A Multi-Disciplinary Approach to Calculate Displacement Due to Random Vibration For A Space Based Focal Plane Anthony J. Davenport Senior Mechanical Engineer Northrop Grumman, ESSS FEMCI Conference

Focal Plane Geometry Housing Filter (x6) Cover Flex Cable Strain Relief

So What Is The Problem? Focal Plane Cross-Section Cover Filter Housing Gap of Concern Sensors 1. Out of Plane Bowing from Cryogenic Loading 2. Random Vibration Displacement of the Cover 3. Lack of Material Properties (Adhesives)

Design & Analysis Path for the Focal Plane Housing Deflection Housing Deflection Bolt Analysis Bolt Analysis Simplified Model Simplified Model Simplified Testing Simplified Testing Model Refinement Model Refinement Apply To Detailed Model Apply To Detailed Model Phase I: Thermal Testing & Correlation Phase II: Detailed Thermal Analysis & Results Phase III: Random Vibration Testing & Correlation Phase IV: Detailed Flight Hardware Analysis & Results Displacement Analysis Displacement Analysis Stress Analysis Stress Analysis Bolt Analysis Bolt Analysis Pre-Qual Testing Pre-Qual Testing Results Testing Results Model Refinement Model Refinement Goals For RandomVib. Goals For RandomVib. Proven Design Proven Design Define Problem Define Problem

Thermal Expansion Analysis Method l Create a simplified model in PTC’s Mechanica using mechanical properties determined by the NG materials group. –Run model between 295 ºK to 110 ºK (  T = 185 ºK) –Examine relative displacement in the out-of-plane direction (Z) l Compare results to testing completed in laboratory and correlate model. l Apply what is learned to detailed model.

Simplified Test Model Dial Gages (x3) Molybdenum Adhesive Substrate TemperatureSensors Cold Finger With Heater Element

Laboratory Test Setup Focal Plane Cold Finger & Heater Measuring Dials (x3) Three Dial Gages Touch The Focal Plane in 3 Locations to Measure Bowing in Focal Plane Temperature Range 295 ºK ºK

1 / 4 Simplified Analysis Model Molybdenum Adhesive Substrate Symmetry Constraint, Y Constraint, Z on Bottom Curve Substrate Substrate Removed Symmetry Constraint, X

Relative Displacement Results From Testing & Analysis Analysis Model Testing Comparison

Detailed Analysis Model Uniform Temperature Load: Cure to Cryogenic (295 º K to 110 º K) Molybdenum Ceramic Substrate Mounting Surface Z Constraint Mounting Surface Z Constraint X,Y Constraint Focal Plane Bows 5.3  m, or +/- 2.6  m Across a Mid-Plane

Random Vibration Derived Requirements From Cryogenic Analysis

Random Vibration Test Setup

Test Setup Focal Plane Accelerometers

Test Results: Housing Mode 2: 1717 Hz Mode 1: 1513 Hz 39.3 G rms

Testing Results: Cover Mode 2: 1717 Hz Mode 1: 1513 Hz G rms

What Can Be Derived From Test? 3  Absolute Displacement Damping Factors Relative Displacement (500 Hz Hz): /- mil Using Method Discussed in Appendix B (3% Diff.)

Method of Correlation l Match the Frequency of the Test Model –Boundary Conditions –Mass of Components –Stiffness l Geometry l Material Properties l Match the Displacement –Acceleration PSD Input –Damping Value:  = 1/(2Q)

Matching Frequency Iso - View Aniso - View Geometry: Built from Unigraphics Model Boundary Conditions: Bolt Stiffness Applied Mass from Tested Components Materials: Varied Young’s Modulus for Molybdenum within range found in multiple sources.

Matching Frequency Results Mode 1: 1477 Hz (2.4% Diff) Mode 1: 1717 Hz (0.0% Diff)

Matching Displacement l Adjust PSD Input to Match Testing. –Tolerance allowed for a +1 dB overall variance. –For a small response, this makes a large difference. –It was found that the PSD input was +0.4 dB higher than Specification. l Adjust Damping to fine tune the model (  = ) l mil Deflection (0.042 % diff. from testing) for Hz.

Conclusions l Bowing due to Thermal Expansion is determined by defining material properties via testing, modeling, and correlation. l Cryogenic deflections help drive the random vibration allowable. l Random vibration correlation helps in examining future changes to the focal plane design and it’s inputs.