Browsing by Author "Lappas, Vaios"

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    Autonomous unmanned heterogeneous vehicles for persistent monitoring
    (MDPI, 2022-04-10) Lappas, Vaios; Shin, Hyosang; Tsourdos, Antonios; Lindgren, David; Bertrand, Sylvain; Marzat, Julien; Piet-Lahanier, Hélène; Daramouskas, Yiannis; Kostopoulos, Vassilis
    Swarms of unmanned vehicles (air and ground) can increase the efficiency and effectiveness of military and law enforcement operations by enhancing situational awareness and allowing the persistent monitoring of multiple hostile targets. The key focus in the development of the enabling technologies for swarm systems is the minimisation of uncertainties in situational awareness information for surveillance operations supported by ‘system of systems’ composed of static and mobile heterogeneous sensors. The identified critical enabling techniques and technologies for adaptive, informative and reconfigurable operations of unmanned swarm systems are robust static sensor network design, mobile sensor tasking (including re-allocation), sensor fusion and information fusion, including behaviour monitoring. The work presented in this paper describes one of the first attempts to integrate all swarm-related technologies into a prototype, demonstrating the benefits of swarms of heterogeneous vehicles for defence applications used for the persistent monitoring of high-value assets, such as military installations and camps. The key enabling swarm system technologies are analysed here, and novel algorithms are presented that can be implemented in available COTS-based unmanned vehicles. The algorithms have been designed and optimised to require small computational power, be flexible, be reconfigurable and be implemented in a large range of commercially available unmanned vehicles (air and ground).
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    Design and structural analysis of a control moment gyroscope (CMG) actuator for cubesats
    (MDPI, 2020-05-11) Gaude, Alexis; Lappas, Vaios
    Following a global trend towards miniaturization, the population of nano- and micro-satellite continues to increase. CubeSats are standardized small size satellites based on 10 × 10 × 10 cm cube modules (1U) and are becoming sophisticated platforms despite their very small size. This paper details the design and the structural analysis of a Control Moment Gyroscope (CMG) actuator for agile CubeSats with a physical size up to 12U, which require high torque actuators. CMGs have inherited torque amplification capabilities and the recent advances in motor miniaturization make them ideal candidates for small satellite missions with slew rate requirements. The system’s requirements are derived based on conceptual agility requirements for an agile (highly maneuverable) CubeSat which needs to achieve a 90° maneuver in 90 s. With specific cost, mass and volume requirements, the proposed CMG design is based on some of the smallest available off-the-shelf electric motors and uses a light aluminum casing design. The proposed design uses stepper motors for the gimbal mechanism as a low cost, compact and low power solution, contributing to an overall low mass of the full CMG cluster. Static and dynamic analyses were performed to assess the mechanical integrity of the system for launch loads. Apart from a necessary custom control electronic board, the complete mechanical assembly has been designed including electrical hardware. Analyses demonstrate that the overall stress levels acting on the system are manageable by the CMG design. Bolted joints are critical and should be studied independently as the chosen model created singularities around these areas. Each individual CMG of the designed pyramidal cluster is shown to weigh about 35 g. Using the proposed CMG design with a customized avionics board, the complete CMG system is shown to weigh 250 g and occupies slightly more than ½U volume for a CubeSat, indicating the feasibility of CMGs for agile CubeSats
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    Design of a Mars ascent vehicle using HyImpulse’s hybrid propulsion
    (MDPI, 2023-12-14) Renault, Maël; Lappas, Vaios
    The recent growth in maturity of paraffin-based hybrid propulsion systems reassesses the possibility to design an alternative Mars Ascent Vehicle (MAV) propelled by a European hybrid motor. As part of the Mars Sample Return (MSR) campaign, a Hybrid MAV would present potential advantages over the existent solid concept funded by NASA through offering increased performance, higher thermal resilience, and lower Gross Lift-Off Mass (GLOM). This study looks at the preliminary design of a two-stage European MAV equipped with HyImpulse’s hybrid engine called the Hyplox10. This Hybrid MAV utilizes the advantages inherent to this type of propulsion to propose an alternative MAV concept. After a careful analysis of previous MAV architectures from the literature, the vehicle is sized with all its components such as the propellant tanks and nozzle, and the configuration of the rocket is established. A detailed design of the primary structure is addressed. This is followed by a Finite Element Analysis (FEA), evaluating the structural integrity under the challenging conditions of Entry, Descent, and Landing (EDL) on Mars, considering both static and dynamic analyses. The outcome is a Hybrid MAV design that demonstrates feasibility and resilience in the harsh Martian environment, boasting a GLOM of less than 300 kg.
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    EuroDRONE, A European unmanned traffic management testbed for U-space
    (MDPI, 2022-02-18) Lappas, Vaios; Zoumponos, Giorgos; Kostopoulos, Vassilis; Lee, Hae-In; Shin, Hyosang; Tsourdos, Antonios; Tantardini, Marco; Shomko, Dennis; Munoz, Jose; Amoratis, Epameinondas; Maragkakis, Aris; Machairas, Thomas
    EuroDRONE is an Unmanned Traffic Management (UTM) demonstration project, funded by the EU’s SESAR organization, and its aim is to test and validate key UTM technologies for Europe’s ‘U-Space’ UTM program. The EuroDRONE UTM architecture comprises cloud software (DroNav) and hardware (transponder) to be installed on drones. The proposed EuroDRONE system is a Highly Automated Air Traffic Management System for small UAVs operating at low altitudes. It is a sophisticated, self-learning system based on software and hardware elements, operating in a distributed computing environment, offering multiple levels of redundancy, fail-safe algorithms for conflict prevention/resolution and assets management. EuroDRONE focuses its work on functionalities which involve the use of new communication links, the use of vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) technology to communicate information between drones and operators for safe and effective UTM functionality. Practical demonstrations that took place in Patras/Messolonghi in 2019 are presented and show the benefits and shortcomings of near-term UTM implementation in Europe.
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    Nonlinear analytical uncertainty propagation for relative motion near J2 -perturbed elliptic orbits
    (2017-10-16) Yang, Zhen; Luo, Ya-zhong; Lappas, Vaios; Tsourdos, Antonios
    An analytical uncertainty propagation method based on state transition tensors (STTs) has been developed for satellite relative motion near J2-perturbed, elliptic orbits. The STTs used to propagate the relative state uncertainty are derived by adding a correction into the original STTs for propagating relative state. A new set of transitive STTs is further derived in order to propagate uncertainties for relative motion with abrupt state jumps, e.g. impulsive maneuvers executing on any of the two satellites. The nonlinear analytical solution for propagating the first two moments and the probability density function are formulated by combining the STTs with a Gaussian mixture model. Numerical results show that the proposed method outperforms the linear covariance method and provides good agreement with Monte Carlo simulations on nonlinear, non-Gaussian uncertainty propagation. Moreover, as the STTs can be analytically computed and account for the J2-perturbation, the proposed uncertainty propagator is computationally efficient, which will be potentially useful for onboard conjunction analysis in satellites formulation flying mission