A guidance strategy for rendezvous and docking to the space station in the Earth-Moon NRHO orbit

With the development of space technology,it is possible to build a space station in Earth-Moon space as a transit for Earth-Moon round-trip and entering in the deep space.Rendezvous and docking is one of the key technologies for building an Earth-Moon space station.A guidance strategy for rendezvous and docking from the Earth orbit to the space station in the Earth-Moon NRHO orbit is proposed in this paper,which is suitable for engineering applications.Firstly,the rendezvous and docking process is divided into three sections,i.e.,the large-range orbit transfer section,far-range guidance section,and close-range approaching section.The suitable terminal of large-range orbit transfer is selected according to the eigenvalue of NRHO orbit state transition matrix.The two-impulse guidance method based on the relative motion equation in the three-body problem is adopted for the far-range guidance section.The impulse time and amplitude are solved with the optimization algorithm.The linear constant three-body relative motion equation is proposed for the close-range approaching section,and the rendezvous and docking is completed by a two-stage linear approximation.Finally,a simulation analysis is carried out,and the simulation results show that the adopted dynamics equations and the designed guidance law are effective,and the three flight phases are naturally connected to accomplish the rendezvous and docking mission from the Earth orbit to the space station on the Earth-Moon NRHO.

Optimal maneuver strategy to improve the observability of angles-only rendezvous

This paper proposes an optimal maneuver strategy to improve the observability of angles-only rendezvous from the perspective of relative navigation.A set of dimensionless relative orbital elements(ROEs)is used to parameterize the relative motion,and the objective function of the observability of anglesonly navigation is established.An analytical solution of the optimal maneuver strategy to improve the observability of anglesonly navigation is obtained by means of numerical analysis.A set of dedicated semi-physical simulation system is built to test the performances of the proposed optimal maneuver strategy.Finally,the effectiveness of the method proposed in this paper is verified through the comparative analysis of the objective function of the observability of angles-only navigation and the performances of the angles-only navigation filter under different maneuver schemes.Compared with the cases without orbital maneuver,it is concluded that the tangential filtering accuracy with the optimal orbital maneuver at the terminal time is increased by 35%on average,and the radial and normal filtering accuracy is increased by 30%on average.

Distributed Cooperative Control Algorithm for Multi-UAV Mission Rendezvous

Multiple unmanned aerial vehicles(UAVs)cooperative operation is the main form for UAVs fighting in battlefield,and multi-UAV mission rendezvous is the premise of cooperative reconnaissance and attack missions.We propose a rendezvous control strategy,which divides the rendezvous process into two parts:The loose formation rendezvous and the close formation rendezvous.In the first stage,UAVs are supposed to reach the specific target locations simultaneously and form a loose formation.A distributed control strategy based on first-order consensus algorithm is presented to achieve this goal.Then the second stage is designed based on the second-order consensus algorithm to complete the transition from the loose formation to the close formation.This process needs the speeds and heading angles of UAVs to reach an agreement.Besides,control algorithms with a virtual leader are proposed,by which the formation states can reach a specific value.Finally,simulation results show that the control algorithms are capable of realizing the mission rendezvous of multi-UAV and the consistence of UAVs′final states,which verify the effectiveness and feasibility of the designed control strategy.

APPLICATION OF VELOCITY GAIN GUIDANCE TO FAR-DISTANCE RENDEZVOUS

Using impulse hypothesis to solve far-distance rendezvous is difficult to be realized in a real project and the guidance accuracy cannot be controlled. A two-maneuver guidance law is designed for the two-impulse rendezvous problem. The velocity gain guidance is applied to the first maneuver and the time-cut-off law is applied to the second one. Theoretical and simulation results show that the plan is credible. Accuracy requirements in fardistance rendezvous and in transform to close-in rendezous can be met.

CRSN中基于信道使用概率的Rendezvous算法

为了解决认知无线传感器网络(CRSN)中公共控制信道受限问题,在不使用公共控制信道情况下,减少信道冲突,提高CRSN的通信效率和频谱适应性。本文提出了一种分布式的Rendezvous信道跳频算法SRP,该算法通过调整步长,动态生成逻辑跳频序列,根据信道的使用概率,将逻辑序列映射到物理信道,实现节点间的信道Rendezvous,算法支持时钟同步和异步模型,保证了节点间的有效通信。通过理论证明和实验对比分析,验证了SRP算法在最大相遇时间(MTTR)和平均相遇时间(ATTR)上优于其他算法。

Laparo-endoscopic “Rendezvous” to treat cholecysto-choledocolithiasis: Effective,safe and simplifies the endoscopist’s work

AIM: To investigate our clinical experience with combined laparo-endoscopic Rendezvous (RV) for the treatment of patients affected by gallstones and common bile duct (CBD) stones and especially to study the never evaluated opinion of the endoscopist concerning the difficulty of the intraoperative endoscopic procedure during the RV in comparison with standard endoscopic retrograde cholangio-pancreatography (ERCP). METHODS: Eighty consecutive patients affected by cholecystolithiasis and diagnosed or suspected CBD stones were treated with a standardized "tailored" RV. The relevant technical features, the feasibility, the effectiveness in stone clearance, the safety but also the simple evaluation of difficulty and agreement of the endoscopist were analyzed with a questionnaire. RESULTS: The feasibility was 97.5% and the effectiveness 100% concerning CBD clearance and solution of coexisting problems at the papilla. Minor morbidity was 3.3%, the operating time was prolonged by a mean of 14 min, the mean hospital stay was 3.8 d and only one stone’s recurrence occurred. The endoscopist evaluated the procedure to be simpler than standard ERCP-ES in 81.2% of the cases.CONCLUSION: Simultaneous RV carries higheffectiveness and safety at least comparable to those reported for other options. The endoscopist is very often satisfied with this approach because of the minimization of some steps of the endoscopic procedure and avoidance of relevant iatrogenic risk factors. If the mandatory collaboration between surgeons and endoscopists is guaranteed, this approach can often be preferable for the patient, the surgeon, the endoscopist and the hospital.

Interesting rendezvous location in a liver transplantation patient with anastomosis stricture

An endoscopic or radiologic percutaneous approach may be an initial minimally invasive method for treating biliary strictures after living donor liver transplantation; however, cannulation of biliary strictures is sometimes difficult due to the presence of a sharp or twisted angle within the stricture or a complete stricture. When an angulated or twisted biliary stricture interrupts passage of a guidewire over the stricture, it is difficult to replace the percutaneous biliary drainage catheter with inside stents by endoscopic retrograde cholangiopancreatography. The rendezvous technique can be used to overcome this difficulty. In addition to the classical rendezvous method, in cases with complete transection of the common bile duct a modified technique involving the insertion of a snare into the subhepatic space has been successfully performed. Herein, we report a modified rendezvous technique in the duodenal bulb as an extraordinary location for a patient with duct-to-duct anastomotic complete stricture after liver transplantation.

Adaptive control for autonomous rendezvous of spacecraft on elliptical orbit

A strategy for spacecraft autonomous rendezvous on an elliptical orbit in situation of no orbit information is developed. Lawden equation is used to describe relative motion of two spacecraft. Then an adaptive gain factor is introduced, and an adaptive control law for auton- omous rendezvous on the elliptical orbit is designed using Lyapunov approach. The relative motion is proved to be ultimately bounded under this control law, and the final relative position error can achieve the expected magnitude. Simulation results indicate that the adaptive control law can realize autonomous rendezvous on the elliptical orbit with relative state information only.

Saturated Adaptive Output-Constrained Control of Cooperative Spacecraft Rendezvous and Docking

This paper investigates the robust relative pose control for spacecraft rendezvous and docking with constrained relative pose and saturated control inputs.A barrier Lyapunov function is used to ensure the constraints of states,so that the computational singularity of the inverse matrix in control command can be avoided,while a linear auxiliary system is introduced to handle with the adverse effect of actuator saturation.The tuning rules for designing parameters in control command and auxiliary system are derived based on the stability analysis of the closed-loop system.It is proved that all closed-loop signals always keep bounded,the prescribed constraints of relative pose tracking errors are never violated,and the pose tracking errors ultimately converge to small neighborhoods of zero.Simulation experiments validate the performance of the proposed robust saturated control strategy.

Comparative study of rendezvous techniques in post-liver transplant biliary stricture

AIM： To investigate the usefulness of a new rendezvous technique for placing stents using the Kumpe （KMP） catheter in angulated or twisted biliary strictures. METHODS： The rendezvous technique was performed in patients with a biliary stricture after living donor liver transplantation （LDLT） who required the exchange of percutaneous transhepatic biliary drainage catheters for inside stents. The rendezvous technique was performed using a guidewire in 19 patients （guidewire group） and using a KMP catheter in another 19 （KMP catheter group）. We compared the two groups retrospectively. RESULTS： The baseline characteristics did not differ between the groups. The success rate for placing insidestents was 100% in both groups. A KMP catheter was easier to manipulate than a guidewire. The mean pro- cedure time in the KMP catheter group （1012 s, range： 301-2006 s） was shorter than that in the guidewire group （2037 s, range： 251-6758 s, P = 0.022）. The cu- mulative probabilities corresponding to the procedure time of the two groups were significantly different （P = 0.008）. The factors related to procedure time were the rendezvous technique method, the number of inside stents, the operator, and balloon dilation of the stric- ture （P 〈 0.05）. In a multivariate analysis, the rendez- vous technique method was the only significant factor related to procedure time （P = 0.010）. The procedural complications observed included one case of mild acute pancreatitis and one case of acute cholangitis in the guidewire group, and two cases of mild acute pancre- atitis in the KMP catheter group. CONCLUSION： The rendezvous technique involving use of the KIVlp catheter was a fast and safe method for placing inside stents in patients with LDLT biliary stric- ture that represents a viable alternative to the guide- wire rendezvous technique,

Analytic Initial Relative Orbit Solution for Angles-Only Space Rendezvous Using Hybrid Dynamics Method

A closed-form solution to the angles-only initial relative orbit determination(IROD)problem for space rendezvous with non-cooperated target is developed,where a method of hybrid dynamics with the concept of virtual formation is introduced to analytically solve the problem.Emphasis is placed on developing the solution based on hybrid dynamics(i.e.,Clohessy-Wiltshire equations and two-body dynamics),obtaining formation geometries that produce relative orbit state observability,and deriving the approximate analytic error covariance for the IROD solution.A standard Monte Carlo simulation system based on two-body dynamics is used to verify the feasibility and evaluate the performance proposed algorithms.The sensitivity of the solution accuracy to the formation geometry,observation numbers is presented and discussed.

Modified rendezvous intrahepatic bile duct cannulation technique to pass a PTBD catheter in ERCP

The rendezvous procedure combines an endoscopic technique with percutaneous transhepatic biliary drainage(PTBD).When a selective common bile duct cannulation fails,PTBD allows successful drainage and retrograde access for subsequent rendezvous techniques.Traditionally,rendezvous procedures such as the PTBDassisted over-the-wire cannulation method,or the parallel cannulation technique,may be available when a bile duct cannot be selectively cannulated.When selective intrahepatic bile duct(IHD) cannulation fails,this modified rendezvous technique may be a feasible alternative.We report the case of a modified rendezvous technique,in which the guidewire was retrogradely passed into the IHD through the C2 catheter after end-to-end contact between the tips of the sphincterotome and the C2 catheter at the ampulla's orifice,in a 39-year-old man who had been diagnosed with gallbladder carcinoma with a metastatic right IHD obstruction.Clinically this procedure may be a feasible and timesaving technique.

Electrohydraulic lithotripsy and rendezvous nasal endoscopic cholangiography for common bile duct stone: A case report

BACKGROUND In patients with large stones in the common bile duct(CBD),advanced treatment modalities are generally needed.Here,we present an interesting case of a huge CBD stone treated with electrohydraulic lithotripsy(EHL)by the percutaneous approach and rendezvous endoscopic retrograde cholangiography(ERC)using a nasal endoscope.CASE SUMMARY A 91-year-old woman underwent ERC for a symptomatic large CBD stone with a diameter of 50 mm.She was referred to our institution after the failure of lithotomy by ERC,and after undergoing percutaneous transhepatic biliary drainage.We attempted to fragment the stone by transhepatic cholangioscopy using EHL.However,the stones were too large and partly soft clay-like for lithotripsy.Next,we attempted lithotomy with ERC and cholangioscopy by the rendezvous technique using a nasal endoscope and achieved complete lithotomy.No complication was observed at the end of this procedure.CONCLUSION Cholangioscopy by rendezvous technique using a nasal endoscope is a feasible and safe endoscopic method for removing huge CBD stones.

Non-linear Dynamics Method to Angles-Only Navigation for Non-cooperative Rendezvous of Spacecraft

Aiming at the problem of relative navigation for non-cooperative rendezvous of spacecraft,this paper proposes a new angles-only navigation architecture using non-linear dynamics method. This method does not solve the problem of poor observability of angles-only navigation through orbital or attitude maneuvering,but improves the observability of angles-only navigation through capturing the non-linearity of the system in the evolution of relative motion. First,three relative dynamics models and their corresponding line-of-sight(LoS)measurement equations are introduced,including the rectilinear state relative dynamics model,the curvilinear state relative dynamics model,and the relative orbital elements(ROE)state relative dynamics model. Then,an observability analysis theory based on the Gramian matrix is introduced to determine which relative dynamics model could maximize the observability of angles-only navigation. Next,an adaptive extended Kalman filtering scheme is proposed to solve the problem that the angles-only navigation filter using the non-linear dynamics method is sensitive to measurement noises. Finally,the performances of the proposed angles-only navigation architecture are tested by means of numerical simulations,which demonstrates that the angles-only navigation filtering scheme without orbital or attitude maneuvering is completely feasible through improving the modeling of the relative dynamics and LoS measurement equations.

Ivar asteroid rendezvous mission system scenario and trajectory design

The asteroid exploration opportunities are searched and calculated with launch dates in 2006 to2010, and with asteroid Ivar 1627 as the target, the spacecraft and its subsystems are designed and analyzed,and the transfer trajectory is designed using △VEGA technology for the asteroid rendezvous. The design resultssatisfied the energy requirements for small explorers.

Combined radiologic and endoscopic treatment(using the “rendezvous technique”) of a biliary fistula following left hepatectomy

Despite the ongoing decrease in the frequency of complications after hepatectomy, biliary fistulas still occur and are associated with high morbidity and mortality rates. Here, we report on an unusual technique for managing biliary fistula following left hepatectomy in a patient in whom the right posterior segmental duct joined the left hepatic duct. The biliary fistula was treated with a combined radiologic and endoscopic procedure based on the "rendezvous technique". The clinical outcome was good, and reoperation was not required.

腹腔镜胆囊切除术中应用Rendezvous技术的系统评价

目的:系统评价腹腔镜胆囊切除术中应用Rendezvous技术治疗胆囊结石合并胆总管结石的安全性和有效性.方法:检索Cochrane Library、Pub Med、Embase、中国生物医学数据库、CNKI、万方数据库、维普中文科技期刊数据库等,查找2006-02-31/2016-02-31公开发表的关于腹腔镜胆囊切除术中应用Rendezvous技术治疗胆囊结石合并胆总管结石的前瞻性随机对照试验(randomized controlled trials,RCT)研究,通过纳入和排除标准筛选文献,对纳入的研究进行分析并提取试验数据.采用Cochrane协助网的RevMan5.3.5软件进行数据分析.结果:本研究共纳入6篇R C T,纳入患者616例,其中应用Rendezvous技术307例,POERCP+L C为309例,Meta分析结果显示:Rendezvous组在结石清除率(OR=2.24,95%C I:1.26-4.65,P=0.08)、插管失败率(OR=0.39,95%CI:0.18-0.83,P=0.01)、术后总并发症发生率(OR=0.41,95%C I:0.22-0.75,P=0.004)等方面均优于POERCP+L C组,亚组分析表明相比POERCP+LC组,Rendezvous技术可有效降低ERCP相关并发症发生率,在LC相关并发症及中转开腹发生率差异无统计学意义(P>0.05).结论:腹腔镜胆囊切除术中联合内镜时应用Rendezvous技术优于POERCP+LC方案,该方案提高了结石清除率和插管成功率,并且可以降低ERCP相关的并发症发生率,缩短住院时间,但仍需大样本、多中心、前瞻性RCT研究来进一步说明两种方案的差异.

Practical Optimization of Low-Thrust Minimum-Time Orbital Rendezvous in Sun-Synchronous Orbits

High-specific-impulse electric propulsion technology is promising for future space robotic debris removal in sun-synchronous orbits.Such a prospect involves solving a class of challenging problems of low-thrust orbital rendezvous between an active spacecraft and a free-flying debris.This study focuses on computing optimal low-thrust minimum-time many-revolution trajectories,considering the effects of the Earth oblateness perturbations and null thrust in Earth shadow.Firstly,a set of mean-element orbital dynamic equations of a chaser(spacecraft)and a target(debris)are derived by using the orbital averaging technique,and specifically a slow-changing state of the mean longitude difference is proposed to accommodate to the rendezvous problem.Subsequently,the corresponding optimal control problem is formulated based on the mean elements and their associated costate variables in terms of Pontryagin’s maximum principle,and a practical optimization procedure is adopted to find the specific initial costate variables,wherein the necessary conditions of the optimal solutions are all satisfied.Afterwards,the optimal control profile obtained in mean elements is then mapped into the counterpart that is employed by the osculating orbital dynamics.A simple correction strategy about the initialization of the mean elements,specifically the differential mean true longitude,is suggested,which is capable of minimizing the terminal orbital rendezvous errors for propagating orbital dynamics expressed by both mean and osculating elements.Finally,numerical examples are presented,and specifically,the terminal orbital rendezvous accuracy is verified by solving hundreds of rendezvous problems,demonstrating the effectiveness of the optimization method proposed in this article.

Time-optimal rendezvous transfer trajectory for restricted cone-angle range solar sails

The advantage of solar sails in deep space exploration is that no fuel consumption is required. The heliocentric distance is one factor influencing the solar radiation pressure force exerted on solar sails. In addition, the solar radiation pressure force is also related to the solar sail orientation with respect to the sunlight direction. For an ideal flat solar sail, the cone angle between the sail normal and the sunlight direction determines the magnitude and direction of solar radiation pressure force. In general, the cone angle can change from 0° to 90°. However, in practical applications, a large cone angle may reduce the efficiency of solar radiation pressure force and there is a strict requirement on the attitude control. Usually, the cone angle range is restricted less more than an acute angle （for example, not more than 40°） in engineering practice. In this paper, the time-optimal transfer trajectory is designed over a restricted range of the cone angle, and an indirect method is used to solve the two point boundary value problem associated to the optimal control problem. Relevant numerical examples are provided to compare with the case of an unrestricted case, and the effects of different maximum restricted cone angles are discussed. The results indicate that （1） for the condition of a restricted cone-angle range the transfer time is longer than that for the unrestricted case and （2） the optimal transfer time increases as the maximum restricted cone angle decreases.

Study on Forced Straight-Line Guidance for the Final Translation Phase of Spacecraft Rendezvous

Aimed at the problem of final translation of space rendezvous for the applications such as docking,inspection and tracking,optimal straight-line guidance algorithm based on pulse/continuous low-thrust in the context of Clohessy-Wiltshire dynamics is proposed.Two modes of guidance strategy:varying-speed and fixed-speed approaching scheme for V-bar and R-bar approach by using constant/finite low-thrust propulsion respectively are studied,and the corresponding fuel-optimal conditions are obtained.Numerical simulation is conducted to verify and test the proposed algorithms.The results show that there is generally no different between the fuel consumptions by using the two different approaching modes for V-bar case.However,the conclusion for Rbar case is different that the using of continuous low-thrust cost more fuel and transfer time.