Inflatable Space Structures Research Articles

Inflatable antenna structures: Deployment analysis of torus bounded Z-fold scalable planar membrane reflector

Compact packaging and smooth deployment reliability, lightweight and large operational size are ideal requirements of inflatable space structures. Space inflatable antenna, one of the recent ask, demands post-deployment surface flatness in addition to ideal necessities. The work in this paper employs a novel technique namely collective zig-zag folding for an inflatable torus and planar reflector assembly. This research accomplishes various tasks with a focus on planar inflatable antenna by solving the drawback of surface flatness in an origami packaging approach. The torus-reflector assembly is compactly packed by employing two different crease orientation strategies. Aiming at large-scale structure, the deployment behaviour of inflatable antenna assembly is investigated experimentally and numerically. The in-plane loading of a torus due to inflation pressure is derived, followed by the calculation of force induced on the outer edge of the inflated torus. The quasi-static deployment by varying the inflation pressure from a few up to several hundreds of kPa is solved to determine the inflated shapes and deployment behaviour of a fully-folded structure. Uniform pressure method was used to observe the effect of fold-lines on deployment instability. Force–displacement response gives insight into the wrinkling in the creased planar reflectors. The shape of the inflated assembly is found to be close to experimental models for the same amount of inflation pressure. The wrinkles and overall surface error lie within expected range as depicted from comparison.

Design and analysis of a gas generator for inflatable space structures

Gas generators have been gradually utilized to inflate inflatable space structures, and normally they use high-energy nitrogenous compounds and solid propellants as gas-generating agents. However, gas generators with a high combustion temperature, fast reaction speed, and massive energy generation will lead to an excessively high gas temperature inside the inflatable structures and an excessively fast unfolding speed, which causes wrinkles or even cracks in inflatable films. This paper proposes a new gas generating device using NaHCO3 as the gas generating agent and resistance wires as heating elements to maintain the advantages of small size and light weight, as well as high security and lack of pollution. The feasibility of the gas generator is computationally analyzed in COMSOL and experimentally verified. Additionally, a tightness test of the gas generation system is undertaken using air pressure sensors. The results show that the device can slowly and steadily generate CO2 gas to deploy thin-film inflatable structures.

Port-Hamiltonian Formulations of Some Elastodynamics Theories of Isotropic and Linearly Elastic Shells: Naghdi–Reissner’s Moderately Thick Shells

The port-Hamiltonian system approach is intended to be an innovative and unifying way of modeling multiphysics systems, by expressing all of them as systems of conservation laws. Indeed, the increasing developments in recent years allow finding better control and coupling strategies. This work aimed to apply such an approach to Naghdi–Reissner’s five-kinematic-field shell model in linear elasticity, while including often-neglected higher-order intrinsic geometric coupling effects, therefore preparing the theoretical background required for the coupling (or interconnection) with an acoustic fluid model and the different types of interactions that can arise among them. The model derived thusly can be used for controller design in a wide variety of applications such as inflatable space structures, launcher tank vibration damping, payload vibration protection using smart materials, and many other related applications.

Dynamic analysis of a rigid-flexible inflatable space structure coupled with control moment gyroscopes

The vibration generated by the inflatable structure after deployment has a great impact on the performance of the payloads. In this paper, the influence of the control moment gyroscopes (CMGs) on the dynamic responses and characteristics of an inflatable space structure is studied, based on the flexible multibody dynamics in a combination of the absolute nodal coordinate formulation (ANCF) and the natural coordinate formulation (NCF). Firstly, the ANCF and NCF are used to accurately describe the large deformations and large overall motions of flexible inflatable tubes and rigid satellites, respectively. Then, instead of modeling gyroscopic flexible bodies, this paper pioneers a rigid body dynamic model of the CMG in detail by using the NCF modeling scheme, which can be attached to and coupled with any flexible bodies without any assumptions. Then, the orbital dynamic equations of the inflatable space structure coupled with distributed CMGs are obtained by considering the effects of Coriolis force, centrifugal force, and gravity gradient through coordinate transformation. The dynamic characteristics of the inflatable space structure are also analyzed by deriving the eigenvalue problem of a flexible multibody system. Finally, the accuracy of the CMG dynamic model is verified via a classic heavy top example. Several numerical examples are presented to study the influence of the magnitudes and directions of the rotor angular momentum of the CMGs on the dynamic responses and characteristics of the inflatable space structure.

О возможности создания крупногабаритных конструкций в условиях открытого космоса

The paper gives a brief overview of the history of the development of inflatable space struc-tures. Further development should be the use of inflatable shells that harden in space. The possibility of using this technology in the framework of the use of simple tasks is considered in the article. On the ex-ample of thick-walled spherical and cylindrical shells, using Lame's analytical solutions, it is shown that the thickness of the shell can be thin. The thin shell design is much easier to inflate. No high pressure is required for this. Using the classical heat conduction equation, the temperature distribution inside a cy-lindrical shell is determined. When setting the boundary conditions, the flux of rays incident both from the side of the Sun and from the side of the Earth was taken into account. The radiation on the surface of the cylinder was calculated according to the Stefan-Boltzmann law. It has been established that a tem-perature occurs in the shell, the maximum value of which is in the range from 150 to 200 degrees Celsi-us. Prepreg casings require the use of a high temperature resin suitable for hot curing.

Development of a miniature dynamic stiffness measurement prototype toward structural health monitoring of space inflatable structures

Inflatable structures are increasingly used in aerospace engineering. However, the space survivability and durability of such structures are of particular concern due to material aging in space environment and unexpected external impact threats. Thus, it is very urgent to in-situ monitor and assess structural health condition for space inflatable structures. Since inflatable structures are often lightweight, large-sized and flexible, their low-frequency vibration response contains much information about structural health condition. To facilitate in-situ structural health monitoring of space inflatable structures, this paper developed a miniature low-frequency dynamic stiffness measurement prototype. The prototype is capable of generating two channels of swept-sine excitation signals, and concurrently acquiring six channels of response signals. Recorded data is communicated and downlinked from the host spacecraft to the ground, and then the dynamic stiffness is derived to determine structural health condition. To validate the developed prototype, two simulated inflatable space structures are fabricated and tested, including an inflatable boom and an inflatable torus, and then Macro-Fiber Composite transducers are attached on two specimens as actuators and sensors in tests. Experimental studies show that the prototype functions well and the outputted results are consistent with that measured by large-bulked commercial ground devices. Additionally, the multi-channel functionality of the prototype is verified by carrying out the multi-input multi-output test. In summary, the prototype features small size, light weight, and low power consumption, which has the potential for future space applications.

Математична модель для визначення проєктних параметрів космічної надувної платформи з корисним навантаженням

The development and application of inflatable space structures is of considerable interest in modern space science and technology. Today, these structures enjoy wide application from aerodynamic inflatable deorbit means to inflatable residential sections for the International Space Station. This is because the masses of inflatable structures are smaller in comparison with others, which in turn minimizes the cost of their orbital injection. In view of the considerable interest in orbital constellations, the authors of this article propose the use of an inflatable space aerodynamic system as a platform for a payload. In doing so, we obtain a distributed satellite system on an inflatable space platform. The advantage of this technology is that it assures the maintenance of the relative position of the elements (payload) of a distributed satellite system of this type with minimal energy consumption. In its turn, to analyze the features of the operation of a particular space technology, its mathematical model is required. Because if this, the aim of the article is to develop a mathematical model for estimating the design parameters of an inflatable payload-bearing space platform. The mathematical model of the operation of an inflatable payload-bearing space platform developed in this work consists of three modules: a module of orbital motion, a module of calculation of the thermodynamic parameters of the inflatable platform, and a module of calculation of its variable inertia tensor. The article also identifies four gas modes of operation of the inflatable segment of the space platform and gives the inertia tensor as a function of the ambient temperature, which is necessary for further research. It should be noted that the application of the mathematical model allows a priori analysis of a wide range of inflatable space platform design parameters. On this basis, a design parameter analysis method that uses this model was developed. The application of this method may greatly simplify further research into the synthesis of an angular motion controller for an inflatable payload-bearing space platform, the choice of the design parameters of inflatable segment shell materials, and the study of the platform operation in different gas modes.

Multi-objective characterization of an inflatable space structure with a quasi-static experimental deflation and finite element analysis

We propose a methodology for the multi-objective characterization of a light, single layer orthotropic fabric inflatable space structure. The presented approach focuses on a custom in-situ experimental quasi-static deflation, semi-empirical development of flow coefficients and structural integrity loss parameters as well as process validation with finite element analysis. The experiments are designed to investigate a collapse of a thin, deployable, one segmented inflatable structure caused by a simulated single leak and passive porous leakage through the fabric material. The acquisition of real time data with a custom designed standalone ambient conditions sensing platform and the wireless internal sensing unit furnishes pressures, temperatures, mass flow rates, dynamic strains and accelerations. Synchronously, geometric changes in the shape of the structure's representative area are recorded utilizing photogrammetry. The non-wireless and wireless outputs are treated with a series of smoothing, best-fitting and refining operations and combined with the corresponding sequence of active surface area photogrammetric results. The formulation of inflatable characterization parameters and a single leak/passive porous leakage structural integrity loss ratios allows for an in depth description of the inflatable structure behavior. A closer examination of the experimental data shows that the majority of the structural integrity loss ~97% is attributed to the sudden and relatively short leak due to puncture and the remaining ~3% to the slow and prolonged pressure loss caused by the passive porous areal leakage through the membrane. A semi-empirical framework based on a thermodynamic equilibrium produces sets of single leak, passive porous leakage and active area coefficients to be validated with the Ls-DYNA® finite element simulation of a polyurethane coated nylon fabric inflatable structure model. We use implicit and explicit fea of a control volume deflation to validate the aforementioned coefficient curves and constants. The subsequent comparison with the experimental internal temperature, internal pressure and mass flow rates results in a 1.83%, 0.61% and 1.19% difference respectively for the single leak events. The successive contrasting with the experimental internal temperature, internal pressure and active area produces 2.04%, 1.26% and 1.68% difference for the passive porous leakage respectively. We demonstrated that the multi-objective, structural integrity loss characterization techniques for the space structures have promising capabilities for the application in inflatable structures of diverse shapes and sizes.

Wireless Sensing of Pressurized Space Structures

This review paper presents new and emerging technologies for structural monitoring of inflatable space structures such as aerospace and space vehicles and habitats. Inflatable structures provide an array of benefits for space operations including low mass and cost, high volume, and versatility. Despite the fact that there has been a fair amount of research on structural monitoring of solid structures in the past, inflatable structures did not receive the attention they deserve until recently. Monitoring an inflatable space vehicle or habitat poses challenges beyond those associated with similar structures on earth. The potential damage caused by micrometeorites and orbital debris (MMOD) requires a rigorous study of the impact to determine the location of impact and, in case of damage, identifying the extent of the damage, and location of the air leak if present. In this review paper, several recent developments in wireless sensing and signal processing that are used for accurate leak detection and localization are presented. Theoretical foundations behind these algorithms and systems, as well as laboratory and field test results (on earth and in space), are presented to paint a complete picture from research and development to flight certification and test.

Piezoresistive nanocomposites for sensing MMOD impact damage in inflatable space structures

Future space exploration requires easy-to-transport, easy-to-build and deployable space habitats. One of the biggest threats faced by the habitat structures is the impact damage caused by micrometeoroid orbital debris (MMOD) traveling at high velocities of few km/s. This work presents fabrication and testing of hybrid nanocomposites with carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) as fillers in a flexible epoxy matrix, that are proposed to be used for sensing the impact damage by MMOD on inflatable space structures. CNTs and GNPs are chosen as fillers owing to their excellent electrical properties and piezoresistivity. A hypervelocity impact is conducted on the nanocomposite sensors to study their functionality in the space environment. The results prove that the piezoresistive nanocomposites can be utilized as a part of damage detection system, which would not only detect the impact damage caused by MMOD of 3 mm diameter traveling at 7 km/s but also discern its location and depth within the inflatable structural layers.

Design and testing of inflatable gravity-gradient booms in space

Inflatable space structures have many advantages such as small size, high reliability, and low cost. Aiming at a gravity-gradient boom for an XY-1 satellite, New Technology Verifying Satellite-1, a slender inflatable boom with low magnetic is presented. First of all, an inflatable boom with six self-supporting thin shells made of carbon and Vectran fiber composite materials on the inner wall was designed for eliminating a magnetic dipole moment and increasing structural stiffness. A precise stowage was designed for a tip mass surrounded by a pair of lightweight honeycomb blocks added on the top of the boom. The stowed boom was tested by sine sweep vibrations with three directions on the ground to verify the reasonable design. The XY-1 satellite which carried the inflatable boom was launched into low orbit. After being stowed state in space for at least 6 months, the inflatable boom orderly unfolded a 2.0 kg tip mass to 3.0 m away in May, 2013. The inflatable boom was successfully deployed from a series of photographs received on the satellite. The results show that this kind of lightweight inflatable boom with self-supporting thin shells can orderly unfold and fulfil the function of gravity-gradient in space for a long time.

Modeling inflatable fabric with undevelopable surfaces by motion folding method

At present, most space inflatable structures are composed of flexible inflatable fabrics with complex undevelopable surfaces. It is difficult to establish a multi-dimensional folding model for this type of structure. To solve this key technical problem, the motion folding method is proposed in this study. First, a finite element model with an original three-dimensional surface was flattened with a fluid structure interaction algorithm. Second, the flattened surface was folded based on the prescribed motion of the node groups, and the final folding model was obtained. The fold modeling process of this methodology was consistent with the actual folding processes. Because the mapping relationship between the original finite element model and the final folding model was unchanged, the initial stress was used to modify the model errors during folding process of motion folding method. The folding model of an inflatable aerodynamic decelerator, which could not be established using existing folding methods, was established by using motion folding method. The folding model of the inflatable aerodynamic decelerator showed that the motion folding method could achieve multi-dimensional folding and a high spatial compression rate. The stability and regularity of the inflatable aerodynamic decelerator numerical inflation process and the consistency of the inflated and design shapes indicated the reliability, applicability, and feasibility of the motion folding method. The study results could provide a reference for modeling complex inflatable fabrics and promote the numerical study of inflatable fabrics.

A Model of Packaging Folds in Thin Metal-Polymer Laminates

Thin metal-polymer laminates make excellent materials for use in inflatable space structures. By inflating a stowed envelope using pressurized gas and by increasing the internal pressure slightly beyond the yield point of the metal films, the shell rigidizes in the deployed shape. Structures constructed with such materials retain the deployed geometry once the inflation gas has either leaked away, or it has been intentionally vented. For flight, these structures must be initially folded and stowed. This paper presents a numerical method for predicting the force required to achieve a given fold radius in a three-ply metal-polymer-metal laminate and to obtain the resultant springback. A coupon of the laminate is modeled as a cantilever subject to an increasing tip force. Fully elastic, elastic–plastic, relaxation, and springback stages are included in the model. The results show good agreement when compared with experimental data at large curvatures.

Hypervelocity impact on flexible curable composites and pure fabric layer bumpers for inflatable space structures

Demands for large space structures recently increased in accordance with the growth of space applications for micro-gravity research and space travel. To satisfy growing demand, inflatable structures have been developed. For hypervelocity impact protection from micrometeoroid and orbital debris with enough structural flexibility to be applied to an inflatable space structure, a Multi-shock shield was developed and adopted. However, the multi-layered ceramic fabric bumper of the Multi-shock shield is inferior to the bumper of the conventional stuffed Whipple shield with respect to its hypervelocity impact protection performance. In this study, the applicability of directly curable carbon, Zylon and Twaron composites as a front bumper of the hypervelocity impact shield was examined through 22 experiments involving a pure fabric layer bumper. Through the experiments, it was found that directly curable composites can be more effectively used as a bumper of hypervelocity shield than pure fabric layers.

Space Inflatable Structure Technologies―Research for the Fields of Activities in Lunar and Martian Exploration

Space Inflatable Structure Technologies―Research for the Fields of Activities in Lunar and Martian Exploration

Experimental research on tape spring supported space inflatable structures

This paper presents experimental research that continues the development of inflatable hybrid structures for space applications. Inflatables provide a concept with much scope for further incorporation into the structures of future spacecraft. They offer considerable savings in mass and stowed volume for spacecraft, providing possible reductions in satellite costs. Existing boom configurations make use of inflatables including solar arrays and the NGST sunshield. However these typically soft systems could be improved by incorporating tape springs as structural stiffeners along the length of the boom, creating hybrid structures. This research builds on previous experimental work undertaken at the University of Southampton looking at cantilever inflatable and hybrid booms.The focus of this research is to identify the structural performance improvement of adding tape springs to cantilever inflatable booms. This is achieved by tip deflection testing to determine the bending moment and rigidity performances of these structures allowing a comparison between the two technologies. Several hybrid booms are created and tested in various orientations to identify the optimal tape spring effectiveness. It was found that adding a pair of tape springs will increase stiffness of the hybrid structure by up to 4.9 times for an increase of 2.4 times the boom mass.

Exponential stability of a joint-leg-beam system with memory damping

In this paper, we consider a system for combined axial and transverse motions of two viscoelastic Euler-Bernoulli beams connected through two legs to a joint. This model comes from rigidizable and inflatable space structures. First, the exponential stability of the joint-leg-beam system is obtained when both beams are subject to viscoelastic damping and memory kernels satisfy reasonable assumptions. Then, we show the lack of uniform decay of thecoupled system when only one beam is assumed to have a memory damping and the second beam has no damping.

Follower Effect of Internal Pressure on Modal Analysis of a Space Inflatable Structure

The stress distribution and modal behavior of a space inflatable torus was investigated by nonlinear finite element numerical method. This paper focused on the effect of follower pressure on the modal analysis of the torus, including the effect of configuration change and follower pressure stiffness, and focused on validating the follower pressure stiffness FEM model and its applicability to modal analysis. Research shows that the changed configuration slightly increases the natural frequencies. The follower pressure stiffness significantly reduces the natural frequencies and changes mode shapes order. The modal results are in good agreement with the corresponding shell theory solutions, indicating that the finite element model of the follower pressure stiffness for the inflatable structure modal analysis in this paper is accurate enough and reasonable.

INITIAL STRESS CORRECTION METHOD FOR THE MODELING OF FOLDED SPACE INFLATABLE STRUCTURES

Initial errors and mesh distortions are inevitable in the modelling of folded space inflatable structures. Aimed at this key technical problem, an initial stress correction method based on finite element theory is proposed in this paper. First, initial stress is calculated through the difference of mapping and reference configurations, the former with initial errors and the later without. Then the initial stress is imposed on the mapping configuration to correct initial errors. Through the correction, the accuracy of the inflation deployment numerical calculation is greatly improved. In order to validate the reliability of this correction method, a typical space inflatable structure-inflatable tube is studied as an example. First of all, the finite element models of both Z-folded and rolled tubes are established with the initial stress correction method. Then the inflation deployment numerical calculations of the folded tubes are carried out applying the segmented inflatable control volume method. Through comparative analysis of the calculation results with and without a correction, the method proposed in this paper is proved to be feasible and accurate. The correction method is a complement to the modelling of folded space inflatable structures and it has a great significance for the improvement of the accuracy of the inflation deployment numerical calculations of space inflatable structures.

Importance of Enclosed Gas for Modal Analysis of Space Inflatable Structure

The stress distribution and modal characteristics of a space inflatable torus is investigated using the nonlinear finite element method. This paper focused on the effect of enclosed air on the modal analysis of the torus, including the effect of follower pressure load and the effect of the interaction between the enclosed air and the torus structure. Research shows that follower pressure stiffness significantly reduces the natural frequencies and changes mode shapes order. The fluid-structure interaction obviously reduces the natural frequencies, and the in-plane translation mode is observed. Follower pressure stiffness has no effect on the in-plane translation mode. Fluid-structure interaction decreases the natural frequencies of the modal considering the follower load effect, but it does not change mode shapes order. The effect of enclosed gas seriously reduces the natural frequencies, changes mode shapes order, and produces the in-plane translation mode.