Space Vehicle Mechanisms: Elements of Successful Design




This course teaches the foundational knowledge integral to all aspects of the space mechanisms field.  The course explores the technologies required for the successful design of moving mechanical assemblies in the space environment and offers a detailed look at many of the key components common to most mechanisms, such as ball bearings, motors, lubrication and feedback devices. With this background, the high-performance materials required for operation in space are reviewed, emphasizing compatibility with the space environment and offering some background in the metallurgy, chemistry, and fabrication of those materials. Examples of all the most common types of mechanism are included illustrating their operation, strengths and weaknesses, and their implementation of the underlying design elements. In addition, the mechanism’s relationship and interface with other vehicle systems will be explored, as a mechanism usually becomes an important part of the vehicles structural, thermal, contamination, survivability, and pointing subsystems. The course includes design and analysis examples to demonstrate the principles involved in understanding how mechanisms should work, common problems to avoid, and how design margins should be evaluated during the evolution of a program. Finally, some important underlying techniques, such as reliability analysis and digital simulation, are covered.

We have found students to be hungry for insights about their questions of ‘How do I select a lubricant /motor / feedback device?’ for various types of mechanisms.  These application questions are addressed with our always popular interactive discussion between the class and instructor regarding the proper selection of motors, lubricants and feedback devices for all the most common types of mechanisms.  This section is well received in the way it transforms the foundational knowledge provided into practical inputs for designing successful mechanisms.




Printed course notes and reference materials are provided to all students.  The course typically includes the textbook Space Vehicle Mechanisms: Elements of Successful Design, edited by P.L. Conley.


This course is valuable both for mechanisms engineers who wish to expand their knowledge and for system engineers and program managers who need a working knowledge of mechanism design and application.


Understanding a mechanism requires a working knowledge of dozens of specialties, such as motors, lubrication, structural metals, and feedback devices. You will acquire this knowledge and become conversant with the many components, materials, and technologies that go into a successful design. In addition, successful application of a mechanism requires a familiarity with the various vehicle subsystems of which a mechanism is an often crucial part, such as the pointing, contamination, or structural system. The design and analysis of these subsystems, and their interface with the mechanism, will be introduced.




  1. Introduction.  
    The course begins with an overview of how all types of mechanisms are used in spacecraft.
  2. Pointing Subsystems. 
    Design and requirements considerations common to all pointing systems, both high and low precision are discussed in preparation for the study of bearings, motors and feedback devices.
  3. Motors. 
    Stepper motors, DC brushless and DC brush motors characteristics and behavior are explained.  The different motors are examined for suitability against various mechanism applications to study the question ‘Which is the best motor to choose for a given application and why?’
  4. Feedback Devices. 
    Optical encoder, inductosyn, resolver and potentiometer characteristics and precision are explained.  The different devices are examined for suitability against various mechanism applications to study the question ‘Which is the best feedback device to choose for a given application and why?’
  5. Bearings and Gears. 
    The fundamentals of high-precision ball bearings are presented along with proper lubrication techniques for long life.  Gears are overviewed with a focus on harmonic drives.
  6. Lubrication Fundamentals.
    Wet and Dry Lubricants.   The fundamental behavior, performance, and life characteristics of liquid and dry lubricants for space are discussed.  The different lubrication choices are examined for suitability against various mechanism applications to study the question ‘Which is the best lubricant to choose for a given application and why?’
  7. Release Systems and Deployment Systems.
    Pyrotechnic and non-pyrotechnic release mechanisms operation and characteristics are presented.  Deployment system basics and key elements such as springs are examined.
  8. Rotating Signal and Power Transfer Systems. 
    Slip ring characteristics, operation and behavior are discussed.
  9. Electrical Interfaces. 
    The interfaces between mechanisms and the spacecraft are examined to give the mechanism designer insight to the implications of this important interface to the spacecraft.
  10. Structural Dynamics. 
    Spacecraft and general structural dynamics are presented to give the mechanism designer insight into the structural aspect of mechanisms and into the interface with the larger spacecraft structure development.
  11. Structural Metals. 
    The most common structural metals or mechanisms including stainless steel, titanium, beryllium and others are reviewed, presenting the characteristics of most interest for mechanisms.  Materials usage for springs and bearings are presented as specialized applications.
  12. Composite Materials. 
    The most common composite materials for mechanisms are examined presenting the characteristics of most interest for mechanisms.
  13. Reliability and Simulation Techniques. 
    Torque Margin analysis is presented and discussed.  Mechanism simulation techniques are presented along with reliability assessment methods.
  14. Contamination. 
    Contamination considerations both from the mechanism to the satellite and into the mechanism are studied.
  15. Radiation and Survivability. 
    The radiation environment and survivability implications for the mechanism are presented.


Instructor: Bill Purdy

Bill Purdy has 31 years of hands-on experience in the space engineering field with wide-ranging involvement in both spacecraft mechanisms and systems engineering disciplines.  Mr. Purdy has been one of the leaders of the space mechanism industry’s transition from explosive release mechanisms to non-explosive devices.  His involvement in numerous space endeavors includes key roles on 33 successfully flown spacecraft, work on well over 30 flown mechanisms including gimbals, release mechanisms, deployables and many other types of mechanisms.  As an educator and space industry consultant to both government and industry, Mr. Purdy applies this broad experience to bring out a clear understanding of the space mechanisms, definition, resolution and integration of mechanism requirements and their relationship to the overall system program success.  Mr. Purdy was the Associate Editor of the industry-standard handbook Space Vehicle Mechanisms – Elements of Successful Design and was the author of the chapter on non-explosive release mechanisms.   He has published eight Aerospace Mechanisms Symposia Papers and was the 1999 winner of the Herzl Award.  Mr. Purdy holds a BSME from the University of Maryland.



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