Assembly Operations: Grapple, Berth, and Dock
NSTS 214921 identifies three legacy on-orbit operations of immediate interest: grappling, berthing, and docking. These three operations, from which most present-day concepts descend, can be abstracted as different mechanical means of one spacecraft asserting Control Authority2 over the trajectory and attitude of a cooperating spacecraft3: Footnotes “Payload Bay User’s Guide”, Johnson Space Center (2000)[↩] Used... read more
Capture Contact Dynamics
The movement of a chase vehicle (the “trajectory”) during a berthing event is dominated by several factors. These include the mass properties of the two elements, forces acting on the in-coming element by the item surrendering control authority, forces exerted by the CBM on the in-coming elements, and constraints deriving from the alignment structures of the... read more
Contact Mechanics Under High-Vacuum
The most basic characteristic of a mechanism is the relative motion of faying surfaces under load. Points, lines, and surfaces of contact are assessed by calculating deformations and the resulting contact stresses1. The objectives of the analysis are to 1) estimate the forces due to friction and 2) predict whether damage occurs2. Footnotes That is,... read more
Field Joints
The issue of “field conditions” is significant because the CBM is Primary Structure with respect to containing pressure in a high vacuum environment. Like a “factory joint”, the elastomeric seals of a “field joint” are susceptible to issues of long term compression set and to local concentrations of stress. Unlike a factory joint, a field... read more
Preloaded Joints
A “preloaded” joint is one where the bolt(s) have been tensioned beyond what it takes to just barely make the two sides touch. When a preloaded joint is subsequently subjected to an external “separating” load, part of that load goes into trying to pull those sides apart, and part of it goes into the bolt... read more
Primary Structure
In the general aerospace industry, primary structural loads are generally those affecting flight, pressurization, or ground handling capability1. In the case of the Common Berthing Mechanism, a product-specific definition applied2: “That part of a flight vehicle or element which sustains the significant applied loads and provides main load paths for distributing reactions of applied loads.... read more
Reach and Access
For the sake of this discussion, engineered systems can be considered in two categories: those that are intended for human-interactive maintenance1, and those that are not. Those that are not so intended are of no interest here. The development of those that are intended for such maintenance must consider the ability of the maintainers to... read more
Thermal Circumstances
Pre-berth temperatures of exterior spacecraft components are a critical issue1. They’re strongly driven by several factors 2: Footnotes MIL-A-83577B “Assemblies, Moving Mechanical, For Space and Launch Vehicles, General Specification for” (1978)[↩]Conley, Peter L. (ed), “Space Vehicle Mechanisms: Elements of Successful Design”, John. Wiley & Sons (1998), Chapter 20 “Thermal Design”[↩]