Table 5. Stress Results After 1 Iteration, Parts in Tension/Compression  Location Part Deflection (mm) F (N) FEA /g305 (psi) FS FEA /g305 (psi) FS Follower 1 1.10E-01 8.42E+04 2.58E+02 2.73 2.55E+02 2.76 1.011 1.016 Rod 1 -9.77E-02 -2.51E+04 3.48E+02 2.02 3.47E+02 2.03 1.004 0.636 Rod 2 1.37E-01 3.41E+04 2.58E+02 2.73 2.59E+02 2.72 0.997 0.835 Door Rod -4.26E-01 -1.06E+05 8 . 0 7 E + 0 20 . 8 78 . 0 0 E + 0 20 . 8 8 1 . 7 3 E + 0 30 . 4 11 . 7 4 E + 0 30 . 4 01.009 0.832 Follower 1 9.00E-02 6.92E+04 2.12E+02 3.31 2.10E+02 3.36 1.013 1.065 Rod 1 -7.99E-02 -2.06E+04 2.84E+02 2.48 2.83E+02 2.48 1.002 0.632 Rod 2 2.55E-01 6.36E+04 4.78E+02 1.47 4.81E+02 1.46 0.994 0.833 Door Rod -3.50E-01 -8.72E+04 6.61E+02 1.06 6.60E+02 1.07 1.001 0.831 Actuator Rod -3.44E-01 -7.56E+04 0.996 1.271Displacement LBC Force LBC /g305 ratio[i] /g305 ratio[i-1] Aft Hinge Fore Hinge

Although these results do show some components with factors of safety less than one, this does not necessarily mean that closure of the ETD during STS-118  would have resulted in yield. Because the  actual rigged door sag was not known at the time, this analysis did not produce a definitive prediction of  additional stress induced in the door drive linkage. Because the minimum computed factor of safety for 25.4 mm (1 in) of door motion was 0.40, the door co uld be forced to move up to 10.16 mm (0.40 in) at its  outboard edge before allowable stresses would be reached. 

Conclusions  Through the use of MSC/ADAMS, a flexible multi-body dynamic simulation of the ETD DDM was quickly  constructed and used to find linkage deflections. The advantage of this type of analysis is its relative  simplicity compared to a full FEA model of the DDM, combined with preserved accuracy of mechanism  kinematics. This simplicity allows for rapid construction of the model in addition to a reduction in computer computation time. Although complex geometry is re duced to lumped equivalent stiffnesses, the analyst  has the ability to select each flexible degree of freedom that will be of primary interest and include it in the  model. The stiffness used for each of these individual degrees of freedom may then be verified using FEA  and iteratively updated as necessary.   The analysis shows that some components of the ETD have factors of safety less than one and may  undergo plastic deformation. However, this is not conclusive because the forcing of the door is based on  the worst case possible within rigging specifications. To complement the analyses described in this paper, actual rigging data from the Orbiter Endeavour  taken before STS-118 could be used to reach a better  estimate of stress in the DDM. Predicted stresses could then potentially be further confirmed through  experimentation using a training mockup version of the DDM.   Acknowledgement  We would like to dedicate this paper to the memory of Marlon C. Batey. Marlon worked as an aerospace  engineer in the Mechanical Systems Branch at NASA Langley Research Center over the past three  years. Without his contributions to the team, the work described here would have been much more difficult. In addition to his diligence and motivation, it was always a pleasure to work with him. Marlon has  been and will be greatly missed. 

References 

1.  Don Picetti, Thermal Analysis and Test Results for ET Door Paint Striping, Boeing Orbiter Element,  S063244, Daily PRCB Presentation  2 .  Rao, Singiresu S. Mechanical Vibrations, Fourth Edition , Pearson Prentice Hall, 2004  3 . Brinkworth, D. “ET/Orbiter Umbilical Door Mecha nism Installation and Rigging Procedure”, Space  Division Rockwell International, Doc. No . ML0308-0058 rev. C, 1982  4 . MatWeb Material Property Data,  http://www.matweb.com/search/DataSheet.aspx ?MatID=13246&ckck=1  258