. @en

Delft University of Technology is currently developing the pico-satellite platform Delfi-PQ, based on the PocketQube standard, in pursuit of a new generation of satellites with lower cost, flexibility and short development time. A technology demonstration payload expected to fly in one of the first Delfi-PQ satellites is a dual thruster micro-propulsion system based on the use of water as propellant. Two different micro-resistojet concepts will be demonstrated in the same satellite flight: one based on vaporization, heating and expansion in a nozzle of pressurized liquid water (Vaporizing Liquid Micro-resistojet); the other based on heating and acceleration in slots with simple geometry of molecules of vapour under transitional or free molecular flow regime (Low Pressure Micro-resistojet). The demonstrator is based on a common propellant storage for the two micro-propulsion concepts, based on the use of the capillarity properties of water in a small diameter tube connected to the two separate MEMS thruster chips with their own dedicated valves. This paper describes the requirements and design of the complete micro-propulsion demonstrator as well as its expected operational envelope for in-orbit functional testing, based on the currently validated performance characteristics of the two thrusters.

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Commercial launch service providers’ low-priced offerings have been a hotly debated topic. However, the strategies with which these firms reduce costs have seen little incorporation into the hardware Cost Estimating Methods (CEMs) and tools prevalent in the aerospace industry. This research changes this, by providing adaptations to agency-focused CEMs that befit a new commercial paradigm, with an emphasis on smallsat launch vehicles. A parametric model for estimating costs in an early phase of development was synthesized, with which it is possible to approximate the full life-cycle costs of small commercial liquid and solid propellant rockets, as well as their cost-based price per flight. Key elements included were reductions in cost achieved by commercial launch operators, by modeling reduced subcontractor management effort and profit retention experienced at lower subcontracting rates. Prices per flight of small commercial launch vehicles were approximated by combining a parametric cost estimating methodology used frequently in the context of space agencies such as ESA and NASA, called the T1 Equivalents method, with another parametric three-part estimate developed by Koelle for development, manufacture and operations phase costs. The first two phases were estimated through the T1 method, while the operations costs were modeled with TRANSCOST. Along with the newly developed methodologies, novel insights such as required launch rates have shone a light on small commercial launch systems’ cost feasibility in the age of public-private spaceflight partnerships. The model developed was able to approximate costs of development, manufacture and price per flight of three commercial rockets to within 20% of actual reported costs or prices. However, it is recommended the model is refined as more reference cost data, especially on a subsystem level, as well as pricing for these smaller rockets becomes available in the coming years.@en

Delft University of Technology is currently developing the pico-satellite platform Delfi-PQ, based on the PocketQube standard, in pursuit of a new generation of satellites with lower cost, flexibility and short development time. A technology demonstration payload expected to fly in one of the first Delfi-PQ satellites is a dual thruster micro-propulsion system based on the use of water as propellant. Two different micro-resistojet concepts will be demonstrated in the same flight of the satellite: one based on vaporization, heating and expansion in a nozzle of pressurized liquid water (Vaporising Liquid Micro-resistojet); the other based on heating and acceleration in slots with simple geometry of molecules of vapour under transitional or free molecular flow regime (Low Pressure Micro-resistojet). The demonstrator is based on a common propellant storage for the two micro-propulsion concepts, based on the use of the capillarity properties of water in a small diameter tube connected to the two separate MEMS thruster chips with their own dedicated valves. This paper describes the requirements and design of the complete micro-propulsion demonstrator as well as its expected operational envelope for in-orbit functional testing, based on the currently validated performance characteristics of the two thrusters.@en

The purpose of this paper is to explain the design process of the pressurised propellant tank for a water micro-resistojet, with application on nanosatellites. The motivation of this propulsion system is its use on future nanosatellite missions of the Delft University of Technology, following the legacy of Delfi C3 and Delfi-n3Xt. The water-based micro-resistojet targets thrust levels in the 0.5-10 mN range by employing MEMS technology in the heating chamber. In order to store the water (propellant), the pressurised tank shall withstand 10 bar as MEOP and have a capacity of 200 ml with a mass limit of 200 grams. The design of the propellant tank is tackled following the Design Trades: a systems engineering approach to the decision-making process. This 10-step methodology begins by framing the decision to be made and outlining the design objectives. Subsequently, the design alternatives are created and analysed via trade-off evaluations, considering the previously-defined objectives. From this analysis, it is possible to draw conclusions that will eventually drive the decision. However, the uncertainty of the trade-off process needs to be assessed, as well as its impact on the final decision. An improved set of design alternatives is developed and new trade-offs are performed, following an iterative process. Finally, an undisputed winning design alternative is achieved and selected, closing the decision process. Regarding the propellant tank, the main objectives of the design are the minimization of cost and risk, with maximum performance and design simplicity. An initial set of characteristics of the design is considered: material, manufacturing process, shape and configuration of the propellant tank. Through table trade-off analyses, the different design alternatives are assessed, and sensitivity analyses are conducted to show the impact of the trade-off weights on the outcome. After a decision on the general characteristics, the lid-tank and tank-bus structure interfaces are evaluated. With the help of Design Option Trees, 5 conceptual designs are modelled in 3D to better understand each design solution. Through an advantages-disadvantages table, the interface characteristics are assessed, and the conceptual designs are refined into a single preliminary design, ready for future structural analysis. In conclusion, a successful implementation of the methodology is achieved. The complete process is documented in order to allow traceability of the decisions taken, facilitating design iterations. Furthermore, a set of recommendations for future work is developed, which include a close relation with the manufacturer from the start and parametrisation of designs.@en

Microelectromechanical systems (MEMS) techniques uncovered new opportunities in satisfying the mission requirements of the growing next generation nano- and pico-satellite missions. In particular, micro-propulsion is universally recognized as one of the key enabling technologies to help this class of satellites making the next step and become credible candidates to a wide range of scientific and commercial applications. In this context, TU Delft is developing a miniaturized electro-thermal propulsion system operating with green liquid propellants, for application on a wide range of nano-satellite formats from CubeSats (10x10x10 cm units) to PocketQubes (5x5x5 cm units). A breadboard of the complete micro-propulsion system is under development at TU Delft, including the thruster, propellant tank, the valve and the driving electronics. The design of the system shall be easily adapted to both CubeSat and PocketQube standards, with particular attention to the second one since the system is scheduled for an initial flight demonstration on the first Delfi-PQ satellite. To address this need and to fill an existing gap in the state-of-the-art of micro-propulsion, two kinds of micro-thrusters are considered in this development; a Vaporizing Liquid Micro-resistojet (VLM) and a Low Pressure Micro-resistojet (LPM). A number of test results will be shown in the paper on the electrical, mechanical and functional characterization of the MEMS thrusters, fabricated in the Else Kooi Laboratory at TU Delft, and the other components of the system. Keywords: Micro-resistojet, Microthruster, MEMS, Cubesats, Pocketqubes @en

The aerospace industry is recently expressing a growing interest in green, safe and non-toxic propellants for the propulsion systems of the new generation of space vehicles, which is especially true in the case of Cubesat micro-propulsion systems. Demanding requirements are associated to the future missions and challenges offered by this class of spacecraft, where the availability of a propulsion system might open new possibilities for a wide range of applications including orbital maintenance and transfer, formation flying and attitude control. To accomplish these requirements, Delft University of Technology is currently developing two different concepts of waterpropelled micro-thrusters based on MEMS technologies: a free molecular micro-resistojet operating with sublimating solid water (ice) at low plenum gas pressure of less than 600 Pa, and a more conventional micro-resistojet operating with liquid water heated and vaporized by means of a custom designed silicon heating chamber. In this status review paper, the current design and future expected developments of the two micro-propulsion concepts is presented and discussed, together with an initial analysis of the expected @en

This paper describes the current developments regarding cryogenic rocket engine technology at Delft Aerospace Rocket Engineering (DARE). DARE is a student society based at Delft University of Technology with the goal of being the first student group in the world to launch a rocket into space. After the launch of the hybrid engine powered Stratos II+ sounding rocket in October 2015, DARE decided to investigate highly efficient liquid rocket engine technology . In this context DARE initiated the cryogenic project with the goal of developing a liquid rocket engine using liquid oxygen and liquid methane as propellants with a nominal thrust in the order of 10kN. Eventually this engine shall power a future sounding rocket into space. As an intermediate step, a 3 kN class engine is being developed. Subsystem development tests and possibly a hot-fire test campaign on this engine are planned for 2016 and its development intends to provide DARE with the required experience and knowledge to develop large scale liquid rocket engines. The engine is developed in cooperation with Heliaq Advanced Engineering and is designed to meet the requirements of the second stage engine of the ALV reusable launch vehicle. The design is a pressure-fed engine, regeneratively cooled using the liquid methane fuel. After passing the coolant channels, the methane is injected into the combustion chamber in gaseous state together with the liquid oxygen in a co-axial manner. The engine is ignited by means of a pyrotechnic igniter using an ammonium perchlorate based propellant. During a test sequence, the propellants are stored in insulated run-tanks and are pressurized using helium. This paper describes the project objective, the current progress on the design and production, and finally four proposed research topics that are indented to be conducted at the faculty of Aerospace Engineering of Delft University of Technology. @en

This paper presents a dynamic system approach for the modeling of fluid flow in microchannels to be used in thrust control applications. A micro-resistojet fabricated using MEMS (Microelectromechanical Systems) technology has been selected for the analysis. The device operates by vaporizing a liquid propellant, in this case water, and expelling it as gas that is accelerated by a micro-nozzle. The pressure variation due to boiling in the chamber might lead to unwanted behavior of the feed system and the frequency analysis in this case can indicate whether or not instabilities will be present. To handle this complex problem, the incompressible Navier-Stokes equations are linearized in the steady-state flow regime and then formulated in state space form to provide the necessary means for control analysis. Controllability and observability of the system are investigated considering low values of Reynolds numbers present in micro fluidics applications. Results from the analytical treatment are compared with CFD (Computational Fluid Dynamics) simulations of the microchannel to demonstrate the validity of the approach investigated. @en

Methane is a promising propellant for liquid rocket engines. As a regenerative coolant, it would be close to its critical point, complicating cooling analysis. This study encompasses the development and validation of a new, open-source computational fluid dynamics (CFD) method for analysis of methane cooling channels. Validation with experimental data has been carried out, showing an accuracy within 20 K for wall temperature and 10% for pressure drop. It is shown that the turbulence model has only a limited impact on the simulation results and that the wall function approach generates valid results. Finally, a cooling analysis is performed to compare two thrust chamber materials. A traditional copper alloy is compared to aluminium as chamber material for a small moderate-pressure oxygen/ methane engine. The analyses show that aluminium is a feasible chamber material only if a thermal barrier coating is applied. In addition, a significantly higher cooling channel pressure drop is incurred for an aluminium chamber than for a copper chamber due to the lower allowable temperature. @en

In the last decade, CubeSat development has shown the potential to allow for low-risk, low-cost space missions. To further improve the capabilities of CubeSats in large scale missions, a novel micro-propulsion system is being developed at Delft University of Technology. The system is based on a Vaporizing Liquid Microthruster (VLM), which is manufactured by means of Micro Electro-Mechanical Systems (MEMS) technology. It aims to achieve a specific impulse of 100 s and thrust of 1.4 mN, using water as propellant. This paper presents a status update of the development project. Design solutions are shown to circumvent manufacturing tolerances in the wafer-bonding and sealing of the interfaces of the VLM. Secondly, performance analysis based on a 1D-flow approximation is shown to provide a useful tool to quickly predict VLM performance. Next, a detailed design of the propellant storage tank for the CubeSat micro-propulsion system is presented. Finally, the test plan and test setup for the VLM are elaborated, presenting solutions to determine chamber temperature and pressure without directly sensing it.@en

This paper presents the development work of the 10 kN hybrid rocket motor DHX-200 Aurora. The DHX-200 Aurora was developed by Delft Aerospace Rocket Engineering (DARE) to power the Stratos II and Stratos II+ sounding rocket, with the later one being launched in October 2015. Stratos II and Stratos II+ are the flagship projects of DARE, a student group working on rocketry at Delft University of Technology. Successors of Stratos II have the eventual goal of reaching space. During the development process two major revisions of the motor have been designed with smaller changes between tests. The second major design revision was made after a first test series showed low combustion efficiency, through the usage of a CFD model to improve mixing. Both revisions have been tested statically in total for 14 times both at facilities of ’Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek’ (TNO) and ’Deutsches Zentrum f ¨ ur Luft- und Raumfahrt’ (DLR). All tests were conducted in a full-scale, flight-ready configuration with the primary goal of demonstrating the required performance for the Stratos II and Stratos II+ sounding rocket. It was found out that the motor suffered from combustion instabilities at around 450 Hz, when operated at its design oxidizer mass flux level of 600 kg=m2=s, that caused low combustion efficiency and elevated heat flux levels in the pre-combustion chamber. Through design changes the instabilities could be lowered and both problems removed. The design goal of total impulse could not be met, but the specific impulse measured was higher than expected. Still, the overall performance proofed to be sufficient enough for the system to be used as the propulsion system for Stratos II+. @en

This paper presents the development status at Delft University of Technology of a low-pressure micro-resistojet based on a sublimating solid propellant. In this particular type of electro-thermal thruster the propellant is water, stored as a solid and operated at very low pressure, under sublimation conditions. The steam is then expelled at high Knudsen numbers, through microchannels. The particle velocity is increased in the microchannels not by geometrical expansion as in conventional thermal propulsion concepts, but by thermal energy of the walls, transferred to the particles through collisions. The Direct Simulation Monte Carlo numerical simulations presented in the paper show that it is theoretically possible to achieve a specific impulse of 63.7 s up to 110.7 s with a plenum pressure of 50 to 300 Pa and a microchannel wall temperature of up to 900 K. A model of the tank was also designed and simulated using, in this case, the COMSOL Multiphysics 4.4 software. The sublimation is controlled inside the tank according to the mass flow needed by the plenum to keep the thermodynamic state required. These designs and simulations are based on DelFFi mission requirements and, in particular, the need to perform a basic formation flying demonstration. Additionally, the results show that by controlling the heater chip temperature, the tank temperature and the mass flow rate one can easily control the thrust and specific impulse allowing an optimal correlation between them. This opens the way to a better understanding of the operational principle of this concept and to its possible use in future demonstration missions.@en