The objective of this appendix is to provide an overview of the vehicles which perform rendezvous and capture in the ISS scenario. Of interest are the features of these vehicles which are most important for the implementation of the rendezvous trajectories and for the mating process. These are:

• masses and inertias of the vehicles;

• actuation means and force/torque capabilities;

• location of thrust engines;

• features of the vehicle geometry related to rendezvous and capture issues, such as size and shape of main body and appendages;

• type and location of mating devices;

• type of rendezvous sensors;

It is not the intention to give here a detailed and exhaustive description of all these vehicles, which may anyway undergo changes in the course of their development.

General information on the various vehicles can be obtained from the NASA, NASDA and ESA web-sites. Detailed information on design and history of the Russian vehicles can be obtained from NASAs ‘Mir hardware heritage’ (Portree 1995). Information on all aspects of space stations can be found in Messerschmid & Bertrand (1999). Some information contained in this appendix has been extracted from technical reports and specifications of the International Space Station Programme for the Station and its visiting vehicles (NASA 1999), and some has been obtained by verbal communication from specialists involved in the development of the various spacecraft.

The objective of this chapter is to provide a basic understanding of the dynamic and kinematic processes which are taking place during docking or berthing of two vehicles, and to give an overview of the design principles used for docking and berthing mechanisms. Design driving requirements for these mechanisms are briefly discussed, and an overview of existing mechanism developments is given. The dynamic processes of contact and capture at docking are discussed using a simple model of an equivalent mass, which represents the masses of both spacecraft plus a central attenuation system. Basic functional concepts of the design elements used for shock attenuation, capture, structural connection and sealing are discussed at the end of the chapter.

Basic concepts of docking and berthing

The main tasks and issues arising during docking and berthing have already been addressed in section 2.5. Definitions of the terms ‘docking’ and ‘berthing’ have been given in chapter 1. For completeness of this chapter, these key definitions shall be recalled here.

• As a general term for the process of achieving contact, capture and connection, the term mating is used. This includes the two cases ‘docking’ and ‘berthing’.

• The term docking is used for the case where the GNC system of the chaser controls the required vehicle state parameters necessary to ensure that its capture interfaces enter into those of the target vehicle, and where the capture location is also the location for structural connection.

• […]

The objective of this chapter is to explain the requirements for trajectory safety, to discuss the causes for trajectory deviations due to the orbital environment and to imperfections and errors of the onboard system, and to investigate the possibilities of employing protection against trajectory deviations. The discussions concerning trajectory deviations and trajectory safety concentrate on the rendezvous phases, since the mission phases of launch and phasing are generally controlled by operators or computer functions on ground. In the rendezvous phases the two spacecraft are relatively close together, their orbital planes are well aligned and the trajectory of the chaser, by definition, leads toward the target, so that any deviation from the planned trajectory can potentially lead to a collision, directly or after one or more orbital revolutions.

Trajectory safety – trajectory deviations

Rendezvous and docking is in fact a ‘planned collision’ of two spacecraft, which is controlled by considering the geometric location of the contact points on the two vehicles and the linear velocities and angular rates at contact. To achieve the contact conditions within the allowed margins, the trajectories have to be maintained within close tolerances prior to contact. Any deviation from such tolerances may lead either to a loss of the rendezvous and mating opportunity or even to the danger of collision of the two spacecraft at unsuitable points and dynamic conditions, with the risk of serious damage. For this reason, rendezvous operations, and all functions and systems involved in them, have to comply with failure tolerance and safety requirements.