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Analysis

Requirements

Analysis is being conducted to ensure that the following requirements placed on MidSTAR are met:

From the mission statement:

"MidSTAR is intended to be a relatively low-cost, quick response platform, accommodating small payloads approved by the DoD Space Experiments Review Board (SERB) and awaiting launch through STP."

In order to achieve this goal, the MidSTAR team opted to forgo detailed stress analysis relying instead on a robust test program to verify the strength and reliability of the structure design.  To mitigate the risk of a test failure, experienced engineers, technicians and machinists were consulted with throughout the design process.

Derivation of design loads: ESPA class payload users guide

Coupled loads analysis: TBS by launch vehicle provider

Analysis Status

The following analysis has been done to date:

Finite Element Model

FEM bending modes (first ten)

Fastener Analysis

Hand calculations for stress in decks and side panels (see table below)

Factor of Safety/Margin of Safety Table For Hand Calculations and FEM Results        
               
Required FOS: 1.25                
Required MOS: 0.25                
Required launch load (minimum): 10.6 g's                
               
Fastener Analysis:                
Scenario mass (kg) g's preload % # bolts mu FOS    
Battery box, loaded in all three directions at once 11.26 15 N/A 4 N/A 19.1    
Battery box, loaded in shear only, with friction 11.26 15 0.5 4 0.5 17.2    
MidSTAR, friction calc to ensure it won't "rack" 120 15 0.5 12 0.5 14.5    
               
Static Loads:                
Max allowable stress (Pa) Actual Max Stress (Pa) MSu MSt
Shelf with heaviest load (shelf with battery box) 1.50E+08     1.37E+08     0.53 0.37
Side Panel 4.49E+04     2.53E+04     1.49  
               
Finite Element Model:                
First Mode frequency Minimum FOS            
72.1 Hz 35 Hz 2.06            

The following equations were used to calculate margins of safety:

MSu = (FSu * Ftu) / Fact -1 > 0

MSy = (FSu * Fty) / Fact -1 > 0

Where

    Msu is the ultimate strength margin of safety

    Fsu is the factor of safety for ultimate strength (Fsu=1.4 for aluminum structure)

    Msy is the yield strength factor of safety

    Fsy is the factor of safety for yield strength  (Fsy=1.25 for aluminum structure)

 

The following analysis and testing remains to be completed: