DSpace Repository

Welcome to the NLR Reports Repository

Royal NLR conducts research, which is published in reports. Only a minor part of these reports is made public. This repository holds these public, so called Technical Publications (TP), mainly produced from 1996 up till now.

Technical publications published before 1996 may be obtained using the request-form. Other types of NLR-reports are Contract Reports (CR) and Technical Reports (TR), which in general are not public. You may however request a copy by using the request-form. In some cases permission may be granted, depending on specific properties and contractor of the report. Reports will be supplied as pdf-file.

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Recent Submissions

Comparative Investigation of Radiation-Driven Failure Mechanisms in Photonic–Electronic Optical Communication Terminals Across Earth Orbits
(IEEE, 2026) Dijks, J.H.C.; Jong, S. de; Menicucci, A.; Akay, I.; Donkers, N.
Optical Communication Terminals (OCTs) integrate photonic and electronic technologies to enable high-speed, secure, and interference-free space communication. Deployment across multiple orbital regimes exposes these heterogeneous systems to diverse radiation environments, each presenting distinct failure mechanisms that challenge conventional Radiation Hardness Assurance (RHA) approaches, particularly for cost-constrained Small Satellite (SmallSat)-class missions where economic feasibility must be balanced against radiation hardness requirements. This paper presents a multi-orbit radiation effects investigation for photonic-electronic architectures by characterizing environment-specificvulnerabilities and failure modesacrossSun-SynchronousOrbit(SSO),LowEarthOrbit(LEO),andMiddleEarthOrbit(MEO). SPENVISbased environment analysis shows that SSO presents a mild radiation environment with Total Ionizing Dose (TID) below 1 krad(Silicon (Si)) per year at 4 mm Aluminium (Al) shielding and low charged particle flux. LEO is dominated by proton-induced Single Event Effects (SEEs) with moderate TID, and MEOexhibits TIDexceeding 30krad(Si) per year at the same shielding level, together with relatively higher heavy-ion fluxes that drive SEE rates. Technology-level analysis reveals fundamental differences between photonic and electronic subsystems. Photonics exhibits predominantly parametric degradation that can be mitigated through margin allocation, whereas electronics remains susceptible to discrete, stochastic failure modes requiring active mitigation. These findings motivate reconfigurable architectures leveraging Field Programmable Gate Arrays (FPGAs), radiation-tolerant photonic subsystems,Wide-Bandgap (WBG) power semiconductors, and emerging Non-Volatile Memories (NVMs) to enable component-level commonality across orbital regimes. Additionally, photonic devices require parametric end-of-life characterization with explicit translation to link budget margins, while electronic systems require mission-tailored mitigation strategies and system-level testing.
Uncertainty in visibility: a scoping review of the probable and fuzzy viewshed for observer location optimization
(Taylor & Francis, 2025) Leenders, N.A.; Oijen, J. van; Lindelauf, R.; Cule, B.
Although the probable and fuzzy viewshed have been recognized as critical in visibility analysis, they remain underutilized in practical applications such as surveillance drone positioning, telecommunications tower placement, and helicopter battle-position selection. Traditional approaches often assume a binary (boolean) notion of visibility, overlooking real-world factors like uncertainty in terrain data, partial occlusion from vegetation, or the effect on visibility by light sources, atmospheric haze, and target size. This scoping review systematically maps research on non-boolean visibility models and identifies several key gaps. First, there is a lack of methods that integrate both probabilistic and fuzzy approaches for observer placement. Second, while research has addressed DEM uncertainty and vegetation, few studies combine multiple factors or apply their methods to multi-observer or path-planning problems. Finally, research into 3D applications remains sparse, even though such work is critical for tasks like military helicopter missions or surveillance drone flights. Consequently, we highlight the need for more robust modeling of combined visibility factors and clearer strategies for incorporating both probable and fuzzy criteria in real-world operational settings. Bridging these gaps will enable more accurate and reliable visibility analyses across diverse domains, from city planning to helicopter mission planning.
End-to-end predict-and-optimize dynamic predictive maintenance planning integrating prognostics - the case of short-range electric aircraft with lithium-ion batteries
(Elsevier, 2026) Oosterom, S.J.M. van; Mitici, M.
Modern assets are continuously monitored by sensors. As a result, large datasets on the health condition of these systems are often available. Using supervised machine learning, recent studies have leveraged such data to generate remaining useful life (RUL) prognostics. Here, the focus of the machine learning regressors is on achieving prognostics of high accuracy. Once obtained, in a second stage, these prognostics are usually integrated into maintenance planning optimisation models. However, aiming for high accuracy prognostics in a first stage does not guarantee that the maintenance costs are also minimized in a second, maintenance planning stage. To address this, we propose an end-to-end, dynamic framework for the predictive maintenance problem that integrates the planning stage into the prediction stage. For this, the maintenance costs are directly estimated from sensor data, instead of being derived based on RUL prognostics. We apply our end-to-end framework for the maintenance planning of a fleet of electric Vertical Take-Off and Landing (eVTOL) aircraft equipped with Lithium-ion batteries. We show that, when compared to state-of-the-art prognostics-based maintenance planning, the proposed framework reduces the number of battery failures by 24% and the total maintenance costs by 9.4%. Overall, our framework proposes an effective, data-driven paradigm for an end-to-end predictive maintenance planning.
Assessing the Impact of Uncontrolled Space Object Re-entries on Air Traffic Management Operations
(IAA, 2026) Chalabi, W.A.A.; Haagsma, A.; Badea, C.A.; Kok, J.T.A.
With the growing number of activities in space, higher airspace, and conventional Air Traffic Management (ATM) domains, the likelihood of uncontrolled space object re-entries impacting airspace operations is increasing. Such events pose a potential safety threat to airborne traffic and challenge the efficiency of current ATM procedures. With the uncertainty of the exact time and location of a space object re-entry, and the velocities involved in orbit, it is proven difficult to have a specific and exact warning for an expected re-entry event. Recent real-world cases have shown inconsistent responses, ranging from complete airspace closures, causing significant disruptions and delays, to inaction, which may become untenable as space activity expands. This research addresses the question: How should ATM deal with uncontrolled re-entries from space? The study develops a use-case scenario in which a returning space object is detected shortly before its expected entry into Dutch airspace above Amsterdam Schiphol Airport, one of Europe's busiest hubs. A traffic simulation was developed to explore possible operational responses within this limited timeframe. Based on the simulation, a set of procedures is proposed to enable ATM to safely and efficiently manage such events. For instance, flights are categorized into critical and non-critical groups to facilitate prioritization, ensuring that aircraft most at risk or constrained by operational needs received immediate attention. In addition, the study identified the importance of providing controllers with visualization tools depicting the predicted impact zone and uncertainty area and time window, allowing for better situational awareness and decision-making under time pressure. The study concludes that a structured approach combining improved space object tracking capabilities, predefined risk assessment zones, and collaborative decision-making between ATM and space operations stakeholders can significantly enhance both safety and efficiency during uncontrolled re-entry events. Recommendations are proposed for integrating these procedures into existing ATM frameworks to better prepare for the increasing interaction between the space and aviation domains.
Measuring the spreadability of pre-treated and moisturized powders for laser powder bed fusion
(Elsevier, 2020) Cordova, L.; Bor, T.; Smit, M.J. de; Campos, M.; Tinga, T.
For AM processes—specifically Laser Powder Bed Fusion (L-PBF) processes—powder flowability is essential for the product quality, as these processes are based on a thin layer spreading mechanism. However, the available techniques to measure this flowability do not accurately represent the spreading mechanism. Hence, this paper presents two novel applicator tools specifically designed to test the spreadability of l-PBF powders in thin layer application. The results were checked by running standard tests to analyze the powder morphology, moisture content, chemical composition and flowability using the Hall-flowmeter. For this study, four common l-PBF metal powders were selected: Inconel 718, Ti6Al4V, AlSi10Mg and Scalmalloy. From the as-received state, drying (vacuum and air) and moisturizing treatments were applied to compare four humidity states and investigate the feasibility of pre-treating the powders to remove moisture, which is known to cause problems with flowability, porosity formation and enhanced oxidation. The tests reveal that AlSi10Mg is the most susceptible alloy to moisture and oxygen pick-up, considerably decreasing the spreadability and relative density on the build platform. However, the results also reveal how challenging the direct measurement of moisture levels in metal powders is.