Sensitive Payloads Research Articles

Alternative Stewart Platform Configuration for the Enhanced Isolation of CMG-Induced Microvibration

AbstractFor sensitive payloads in satellites, microvibration is a cause of significant performance degradation. The Control Moment Gyro (CMG), an attitude control device for agile satellites, generates microvibration due to imbalance and irregularities in its high-speed flywheel. As the satellite body transmits microvibration to the sensitive payloads due to its low damping characteristics, it is imperative to isolate microvibration at the source. In this study, a hexapod microvibration isolator based on the Stewart platform is proposed with an alternative configuration. This alternative configuration, originally proposed to reduce coupling transmissibility, is adopted to provide stable performance across a broad frequency range with less weight compared to the widely used cubic configuration in Stewart platform microvibration applications. Modal analysis showed that the alternative configuration is stiffer compared to the cubic configuration. The performance of the isolator was experimentally tested with a high-torque CMG. The proposed hexapod microvibration isolator with an alternative configuration successfully isolated microvibration from the CMG without severe performance degradation.

Degradation and in vivo evaluation of an innovative delayed release implant of medical grade poly(glycolide-co-trimethylene carbonate-co-ε-caprolactone)

Degradation and in vivo evaluation of an innovative delayed release implant of medical grade poly(glycolide-co-trimethylene carbonate-co-ε-caprolactone)

Separation and Release Devices for Aeronautical and Astronautical Systems: A Review

AbstractThis review presents an in-depth examination of the advancements, current state, and future trends of separation and release devices in aeronautical and astronautical systems, focusing on their classification into one-point and linear devices as well as the move from pyrotechnic to nonexplosive methods. For one-point separation devices, this review discusses the evolution from traditional explosive bolts, which use high explosives to operate, to nonexplosive actuators such as shape memory alloy devices that offer resettable, low-shock options. It also highlights devices that rely on pyrotechnic initiators without using high explosives as key developments for reducing shock and increasing safety. In the section on linear separation devices, the review examines flexible linear shaped charges and mild-detonating fuses, which are crucial for precise separations such as stage and fairing detachments. Introducing expanding tubes as a new method to avoid the usual debris and damage from pyrotechnics is a big improvement. In addition, the use of clamp-band joint systems for satellite separation, secured by either pyrotechnic bolts or nonexplosive dual-initiator devices, is a common approach. The recent focus on developing pneumatic linear separation devices marks a shift toward systems that can be reused and reduce shock without explosives. Moreover, the emergence of nonexplosive satellite separation systems represents a shift toward safer and more adaptable deployment technologies. These fully mechanical actuation methods facilitate shock-free separations, which are crucial for the integrity of sensitive payloads. This review suggests that continuous innovation in nonexplosive separation technology will significantly change mission planning and system design in the aeronautics and astronautics fields.

Micro-vibration control of spaceborne payload with smart parallel struts

Currently, the observation resolution of Earth observation satellites and space telescopes is progressively increasing. However, vibrations induced by solar panel vibrations, control torque gyroscopic reaction forces, and internal satellite noise significantly impede the observation accuracy of space-borne precision optical payloads. To mitigate the impact of vibrations on precision payload, it is necessary to incorporate isolation devices into the transmission path between the payload and spacecraft bus. This paper aims to design a six-degree-of-freedom parallel struts for active control of vibration in sensitive payloads. An optical payload isolation system is constructed using a Gough-Stewart parallel configuration with flexible hinges. The dynamic model of the system is established by the Newton-Euler method. The dynamic characteristics and response of the isolation system are analyzed. Then the active controller is designed based on the Fuzzy Auto-Disturbance Rejection Control strategy, and the effectiveness of the controller is simulated and compared with the fuzzy Proportion Integration Differentiation (PID) control algorithm. The results show that the active parallel struts exhibit excellent vibration isolation performance and possess strong robustness, which provides a theoretical reference for further space applications.

Microvibration isolation in sensitive payloads: methodology and design

Microvibration isolation in sensitive payloads: methodology and design

Multi-Degree-of-Freedom Active Isolation Platform for Microvibrations

Reaction wheels are widely used in the attitude control of spacecraft due to their capability of applying control torques, greatly reducing the propellant requirements and limiting its use to reaction wheel desaturation. However, the presence of unavoidable mechanical imperfections results in significant mechanical disturbances, being applied to the spacecraft, which can severely impact the operation of sensitive payloads. These microvibrations are broadband in nature, and therefore the effective mitigation of their effects requires a high isolation factor throughout a wide frequency range. This paper presents the development and experimental verification of a six-degree-of-freedom active isolation platform for a reaction wheel, integrating a soft suspension and active control using self-sensing actuators. A reduction in the transmitted forces of 65 dB at 270 Hz was experimentally demonstrated, while exhibiting negligible amplifications by its suspension resonance, which constitute very attractive performances.

Research on the Vibration Reduction Mechanism of a New Tensioning Platform with an Embedded Superstructure

Aiming at the problem of precision driving and vibration suppression for sensitive payloads on-orbit, this paper proposes a new compliant platform based on an embedded superstructure and a smart material actuator. Firstly, the main structure of the platform is designed and optimized to achieve the expected indicators via the response surface method. Then, the vibration reduction mechanism of the platform with the embedded superstructure is studied by establishing an equivalent model. Following that, a four-phase superstructure is matched and designed with a compact space, and the results are verified by finite element modal analysis. Finally, both the tensioning performance and vibration reduction performance under fixed frequency harmonic disturbance are studied via transient dynamic simulation. Based on the obtained results, directions for future improvements are proposed. The relevant conclusions can provide a reference for function integration of precision tensioning and vibration suppression.

A General Method to Obtain the Frequency Response Function from the Disturbance Source to the Sensitive Payload

Microvibrations are one of the main factors contributing to platform jitter and a decline in pointing stability and precision. Among various disturbance sources, reaction wheel assembly (RWA) is one of the most significant ones and has drawn the interest of numerous scholars. How to evaluate the influence of the disturbances of RWA on the pointing accuracy of a spacecraft is an arduous task because it involves multiple disciplines. The acquisition of the frequency response function (FRF) from the disturbance source to the sensitive payload is one of the most crucial stages in integrated modeling. Direct measurement of the FRF in the six directions is challenging because of the restricted room for RWA installation in a spacecraft, particularly in small satellites. In this paper, a general method based on the Hv algorithm to obtain the FRF is presented. This method only needs the RWA, itself, as an excitation source. Then, in order to acquire the FRF, we use an optical remote-sensing satellite as the research object. The peak positions of FRF obtained by different RWAs are basically the same, while the amplitudes are slightly different, indicating that this method is effective. This method takes into consideration the coupling between the RWA and the spacecraft, making it possible to multiply the RWA disturbance measured at a fixed interface with the FRF, to determine the image motion of the sensitive payload.

Active Damping, Vibration Isolation, and Shape Control of Space Structures: A Tutorial

This tutorial reviews the author’s contributions to the active control of precision space structures over the past 35 years. It is based on the Santini lecture presented at the IAC-2022 Astronautical Congress in Paris in September 2022. The first part is devoted to the active damping of space trusses with an emphasis on robustness. Guaranteed stability is achieved by using decentralized collocated actuator–sensor pairs. The so-called integral force feedback (IFF) is simple, robust, and effective, and the performances can be predicted easily with simple formulae based on modal analyses. These predictions have been confirmed by numerous experiments. The damping strategy for trusses has been extended to cable structures, and also confirmed experimentally. The second part addresses the problem of vibration isolation: isolating a sensitive payload from the vibration induced by the spacecraft (i.e., the unbalanced mass of attitude control reaction wheels and gyros). A six-axis isolator based on a Gough–Stewart platform is discussed; once again, the approach emphasizes robustness. Two different solutions are presented: The first one (active isolation) uses a decentralized controller with collocated pairs of the actuator and force sensor, with IFF control. It is demonstrated that this special implementation of the skyhook, unlike the classical one, has guaranteed stability, even if the two substructures it connects are flexible (typical of large space structures). A second approach (passive) discusses an electromagnetic implementation of the relaxation isolator where the classical dash-pot of the linear damper is substituted by a Maxwell unit, leading to an asymptotic decay rate of −40 dB/decade, similar to the skyhook (although much simpler in terms of electronics). The third part of the lecture summarizes more recent work done on the control of flexible mirrors: (i) flat mirrors for adaptive optics (AO) controlled by an array of piezoelectric ceramic (PZT) actuators and (ii) spherical thin shell polymer reflectors controlled by an array of piezoelectric polymer actuators (PVDF-TrFE) aimed at being deployed in space.

Control of High-Temperature Impinging Jet Issued from Overexpanded Rocket Nozzle

High-speed impinging jets issued from the exhaust of a launch vehicle are highly oscillatory and create hazardous conditions for the vehicle structure, affecting the sensitive payloads and personnel due to intense acoustic loads. Therefore, to reduce the unsteadiness of a jet and mitigate its adverse effects, a fundamental understanding of the associated flow and acoustic field is of utmost importance. The present experimental study is one such step to characterize the aeroacoustic properties of a high-temperature jet issued from an overexpanded rocket nozzle. Further, the effectiveness of microjet-based active flow control in reducing the flow unsteadiness and near-field noise levels is also explored. The experiments were performed at different jet stagnation temperatures, and the results were quantified at different impingement heights simulating the takeoff and landing environment of reusable launch vehicles. Mean pressure measurements were mapped on the ground plane using discrete pressure taps. The time-varying pressure component was measured using an unsteady pressure transducer located at the impingement point, and near-field acoustic measurements were carried out using a microphone. In addition, the velocity field was mapped using planar particle image velocimetry. The near-field pressure spectra are broadband, and the magnitude of noise content is a function of jet stagnation temperature. Furthermore, the injection of microjets resulted in a significant attenuation of near-field noise, impingement point pressure fluctuations, and turbulent kinetic energy.

Constrained Attitude Maneuvering via Modified-Rodrigues-Parameter-Based Motion Planning Algorithms

The attitude dynamics and control of a spacecraft becomes complex in the presence of constraints in its orientation. Such constraints consist in not pointing sensitive payload toward bright objects in space or, vice versa, keeping the same bright objects within some instrument’s field of view. This paper investigates the applicability of nonsingular attitude motion planning algorithms to navigate a three-dimensional grid in the Modified Rodrigues Parameter configuration space. The aim is to compute a constraint-compliant reference trajectory in Modified Rodrigues Parameter space that can be tracked to reorient a spacecraft from an initial attitude to a final attitude while also attempting at minimizing the required control effort. Nonzero initial and final angular rates are considered to yield a general solution. The path is constructed with B-spline curves that pass through each attitude waypoint. Further, a constant angular maneuver rate is imposed, which influences the speed at which the reference attitude traverses the B-spline solution. Simulations illustrate that constraint-compliant, control-torque-minimizing paths are found if the grid spacing is chosen to be fine enough.

Bio-Orthogonal Nanogels for Multiresponsive Release.

Responsive nanogel systems are interesting for the drug delivery of bioactive molecules due to their high stability in aqueous media. The development of nanogels that are able to respond to biochemical cues and compatible with the encapsulation and the release of large and sensitive payloads remains challenging. Here, multistimuli-responsive nanogels were synthesized using a bio-orthogonal and reversible reaction and were designed for the selective release of encapsulated cargos in a spatiotemporally controlled manner. The nanogels were composed of a functionalized polysaccharide cross-linked with pH-responsive hydrazone linkages. The effect of the pH value of the environment on the nanogels was fully reversible, leading to a reversible control of the release of the payloads and a “stop-and-go” release profile. In addition to the pH-sensitive nature of the hydrazone network, the dextran backbone can be degraded through enzymatic cleavage. Furthermore, the cross-linkers were designed to be responsive to oxidoreductive cues. Disulfide groups, responsive to reducing environments, and thioketal groups, responsive to oxidative environments, were integrated into the nanogel network. The release of model payloads was investigated in response to changes in the pH value of the environment or to the presence of reducing or oxidizing agents.

Micro-vibration Test of High Resolution Spacecraft

The accuracy of the high resolution earth observation spacecraft has remarkably increased in recent years. The micro-vibration induced by moving machine, such as moment wheels, may cause severe disturbance to the sensitive payload onboard the spacecraft. It is crucial to perform ground micro-vibration test to verify the observation performance of the spacecraft on orbit. This paper focuses on the system level micro-vibration test method of high resolution spacecraft. The key requirements of the micro-vibration test are firstly presented, and then the test system development is introduced. Finally, the micro-vibration application technique is given to demonstrate the whole process of the micro-vibration test. It is concluded that the test method and the test system are effective for the verification of the high resolution spacecraft.

Experimental investigation on a new sensitive payload platform with simultaneous positioning and vibration suppression capabilities

Precision positioning and vibration isolation are two main challenges for the sensitive payloads, to realize high quality observation. It means that on the one hand the sensitive payload should keep pace with the changes of target location for achieving alignment; on the other hand, the micro-vibrations from space cabin equipment should be suppressed for avoiding image jitter. A six-degree-of-freedom platform with simultaneous positioning and vibration suppression capabilities is proposed for replacing the original scheme with series connection of a positioning platform and a vibration isolation platform. The theoretical model of the platform with rigid payload is established and then is utilized as a constraint to conduct the passive vibration suppression optimization. Subsequently, a finite element model is constructed to verify the optimization results. Finally, experimental setups are built and tests are carried out to validate the performances. The test results demonstrate that the proposed platform possesses good simultaneous positioning and vibration suppression capabilities.

Integrated design, fabrication, and experimental study of a parallel micro-nano positioning-vibration isolation stage

• A novel parallel micro-nano positioning-vibration isolation stage (PVI stage) is proposed for sensitive load to realize the precision positioning and vibration isolation simultaneously in space environment. • The requirements of large-stroke positioning and passive vibration isolation could be achieved through combination of giant magnetostrictive actuator (GMA) and compliant amplification mechanism. • Some appurtenances are designed for preventing static deformation and ensuring assembly accuracy. • Theoretical simulation and experimental research are performed to verify the positioning and vibration isolation performances of the proposed stage. Positioning and vibration isolation are two important steps for sensitive payloads to realize precision observation in space environment. However, current base stages applied to sensitive payloads often focus on one function, thus limiting their engineering applications. This paper presents a novel parallel micro-nano positioning-vibration isolation stage (PVI stage), which could realize the two functions simultaneously. The advantages of the presented stage lie in the compactness and convenience, which determine its feasibility in limited volume. Through combination of giant magnetostrictive actuator (GMA) and compliant amplification mechanism, the requirements of large-stroke positioning and passive vibration isolation could be achieved. And three auxiliary unloading devices are designed to bear the sensitive payload for resisting the static deformations of compliant mechanism. The detailed scheme and corresponding dynamic model are constructed for showing the stage. Furthermore, finite element simulation is carried out to verify the desired performance. Finally, a prototype is fabricated and experimental tests are conducted to validate the capabilities of the stage. The test results prove that the proposed positioning-vibration isolation stage owns a compact structure and realizes micro-nano positioning and vibration isolation simultaneously, and thus shows a promising prospect in aerospace field.

Size matters - The shell lander concept for exploring medium-size airless bodies

Once addressed as a side topic in planetary exploration, the investigation of small solar system bodies has now become one of the corner stones in the international science community in order to study the formation of the solar system and the evolution of life within. For rendezvous spacecraft, small carry-on landers have proven to be valuable assets, and to have a positive impact on the overall mission cost, by avoiding additional complexity of the main satellite and transferring the risk of close surface maneuvers entirely or at least to some extend to an independent deployable system. However, carry-on landers have been designed currently to land on very small bodies only, but medium-size class objects between diameters of 10–50 km are of great interest as well. In this paper we classify carry-on landers with respect to their touchdown and operational strategy, evaluate the constraints of ballistic deployments for different target bodies as well as identify the niche for using simple honeycomb impact dampers compared to optional retro-propulsion systems. Further, we introduce the system design of an attitude-stabilized Shell Lander using a generic instrument carrier attached to a single ejectable crash-pad with stabilizing capability to protect the instrument carrier from structural damage, limit internal shock loads for sensitive payloads as well as reduce the amount of bounces on the surface. Finally, we present a mission architecture for a reference case to the Martian moon Phobos as well as provide a proof of concept based on laboratory impact tests and a multi-body simulation to analyze touchdown dynamics including terrain interaction, shell-shedding and bouncing. • A new concept for a small body lander is proposed. • We evaluate the constraints of ballistic deployments for different target bodies. • We introduce the system design of an attitude-controlled Shell Lander. • We present a mission architecture for a reference case to the Martian moon Phobos. • We provide a proof of concept based on laboratory impact tests and MBS analysis.

Photocontrolled Release of the Anticancer Drug Chlorambucil with Caged Harmonic Nanoparticles

AbstractWhile chemotherapy is one of the most used treatments in oncology, the systemic administration of chemotherapeutics generally results in undesired damages to healthy tissues and cells, side effects such as severe nausea and leukopenia, and reduced efficacy due to multidrug resistance and poor target accessibility. The limitations of conventional chemotherapy formulation have prompted the development of alternative nanomaterials‐based strategies to achieve targeted and stimuli sensitive payload delivery to reach optimal local drug concentration at tumor sites. In this study, the anticancer drug chlorambucil (Clb) was conjugated to the surface of silica coated lithium niobate (LNO) harmonic nanoparticles (HNPs) using a photocaging tether based on coumarin‐4‐yl methyl derivative. Upon laser pulsed femtosecond irradiation at 790 nm, the second harmonic emission from the metal oxide core induced the efficient release of Clb, with concomitant contribution from the nonlinear absorption of the coumarin (CM)‐based moiety.

Modeling and collision avoidance control for the Disturbance-Free Payload spacecraft

The Disturbance-Free Payload (DFP) spacecraft, which includes the payload module (PM) and the support module (SM) connecting through voice coil motors (VCM), can provide unprecedented control and motion stability for the sensitive payload. The payload module and the support module have a high collision probability because of close proximity formation. In order to perform collision avoidance control on two modules, this paper establishes the dynamics model of the DFP spacecraft and proposes a collision avoidance control strategy based on the model predictive control (MPC). The established model synthesizes the back-Electromotive-Force (back-EMF) of the VCM and the stiffness and damping of the flexible cables. The MPC controller converts the collision avoidance problem into a quadratic programming problem. The control forces are obtained by solving the quadratic programming problem. The collision avoidance control simulation of the DFP spacecraft has performed while the payload module subjects to sudden disturbance. The simulation results verify the effectiveness of the proposed control strategy and show that the proposed MPC controller exhibits better collision avoidance capability than that of the PD controller.

Modeling and Control of a Six Degrees of Freedom Maglev Vibration Isolation System.

The environment in space provides favorable conditions for space missions. However, low frequency vibration poses a great challenge to high sensitivity equipment, resulting in performance degradation of sensitive systems. Due to the ever-increasing requirements to protect sensitive payloads, there is a pressing need for micro-vibration suppression. This paper deals with the modeling and control of a maglev vibration isolation system. A high-precision nonlinear dynamic model with six degrees of freedom was derived, which contains the mathematical model of Lorentz actuators and umbilical cables. Regarding the system performance, a double closed-loop control strategy was proposed, and a sliding mode control algorithm was adopted to improve the vibration isolation performance. A simulation program of the system was developed in a MATLAB environment. A vibration isolation performance in the frequency range of 0.01–100 Hz and a tracking performance below 0.01 Hz were obtained. In order to verify the nonlinear dynamic model and the isolation performance, a principle prototype of the maglev isolation system equipped with accelerometers and position sensors was developed for the experiments. By comparing the simulation results and the experiment results, the nonlinear dynamic model of the maglev vibration isolation system was verified and the control strategy of the system was proved to be highly effective.

Micro-vibration Influencing Characteristic on Image Quality and Solutions for High-Resolution Satellites

Micro-vibration has been a critical factor for image quality of high-resolution satellites, and with the increase of resolution, especially for the ultrahigh-resolution satellites, it is not enough to get high-quality images if only depends on front-end suppression. In this paper, the influencing characteristic of micro-vibration on image quality was first analyzed to provide guidance for micro-vibration suppression and image processing, including direction, amplitude, frequency, phase and TDI series. Then, several solutions were introduced to reduce the influence of micro-vibration on image quality in VRSS-2 from whole-path factors: disturbance sources, transmission path, sensitive payload and image processing, which can provide reference for system design of following ultrahigh-resolution satellites.