Stratospheric Airship Research Articles

Artificial neural network–based constitutive relation modelling for the laminated fabric used in stratospheric airship

There have been gradually increasing interests in the stratospheric airship (SSA) as a cost-effective alternative to earth orbit satellites for telecommunication and high-resolution earth observation. Lightweight and high strength envelopes are the keys to the design of SSAs as it directly determines the endurance flight performance and loading deformation characteristics of the airship. Typical SSA envelope material is a laminated fabric, which is composed of fabric layer and other functional layers. Compared with conventional composite structures, the laminated fabric has complex nonlinear mechanical characteristics. Artificial neural network (ANN) has good processing ability to nonlinear information so that it is suitable to model the constitutive relation of laminated fabrics. In this work, an ANN based on the Scaled Conjugate Gradient (SCG) algorithm is proposed firstly to model the constitutive relation of fabric Uretek3216LV. Considering significant errors of the SCG ANN results, the network model is optimized through methods of selecting the number of hidden-layer nodes and training algorithms. Results show that the improved network model based on Bayesian Regularization (BR) algorithm and eight nodes of single hidden layer can better describe the constitutive relation of the laminated fabric than other conventional training algorithms. The proposed constitutive modelling method with ANN is expected to gain a deeper understanding of the mechanical mechanism and guide structural design of envelope material in further work.

Adaptive fault-tolerant control for stratospheric airships with full-state constraints, input saturation, and external disturbances

This study addresses the trajectory tracking problem of a stratospheric airship subject to actuator faults, full-state constraints, input saturation, and unknown external disturbances. Improved airship state-space equations are obtained by simultaneously considering actuator faults, input saturation, and external disturbances. An adaptive fault-tolerant controller with a neural network (AFTCNN) was proposed with backstepping as the main framework. A tan-type barrier Lyapunov function (TBLF) and auxiliary systems are combined to address the full-state constraints and input saturation. Adaptive fault-tolerant and radial basis function neural network (RBFNN) control laws are proposed to estimate the actuator faults, and to approximate the disturbances, respectively. Stability analysis indicates that the tracking error converges to a neighborhood of zero; the error estimation of actuator faults and disturbances is bounded, and the state constraints are never violated. The standard backstepping method with and without RBFNN, and an adaptive fault-tolerant controller with and without RBFNN are compared in the numerical simulation. The results verify that the proposed method is superior to other methods in terms of trajectory-tracking performance and estimation of actuator faults and external disturbances, with smaller forces and torques to track the trajectory.

Basic Problems Research in Stratospheric Airship Design

Basic Problems Research in Stratospheric Airship Design

Stochastic optimization of high-altitude airship envelopes based on kriging method

High-altitude airships can be used to transport substantial payloads to the stratosphere and remain there over long periods of time. In this paper, an algorithm for the design of high-altitude airship envelopes, accounting for uncertainties, is developed and applied. The algorithm is based on the non-intrusive polynomial chaos expansion scheme, which is employed to build a stochastic kriging metamodel. Two uncertainties are examined and characterized: 1) the stratospheric wind fluctuations using reanalysis datasets and 2) the variability in the turbulence levels. The method results are discussed to address the relevancy of the uncertainties. It is found that the drag coefficient of stratospheric envelopes can vary by as much as 30 percent. As a case of study, an ideal stratospheric airship is considered, operating at an altitude of 20 km, at a latitude of 30cN and carrying a payload of 250 kg. The baseline design follows the shape of the ZHIYUAN-1 envelope and the cost function to be minimized is the average mission drag coefficient. Due to the new method, a significant reduction (4%) of the average drag of the aircraft is achieved.

Three-dimensional path-following adaptive control of stratospheric airship based on improved chemical reaction optimization algorithm

Three-dimensional path-following adaptive control of stratospheric airship based on improved chemical reaction optimization algorithm

A survey on modelling, control and challenges of stratospheric airships

The stratospheric airship, which is a new concept of autonomous atmospheric flight platforms, can operate over a period of time at very high altitudes to accomplish various military or commercial missions, such as monitoring, surveillance, and scientific exploration. The worldwide interest in stratospheric airships is still growing. However, modelling and control techniques for airships have fallen far behind those for fixed-wing aircraft. To show recent advances in modelling and control for stratospheric airships, this paper provides an insightful description of the related problems and a list of references for researchers and engineers focusing on this area. The literature is categorized according to major topics in this area: dynamic modelling, control design, and ascent/descent flight control. Moreover, an application of the path-following control with real-time flight test results is presented for an autonomous prototype airship. Finally, some challenging issues are addressed for future research.

Survey on security issues of routing and anomaly detection for space information networks

Space information networks is network systems that can receive, transmit, and process spatial information lively. It uses satellites, stratosphere airships, Unmanned Aerial Vehicles, and other platforms as the carrier. It supports high-dynamic, real-time broadband transmission of earth observations and ultra-long-distance, long-delay reliable transmission of deep space exploration. The deeper the network integration, the higher the system’s security concerns and the more likely SINs will be controlled and destroyed in terms of cybersecurity. How to integrate new IT technologies such as artificial intelligence, digital twins, and blockchain to diverse application scenarios of SINs while maintaining SIN cybersecurity will be a long-term critical technical issue. This study is a review of the security issues for space information networks. First, this paper examines space information networks’ security issues and figures out the relationship between the main security threats, services, and mechanisms. Then, this article selects secure routing and anomaly detection from many security technologies to conduct a detailed overview from two perspectives of traditional methods and artificial intelligence. Subsequently, this paper investigates anomaly detection schemes for spatial information networks and proposes a deep learning-based anomaly detection scheme. Finally, we suggest the potential research directions and opening problems of space information network security. Overall, this paper aims to give readers an overview of the newly emerging technologies in space information networks’ security issues and provide inspiration for future exploration.

Error-constrained fixed-time trajectory tracking control for a stratospheric airship with disturbances

In this paper, a novel fixed-time trajectory tracking control method is presented for a six degrees of freedom (6-DOF) stratospheric airship with time-varying error constraints and disturbances. The tan-type barrier Lyapunov function (BLF) method is extended by the adding a power integrator technique to deal with the time-varying error constraints with the fixed-time stability guaranteed, which ensures that the convergence of a stratospheric airship to the reference trajectory can be achieved in a finite time regardless of its initial condition. Also the complex differential calculation is avoided in the backstepping design. A new fixed-time disturbance observer (DO), which counts on less prior knowledge of disturbances, is constructed to estimate the unknown disturbances. The proposed control method is developed based on the transformed error model, thus can be readily extended to a wide range of second-order mechanical systems. Finally, numerical simulations demonstrate the effectiveness of the proposed control scheme.

Stratospheric balloon tracking system design through Software Defined Radio applications: STRAINS experiment

The new concept aerospace mission profiles, such as stratospheric airships or suborbital vehicles, impose new requirements for the tracking and surveillance systems, with particular regards to manned missions. New technologies and innovative tracking systems can be supporting such operations. The STRAINS (Stratospheric Tracking Innovative Systems) Experiment, conceived by Sapienza University of Rome and ALTEC (Aerospace Logistics Technology Engineering Company) and supported by ASI (Italian Space Agency), to be launched in Q3/Q4 2021, is aiming at demonstrating TDOA (Time Difference of Arrival), FDOA (Frequency Difference of Arrival) and single station tracking for a Zero-Pressure Balloon Flight in the framework of the HEMERA H2020 balloon launch infrastructure. This paper describes the design of the STRAINS stratospheric experiment, including the stratospheric and the ground segment, the analyses carried out for optimizing the experiment functionalities, the mission analysis for defining the multi-lateration stations locations and the performance evaluation for the designed TDOA tracking system.

Conceptual Design of an Energy System for High Altitude Airships Considering Thermal Effect

High altitude airships possess tremendous potential for long-endurance spot hovering platforms for both commercial and strategic applications. The energy system, which is mainly made up of solar array and regenerative fuel cell, is the key component of a high altitude airship. The thermal effect is a major factor that affects the performance of the energy system of long endurance stratospheric vehicles. In this paper, a conceptual design method focusing on the thermal and power characteristics of an energy system for stratospheric airships is proposed. The effect of thermal behavior of solar array on the energy system is analyzed. An optimized case is obtained on the consideration of power supply, thermal behaviors of helium and solar array. Results show that the maximum temperature difference of the solar array may be reduced by about 20 K and the mass of payload can be improved by up to 5%.

Single edge crack effect on mechanical property of polyimide flexible composite envelope

The existence of cracks has a great influence on the life span of the envelope material of aerostats, especially for stratospheric airships that operate in harsh environments. Understanding the relationship between fracture mechanism and composite structure of envelope materials is of great significance to the design and development of envelope materials. To explore the fracture mechanism of envelope material, a novel polyimide (PI) envelope was developed by lamination method. Then, the fracture behavior and mechanism of PI envelope with single edge crack was studied and analyzed in detail by means of experimental method and theoretical model analysis. It was found that the crack orientation has no significant effect on the fracture strength of PI envelope, while the increase of crack length will increase the strength loss rate and decrease the crack sensitivity. These phenomena suggest that the fracture strength loss of envelope is mainly determined by the number of cut-off longitudinal yarns. And the stress transfer effect of coating and transverse yarns which causes stress concentration in the crack tip region is another important factor affecting the fracture strength of PI envelope. Besides, the interfacial properties between coating and fibers as well as the size effect of coating also play an important role in the fracture property of PI envelope. Finally, stress intensity factor theory and critical stress field theory were chosen to study the fracture behavior of PI envelope. The calculation results indicated that critical stress field theory can better predict the fracture strength of PI envelope.

Moving-mass-based station keeping of stratospheric airships

ABSTRACTStratospheric airships are lighter-than-air vehicles that work at an altitude of 20km in the lower calm portion of the stratosphere. They can be used as real-time surveillance platforms for environment monitoring and civil communication. Solar energy is the ideal power choice for long-endurance stratospheric airships. Attitude control is important for airships so that they can point at a target for observation or adjust the attitude to improve the output performance of solar panels. Stratospheric airships have a large volume and semi-flexible structure. The typical actuators used are aerodynamic surfaces, vectored thrust and ballonets. However, not all these actuators can work well under special working conditions, such as low density and low speed. In this study, moving-mass control is introduced to stratospheric airships because its control efficiency is independent of airspeed and atmospheric density. A nonlinear feedback controller based on generalised inverse with a nonlinear mapping module is designed to implement moving-mass control. Such a new station keeping scheme with moving masses is proposed for airships with different working situations.

Performance Prediction and Design of Stratospheric Propeller

In this paper, a performance prediction method is proposed for the design of a stratospheric propeller. The Spalart–Allmaras (S–A) model was used to calculate the airfoil performance of FX63, and the polynomial fitting method was utilized to establish the airfoil database of the lift and drag coefficient. A computational fluid dynamics (CFD) model was applied at different altitudes to prove the feasibility of the method. The CFD results were compared with the results of the vortex theory and prediction; the prediction result accuracy was improved compared with that of the vortex theory over a greater range of advance ratios. The airfoil performance data requirements and the number of iterative calculations were reduced. These results indicate that the proposed propeller design meets the requirements of stratospheric airship propulsion systems.

Mechanical characterization of a woven multi-layered hyperelastic composite laminate under uniaxial loading

We characterize the material properties of a woven, multi-layered, hyperelastic composite that is useful as an envelope material for high-altitude stratospheric airships and in the design of other large structures. The composite was fabricated by sandwiching a polyaramid Nomex® core, with good tensile strength, between polyimide Kapton® films with high dielectric constant, and cured with epoxy using a vacuum bagging technique. Uniaxial mechanical tests were used to stretch the individual materials and the composite to failure in the longitudinal and transverse directions respectively. The experimental data for Kapton® were fit to a five-parameter Yeoh form of nonlinear, hyperelastic and isotropic constitutive model. Image analysis of the Nomex® sheets, obtained using scanning electron microscopy, demonstrate two families of symmetrically oriented fibers at 69.3°± 7.4° and 129°± 5.3°. Stress-strain results for Nomex® were fit to a nonlinear and orthotropic Holzapfel-Gasser-Ogden (HGO) hyperelastic model with two fiber families. We used a linear decomposition of the strain energy function for the composite, based on the individual strain energy functions for Kapton® and Nomex®, obtained using experimental results. A rule of mixtures approach, using volume fractions of individual constituents present in the composite during specimen fabrication, was used to formulate the strain energy function for the composite. Model results for the composite were in good agreement with experimental stress-strain data. Constitutive properties for woven composite materials, combining nonlinear elastic properties within a composite materials framework, are required in the design of laminated pretensioned structures for civil engineering and in aerospace applications.

A comparative study of conventional and tri-lobed stratospheric airships

Abstract The design and development of Stratospheric Airships for High-Altitude Long-Endurance missions (HALESAs) has generated interest worldwide. Conventional airships usually have a single-lobed axisymmetrical envelope shape. In contrast, several non-axisymmetric envelope configurations have been proposed for the HALESAs, such as flattened single lobed and multi lobed. This paper describes a methodology for carrying out a comparative analysis of a conventional HALESA and the multi-lobed HALESA designed for the same design mission. A sizing methodology which enables the estimation of its design parameters to meet some user-specified requirements has been developed for airships with envelopes of both these shapes. A Multidisciplinary Design Optimisation (MDO) approach has been followed in this methodology, which includes considerations from the disciplines of aerodynamics, energy, environment and structures. The study indicates that the envelope volume, solar array area and total mass of the single-lobed conventional airship are better than those of the tri-lobed HALESA. While the multi-lobed HALESA has the advantage of a flatter upper surface resulting in higher efficiency of the solar panels, the conventional airship has lower drag, which results in superior mission performance.

Envelope radiation characteristics of stratospheric airship

To investigate the envelope radiation characteristic of stratospheric airship, three kinds of airship models with different dimensions (fineness ratio of 3, 4, 5) are selected. After establishing the thermal equilibrium equations of the selected models, the influence of the envelope radiation characteristic on the envelope and airship gas is first addressed to determine the optimal fineness ratio by considering the flight dynamics characteristics. Furthermore, the effects of envelope emissivity, envelope absorptivity, solar cells radiation characteristics, and typical envelope materials on the envelope radiation characteristics of airship are discussed in depth. The results show that: (1) With the assumption of same absorptivity and emissivity, the larger the fineness ratio of the airship, the smaller the diurnal temperature difference of the main helium gasbag, and the better the thermal characteristics of airship as well. When the envelope radiation characteristics vary, the temperature difference of main helium gasbag with a fineness ratio of 4 in one day is always less than 1 K, compared with the fineness ratio of 5. However, the temperature difference of main helium gasbag with a fineness ratio of 3 exceeds that with the fineness ratio of 5, and reaches its maximum of 6 K. Therefore, the fineness ratio of 4 is regarded as optimal by considering the floating constraints of low drag and high buoyancy. (2) In the case of higher long-wave emissivity and lower short-wave absorptivity of the envelope material and solar cells, the diurnal helium temperature difference is the smallest, and the thermal performance of the aerostat is better. (3) Among the five typical envelope materials, i.e., white Tedlar film, white PU film, silver-plated Teflon film, aluminized PET film, and white PVF film, the aluminized PET film is more conducive to controlling the helium temperature difference and reducing the volume change of gasbags. The aforementioned results can provide a theoretical basis for improving the thermal performance of stratospheric airships.

A transversely hyperelastic constitutive model of flexible film composite

This paper presents a transversely hyperelastic constitutive model for predicting mechanical properties of flexible composites under unidirectional tension. A strain energy function which reflects the behavior of anisotropic elastic material is decomposed into three parts: matrix, fiber and fiber-matrix interaction. The fiber-matrix interaction was decomposed into in-plane shear stresses and out-of-plane shear stress, the in-plane shear stresses were related to the fiber elongation invariants, and the out-of-plane shear stress was related to the fiber elongation invariants and the matrix invariants. The fiber-matrix interaction considering shear factor was established. Based on fiber reinforced continuum mechanics, a transverse hyperelastic constitutive model including fiber, matrix and their interaction is developed. The transversely hyperelastic constitutive model is verified by the uniaxial tension tests. The constitutive model can be used to design the flexible structure of stratospheric airship.

The study of rotate speed influence on the performance of Contra-Rotation-Propeller in stratospheric airship

According to the requirements of a foreign high-altitude airship project, the Single-Rotation-Propeller (SRP) was designed under the maximum endurance factor criterion. The spacing influence on the Contra-Rotation-Propeller (CRP) was studied by numerical simulation analysis, the performance of front and rear propeller was compared with SRP. The result indicated that CRP was more efficient than SPR, the CRP has enormous potential in enhancing the aerodynamic performance.

Multi-parameter sensitivity analysis on thermal characteristics of stratospheric airship

Thermal characteristics analysis of stratospheric airship is pivotal in airship design. Many factors can affect the thermal performance. Though the separate influence of each factor was examined in detail by single factor analysis, the multi-parameter sensitivity analysis is still a terra incognita. Here, ten factors were selected to analyze the multi-parameter sensitivity based on the heat transfer process analysis of stratospheric airship and the simplification of thermal equilibrium equations. The orthogonal test design method was used to build the prediction model. In addition, response surface methodology based on the binomial equations was employed as a numerical solver for the fitting equations of the influencing factors. The solutions obtained satisfied the requirements and the relative error of optimal point was 1.7%. The results show that: (1) Among ten parameters, the photovoltaic cells conversion efficiency is an insensitive parameter. (2) An optimum combination scheme is the envelope emissivity of 0.9, envelope absorptivity of 0.1, photovoltaic cells emissivity of 0.9, photovoltaic cells absorptivity of 0.5, photovoltaic cells equivalent thermal resistance of 0.8 m2 K/W. And the helium temperature difference in this condition is 17.404 K. (3) Considering the real situation, five alternatives are recommended according to their performance close to the optimal results.

Model for Predicting the Operating Temperature of Stratospheric Airship Solar Cells with a Support Vector Machine

The stratospheric airship is a kind of aircraft that completely relies on the cycle of photovoltaic energy systems to achieve long duration flight. The accurate estimation of the operating temperature of solar cell modules on stratospheric airship is extremely important for the design of photovoltaics system (PV system), the output power calculation of PV system, and the calculation of energy balance. However, the related study has been rarely reported. A support vector machine prediction method based on particle swarm optimization algorithm (PSO-SVM) was established to predict the operating temperature of solar cell modules on stratospheric airship. The PSO algorithm was used to dynamically optimize the SVM’s parameters between the operating temperature of the solar cell modules and the measured data such as atmospheric pressure, solar radiation intensity, flight speed, and ambient temperature. The operating temperature data of the two sets of solar cell modules measured in the flight test were used to verify the accuracy of the temperature prediction model, and the prediction results were compared with a back propagation neural network (BPNN) method and the simulation results calculated by COMSOL Multiphysics of COMSOL, Inc., Columbus, MA, USA. The results shown that the PSO-SVM model realized the accurate prediction of the operating temperature of solar cell modules on stratospheric airship, which can guide the design of PV system, the output power calculation of PV system, and the calculation of energy balance.