Reliable and computationally efficient prediction capabilities for combustion instabilities in liquid propellant rocket combustion chambers are still rare. This study uses a low-order tool based on the well-known acoustic network model principle to map the stability limits of two different research rocket combustors with different cryogenic propellant combinations. New elements were derived capable of describing any isentropic background flow field in a contoured chamber, resolving acoustic chamber modes in three dimensions, and supporting distributed flame response models. Furthermore, an improved boundary condition element for the sonic throat of a rocket nozzle was implemented. The new network elements were benchmarked against two different research rocket combustion chambers, one single injector experiment using liquid oxygen and natural gas, exhibiting longitudinal mode instabilities and one multi-element thrust chamber with transverse mode instabilities. The acoustic resonant frequencies are predicted with an average absolute error of less than 5% for both cases. The tool is capable of predicting stability based on classical time lag and gain parameters applied to the new distributed flame model. The resulting stability maps are consistent with the benchmark cases for flame response time lags which are close to those reported in literature from computational fluid dynamics simulations and experiments.

In-air capturing is a promising concept for recovering winged reusable launch vehicles (RLVs) using a towing aircraft (TA), without the need for any propulsion on board the RLV during descent. In this paper, the preliminary electromechanical design of an airborne device is presented, which is central to in-air capturing. The device is an autonomous system, towed by the TA, and docks with a boom attached to the nose of the RLV. A design space exploration and load analysis are performed using a simplified towing model, revealing significantly higher towing loads compared to previous estimates. The design of a probe-drogue docking mechanism is proposed, which uses a set of actuated wedges to lock the RLV boom in place. Actuator and sensor solutions are studied, aiming at a redundant and robust mechanism design. Based on reference commercial-off-the-shelf components, the size, weight, and power footprints of essential avionics are estimated, and a preliminary dimensioning of the required battery system is performed. Finally, a comprehensive, electromechanical computer-aided design model is developed, with which the overall inertial properties of the vehicle are estimated. The position of its centre of gravity is studied, revealing the need for a forward trim mass. Compared to previous design studies, the estimated total mass is increased to 175.44 kg, while the design’s overall safety factor grows to 1.51.

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.

The space community is currently focusing on defining mission architectures able to perform multiple interplanetary missions to support deep space exploration. In particular, placing orbital propellant depots in strategic locations in space would allow to increase the useful mass transferred. The design of the propellant depot depends greatly on the propellant storage duration and the thermal environment the depot experiences. Furthermore, different cryogenic propellant combinations are being considered for use, including hydrolox and methalox. For both, efficient boil-off reduction strategies are fundamental. The aim of this work is to evaluate different depot architectures for different thermal environments and mission durations. The approach taken in this work included the development of a propellant depot sizing model that allows determining the effect of different thermal control design options, thermal environments, and depot configurations for varying mission duration. The design options include, amongst others, Multi-Layer Insulation and Vapor Cooled Shields. The model also allows for a multi-nodal thermal analysis to estimate boil-off rates for the different designs. Main objective for the studies is to identify the architecture that is most mass efficient. Preliminary results show that mass efficient designs can be achieved with only passive insulation for mission durations below one year, with further improvements when adding a vapor cooled shield to the design.

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.

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.