minimized and reliability maximized if the geometry is dim ensioned to allow for “natural separation”  concepts. However, the need for a controlled separation event necessitates the use of applied force  actuators to overcome any potential external forces. The la st lesson learned was that there exists a very  steep curve between separation clearance and the vehicle main parameters of mass, inertia and geometry with that sensitivity often resulting in inadequate clearance dynamics.  Summary  The simulations conducted indicate that a low fidelity, 2-D equations of motion model can be useful in  separation mechanism design. It provides insight into separation events and the many parameters and  their relative sensitivities. A more detailed 3-D geometric dynamics model is also required to clearly define  the actuator requirements while accounting for all factors in  three dimensions and  can also identify  interferences due to other hardware on the vehicle. The overall design conclusions drawn are that a simple, dependable spring system can be used for the Orion crewed vehicle separation system.  Minimizing the actuator force is preferred in terms of mass, reliability, and cost. However, ensuring the  separation system controls the event and all potential external forces is still paramount. This is especially true in an abort scenario. Additional effort needs to be invested to assure second order effects due to  propellant slosh or thruster imbalance does not violate the design criteria used in the analysis.   Acknowledgments  The authors would like to acknowledge the contributions, advice, and suggestions of Keith Schlagel and  Lance Lininger of Lockheed Martin Corporation who aided in the development and compilation of this  work.  References  1.http://www.spacex.com/media.php?page=57 2. Onoda, J. “The Development of Staging Mechanisms for the Japanese Launcher Mu-3SII,” 19th  Aerospace Mechanisms Symposium, NASA Ames Research Center, August, 1985.  3. Harrington, T.G. “Compression Spring  Separation Mechanisms,” First Aerospace Mechanisms  Symposium, University of Santa Clara, Santa Clara, California, May 19-20, 1966.  4. Abdul Majeed, M. K., Matarajan, K., Krishnankutty, V. K. “Separation and Staging Mechanisms for the  Indian SLV-3 Launch Vehicle,” 18th Aerospace Mechanisms Symposium, NASA Goddard Space  Flight Center, May 1984.  5. AIAA-S-114-2005, Movinq Mechanical Assemblies Standard for Space and Launch Vehicles , American Institute of Aeronautics and Astronautics standard, July 2005.  6. Conley, Peter L. Space Vehicle Mechanisms,  New York, John Wiley & Sons, Inc. 1998.  7. Brennan, Paul C., NASA Space Mechanisms Handbook,  July 1999.  8. Purdy, W., Hurley, H., “The Clementine Mechanisms,” 29th Aerospace Mechanisms Symposium,  NASA Johnson Space Center, May 1995. 9. Hanna, W. D., Chang, R. S., Sheckel, G. L., “Stress Relaxation of Spring Materials,” Fortieth  Anniversary: Pioneering the Future, May 1998.  10. Chew, M. “On the Danger of Redundancies in Some Aerospace Mechanisms,” 22nd Aerospace  Mechanisms Symposium, NASA Langley Research Center, May 1988.  11. Holmanns, W., Gibbons, D., “Misconceptions in Mechanical Reliability,” 34th Aerospace Mechanisms  Symposium, NASA Goddard Spaceflight Center, May 2000.  12. Simulink program Ver.7.0.1.29704, The Math Works Corporation, September 2004.  13. ADAMS dynamic software code Ver. 2005 r2.0, MSC Software Corporation, August 2005.   358