As materials and engineering design tools become more complex, engineers are looking to mimic structures and systems, occurring in nature, to design more efficient mechanical structures. One such structure is a morphing composite lattice structure, whose design was inspired by the tail of the bacteriophage T4 virus [1]. To date the morphing behavior of the tail structure of the virus has been simplified by neglecting the intermolecular mechanisms that actuate the bistable behavior of the tail. This behavior has been achieved using prestressed composite flanges that are mechanically joined in alternating clockwise and anti-clockwise chiralities. The composite lattice structure has previously been proposed as an actuator for aerospace structures, replacing more complex and heavier traditional actuator structures. McHale et al. [2] have shown that the composite lattice is capable of greatly improving upon the state-of-the-art in the form of a telescopic boom for CubeSat systems. This utility provides validity in studying further enhancements on the capabilities of the structure to enhance its potential applications in the aerospace industry. This work proposes a mechanism for replicating the inter-molecular behavior that occurs in the bacteriophage T4 tail. The bonds between the inner and outer tail structures are broken and reformed, thus, driving the actuation process. This method will form a variable topology morphing system. As such, a novel category of morphing structure is presented here for the first time. The morphing topology behavior is proposed by replacing mechanical fasteners in the traditional lattice structure in select locations with a series of permanent magnets. Finite element analysis is used to calculate the difference in energies between the states before and after discrete topology changes occur, allowing the associated change in energy to be converted to a required actuation force. Varying the topology of the lattice structure allows the lattice to transition from a linear morphing actuator system to a bespoke and tunable curved actuator with potential applications in satellite dish actuation, for example.

Multifunctional Structures for Attitude Control (MSAC) is a new spacecraft attitude control system that utilizes deployable panels as multifunctional intelligent structures to provide both fine pointing and large slew attitude control. Previous studies introduced MSAC design and operation concepts, simulation-based design studies, and Hardware-in-the-Loop (HIL) validation of a simplified prototype. In this article, we expand the scope of design studies to include individual compliant piezo-electric actuators and associated power electronics. This advance is a step toward high-fidelity MSAC system operation, and reveals new design insights for further performance enhancement. Actuators are designed using pseudo rigid body dynamic models (PRBDMs), and are validated for steady-state and step responses against Finite Element Analysis. The drive electronics model consists of a few distinct topologies that will be used to evaluate system performance for given mechanical and control system designs. Subsequently, a high-fidelity multiphysics multibody MSAC system model, based on the validated compliant actuators and drive electronics, is developed to support implementation of MSAC Control Co-design optimization studies. This model will be used to demonstrate the impact of including the power electronics design in the Optimal Control Co-Design domain. The different control trajectories are compared for slew rates and the vibrational jitter introduced to the satellite. The results from this work will be used to realize closed-loop control trajectories that have minimal jitter introduction while providing high slew rates.

The Engineering Systems Design Lab (ESDL) at the University of Illinois introduced Strain-Actuated Solar Arrays (SASAs) as a solution for precise satellite Attitude Control System (ACSs). SASA is designed to provide active mechanical vibration (jitter) cancellation, as well as small slew maneuver capabilities to hold a pose for short time periods. Current SASA implementations utilize piezoelectric distributed actuators to strain deployable structures, and the resulting momentum transfer rotates the spacecraft bus. A core disadvantage, however, is small strain and slew capability. Initial SASA systems could help improve pointing accuracy, but must be coupled with another ACS technology to produce large reorientations. A novel extension of the original SASA system is presented here that overcomes the small-displacement limitation, enabling use of SASA as a sole ACS for some missions, or in conjunction with other ACSs. This extension, known as Multifunctional Structures for Attitude Control (MSAC), can produce arbitrarily-large rotations, and has the potential to scale to large spacecraft. The system utilizes existing flexible deployable structures (such as solar arrays or radiators) as multifunctional devices. This multi-role use of solar panels extends their utility at a low mass penalty, while increasing reliability of the spacecraft ACS.

The Starshade is a future exoplanet discovery mission consisting of a satellite and a 34 meter diameter starshade used to block the light of a star of interest, enhancing visualization of the orbiting planets. The starshade itself is composed of a number of 7 meter long petals surrounding a 20 meter diameter optical shield. A critical design requirement of the optical shield is stowage in a 3 meter diameter area during launch. Origami has been investigated as a means of collapsing the optical shield, specifically a family of action origami models known as “flashers.” In this paper a dynamic model of an optical shield design candidate based on a flasher pattern is created in Adams 2014. As these patterns can have many parts and joints, a method for the automatic creation of dynamic models using information about the geometry of the crease pattern is utilized. As the fabricated optical shield panels will be somewhat flexible, each quadrilateral panel is modeled as two rigid triangles connected with a joint. The effect of joint stiffness on the forces and torques developed during deployment is investigated. It is found that the optical shield design is rigid foldable if the panel flexibility is taken into account by additional joints, which are found to bend from 10° – 40°. Joint forces are predicted over the deployment, and maximum and average joint forces are tabulated. These and other insights gained from the dynamic model can help guide future Starshade design decisions, and similar analyses can be performed for other origami-inspired deployable structures.

Satellite Laser Ranging (SLR) makes an important contribution to Earth science providing the most accurate measurement of the long-wavelength components of Earth’s gravity field, including their temporal variations. Furthermore, SLR data along with those from the other three geometric space techniques, Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS) and DORIS, generate and maintain the International Terrestrial Reference Frame (ITRF) that is used as a reference by all Earth Observing systems and beyond. As a result we obtain accurate station positions and linear velocities, a manifestation of tectonic plate movements important in earthquake studies and in geophysics in general. The “geodetic” satellites used in SLR are passive spheres characterized by very high density, with little else than gravity perturbing their orbits. As a result they define a very stable reference frame, defining primarily and uniquely the origin of the ITRF, and in equal shares, its scale. The ITRF is indeed used as “the” standard to which we can compare regional, GNSS-derived and alternate frames. The melting of global icecaps, ocean and atmospheric circulation, sea-level change, hydrological and internal Earth-mass redistribution are nowadays monitored using satellites. The observations and products of these missions are geolocated and referenced using the ITRF. This allows scientists to splice together records from various missions sometimes several years apart, to generate useful records for monitoring geophysical processes over several decades. The exchange of angular momentum between the atmosphere and solid Earth for example is measured and can be exploited for monitoring global change. LARES, an Italian Space Agency (ASI) satellite, is the latest geodetic satellite placed in orbit. Its main contribution is in the area of geodesy and the definition of the ITRF in particular and this presentation will discuss the improvements it will make in the aforementioned areas.

Bio-logging devices are systems mounted to an animal that measure parameters associated with the animal or its environment. These devices date back to the 1930’s in their simplest form, while modern devices use suites of digital sensors, microcontrollers, and wireless data communication. Despite these advances, there has always been a fundamental relationship between power consumption and the amount of science that can be conducted. There are now a number of commercially available devices that use solar cells to supplement their daily energy budget, but supplemental solar power is not useful for species that are nocturnal, subterranean, aquatic, or spend significant time beneath dense forest canopies. As such, there have been calls from the marine biology community for devices that could harvest power from their environments. For these marine species, alternative energy harvesting techniques are required. Here we explore a new application for energy harvesting as a power source for marine wildlife bio-logging tags. Marine animals cover wide swaths of the ocean, making tracking and data collection challenging. Tagging these animals with devices that track their location and/or collect data about the animal or its surroundings require large batteries and have limited life spans due to high power requirements for satellite data relays. With limited solar irradiance at depth making solar power less attractive, we review and explore other forms of energy that could be harvested, such as energy from fluid flow and hydrostatic pressure cycles. We investigate the energy potential from a number of sources and compare these values with the requirements of current bio-logging systems to assess required transduction efficiencies. The application of energy harvesting on animal tags could result in nearly indefinite life systems allowing for data collection from a single animal over the course of many years.

Energy harvesting is widely used in terrestrial and aerial sensor applications but is conspicuously absent in the marine environment despite several possible harvesting modalities and numerous applications. One such energy harvesting modality is to use magnetohydrodynamic (MHD) power generators to directly produce electricity from flowing seawater. Fundamentally, MHD generators convert the kinetic energy of a conductive fluid directly into electricity by separating charged particles, thereby generating an electric field transverse to the direction of fluid flow and the magnetic field. The electric field is then accessed with an external circuit to provide power to a load. Since the power output from an MHD generator is linearly related to the conductivity of the flowing fluid and to the square of both the magnetic field strength and the fluid velocity, strong magnets and high fluid velocity are desirable. Thus, there are a myriad of possible MHD generator configurations available to maximize power output under various conditions and constraints. These include configurations of permanent magnets that offer localized high magnetic fields or geometries of the fluid duct that can be used to increase the fluid velocity through the magnetic field. One novel application for MHD generators is to power sensors and bio-loggers used in marine animal telemetry. The animal sensors are designed to take time-series measurements and store the data on the logger for transmission to satellite networks or human retrieval. These sensors and loggers are often battery-limited which constrains either the data fidelity or the longevity, or both. An MHD generator attached to a marine animal can help to supplement some of the sensor or bio-logger power requirements, thereby increasing sensor lifetimes and data fidelity. Thus, MHD generators will enable new research in the marine sciences, climatology, and biology, among others. The MHD generator can be positioned above the fluid boundary-layer so that the fluid flow around the animal is channeled through the MHD generator, producing electricity. In this work, we will develop some of the fundamental equations that describe the physics of an MHD generator and use them to make estimates of the potential power outputs that could be expected from various marine animals. We will also investigate several electrical configurations of the MHD to determine the most suitable MHD generator for different flow regimes. Initial studies suggest that MHD generators are viable power sources in the marine environment and can easily supplement the entire energy budget of a bio-logger under certain conditions.

The NASA Ames Research Center (NASA Ames) Center Chief Technologist (CCT) Office sponsors the Advanced Digital Materials and Manufacturing for Space (ADMMS) Initiative, which focuses on advanced manufacturing technologies for space, including identifying several target products, areas and applications, approaches for advanced manufacturing, mechanisms for collaboration, and complementary facilities. The pilot project for this initiative is the Multi-Purpose Avionics Core Element (M-PACE). The primary goal of M-PACE is to demonstrate advanced manufacturing techniques, such as additive manufacturing and Digital Materials, to minimize the cost of cube satellites and increase their modularity. M-PACE will be designed and built at the NASA Ames’ SpaceShop, which is a state-of-the-art advanced manufacturing facility built for NASA researchers to formulate ideas for projects. The final products of M-PACE are several completed side panels of a one-unit (1U) (10 cm cube) cube satellite prototype built using commercial off-the-shelf (COTS) components, which will show the basic functionality of the internal payload by connecting it to the side panels for power and other subsystem capabilities. Within the structure, we are investigating the use of Digital Materials, which are universal building materials with the ability to increase precision and ease of assembly and disassembly of three dimensional (3D) objects. M-PACE will use COTS power systems and open-source hardware and software to distribute data through Ethernet through the use of snap-fit card connectors. Similar to Peripheral Component Interconnect (PCI) Express cards, we envision the spacecraft subsystems and payloads to be on a PC104-like board that will slide into the side panel connectors to enable distribution of power and data. This design has the potential to greatly reduce the cost of Cube Satellite testing and integration due to the absence of wires and ease of access to internal boards for any necessary modifications.

Vital components of inflatable antenna structures in light-weight satellites, Kapton© membranes, are prone to wrinkling due to high thermal gradients experienced in space; resulting in a decrease in performance. Simple, robust and compact actuators are required for automated removal of localized wrinkling in these membranes. Leveraging the large force and small displacement of Macro-Fibre Composites (MFCs) by mimicking the mechanics of the ciliary muscle in the human optical system, an actuator was designed and experimentally tested in the control of localized wrinkling of Kapton© in tension. Three configurations were built and tested utilizing M-5887-P1 MFC units. The force-displacement relationships were determined through testing. The control logic and circuit were developed. The actuator proved successful in local membrane wrinkling experiments. It was shown that by leveraging the high force and low displacement of MFCs a reliable actuator can be developed to effectively eliminate localized wrinkles in Kapton© membranes for space applications.

Recently, some components and payload systems installed in satellites are exposed to various disturbance sources, such as the reaction wheel assembly, the control moment gyro, coolers, and others. Because there is low damping in space, the continuous microvibration causes the degradation of the performance of various payload systems. Therefore, the development of a practical isolation system that shields against microvibration are very important and the author is on the way to developing the microvibration isolation system for the improvement on the performance of the optical payload. In order to develop appropriate microvibration isolation device for a specific payload, it is necessary to understand vibration characteristics of the main disturbance sources; modeling and analysis of disturbance sources including reaction wheel assembly and control moment gyros have been studied by many researchers. However, there are practical difficulties to obtain and perform an experiment with real flight model (FM) reaction wheel assembly and control moment gyros because of expensive price and security reasons. Generally, the disturbance characteristics of a prototype of the reaction wheel assembly or control moment gyros are significantly different from those of FM ones even when the reaction wheel type, size and wheel speed are the same. Therefore, in order to facilitate the microvibration isolation experiment during the satellite development process, this paper proposes a microvibration emulator that could generate the real disturbance spectrums of FMs. Note that the disturbance profiles are quite complex, consisting of several higher harmonics, and also changing for varying operational wheel speeds. The disturbance characteristics of FMs are typically measured in advance. First an analytical model for the RWA is presented and the development procedure for the emulator is also described. The performance of the first prototype emulator is demonstrated.

Current satellite validation tests involve numerous procedures to qualify the space vehicle for the vibrations expected during launch and for exposure to the space environment. Structural Health Monitoring methods are being considered in an effort to truncate the number of validation tests required for satellite checkout. The most promising of these monitoring techniques uses an active wave-based method in which an active piezoelectric transducer propagates a Lamb wave through the structure, where it is then received by a second sensor and evaluated over time to detect structural changes. Thus far, this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and interfaces. This study establishes a method to identify important features in the sensor signal that may otherwise be missed. In this work, an FE model of a plate is developed, and variability is introduced for each state observation. Different states are modeled as masses distributed at 12 locations. Signals are obtained through an explicit time-domain analysis. Matching Pursuit Decomposition is used to extract physically significant parameters from the signal, the features are reduced to a more manageable subset, and Support Vector Machines are utilized to identify important features in the sensor signal. The results of the classification indicate that for a plate specimen the extracted feature corresponding to anti-symmetric wave mode interaction with damage does the best job of differentiating damage states.

Research at the AFRL Space Vehicles Directorate is being conducted to reduce schedule times for assembly, integration, and test, to make satellite-based capabilities more responsive to user needs. Structural Health Monitoring has been pursued as a means for validating workmanship and has been proven on PnPSat-1. Embedded ultrasonic piezoelectric wafer active sensors (PWAS) have been utilized with local and global inspection techniques, developed both in house and by collaborating universities, to detect structural changes that may occur during assembly, integration, and test. Specific attention has focused on interface qualification. It is now reasonable to believe that evaluation of interfaces through the use of such sensors can also be used to indirectly qualify the structure thermally and that tedious thermal-vacuum testing may be truncated or eliminated altogether. This paper focuses on the computational development of extracting thermal properties from ultrasonic transmission records. Methods are validated on simple bolted lap-joint cantilever beams.

The development of on-demand satellites has created the need for methods that quickly assess the structural integrity of the system. In particular, because of rapid testing and assembly, workmanship errors such as loose bolts within the satellite structure are a concern. Current methods of loose bolt detection, which often rely on baseline data or analytical models, are not practical due to the variable geometry of the satellites and the time constraints on testing. The method of impact modulation is a nonlinear vibration method which is quick to perform and is robust to changes in the geometry of the structure. This paper presents the results of applying impact modulation to a simplified structure used to model a single bolted joint within a satellite. Results show that impact modulation can distinguish changes in torque within the bolted joint. In addition, several examples of how the underlying linear characteristics of the system affect impact modulation results are given.

This work focuses on the analysis of wave propagation in rib-stiffened structures as it is related to Structural Health Monitoring (SHM) methods. Current satellite validation tests involve numerous procedures to qualify the satellite for the vibrations expected during launch, and for exposure to the space environment. SHM methods are being considered in an effort to truncate the number and duration of tests required for satellite checkout. The most promising of these SHM methods uses an active wave-based method in which an actuator propagates a Lamb wave through the structure, which is then received by a sensor. The received waves are evaluated over time to detect structural changes. Thus far, this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and joining features. Complex isogrid reinforcements within the satellite panel significantly affect any conclusions that can be made about the arriving waves. For this purpose, an experimental and numerical study of wave propagation within rib-reinforced plates has been undertaken. Wave propagation was modeled using finite element software. These results were analyzed for an understanding of dispersion within the structure, particularly how the group velocity and mode conversion are affected by the rib interaction. Experiments were carried out to validate the model and gain further insight into the wave propagation phenomena in the structure. The analysis indicates that mode conversion plays a significant role in the first wave arrival, although this can be accounted for through proper frequency selection, and signal analysis. A range of excitation frequencies which are most appropriate for the structure are presented.

Bolted joints are critical components in aerospace structures. Checking the integrity of these connections, although time consuming, is a necessary step before launching aerospace vehicles and satellites. Recent advances in structural health monitoring (SHM) suggest the possible use of SHM technologies to assess the integrity of these joints. Moreover, there exists a need for continuous monitoring of aerospace structures after launching. This continuous monitoring requires relating damage features that can be extracted using sensing techniques (e.g. ultrasonic methods) to physical quantities representing the structural integrity of bolted joints typically related to contact pressure. This paper describes an experimental effort to correlate shear slip measurements of a bolted connection to contact pressure. The contact pressure map (spatial distribution of contact pressure) is calibrated to the torque applied to the bolted connection. Loading and unloading experiments on the joint allowed separating elastic and shear slip displacements. Shear slip is then correlated to contact pressure maps. Further efforts are underway to connect these measures to SHM metrics.

The Air Force Research Laboratory/Space Vehicles Directorate (AFRL/RVSV) is developing Structural Health Monitoring (SHM) technologies in support of the Responsive Space (RS) initiative with plans for future capabilities on orbit to assist in overall awareness. Such technologies will significantly reduce the amount of time and effort required to assess a satellite’s structural surety without increasing system level risk associated with changed testing. Furthermore, successful implementation of multifunctional sensor capabilities may lead to savings in size, weight, and power (SWAP) allowing more options for technical performance. Although SHM development efforts abound, RS drives unique requirements on the development of these SHM systems; the biggest difference being that deviation from maintenance requires a technology driver. This paper describes several potential niches for SHM technology development efforts by AFRL, aimed at solving those technical issues unique to responsive space, as well as how an ideal SHM system could be implemented within various other processes including the potential for on-orbit performance.

Structural Health Monitoring (SHM) is a valuable tool for in-service assessment of structural condition. Despite a broad use in many engineering fields, SHM has seen limited application to space systems. The paper explores specifics of SHM applied to space systems and satellites in particular. It is suggested that SHM may be considered for aiding rapid assembly of satellite components, monitoring system dynamics during launch and assessing in-service variation of structural properties suitable for model updating. In this paper, we present a discussion of factors affecting realization of the SHM system for satellites and provide recommendations for the system configuration and its practical use. The SHM system design based on a network of piezoelectric active sensors is considered. Piezoelectric sensors were selected due to availability of both active and passive operation modes. The passive SHM mode may find applications related to spaceship launch process and on-orbit structural monitoring. It is anticipated that the active structural assessment may be exercised during satellite pre-launch qualification and possible on-orbit characterization. Hence, the present contribution focuses on SHM of improperly tightened bolts as one of major satellite integrity concerns and embedded material characterization techniques. The developed SHM method utilizes the acousto-elastic effect manifested through the elastic wave phase shift caused by stress-induced localized changes in the sound speed. Experiments aimed at improving fundamental understanding of this technique are discussed and applicability of the technique to realistic structures is investigated. The methodology for in-situ material characterization is tested on structural elements of simple geometry and extension to complex structural systems is suggested. Synergistic use of the same hardware for acoustoelastic and material characterization methods is recommended and further system integration options are proposed.

During the past few years inflatable technology has received much attention by space industry due to its significantly reduced launch volume and mass. While this technology meets the mass goals, because of being ultra-light the structures become very susceptible to disturbances in space. One of the main sources of disturbances is the abrupt temperature changes for a satellite upon passing the Earth’s shadow. While much research has been carried out on the static thermal loading for such structures, very little is known about their dynamic behavior with respect to temperature changes. The presented work is intended to fill this gap. The frequency response functions for a 3 meter inflatable rigidized boom for various temperatures are studied and compared using FEA models in ABAQUS.

To overcome current limitations of satellite operation timelines, Operationally Responsive Space (ORS) satellites are being developed for rapid configuration and assembly. Time spent on flight qualification tests aimed at assembly verification and launch vehicle integration must be reduced to less than a week. Structural health monitoring (SHM) is seen as a possible avenue for real-time assessment of satellite integrity and qualification before launch. Embedded ultrasonics and magneto-mechanical impedance (MMI) were considered as potential candidates for diagnostics of critical system elements. Piezoelectric wafer active sensors in conjunction with an acousto-elastic SHM were used for assessment of aerospace structures with bolted joints. In the presented analysis, the acousto-elastic behavior of the joint was used as an indicator of structural integrity. Experimental results show changes in the nonlinear response of joints as a result of differing bolt torque. Localization potential of the acousto-elastic technique was demonstrated in a complex structure analogous to a typical satellite panel. The MMI method has shown utility in assessing condition of bolted joints in thin plates and a satellite structure. Experimental data reveal changes in magnitude and position of impedance peaks induced by the difference in structural loads applied to the joint. It is suggested that both the acousto-elastic and MMI methods have indicated possibilities for detecting and characterizing damage in satellite bolted joints.

A three-dimensional dynamic analysis of a satellite dish in spherical coordinate system is investigated. The method of separation of variables is employed to obtain the explicit 3D solution of the partial differential governing equation of the active composite satellite dish (ACSD). Then, the mode shape functions are expanded as a combination of periodic functions, associated Legendre functions, and spherical Bessel functions. The validation of the theoretical model is performed by comparing the developed analytical mode shapes with finite element method (FEM) mode shapes. Also, using the developed analytical model, the disturbance observer (DOB) controller is employed for the ACSD shape control. The numerical results show that, by employing the DOB controller, more accurate shape control of the satellite dish is achieved and less control energy is consumed, when piezoelectric actuator patches are placed on their optimal locations.