AAE450 Spring 2009 Support structure for Orbital Transfer Vehicle (OTV) Tim Rebold STRC [Tim Rebold] [STRC] [1]

AAE450 Spring 2009 Propulsion System Support Structure  Truss / Frame –Statically determinate Less members, less complex More efficient (mass savings) –Only carry axial loads Hard to realize Joints need to carry predicted bending & shear –Loads (launch) are evenly distributed [Tim Rebold] [STRC] *Not to scale **Contingency mass unrepresented Electronics Module Xenon Tank & Propellant Plumbing / Valves / Etc. m = 1.6 kg m = 106 kg m = 5.7 kg Thruster Reduces cabling Easier Integration Easier Testing Thermal balance issue PPU PSU Longer cabling [2]

AAE450 Spring 2009 OTV Configuration [Tim Rebold] [STRC] *Not to scale Electronics Module Propulsion System & Support Structure Lander A A  Conclusions  Primary Mass: 31 kg  Support Mass: kg  M inert budget: <3.76 kg f inert = 0.3  Goals –Center of Mass (CM) as close to aft (base) of spacecraft (s/c) –Design truss efficiently to minimize mass –Factor of Safety = 1.5 [3]

AAE450 Spring 2009 References [Tim Rebold] [STRC] (1) Delta II Payload Planners Guide Guide_Update_0103.pdf (2) Skullney, W.E. Fundamentals of Space Systems. 2 nd Edition. Ch. 8, pp Oxford University Press, (3) “Properties of Materials.” Purdue University. kk kk (4) Sun, C.T. Mechanics of Aircraft Structures. New York: John Wiley and Sons, (5) Dnepr User’s Guide uide.pdf uide.pdf (6) Larson, W.J. Spacecraft Structures and Mechanisms. Microcosm, Inc., 1995 [4]

AAE450 Spring 2009 Future Work  Mount Solar Arrays, Reaction Control Wheels, Antenna, and Thermal components into OTV  Matlab script –Read data from Excel spreadsheet to calculate entire OTV (with payload) CM, and inertia matrix (about CM coordinates) in stowed (launch) and deployed (trans-lunar) stages  FEM analysis –Obtain better approximation of CM and inertia values –Perform modal analysis to see if OTV meets stiffness requirements placed on launch vehicle payloads [Tim Rebold] [STRC] [5]

AAE450 Spring 2009 OTV CM Tracker - Current Best Estimate (Axial) [Tim Rebold] [STRC] *Not to scale Electronics Module, 1.25m, 24.3 kg PPU PSU Lander, 1.75 m, 220 kg Acronyms PPU: Power Processing Unit PSU: Power Supply Unit RCS: Reaction Control System M OTV = 550 kg CM = m x 0 m 1.5 m 1 m Structural / Thermal Control, 0.75 m, kg Xenon Tank & Propellant, m, 106 kg Solar Arrays, 0.50 m, 13.3 kg Electric Propulsion Thruster, 0.10 m, 5.7 kg Antenna / Mount, 0 m, 9.12 kg RCS Wheels, 0.05 m, 6 kg Feed system & Contingency Mass, 0.45 m, 4.7 kg [6]

AAE450 Spring 2009 Truss Configuration – 2D Planar [Tim Rebold] [STRC] F 1y F 1x F 2x F 2y R 2x R 1x R 1y Distributed forces from propulsion system through launch 4 joints (j) 4 Reaction DOF’s (r)* 4 members (m) 2j = m + r 8 = 8 Stability Criterion *4 th reaction DOF not utilized for given applied loads Aluminum 7075-T6 material selected for all structural elements [7]

AAE450 Spring 2009 Support Structure Analysis Summary [Tim Rebold] [STRC] [8] Propulsion Frame Support MemberCross Sectional Area (mm 2 ) Electronic Module Support No. Beamst (mm)b (cm)h (cm) SYSTEM SUPPORT MASS Mass (kg) Equatorial Mount4.48 Bottom Mount1.08 Frame1.61 Electronic Module8.07 Total15.24 t b h

AAE450 Spring 2009 Dimensions [Tim Rebold] [STRC] *Not to scale Electronics Module PPU PSU [9] 0.5 m m m 0.2 m φ = m m m 1.03 m

AAE450 Spring 2009 Tank Support - Equatorial Mount [Tim Rebold] [STRC] *Figure based from Reference 6 Tank Mounting Flange Support Structure Bolted Attachment Xenon Tank To avoid high shell stresses, introduce loads tangentially to tank surface rather than radially [10]