SPACECRAFT DOCKING DEVICES Vladimir S. Syromiatnikov Chief and Professor, Electromechanical Engineering Branch for Large Deployable Structures Soviet Technical Paper Number SSI VSS-1 Copyright 1990 Space Studies Institute ANDROGYNOUS PERIPHERAL ASSEMBLING SYSTEM
Space Studies Institute copyright 1990
Space Studies Institute P.O. Box 82 Princeton, New Jersey 08542 Telephone: (609) 921-0377 FAX: (609) 921-0389 Gerard K. O'Neill President Gregg E. Maryniak Executive Vice President TECHNICAL PAPERS ON THE SOVIET SPACE PROGRAM The following technical papers are available through Space Studies Institute. Proceeds from the sale of these papers enable the authors to travel abroad and attend conferences. 1. Vjacheslav M. Filin, Deputy chief designer of the Energia heavy lift launch vehicle NPO Energia. A. Doc. No. SSI VMF-1 "ECOLOGY PROBLEMS OF THE ROCKET SPACE TECHNOLOGY". This paper addresses the potential near future environmental threat posed by a growing world space transportation fleet. Filin suggests that new booster development should avoid the use of toxic propellants. 23 pages. Price $20.00 B. Doc. No. SSI VMF-2 "ROCKET-SPACE TECHNOLOGY SAFETY". A excerpt was featured in the July/August 1990 issue of "SSI Update." The paper summarizes the categories, systems, and philosophy involved with safety in Soviet manned launch vehicles. 39 pages. Price $25.00 2. Boris Ivanovich Gubanov, Chief designer of the Energia heavy lift launch vehicle. A. Doc. No. SSI BIG-1 "THE IMMEDIATE PROSPECT OF THE REUSABLE SPACE TRANSPORT SYSTEMS". Featured in the November 19, 1990 issue of "Aviation Week and Space Technology" (page 23) This paper describes the overall design of a fully reusable next-generation Energia. All stages of the unmanned vehicle are recovered by winged fly-back to the launch site. 28 pages with drawings and diagrams. Price $70.00
Gubanov continued B. DOC. No. SSI BIG-2 "THE SPACE VEHICLE FOR TODAY AND TOMORROW”. Referenced in the January/February 1990 issue of "Interavia Space Markets" (page 25). Gubanov discusses Energia engine performance capabilities as well as different core block and stage configurations. Performance of the upper stages, payload sizes to various orbits, and possible missions are outlined by Gubanov. 23 pages with drawings and diagrams. Price $60.00 3. Vladimir S. Syromiatnikov, Chief and Professor of electromechanical engineering branch for large deployable structures. A. Doc. No. SSI VSS-1 "SPACE CRAFT DOCKING DEVICES". Syromiatnikov's book examines the theory and technique of docking spacecraft. Technical information is presented on structures created in the USSR and USA. Various designs of docking devices are analyzed, as well as their basic mechanisms. This book is recommended for engineering and technical personnel specializing in the docking of spacecraft. 300 pages with diagrams and technical drawings. Price $80.00 B. Doc. No. SSI VSS-2 "MANNED SPACECRAFT" This booklet discusses US and USSR manned spacecraft, which are central among the various types of space vehicles. A description is offered of their structure, basic systems, and equipment from the first Vostoks to today's improved transport vehicles. 64 pages with drawings and schematics. Price $ 35.00 SEND ORDERS TO: SPACE STUDIES INSTITUTE
TABLE OF CONTENTS Foreword........................................................ 1 Introduction.....................................................2 CHAPTER 1. DOCKING EQUIPMENT OF SPACECRAFT........................... 7 1.1. Basic Terminology.......................................7 1.2. Requirements, Functions, and Operations Structure of the Docking Device...................... 8 1.3. Docking System........................................ 10 1.4. Initial Docking Conditions.............................. 13 1.5. Docking Devices and their Functions.......................19 CHAPTER 2. PRINCIPAL CONSTRUCTION SCHEMES FOR DOCKING DEVICES..... 61 2.1. Classification of Docking Devices.........................61 2.2. General Issues........................................ 62 2.3. Issues Regarding the Reliability of Docking Devices......... 65 2.4. Provision of Compatibility and Androgyny...................73 2.5. Basic Groups of Mechanisms and Elements of the Docking Device.......................................... 76 2.6. "Rod and Cone" Type Docking Devices.......................82 2.7. Peripheral Docking Devices.............................. 86 2.8. Comparative Analysis of the Principle Schemes of Docking Mechanisms.......................................92 2.9. Redundancy in the Principal Schemes.......................95 CHAPTER 3. ISSUES CONCERNING THE CONSTRUCTION OF DOCKING DEVICES........99 3.1. Requirements of the Construction of Docking Devices General Design Considerations....................... 99 3.2. General Configuration. Hulls of the Docking Assemblies......103 3.3. The Locks of Docking Frames.............................104 3.4. Construction of the Docking Mechanisms................... 114 3.5. Basic Elements of the Docking Device..................... 127 3.6. Seals of Hermetic Constructions......................... 145 3.7. Lubricant Materials in Docking Devices................... 149 3.8. Provision of the Temperature Conditions of Docking Assemblies.......................................... .150 CHAPTER 4. DYNAMICS OF DOCKING................................... 153 4.1. The Tasks and Varieties of Mathematical Models.............153 4.2. Structures of Models, Assumptions, Systems of Coordinates......................................... 155 4.3. Models for the "Rod and Cone" Docking Device.............. 157 4.4. Mathematical Models for Peripheral Devices................ 166 4.5. Model Considering the Inertia of the Shock Absorbers........177
CHAPTER 5. SIMPLIFIED MATHEMATICAL MODELS OF DOCKING DYNAMICS CALCULATION OF SHOCK ABSORPTION SYSTEMS..................181 5.1. Problems Solved Using Simplified Models..................181 5.2. Equivalent Mathematical Models of Shock Absorption Before Linkage.......................................182 5.3. Equivalent Mathematical Models of Shock Absorption After Linkage........................................192 5.4. Requirements on the Shock Absorption Systems..............202 5.5. Shock Absorption Systems of "Rod and Cone" Docking Devices.............................................204 5.6. Shock Absorption Systems of Peripheral Docking Devices..... 216 CHAPTER 6. ELEMENTS OF SHOCK ABSORBERS. ELECTROMECHANICAL DAMPING.... 233 6.1. Energy Absorbing Elements..............................233 6.2. Spring Mechanisms.................................... 238 6.3. Friction Self-Adjusting Brake.......................... 242 6.4. Electromechanical Damping..............................243 6.5. Hydraulic and Pneumatic Shock Absorbers..................253 CHAPTER 7. TESTING OF DOCKING DEVICES TEST UNITS FOR EARTH TESTING........................... 256 7.1. Problems, Types of Testing.............................256 7.2. Stages of Creation and Testing......................... 257 7.3. Testing and Reliability............................... 259 7.4. Content and Volume of Testing.......................... 261 7.5. Types of Test Equipment............................... 271 7.6. Goals of Dynamic Testing, Types of Test Units.............271 7.7. Complex Dynamic Test Units.............................274 7.8. Dynamic Test Units to Test Shock Absorbers............... 289 Bibliography...................................................297
Abstract This book examines the theory and technique of docking spacecraft. Information is presented on structures created in the USSR and USA. Various designs of docking devices are analyzed, as well as their basic mechanisms. For engineering and technical personnel specializing in the docking of spacecraft. Foreword The mastery of space has led to the origin and development of new areas of science and technology. The creation of unique spacecraft systems required the development of methods of construction and the solution of a number of scientific and technical problems associated with design, calculations, and the simulation of the working conditions of these systems in Earth conditions. One of these systems is the docking device, which is intended to directly link spacecraft in orbit. The docking device is one of the most complex and labor intensive devices to manufacture among spacecraft systems, due to the variety of functions it fulfills, difficulties in planning, and the reproduction of working conditions on Earth. At present the USSR and USA have accumulated a significant amount of experience in the design and use of docking devices. Comprehensive material was obtained in the Apollo-Soyuz program. However, publications in periodicals and papers from scientific and technical conferences have been mainly dedicated to a brief description of the devices which have been developed and individual issues in the dynamics of docking. At the same time, it is critical that this gap be filled for the further improvement of space technology, generalization and use of the accumulated experience, and training of highly-skilled specialists in institutions of higher learning. This book systematically presents scientific and technical aspects of space docking. It also examines issues of design, testing, and the use of docking devices. *numbers in margin indicate foreign pagination.
Much of the material is based on the experience obtained in the Apollo-Soyuz project. The book is primarily intended for docking system specialists. However, the approach to the solution of many scientific and technical problems is the same for space technology as a whole; thus, the book may be useful to a wider range of specialists. The authors would like to thank all of those who participated in the creation of the docking devices and in the execution of orbital docking, and those who directly or indirectly participated in the preparation of this book for publication. The author is grateful to the reviewer, Member-Correspondent of the USSR Academy of Sciences V. I. Feodosyev for his valuable comments on the manuscript. Reviews and comments can be mailed to 107076, Moscow, B-76, Stromynskiy Per. D. 4, Mashinostroyeniye. Introduction Orbital docking is being used more and more in the current state of space flight. The requirements made on docking devices and their complexity have increased. The practice and theory of orbital docking accumulated in the 60s and 70s has turned into an independent field of space technology. The first dockings in orbit were done at the end of the first decade of the space era, but work on the execution of docking began even earlier, in the early 60s, shortly after the flight of Yu. A. Gagarin. The second decade was marked by the widespread use of docking, primarily in the Soyuz, Soyuz-Salyut, Gemini-Agena, Apollo, Apollo-Skylab, and Apollo-Soyuz programs. Their execution fulfilled the prediction of the founder of theoretical cosmonautics, K. E. Tsiolkovskiy, on the great prospects provided by docking in space. These dockings significantly expanded the ideas of specialists on the possibilities and means of accomplishing docking. This was especially clearly demonstrated by the creation and use of the Soyuz-Salyut-Progress space complex. The use of a long-term orbital station with two docking assemblies provided a rigid union with the formation of a hermetic tunnel, as well as electrical and hydraulic
connections. The use of transport and cargo ships provided great opportunities for long and efficient use of the space complex. The first docking devices were created for the Soyuz (USSR) and Gemini (USA) spacecraft. They did not provide for the formation of a hermetic transition tunnel between spacecraft. Even in these first developments different types of mechanisms were used: simply electromechanical mechanisms using electromechanical damping in the shock absorbers was used for Soyuz, and combined electrohydraulic mechanisms were used for the Gemini. Another significant difference is that the Soyuz was capable of completely automatic control of approach and docking, as well as manual control by cosmonauts, while Gemini required the crew's participation in the control. Thus began two different approaches to the development of docking equipment in the USSR and USA. The Soyuz-Salyut program and the Apollo lunar program were great steps forward in the development of docking equipment. A number of fundamental technical problems were solved, and structures were created which formed a rigid hermetic joint with a transition tunnel. Docking in the first projects was done using “rod and cone” type devices. One of the assemblies, which had a docking mechanism with a rod, executed the active role, and the second, with a receiving cone, was passive. Tn the next stage, the USSR and USA joined forces to create compatible docking devices. It was decided to develop a principally new design, an androgynous peripheral type which could be used in the future in national and international projects and to render aid in orbit if necessary. As the project was executed, all stages of work were conducted which were necessary to create a complex comprehensive system of space technology, which the docking device is. Specialists from both countries drafted and formulated a design for a compatible docking device. In accordance with this design both countries developed a docking assembly design. Despite common basic ideas and a matching configuration, the designs of the main mechanisms of the androgynous peripheral docking assemblies (APDA) of the Soyuz and Apollo were substantially different. Both groups of specialists maintained their approach to the design. This was possible due to the method of providing for the compatibility of assemblies differing in design: compatibility was achieved by unifying the minimum number of
interacting elements. The main role was played by the general principle of providing for androgynous docking designs, which had been proposed earlier in the creation of the docking device of the Soyuz-Salyut complex. The principle was that of inverse symmetry of the position of interacting and joining elements. To test the structures and confirm their compatibility, a large body of experimental work was done. Testing was done in both countries, both jointly and separately. In the final stage, an Earth-based control docking of flight models of the docking assemblies was done. Four years of tense work was crowned by two successful dockings in space, where each of the androgynous assemblies played active and passive roles, one after the other. Overall, the successful execution of the Apollo-Soyuz project assisted the further progress of docking technology. The exchange of experience and ideas, the concentration of substantial efforts in a relatively short period of time, and to some degree, the competitive nature of the work, were very useful. The content of the book, like the methods of planning, analysis, and testing presented here, is based on factual material on the docking devices created up until present in the USSR and USA: their description, and basic specifications are presented in Chapter 1. Here too we examine general information on the docking devices, technical requirements, classification, structural analysis, etc. A great deal of the interacting mechanisms and linked elements are concentrated in a limited area of the docking assembly. Thus, there are substantial difficulties in designing the principal design of the device as a whole and the general configuration of the docking assemblies. The complexity of the operations to be performed, the expanse of the kinematics, and the multi-functionality complicates the selection and planning of the principal designs of the main mechanisms. The external configuration, the position and size of the controlling elements determine the interaction after the first contact. The selection is mainly determined by the initial docking conditions provided by the approach systems of the spacecraft in the final portion of the approach. Development, analysis, and classification of docking devices and their main mechanisms made it possible to determine general and detailed recommendations for the choice of designs and individual parameters of the design. These issues are discussed in Chapter 2.
A high level of reliability is one of the most important requirements made on space equipment. The task is complicated by the fact that one must insure the reliability of a complex comprehensive system which is designed with minimal developed forces and durability. This structure should execute the assigned functions in harsh space conditions, the range of change of which, and whose effect on the elements may not always be ascertained with sufficient confidence. Due to the uniqueness of each space experiment, the high “cost” of failures in flight, one must insure execution of the task, as a rule, on the first try. All of these are reasons for the need for a carefully thought out program of experimental testing. The program of experimental testing should be linked with theoretical analysis of, primarily, reliability. Chapter 2 outlines a method of analysis and a method of insuring reliability based on estimates of the criticality of potential failures for multi-functional systems, including the docking device. This method is effective not only at the development stage, but it also makes it possible to prepare a general program of testing and system use. Tn the preparation for flight testing, a list is compiled of emergency situations which arise when there are failures in the spacecraft systems, and means are devised of getting out of these situations. Methods are also described for insuring the compatibility of docked assemblies and androgyny. The structure of docking devices is examined in more detail in Chapter 3. Requirements on the structure are systemized and detailed. The approach to the planning of basic mechanisms, units, and elements is presented and generalized. Since many of the mechanisms of the docking device operate in open space, measures are described which are taken to insure that the units will work in these conditions. Great attention is given to the planning of the locks of the docking frame, which is, as a rule, the most critical mechanism of this device. A list is presented of the measures which insure the high level of reliability in the execution of all of these functions. Features of structures developed in the USA are described. A great deal of the book is devoted to the dynamics of docking. Tn essence, the problem of shock absorption in the random collision of two structure free in space was posed for the first time in space docking. This required not only the development and use of a whole shock absorption system, but it was also necessary to create methods of mathematical modeling of this process. The bases of these methods are presented in Chapter 4. The analysis used elements of the theory of
classical collision of solid bodies as well as equations which consider final deformations of the shock absorbers and structures. The most difficult was the description of the geometry of the interacting surfaces and the search for the points of interaction, especially for peripheral docking devices. To plan, synthesize, and analyze the shock absorption system required simpler engineering methods. Chapter 4 outlines a method which is based on the reduction of a random interaction of two solid bodies through a system of shock absorbers to a much simpler model described by a system of differential equations of the deformation of shock absorbers. The problem is examined for different types of links at the point of interaction, which are characteristic for the process of shock absorption before and after linkage. Equations are presented which consider the inertia of the moving parts of the shock absorbers. The method which is presented is then used to analyze and design the shock absorption systems of two basic types of docking devices, “rod and cone” and peripheral devices. The effect of the mass and geometric characteristics of the docked spacecraft on the shock absorption process is examined. Different designs of shock absorption systems are analyzed, as well as typical cases of operation in different phases of docking and the corresponding equations which describe their behavior. The effect of individual parameters of the system on the process of shock absorption is shown, and specific recommendations are given for planning. The creation of docking devices required an improvement of known mechanisms and elements and the development of new ones. This includes several energy absorbing elements of the shock absorbers (Chapter 6). The central elements are the electromechanical dampers. The use of these dampers made it possible to avoid hydraulic mechanisms and to create a purely electromechanical docking device. The work of electromechanical dampers in heavy-duty shock absorbers, for which there is no precedent, has essential features. In shock absorption the brake rotor may accelerate in milliseconds to a speed of several thousand revolutions per minute. Care is needed in the choice of parameters of the brake and damper as a whole. Chapter 7 presents materials on the testing of docking devices and the Earthbased testing equipment. The most difficulty is presented by the replication on Earth of the movement and interaction of spacecraft in weightlessness. At present, dynamic test units are used which are based on purely mechanical models of the
docked spacecraft. Also in use are combined methods of modeling, so called hybrid test units, which use computers and heavy-duty servo drives to recreate the relative movement of the tested assemblies in docking. Issues are examined regarding the theory and planning of test units, and a comparative analysis is made. Chapter 1. Docking Equipment of Spacecraft 1.1 Basic Terminology Spacecraft controlled by an orientation and approach system are brought into contact with a specific speed and position (initial conditions). At this moment the docking process begins, which ends with rigid connection. After flight in a docked state is completed, undocking is done by releasing the mechanical connections and separating the spacecraft. In manned flights, as a rule, there is a hermetic connection, with the formation of a transition tunnel. The spacecraft are linked by two docking assemblies which are installed on the spacecraft. The two matching (made for each other) assemblies are called docking devices. The docking assembly, in addition to docking with the matching assembly, may also dock with another craft which differs substantially in structure but is compatible with it. The docking device is usually designed so that all docking and undocking operations are carried out by one assembly, called the active assembly; the second assembly is passive. An assembly which may be active or passive is called androgynous. An androgynous assembly matches an identical docking assembly, that is it can dock with itself; it may also be compatible with another active or passive assembly. Tn contrast to direct docking using a docking device, spacecraft may be docked using an intermediate mechanism, a manipulator, which makes the initial mechanical capture of the spacecraft, and is the analog of the links of the docking mechanism.
Figure 1.1. Equipment for approach and docking of Soyuz spacecraft, a. passive; b. active. 1.2. Requirements, Functions, and Operations Structure of the Docking Device The main task of any docking device is the mechanical linkage of spacecraft with the capability of multiple dockings and undockings. Requirements for this union (docking) may vary in accuracy, rigidity, durability, hermeticity, etc. The most widespread requirement is the formation of an accurate (the allowable displacement is about two orders of magnitude less than the diameter of the joint), durable, and rigid (on the same order as the durability and rigidity of other compartments of the spacecraft) joint. When two manned spacecraft are linked, there must usually be a hermetic connection, and the docking device should provide for the flight of the spacecraft while docked, after which they should undock. In addition to the three basic functions (docking, maintenance of docked state, and undocking), the docking device can carry out additional functions. The docking device should carry out its functions in a given range of initial docking conditions, considering the work of the control systems of both spacecraft. Tn joint flight all calculated loads on the joint should be supported in space conditions for all possible schemes and conditions of flight. The docking device should carry out these functions after Earth preparation and injection into orbit. There are two basic requirements made on the docking device: high reliability (and crew safety in manned flight) and low mass. Other technical, usage, and economic factors are also important: compatibility and configuration for given
spacecraft, technological efficiency of manufacturing, testing, and use; time needed to create the device; convenience and efficiency of control and monitoring; energy consumption; time to execute operations; cost, etc. To dock, maintain a docked state, and undock, the docking device should carry out the following basic operations: 1) shock absorption; 2) compensation for initial error; 3) linkage (formation of the primary connection); 4) equalization; 5) coupling; 6) combining the joint with final equalization; 7) rigid connection with hermetization of the joint (formation of secondary connection); 8) undocking (with separation of primary and secondary connections); 9) separation of spacecraft after separation of connections; 10) signaling to monitoring and control system of spacecraft. Some of these operations may not be done, for example, the formation of a secondary connection, hermetization, etc. The docking device also carries out other operations: 1) opening of hatches; 2) release of tunnel; 3) connection of electrical and hydraulic junctions; 4) pressurization and depressurization of tunnel; 5) verification of hermeticity, etc. Docking and undocking may be done 1) automatically; 2) from remote control from the cosmonaut's panel; 3) from remote control from Earth along the command radio line; 4) manually. The execution of the operations is monitored on the cosmonaut's panel (on manned flights) and using the radio telemetry system at Flight Control Center. The docking device has mechanisms which fully or partially back up the execution of the critical operations. Redundancy is one of the main ways of increasing the reliability of the docking device. The docking device consists of two assemblies. The mechanisms and elements of the docking assembly are intended for the formation of an accurate and rigid joint, structurally and/or functionally divided into four groups: 1) hull; 2) docking mechanism; 3) docking frame; 4) additional units and elements. The hull with the docking frame is the main and the bearing element of the docking assembly on which the docking mechanism and the mechanisms of the docking frame are installed. The docking mechanism executes the main operations for the formation of the primary mechanical connection from the first contact, including shock absorption,
compensation for error, linkage, equalization and coupling, to the contact of the docking frames. After the formation of a secondary mechanical connection during docking and during undocking, uncoupling is done. The docking frames of the two assemblies are joined by locks installed on them. The frames also have other elements which provide for connection, hetmetization, and undocking. These basic groups of mechanisms carry out operations on the direct mechanical union of spacecraft and undocking. Tn addition, the docking assembly, as a rule, includes units and elements which are intended for additional operations, which are, to a greater or lesser extent, associated with docking and undocking. This includes the hatches of the transition tunnel with mechanisms for opening and hermetization; elements of the system to pressurize the tunnel, verification of the hermeticity of the joint, and depressurization; attachments for carrying out manual operations, and electrical, pneumatic, and water connections. The docking mechanism and the mechanisms of the docking frame have essential features in their design as well as in their manufacturing technology, and they require different testing methods and equipment. Thus, this division is not formal, but provides for a certain organization of planning, production, and testing. Usually the docking mechanism is divided into a structurally and technologically complete assembly. 1.3. Docking System The majority of docking and undocking operations are performed using electrical, hydraulic, or pneumatic drives. For single operations, pyrotechnics are frequently used. The drives are turned on and off by commands from the control panels of the spacecraft, from automatic control systems of the spacecraft, or from Earth. For automatic actuation of the drive, end switches are provided, and in a number of cases these are electromechanical sensors located on moving elements of the mechanisms, for example, contact sensors on the joint, etc. These sensors are also used to automatically control docking. They are needed to monitor the execution of operations in docking and undocking, to monitor the position of mechanisms, and the state of the structure. This monitoring is done by cosmonauts and specialists at the Flight Control Center.
The term “docking system” is used to refer to domestic equipment, the complex of on-board equipment for monitoring and control, and the executive mechanisms of the docking device, including elements of automation and communications with other spacecraft systems. To control the docking device mechanism, an instrument is used which is usually called the docking control block, which performs two basic functions: 1) commutation of the engines and electromagnets of the drives; 2) logical processing of the control signals (from the operation execution sensors and from other interacting systems of the spacecraft) and processing of the commands issued in the commutation part of the instrument and in other systems. Figure 1.2 shows the main on-board and Earth-based means of control and monitoring which are used in docking and undocking of the Soyuz space transport ship and the Salyut orbital station. The interconnection of systems to perform operations is done through a central control system by equipment which provides for: 1) transmission of commands from the command radio line and from the cosmonaut panel; 2) exchange of commands with other systems (for example, switching off the spacecraft orientation and movement system on first contact); 3) blocking of the issuing of commands transmitted from the cosmonaut's panel and on the command radio line or automatically processed by the system for certain states of the mechanisms and sensors; 4) temporary monitoring and control of individual operations and automatic cycles. Blocking is widely used in the docking system, as it is in other spacecraft systems, to eliminate undesirable and dangerous actions, incorrect sequences of commands, etc. For example, to avoid unexpected or accidental undocking, before the issuing of the main command for separation of the spacecraft one must issue a preliminary command. In the absence of the preliminary command the electrical circuit of the main command remains open. To automatically shut down electrical power supply in case of premature stoppage of the drives or incomplete execution of operations, temporary monitoring is used. A special instrument processes electrical signals in a specific time sequence which is used in the docking control block to query the state of the system. For example, if by a certain time the drive has not reached a given position, the electrical supply to the system is shut off, and the warning indicator lights up on
Figure 1.2. Interconnection of systems and equipment to control and monitor docking of the Soyuz craft and the Salyut station. 1. orbital station control system; 2. station automatic control block; 3. electrical supply system; 4. cosmonaut's panel; 5. docking control block; 6. spacecraft automatic control block; 7. spacecraft control system; 8. command radio line; 9. radio telemetry line; 10. voice communications line; 11. Flight Control Center; 12. Earth-based measuring point. the cosmonaut's panel. Electrical signals from the program instrument are also used to control the main mechanisms during normal operation, and are back-ups in case of failures in the system and for sending the appropriate signals to the cosmonaut's panel. Tn general, both docked spacecraft have docking control blocks. Tn the interaction with different systems these blocks are used to control mechanisms of the active and passive docking assemblies. When the electrical junctions of the joint are automatically connected it is possible to control individual mechanisms of the docking assembly of one spacecraft from the other. Thus, in the docking of the Soyuz spacecraft, after the junctions are connected, the cosmonauts may issue commands to open and close the locks of the docking frame from the passive assembly of the Salyut station. These junctions are also used for communication between the interacting crews during docking.
During control from the Flight Control Center (see Figure 1.2) information and commands are issued and received by a whole complex of on-board and Earth- based equipment. After automatic processing, the information enters the monitoring and control panel of the on-duty operators, including docking system specialists in the control and analysis group. 1.4. Initial Docking Conditions In docking the spacecraft approach each other so that the docking assemblies are maintained in a coaxial position. A specific longitudinal and zero velocity is held in the remaining linear and angular coordinates [14, 15]. Naturally, the parameters of relative motion have a scatter which is defined by the properties of the measurement equipment for relative position and velocity, and by the characteristics of the control systems. Possible values of relative coordinates which define the deviation from a coaxial position and their first derivatives during mechanical contact (Figure 1.3) are called the initial docking conditions, and define one of the main technical requirements for planning and testing docking devices. The relative position and velocity of gradual shifting are usually maintained using the motion control system of the active spacecraft, and orientation and stabilization (rotation around the centers of mass) of both spacecraft. In fully automatic control, radar systems are used, and these measure the relative linear and angular coordinates and their derivatives. When the crew is participating in the control, optical visors and television cameras are used on the active spacecraft, as well as targets and spatial optical indices on the passive spacecraft (see Figures 1.1 and 1.4). These targets make it possible to measure both linear and angular deviations of the spacecraft from a coaxial position. The coaxial position of the visors and targets, as well as the matching antennas of the radar devices, agrees with the coaxial position of the docking assembly. Observing the target on the screen of the visor, the pilot of the active spacecraft, using two three-stage control sticks affects the executive organs of the craft to maintain the coaxial approach with the passive craft at a given speed. In the approach the passive spacecraft maintains angular stabilization, and, when there is an automatic radar, its orientation on the active spacecraft. The
Figure 1.3 Initial docking conditions, z, y, z are the reference system of coordinates for the parameters of the initial conditions; arc the relative velocities; are the angles between the axis z and the projection of axis into plane . Figure 1.4. Visor equipment of the Soyuz and Apollo spacecraft, a. for redocking; b. for docking using APDA; 1. target on adapter of the booster; 2. image of a grid in the field of vision; 3. left forward window of the command module; 4. position of the right eye of the astronaut; 5. main target; 6. back up target; 7. visor; 8. target of the docking module.
active craft usually decreases the scatter of initial deviations and velocities. Deviations from the coaxial position are conveniently given (see Figure 1.3) by two linear coordinates and along axes y and z associated with the passive docking assembly (the plane is located along the section of the receiving cone or a section of the control projections) and two solid angles and between the longitudinal axis of the spacecraft, and lying in planes and and the angle of the intersection of planes and into plane The relative velocities of the centers of mass are given in projections on axes x, y, z, and angular velocities and arc given in projections on their associated axes. The total deviations of the docking assemblies from the coaxial postion are added from the errors: 1) errors in the adjustment of the measurement equipment (targets, visors, antennas); 2) errors in the adjustment of the docking assembly; 3) measurement errors; 4) dynamic errors arising in the control process. To decrease the adjustment errors and to avoid significant systematic errors, for example, rotation by 180 verification and tuning are provided for. Thus, when the APDA is used aids are used to sequentially verify the correctness of the two joints (the command module of the Apollo with the docking module during redocking and the docking module of the Soyuz with the APDA); simultaneously, the targets are adjusted (Figure 1.5). As has already been said, control during the approach is structured so that individual channels of the system rotate the spacecraft relative to the , and axes and shift the center of mass of the active spacecraft along axes At the same time the regulating effects in the control system are deviations from the coaxial position, measured, in the general case, in another coordinate system. For example, the observed deviations of the center of the target from the cross hairs of the visor may be due to linear or angular shifts in the line of sight relative to the longitudinal axis of the docking device; angular banking errors cause additional lateral deviations. As a result, the angular and linear deviations are usually interconnected along different coordinates. Nonetheless, due to the random character of the errors, for small values of deviations along different coordinates, in the first approximation, they may be considered independent random values with normal distribution laws.
Figure 1.5. Schematic of the verification and adjustment of targets (APDA). a. equipment for docking the command module and the docking module; b. equipment for docking the Soyuz and Apollo spacecraft. 1. docking mechanism on the command module; 2. target adjustment; 3. adjustment to command module visor imitator; 4. target; 5. frame of the rocket booster; 6. receiving cone on the docking module; 7. Apollo spacecraft imitator; 8. adjustment to visor imitator; 9. APDA; 10. target on the Soyuz spacecraft. Table 1.1. Initial docking conditions for designing docking devices, a. Docking device projects; b. m/s; c. m; d. degrees; e. degrees/second; f. Soyuz-Salyut; g. Gemini-Agena; h. Apollo-Skylab; i. APDA; j. APDA after changes.
In order to determine the possible range of initial parameters (deviations and velocities), all types of error are analyzed. The dynamic components are defined by modeling. Table 1.1 gives the maximum values of deviations and velocities along various coordinates, which are, in principle related to different combinations. However, in planning and testing of the docking device, one usually examines the worst combinations, for example, those in which the kinetic energy of relative movement is maximal, or for which linkage may not occur. Maximum values are used for several parameters. This approach to the creation of a docking device leads to a certain excess of its characteristics (larger energy capacity of the shock absorbers, etc.). Sometimes it becomes necessary to use this excess, for example, to decrease size and lighten construction. Analysis of the visibility zones of the target during manual control or possible combinations of maximum deviations and velocities in various coordinates in automatic control make it possible to judge the range of initial conditions. This approach was demonstrated by NASA specialists in one of the stages of testing of the APDA. Based on the analysis of data obtained in the training of astronauts on trainers (Table 1.2) the maximum values of the angular deviations and lateral velocity were reduced. Analysis of the results of flight testing in fully automatic control mode and with the participation of the pilot confirmed that usually the initial parameters are signifiicantly less than the given maximum values. Table 1.2. Initial docking conditions obtained in the training of astronauts on an APDA trainer at the NASA Johnson Space Flight Center, 7 December 1974. a. Test number; b. m/s; c. m; d. degrees; e. degrees/second.
An interesting analysis was made after the commander of Apollo 14, A. Shepard, docked with the lunar cabin only on the sixth attempt [43]. The head latch of the docking mechanism did not work, and the receiving cone was rotated toward Earth. Tracks on the cone (Figure 1.6) made it possible to determine the errors during the six dockings and evaluate the possiblity of flights in the stressed state. Figure 1.6. Receiving cone with traces of the impacts of the docking mechanism head during the dockings of Apollo 14. 1, 2, 3, 4. wide continuous tracks with weak dents and scratches on the solid lubricant coating; 5, 6 shiny tracks on the coating. Legend in circle: socket of receiving cone. It is assumed that measurement of the parameters of relative motion will be made with greater accuracy in the future. This, along with improvement of spacecraft control in the approach will make it possible to decrease the initial displacements and scatter of velocities. It is also interesting to consider the limits of initial conditions at which one may consider the development of a docking device, which directly joins the docking frames, without using a docking mechanism. Estimates show that the accuracy of the approach systems must be increased by an order of magnitude compared with the existing systems. The values of the lateral and, partially, the angular deviations determine the size of the guiding and buffer elements of the docking mechanism (the diameter of the section of the receivnig cone, the length of the guiding protrusions, etc.). The maximum values of the deviations have a different effect on the selection of element size and the size of different types of docking devices (see sections 2.6.2 and 2.7.2).
The maximum linear and angular velocities of the spacecraft, their inertial and their geometric characteristics determine the energy capacity of the docking mechanism shock absorbers. In the approach the spacecraft transfer a certain longitudinal (along the x axis) approach velocity since there must be a certain amount of energy for the latch to work and make the link. Moreover, before the link part of the energy is lost in collisions. Due to the error at the moment of the link, the approach velocity of the spacecraft decreases in comparison with the initial velocity. There is a lower limit of the longitudinal velocity guaranteeing linkage. The possible scatter gives a maximum value of the longitudinal velocity which defines the maximum energy of collision of the spacecraft. To facilitate linkage and decrease the lower limit of velocity the engines of the jet control system are used in the direction of the longitudinal axis x. During docking, after contact, the control systems of the spacecraft may make coupling more difficult. After the linkage, the action of the working control systems may increase the energy of relative motion absorbed by the shock absorbers, and create a disturbance in the coupling process. Thus, after linkage, the control systems are usually shut off, or their work mode is changed. If they remain switched on, their action should be considered in the planning, analysis, and testing of the docking device. Tn principle, this control is possible for one or both docked spacecraft. Tn this case, loads and relative displacements are decreased. In docking using a universal manipulator, “hovering” of the spacecraft very close to each other (about 5-10 m apart) is provided for. The velocities of the gradual shift should be maintained with a substantially larger accuracy than in direct docking. Moreover, small forces developed by the manipulator cause additional limitations on the relative velocities during capture. 1.5. Docking Devices and their Features 1.5.1. Docking Device of the Soyuz Spacecraft This device (Figure 1.7) was the first domestic design tested in orbit. This docking device was used on October 30, 1967 to make the first automatic docking of the unmanned Kosmos-186 and Kosmos-188 spacecraft. The active and
passive docking assemblies were installed on the manned Soyuz-4 and Soyuz-5 spacecraft, and they were docked. The docking device did not provide for the formation of a hermetic transition tunnel; thus, cosmonauts A. S. Yeliseyev and Ye. V. Khrunov moved from one ship to the other through open space. Figure 1.7. Soyuz docking device. 1. active docking assembly; 2. socket; 3. docking mechanism; 4. guide rod; 5. passive docking assembly; 6. receiving cone; 7. socket; 8. grooves for latches; 9. electrical connections. The Soyuz docking device was designed in the form of an electromechanical structure [49], and laid the foundation for a purely electromechanical trend in the construction of docking devices. A number of design, construction, and testing problems were resolved. For the first time electromechanical damping was used [48] in heavy-duty shock absorbers. Overall, the development and use of this docking device was an important step in the creation of docking equipment. The Soyuz docking device was intended for: 1) multiple docking of a spacecraft for the initial conditions given in Table 1.1, with the formation of an accurate union of docking frames; 2) the connection of the electronic connectors to form inter-ship communications; 3) multiple undocking; 4) back-up undocking by firing of the docking mechanisms and the supports of the socket in the passive docking assembly. The docking device consists of active and passive assemblies. Tn the center of the active assembly is a docking mechanism with a rod, which is placed in the receiving cone of the passive assembly during docking. The docking frames of the assemblies have guide rods (passive) and matching sockets (active), plugs and sockets of the electric connector and docking compatibility sensors.
The docking mechanism was installed on the adapter, which is attached to the active docking assembly by four pyrotechnic locks. The receiving cone of the passive assembly ends in a socket, which contains linkage sensors and pyrotechnic bolts for back-up undocking. Docking begins after the head of the rod makes contact with the receiving cone. On a signal from the contact sensor the control system of the active spacecraft shuts off, and the engines of the jet control systems are turned on, creating a force along the x axis to accelerate linkage. Tn the contacts, the shocks of the collisions of the spacecraft are absorbed. After several impacts the head of the rod enters the socket of the receiving cone, where linkage occurs. The latches, falling into the matching grooves of the socket, are compressed into an intermediate position, and the linkage sensor fires. On a signal from this sensor the jet control system of the active spacecraft is shut off; the control system of the passive spacecraft is shut off on a signal from the linkage sensor in the socket of the receiving cone. If the firing of contact sensor 2 occurs on first contact (the end of the docking frame), the jet control system is automatically turned on at the extraction of the active spacecraft. After linkage the energy of the collision is absorbed by a longitudinal shock absorber and a flexible rod. Turning of the spacecraft after linkage is limited by a circular bracket, and the energy of the rotation is absorbed by deformation of the rod and other parts of the docking assembly. The drive of the docking mechanism is turned on for coupling when a signal is given on linkage and the contact sensor fires. Equalization in roll, pitch, and yaw are done during coupling by a leverage mechanism. In the initial course of coupling the bracket is held immobile relative to the hull, and the levers are separated until they rest in the cone. The latches of the head are drawn inside the tapering grooves of the socket. When they rest in the tapered grooves, a torque is created relative to the longitudinal axis and roll is equalized. Tn the coupled position the latches of the head are fixed in the grooves of the socket to insure separation of the spacecraft during undocking. At the end of equalization the rods of the bracket are released, and the bracket moves with the rod. The final equalization is done by the guiding rods and the sockets, and in the final part of coupling the plugs and sockets of the electrical connectors are joined.
Figure 1.8. Docking mechanism. 1. guides of large screw; 2. spring recoil shock absorber; 3. large screw; 4. spring of initial stage of shock absorber; 5. spring cable; 6. rod; 7. drive; 8. spring of second stage of shock absorber; 9. bearing-screw converter of shock absorber; 12. small screw; 13. head; 14. latch; 15. contact sensor 1; 16. contact sensor 2; 17. mechanism to remove latches; 18. mechanism to separate levers; 19. equalization lever; 20. lever separation rods; 21. small screw guides; 22. rod stopper.
A signal to shut off the drive comes from the docking compatibility sensors. For the drive to couple the frames with maximum force, the drive is turned on several seconds after the sensor fires. The rod is held in a coupled position by the stopper coupling, and by a braking reducer after the electrical engines are switched off. Standard undocking occurs is done with the docking mechanism drive. To prepare for undocking the rod is moved out to the extreme forward position. Using average thrust and a clamp brace, a small screw is initially held immobile; the springs of the shock absorbers are compressed, storing energy for subsequent separation of the spacecraft. Tn the extreme forward position the clamp triggers, the screw is released, and the head moves forward due to the action of the springs. The latches of the head are recessed by the internal thrust. Due to the energy of the springs and additional action of the jet control system of the active spacecraft, the spacecraft separate. Rack-up undocking may be done by the active or the passive spacecraft. On command for back-up undocking, the active docking assembly fires the docking mechanism. On the passive docking assembly the pyrotechnic bolts are fired, releasing the latches of the socket. The docking mechanism (Figure 1.8) is functionally and structurally the most complex part of the active docking assembly. The rod of the docking mechanism is installed on guides, which consist of four cruciform bearings in grooves of the tail part of the hull. The rod is in the form of a screw with a bearing-screw converter. This converter has a number of unique properties, including the ability to convert the rotational motion of the nut in the gradual shifting of the screw. This property made it possible to use the same type of converter in the longitudinal shock absorber; a gear on the nut of the small screw converter is the rod of the shock absorber, which is linked with the rods on the output shafts of the electromechanical brake. These elements are used in all subsequent modifications of the electromechanical type docking device. Control of the docking of the Soyuz spacecraft (Figure 1.9) is possible for manned and unmanned flights. Standard docking is done automatically, as a direct continuation of the approach process. This transition occurs on a signal from contact sensor 1. If in 10 seconds the linkage sensor does not fire, then the
RkJQdWJsaXNoZXIy MTU5NjU0Mg==