Deep reinforcement learning (DRL) and evolution strategies (ESs) have surpassed human-level control in many sequential decision-making problems, yet many open challenges still exist. To get insights into the strengths and weaknesses of DRL versus ESs, an analysis of their respective capabilities and limitations is provided. After presenting their fundamental concepts and algorithms, a comparison is provided on key aspects, such as scalability, exploration, adaptation to dynamic environments, and multiagent learning. Current research challenges are also discussed, including sample efficiency, exploration versus exploitation, dealing with sparse rewards, and learning to plan. Then, the benefits of hybrid algorithms that combine DRL and ESs are highlighted.

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We are developing content and software to automate the homologation for our Electronics courses to deal with the increasing diversity in knowledge and skills of the master students who have completed their bachelor’s at other universities. The courses’ content has been structured such that dependencies between topics become explicit. A parameterized database was created with questions characterized with, e.g., subject, Bloom level, and many other tags. It enables the generation of questions and personalized quizzes for individual students at any time. This allows teachers and students to gain insight into the student’s level of knowledge and skills and provide adequate feedback at any time. The questions and complete quizzes can also be exported to learning platforms like Brightspace.@en

As the complexity of nanosatellite missions have increased over time, the data generated on-board nanosatellites have increased multiple folds. As a result, there is a need to downlink large amounts of data. Multiple nanosatellite missions have started using spectral efficient modulation schemes recommended in DVB.S2 and DVB.S2X to make the best use of the available spectrum. One of the main challenges in adopting higher order modulation schemes is to power-efficiently upconvert and amplify the baseband signals. All the lost efficiency in converting the DC power to the RF output is dissipated as heat and the relatively small thermal mass of nanosatellites poses thermal management challenges. As a first step to addressing the challenge of improving the power efficiency of the communication module, optimization techniques to improve the Peak to Average Power Ratio (PAPR) of the modulation schemes (16/32-APSK) are discussed in this paper. The PAPR of 16-APSK reduces by ~2 dB by incorporating filtering techniques discussed in this paper. Further, a well-known efficiency and linearity enhancement technique; Out-phasing/LINC (Linear Amplification using Non-linear Components) is discussed. As a variant of the out-phasing architecture, a novel approach is proposed using two circularly polarized antenna to transmit the constant envelope signals in opposite polarizations and signal combining is performed at the receiver. Simulations results are used to demonstrate how higher efficiencies can be achieved using the proposed architecture.@en

In the last decades, there has been a steady adoption of digital online platforms as learning environments applied to all levels of education. This increasing adoption forces a transition in educational resources which has further been accelerated by the recent pandemic, leading to an almost complete online-only learning environment in some cases. The aim of this paper is to outline the methodology involved in setting up a framework for mapping course-specific data based on student activity to standard learning indicators, which will serve as an input to performance prediction algorithms. The process involves systematically surveying, capturing, and categorising the vast range of data available in digital learning platforms. The data are collected from two sample courses and distilled into five dimensions represented by the generic learning indicators: prior knowledge, preparation, participation, interaction, and performance. The data is weighted based on course development and teaching member’s perspectives to account for course-wise variations. The framework established will allow portability of prediction algorithms between courses and provide a means for meaningful and directed learner formative feedback. Two courses, both bachelor-level and worth 5 European Credits (ECs), that use several online learning platforms in their teaching tools have been chosen in this study to explore the nature and range of student interaction data available, accessible, and usable in a course. The first course is Electromagnetics II at Eindhoven University of Technology, and the second course is Electronics at Delft University of Technology. Both Universities are located in the Netherlands. This work is in the scope of a broader study to use such learning indicators with predictive algorithms to provide a prognosis on individual student performance. The findings in this paper will enable the realization of student performance prediction at a very early stage in the course.@en

The past two decades have witnessed a renewed interest in low frequency radio astronomy, with a particular focus on frequencies above 30 MHz e.g., LOFAR (LOw Frequency ARray) in the Netherlands and its European extension ILT, the International LOFAR Telescope. However, at frequencies below 30 MHz, Earth-based observations are limited due to a combination of severe ionospheric distortions, almost full reflection of radio waves below 10 MHz, solar eruptions and the radio frequency interference (RFI) of human-made signals. Moreover, there are interesting scientific processes which naturally occur at these low frequencies. A space or Lunar-based ultra-low-frequency (also referred to as ultra-long-wavelength, ULW) radio array would suffer significantly less from these limitations and hence would open up the last, virtually unexplored frequency domain in the electromagnetic spectrum. A roadmap has been initiated by astronomers and researchers in the Netherlands to explore the opportunity of building a swarm of satellites to observe at the frequency band below 30 MHz. This roadmap dubbed Orbiting Low Frequency Antennas for Radio Astronomy (OLFAR), a space-based ultra-low frequency radio telescope that will explore the Universe's so-called dark ages, map the interstellar medium, and study planetary and solar bursts in the solar system and search them in other planetary systems. Such a radio astronomy system will comprise of a swarm of hundreds to thousands of satellites, working together as a single aperture synthesis instrument deployed sufficiently far away from Earth to avoid terrestrial RFI. The OLFAR telescope is a novel and complex system, requiring yet to be proven engineering solutions. Therefore, a number of key technologies are still required to be developed and proven. The first step in this roadmap is the NCLE (Netherlands China Low Frequency Explorer) experiment, which was launched in May 2018 on the Chinese Chang'e 4 mission. The NCLE payload consists of a three monopole antenna system for low frequency observations, from which the first data stream is expected in the second half of 2019, which will provide important feedback for future science and technology opportunities. In this paper, the roadmap towards OLFAR, a brief overview of the science opportunities, and the technological and programmatic challenges of the mission are presented.

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This paper discusses some of the solutions to the issue of data congestion in Nano-satellite missions. The complexity of Nano-satellite missions has increased over the years, generating more data than ever and this paradigm shift has in-turn resulted in the need for larger downlink bandwidth requirements. The larger bandwidth's necessity and limited availability of frequency spectrum in lower frequencies spectrum has resulted in the problem of data congestion and invoked the need to investigate the use of mmWave frequency bands for Nano-satellite missions. In this paper, three use cases are discussed to demonstrate the need for using frequency bands higher than X-band and the communication strategy discussed in the use-cases are not restricted to the specific application mentioned in the use-cases but can be extended to similar applications. Irrespective of the frequency bands, there is a need to adapt standards such as DVB.S2 and DVB.S2X (Satellite digital broadcasting standard) that provide spectral efficient modulation schemes. Although these well-established standards are already used in satellite communications, this work proposes further optimization on the modulation schemes that helps improve efficiency of the transmitter front-end. A comparison between 16/32-QAM, 16/32-APSK, 16/32-oAPSK and the proposed 16/32-pAPSK (Polar-filtered Amplitude Phase Shift Keying) modulation schemes are discussed. Some of the practical challenges in using mmWave communications for nano-satellite missions are addressed in this paper with a study on the state-of-the-art mmWave semiconductor technology that are suitable for SSPA (Solid State Power Amplifier) design specifically for nano-satellite missions.

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The inter-satellite link (ISL) in swarm and constellation missions is a key enabler in the autonomy of the mission. OLFAR (Orbiting Low Frequency Array for Radio astronomy) is one such mission where 10 to 50+ nanosatellites are placed in the Lunar orbit and perform astronomical observations from the far-side of the moon. Each of the nanosatellite in the swarm would carry a receiver that performs observations between 0.3 - 30 MHz, which are the least explored frequency bands in radio astronomy, thus attracting a large scientific interest.
Observations in this frequency bands from Earth are highly challenging as the ionosphere is opaque to these frequency bands. Furthermore, RFI (Radio Frequency Interferences) generated on Earth makes it highly challenging to perform astronomical observations below 30MHz band. The impediments faced by Earth-based or near-Earth-based radio astronomy for these frequency bands is the motivation to perform measurements from the far-side of the moon.
The purpose of using a swarm of nanosatellites to perform low frequency observations is to enable the realization of long observation baselines and additionally, the effective aperture of observation increases with the number of satellites. For the swarm of nanosatellites to operate as a single aperture, it is very important to cross-correlate the information collected by each satellite and this is where the ISL becomes very crucial. Apart from exchanging data collected by the payload, other information such as attitude and timing information needs to be exchanged.
This work derived mission level requirements which would be used to define a suitable communication architecture for space-based radio astronomy missions such as OLFAR. The approach chosen for communication system for such a swarm mission will comprise of two types of ISL: High data-rate directional link that will be used to exchange payload date and low data-rate omni-directional link that will be used to exchange attitude, timing information and be used for localization, positioning and ranging of the nanosatellites in the swarm. This work will present link budgets to show the feasibility of the proposed communication architecture and derive the specs to further design the transceivers.@en

The frequency range below 30 MHz remains one of the last unexplored frequency ranges in radio astronomy However, Earth-based observations at these wavelengths are severely impeded, due to man-made radio frequency interference (RFI) and atmospheric opacity. To overcome this impediment, various space-based radio astronomy studies have been proposed in the past decade, notably the OLFAR (Orbiting low Frequency Antennas for Radio Astronomy) study, which proposed a satellite swarm for ultra-long wavelength observation. To realize this mission, various technological challenges of a satellite swarm are currently being addressed, particularly antenna design, navigation, communication, distributed processing, and overall system and mission design. Secondly, the RFI levels at various altitudes from Earth is currently unknown, which is a hindrance in general for radio astronomy. To this end, we propose the use of high-altitude ballooning experiments to validate OLFAR sub-systems in pseudo-representative conditions. Furthermore, these ballooning experiments will measure the RFI in the ultra-long wavelength spectrum at various altitudes from Earth. Our project is termed LOBE (Low-frequency observations using high-altitude Balloon Experiments), and in this paper, we present an overview of the science objectives, payload, and the technological and programmatic challenges of the LOBE project.

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A distributed space system (DSS) is an architecture with more than one spacecraft to achieve a common objective. A number of questions arise with respect to the characteristics and dynamics of distributed system in space. How fast is the system spreading? How are the elements within the system distributed? Is it tightly or loosely packed? What is the effect of perturbations on its absolute and relative dynamics? What are the chances of a collision within the system? There has not been much research in these areas concerning a DSS. In this paper, quantitative metrics are established that allow characterizing DSS and assisting in answering above questions.Key performance indicators for a DSS are identified as size or envelope of the cluster, a distribution measure, and a measure for collision. Determining the geometric system size is straightforward through numerical or analytical propagation methods. The focus of this paper will be on the other two metrics: a cluster distribution index (CDI) and a measure for collision probability within the system. The distribution index can be used to assess the effectiveness of DSS in meeting system requirements such as coverage and resolution. An n-dimensional grid-based numerical approach is used to evaluate CDI. The collisions analysis using line-integral method (CALM) is proposed as an effective and efficient approach to analyzing collision probability within DSS. Results show that the CDI is an effective indicator to assess the influence of perturbations, such as differential drag, on spatial distribution of the system. The CALM approach is three orders of magnitude faster than existing approaches that evaluate collision probability for non-linear motion.

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Nano-satellite IoT/M2M missions are gaining popularity in recent time. Various companies have launched their pilot missions last year in 2018 and all these companies intend to place a constellation in (V)LEO that can communicate with low power sensors on the ground (sometimes remote locations) and relay it back to the end-user who is monitoring these sensors. This paper discusses two possible architectures of using nano-satellites for low latency IoT/M2M, by presenting information such as, number of satellites needed, number of orbital planes needed and communication strategy. The first proposed architecture will comprise of a self-sustaining network of nano-satellites that communicate with low power, low data-rate sensors on the ground and relay the data to rest of the nano-satellites in the network using inter-satellite links, which is downlinked by a nano-satellite that is in the view of a ground station that is connected to IMT. The second proposed architecture will use nano-satellites to communicate with low power, low data-rate sensors on the ground and relay it to satellites that intend to provide internet from space (Mega-constellation). The internet constellations considered in this study for the second architecture are: Telesat’s constellation, SpaceX’s Starlink, OneWeb’s constellation, Astrome’s SpaceNet constellation and Audacy’s constellation. Using both these architectures, it can be seen that the latency can be reduced considerably. @en

Deep space missions are exposed to a broad range of temperatures and extremely high doses of radiation when compared to Earth bound space missions. Although standard passive and active strategies have been developed to protect spacecraft subsystems from fatal levels of radiation and unacceptable temperature levels inside the spacecraft, environmental analysis is a non-linear discipline which changes from project to project and therefore needs to be analyzed independently. Specially, taking into account the singular features which characterize each space mission. On the other hand. given that every kilogram launched beyond Earths orbit has signicant associated costs, space systems miniaturization has become a necessity with increasing popularity, which has driven the recent trend in the enhancement of this technology. These small complex systems need to be precisely simulated and verified with realistic simulations and experimental tests so that in an unexpected environmental situation, the risk of a total mission failure is reduced to the minimum. To accomplish mission requirements in terms of cost, mass and energy utilization for miniature spacecraft, passive thermal control systems (PTCS) are sought. In this project, Lunar Zebro, miniature space exploration surface vehicles will be connected together in a network, analyzing data from multiple nodes using interferometry; acting all together as a single dish. After introducing and analyzing the technological goals and objectives of this mission, the focus shifts into the environmental analysis of a single rover from this swarm. Its thermal behaviour is addressed in all mission phases, beginning from its performance on ground through to the Moon's surface, taking into account different possible scenarios. To do so, an own program is created (in MATLAB), in which an easy-to-apply and computationally efficient Ray Method is implemented. Among other applications, Visual Factors between the various faces of the rover and different heat sources (e.g. the Sun or Moon albedo) are computed using that methodology, which is explained in a step-by-step guide to be applied in any other software for other missions. To validate the model's accuracy and enhance the rover's thermal scope of knowledge, results will be compared to those obtained from ANSYS, a dedicated program for thermal applications. Recommendations for implementing the thermal analysis, together with limitations and future improvements of the method are also addressed. On the other hand, to get the complete overview of the environmental analysis of the mission, radiation issues are analyzed as well, taking into account the worst possible scenario. Outputs coming from this analysis will determine what is the optimal solution for protecting the rover. Finally, conclusions and future work to do in this mission are covered.@en

This paper presents a software-defined testbed to perform hardware-in-The-loop test of miniaturized coherent transponders. Such a setup has been designed to minimize the access threshold for future users, heavily relying on available open source applications and commercial hardware, targeting future coherent transponders for interplanetary CubeSats. The paper presents the overall architecture of the testbed, a tradeoff to select the most suited development framework and the detailed design of the different blocks. Upcoming interplanetary CubeSat missions that would require a coherent transponder are also presented to highlight the need sof such a system. Software qualification, given the use of third-party software with multiple developers, was also addressed to guarantee performances can be consistent and reliable.

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Progress in low power miniaturized electronics and wireless technologies have enabled many innovative applications. Of particular interest is the Internet of Things (IoT) that has dominated the world of ICT in the last half a decade enabling many smart systems and applications. At the same time, we also see much enthusiasm with respect to space missions and applications including terrestrial applications, apart from exploring the universe. We believe that innovations in the domain of IoT will significantly influence the space related activities – both research and development. In this article, we chart out the innovations in space and the vision with respect to embedded and wireless systems for space applications. In particular, we bring in the notion of Sensor Wireless Actuator Networks in Space (SWANS) and Space Pixels to explain IoT in space. We explain with examples what we envision for the next decade and also the challenges therein. We briefly put forth our four major targets in the next five years.@en

This paper presents a new feedback model that focuses on the synthesis rather than the analysis of feedback amplifiers. First, a single-loop synthesis-oriented feedback model is developed that enables the full synthesis of such amplifiers in a hierarchical and systematicway. This model is subsequently extended to a double-loop synthesismodel, so that also feedback amplifierswith a characteristic input or output impedance-employing two feedback loops-can be synthesized through the same systematic approach. That these new models are suitable for synthesis lies in the fact that they map directly to the circuit level, such that the intended, asymptotic behavior as well as the various individual contributors to the deviation from this intended behavior, like finite loop gain, non-ideal input and output impedances of the forward gain block, direct feed-through and attenuations outside the feedback loop(s), are clearly distinguished and can be assigned to the responsible sections of the network. For this purpose, the double-loop synthesis model makes the transfers of the two feedback networks explicitly visible, so that it gives immediate insight in how to design these networks to get the required signal transfer and characteristic impedance.@en

The effect of second-order intermodulation (IM2) distortion produced by out-of-band, high-frequency interference on baseband/IF amplifiers is analyzed using the Volterra series. It is shown that a compensation loop designed to trap nonlinear currents improves the immunity of differential stages to IM2 distortion generated by local feedback. Measurements of a single-ended amplifier example implementing the proposed method demonstrate an IP2 increase of more than 30 dB@en

Driven by wide interest among TU Delft (Delft University of Technology) students to acquire focussed knowledge on space engineering, missions and planetary exploration, a new spaceflight minor was developed for the minor program of the university. With its minor program, TU Delft affords its students an opportunity to dedicate the first semester of their 3rd BSc year to a set of courses chosen among the numerous options offered specifically by the TU Delft or another university. Students are not only allowed but encouraged to explore topics and study fields outside their main BSc track. The spaceflight minor is designed as a multidisciplinary, thematic program, in which the students gain insight in the demand for space applications, mission analysis, system requirements and sizing. This multidisciplinary setup is facilitated by the recently established TU Delft Space Institute (DSI), of which all the faculties involved in the minor are members. The minor and the DSI provide a unique opportunity to strengthen space education and research across TU Delft. The minor covers two quarters of the academic year, spanning twenty weeks, and includes six courses. Offered in the first quarter are: Introduction to Spaceflight (for students without Aerospace Engineering background) or Electronic Circuits (for the other students); Space Exploration, with basics and examples of planetary and astronomical exploration and an introduction to space law; Earth Observation, covering basics of remote sensing of the Earth. The second quarter includes: Spacecraft Technology, providing an overview of the technology of spacecraft subsystems with emphasis on small satellites; Satellite Tracking & Communication, on telecommunications, ground station operations and telemetry analysis from a theoretical and practical point of view; Spaceflight Assignment, the final project in which students produce real, small-scale space deliverables, and reflect on the process and results of development and analysis in the complex space engineering and scientific environment. In total, 15 lecturers from three TU Delft faculties and one from Leiden University contributed to the minor. Many of the courses employ innovative education techniques, such as flipped classrooms and videos produced by the lecturers. Some courses are simultaneously offered to campus students and external participants in a full online format. The first edition of the minor, delivered from September 2015 to January 2016 to 44 students from various TU Delft faculties, can be considered a success with excellent feedback from participants. The paper elaborates on the minor design and learning objectives, showing how multidisciplinary, innovative education can be effectively implemented for students with different academic backgrounds. @en

This paper proposes a novel phase synchronization technique that enables beamforming with multiple resource-limited spacecraft in space and capitalizes on their spatial geometry. The proposed technique employs an external beacon to obviate the need for explicit time synchronization and reduces the accuracy requirements on localization. Results show that subcentimeter (subnanosecond)-level phase synchronization can be achieved with localization accuracy in the order of meters.@en