NASA Goddard Space Flight Center

Systems Engineering Seminar

Designing and Managing for Reliability of Zero

Presented by:
Mike Hurley, Naval Research Laboratory
Bill Purdy, Purdy Engineering

May 3, 2011, 1:00 p.m.
Building 3 Auditorium


Designing and Managing for Reliability of Zero

The goal of this presentation and paper is to provoke the reader to evaluate their thoughts on reliability. All space systems desire high reliability however, if a program delivers late, then the true reliability for users is zero for every year it is late. Ironically, efforts to achieve high reliability often prove counterproductive. The lack of a sound understanding about reliability can drive unnecessary design complexity, excessive process controls, unacceptable costs, schedule delays, and reduced availability to the user. This paper discusses what reliability is, and what it is not, while highlighting common misunderstandings that often mislead designers and managers. Historical space and non-space systems are examined as tangible examples studying the effects of various philosophies and approaches. Ultimately this paper strives to advance the industry-wide understanding necessary to better achieve reliable, available systems for users.



Photo of Mike Hurley Mike Hurley is the Spacecraft Development Section Head at the Naval Research Lab in Washington DC. His work experience includes mission formulation, spacecraft design, integration, testing, flight operations, and user interfacing. His previous and active programs include Clementine, TiPS-Tether Physics & Survivability experiment, NEMO hyperspectal program, SLDCOM tactical UHF comms, TacSat-1, TIE AIS Payload, TacSat-4, Virtual Mission Operations Center (VMOC), and National programs. Mr. Hurley was involved in shaping and implementing Operationally Responsive Space (ORS) and TacSat experimentation as the program manager for OSD’s ORS Initiative beginning April 2003. He is also the principle investigator for Office of Naval Research’s Tactical Microsatellite “Space INP” program. In 2005 he received the DoD Civilian Meritorious Medal. He is an engineering graduate of Virginia Tech, a MBA graduate of George Mason University, and holds his Professional Engineering license in the state of Virginia.


Photo of Bill Purdy Bill Purdy has 24 years of hands-on experience in the space engineering field with wide-ranging involvement in both spacecraft mechanisms and systems engineering disciplines. His involvement in numerous space endeavors includes key roles on over 25 successfully flown spacecraft, work on over 30 flown mechanisms including gimbals, release mechanisms, deployables and many other types of mechanisms. Mr. Purdy is currently the lead systems engineer for the Microwave Imager/Sounder flight program and has led systems engineering efforts for developmental robotic systems and other flight sensors. 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 seven 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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