Low Impact Docking Research Articles

Prediction models for seal performance of a space seal considering atomic oxygen effects

A low impact docking system with advanced capabilities has been developing for future spacecrafts, and its main interface docking seal (MIDS) is both a critical component and a research topic of interest. It is a typical design for the MIDS that adopts the elastomer seal-on-seal structure made of silicone rubbers, and the atomic oxygen (AO) in space had been found to take great effects on the sealing performance by previous experimental studies, especially for the seal leak, seal adhesion, and compression set. Exposure to AO may cause obvious changes on the sealing surface of the MIDS, and some characteristic parameters of morphology are proposed to characterize the changes in this study, including of the porosity, roughness and radius of curvature. Both the leakage model and the adhesion model of the MIDS are further developed to predict the sealing performance considering AO effects, which had been confirmed by the application experiments. The experimental data are in good agreement with the calculation data. The effects of AO on the sealing performance are simulated and analyzed by the proposed prediction models. The results are beneficial to the developments of the MIDS and other space seals.

Analysis and Optimization of Transmission Performance of Low-Impact Docking Mechanism

Analysis and Optimization of Transmission Performance of Low-Impact Docking Mechanism

Optimization of low impact docking mechanism based on integrated joint design and task-oriented force ellipsoid index

Optimization of low impact docking mechanism based on integrated joint design and task-oriented force ellipsoid index

Micro- and Nanosatellite Sensorless Electromagnetic Docking Control Based on the High-Frequency Injection Method

This paper proposes a sensorless electromagnetic docking method suitable for micro- and nanosatellites. Based on the circuit model of the electromagnetic docking device, an algorithm for calculating the distance between two satellites on the basis of the high-frequency injection (HFI) method has been developed. In the specific implementation, first, a high-frequency (HF) voltage is injected into one of the two electromagnets; second, the HF currents induced by both electromagnets are measured and their respective root-mean-squares (RMSs) are calculated; third, two RMSs are substituted into a specific formula to obtain a variable carrying distance information; finally, the variable is utilized to calculate the distance estimation using the look-up table interpolation method. This paper presents a closed-loop electromagnetic docking controller which includes an outer distance loop and an inner speed loop and adopts the distance estimation as the feedback. The proposed sensorless electromagnetic docking method is verified by the distance estimation tracking response test and the ground-based docking test. The results indicate that low-impact docking can be achieved under the initial condition that the two satellites have a certain degree of misalignment. The proposed method can be adopted as a primary or as a redundant electromagnetic docking solution for resource-critical micro- and nanosatellites.

Dynamic modeling and identification of low impact docking mechanism based on symmetric excitation trajectory

Dynamic modeling and identification of low impact docking mechanism based on symmetric excitation trajectory

A mathematical model for evaluating adhesion contact of an elastomeric seal-on-seal structure

For low impact docking systems (LIDS) developing for rendezvous and docking of spacecraft, the main interface docking seal (MID seal) is one of the key components, and its seal and adhesion performances are crucial for mating LIDS-adapted spacecrafts. An elastomeric seal-on-seal structure is one of the mainstream designs of the MID seal and is generally made of silicone rubbers that can adapt to complex space environments. For the MID seal of seal-on-seal structure, the adhesion performance has been confirmed to have significant effects on the separation reliability of mating spacecrafts. By analyzing the sealing and adhesive mechanisms of the MID seal that is an elastomeric seal-on-seal structure, an adhesive contact model of single rough peak is derived on the grounds of Johnson, Kendall and Roberts (JKR) theory. Utilizing the asperities model and the adhesive contact model of single rough peak, an adhesive contact model of the elastomeric seal-on-seal structure is further proposed. The experiments were performed to verify the adhesion model, and the satisfied consistencies were presented in the comparative studies of the experimental data and the calculated data. Based on the proposed mathematical model, the simulation analyses were performed to disclosure adhesive performances of the MID seal. The influence rules of some parameters on adhesive performances were presented, including material parameters, geometric parameters, and parameters of surface morphology. The research findings are proven to be favorable for the design, machining, assemblage and actual service of the MID seal, and can be also used for other elastomeric seals.

A leakage model for a seal-on-seal structure based on porous media method

The main interface docking seal (MID seal) is one of the key components in the developing low impact docking systems for future space vehicles, and its sealing property is crucial to the spacecrafts docking in space. A seal-on-seal structure is one of the mainstream designs of the MID seal, and is generally made of rubber materials that can adapt to the complex space environment. For the MID seal of the seal-on-seal structure, it is further confirmed that the porous media theory is suitable to study the sealing property by investigating the micromorphology characteristics of seal contact faces, which based on a leakage model is proposed by this paper. In this model, both the primary seal and the secondary seal are considered as a whole, which is more consistent with the structure and the physical process of sealing face leakage. By comparison with the performed experiments, the leakage model was verified. Based on the proposed leakage model, some simulation results about the studied MID seal are presented and discussed, which mainly correspond with pressure distributions, compression levels, design parameters and operating temperatures. These analyses clearly present some intrinsic relationships implicated in the leakage model. This study is favorable for the mechanism researches, designs, assemblies, and applications of the MID seal, and other seals like that are also included.

Monocular Vision-Based Pose Determination in Close Proximity for Low Impact Docking.

Pose determination in close proximity is critical for space missions in which monocular vision is one of the most promising solutions. Although numerous approaches such as using artificial beacons or specific shapes on spacecrafts have proved to be effective, the high individuation and the large time delay limit their use in low impact docking. This paper proposes a unified framework to determinate the relative pose between two docking mechanisms by treating their guide petals as measurement objects. Fusing the pose information of one docking mechanism to simplify image processing and creating an intermediate coordinate system to solve the perspective-n-point problem greatly improve the real-time performance and the robustness of the method. Experimental results show that the position measurement error is within 3.7 mm, while the rotation error around docking direction is less than 0.16°, corresponding to a measurement time reduction of 85%.

Mechanical Properties of Silicone Elastomer Seals for Space Docking Vehicles

Low impact docking mechanisms (LIDM) are developing. The LIDM seal is one of the key components of the LIDM, and play very critical roles during the docking and berthing of space vehicles. Due to the severe functional requirements, it is difficult to develop the LIDM seal that is a silicone elastomer seal. The excellent mechanical property is firstly required for the LIDM seal. Five design schemes of the LIDM seal are proposed by this paper, and their mechanical properties are studied by the proposed finite element method. The mechanical properties of the LIDM seal have important impacts on the required sealing performance, docking feature and separation feature. The findings are beneficial for the development of the LIDM seal for space docking vehicles.

A velocity-based impedance control system for a low impact docking mechanism (LIDM).

In this paper, an impedance control algorithm based on velocity for capturing two low impact docking mechanisms (LIDMs) is presented. The main idea of this algorithm is to track desired forces when the position errors of two LIDMs are random by designing the relationship between the velocity and contact forces measured by a load sensing ring to achieve low impact docking. In this paper, the governing equation of an impedance controller between the deviation of forces and velocity is derived, and simulations are designed to verify how impedance parameters affect the control characteristics. The performance of the presented control algorithm is validated by using the MATLAB and ADAMS software for capturing simulations. The results of capturing simulations demonstrate that the impedance control algorithm can respond fast and has excellent robustness when the environmental errors are random, and the contact forces and torques satisfy the low impact requirements.

Experimental Investigation of Leak-Rate Performance of a Subscale Composite Elastomer-Retainer Docking Seal

A novel docking seal was investigated for application to the main interface seal of NASA’s low-impact docking system. This interface seal was designed to maintain acceptable leak rates while being exposed to the harsh environmental conditions of outer space. In this experimental evaluation, the leak rate of a candidate docking-seal assembly was characterized and evaluated. The composite seal was manufactured from silicone elastomer S0383-70, vacuum molded into a metal retaining ring. Four seal designs were considered with unique characteristic heights. The leak-rate performance was characterized through a mass point leak-rate method by monitoring gas properties within an internal control volume. The leak rates of the seals were measured at representative docking temperatures of , , and for all four seal designs and characterized at 100, 74, and 48% of full closure. For all conditions, considered the candidate seal assemblies met the leak-rate criteria derived from the approximate mission requirements.

Force control in a parallel manipulator through virtual foundations

An overwhelming controller provides robustness against uncertain parameters, disturbances and un-modelled dynamics. A simplified inverse dynamics model is used in the present paper to develop an overwhelming controller for a parallel manipulator (a Stewart platform), where the controller accommodates modelling uncertainties such as the simplifications made for development of the inverse model in order to improve the computational efficiency. Such a control strategy leads to good trajectory tracking accuracy in the presence of unknown disturbances. However, in addition to trajectory tracking performance, the controller for a Stewart platform should also be able to control or limit the interaction forces in applications such as robot assisted surgery and low-impact docking. The environmental forces can be accommodated during the interaction period by modulating the impedance at the interface of manipulator and environment through virtual flexible foundations. The positional error induced during the force control phase can be recovered during the free flight or idle phase. While this approach has been used successfully in the past to control serial manipulators, the closed loop kinematic architecture in a parallel manipulator introduces many difficulties. This paper proposes a modified overwhelming control scheme for parallel manipulators with compensations for interaction force control and positional error recovery. Bond graph modelling is used as an integrated model and controller development tool. Force controlled machining on a spherical surface, which is akin to a surgical operation, is considered as an example application of the developed control strategy. The simulation results from the bond graph model of the controlled Stewart platform are presented to demonstrate the performance of the developed hybrid position force controller.

ＥＴＳ‐ＶＩＩランデブ・ドッキング実験の結果

ETS–VII is a test satellite to perform in-orbit demonstration of autonomous rendezvous docking (RVD) technology, which will be necessary for advanced space activities in the early 21st century. ETS–VII performed three RVD experiment flights, and verified all technical items. ETS–VII demonstrated first autonomous RVD between unmanned vehicles, and remote piloted rendezvous flight position accuracy at docking was about 1cm, and acceleration was less than 1.5mG (low impact docking). In the second RVD experiment flight, ETS–VII detected attitude anomaly and executed disable abort for safety insurance. We present the results and evaluation of three RVD experiment flights in this paper.