Telescope - Mechanical Albert Lin The Aerospace Corporation Mechanical Engineer (310) 336-1023 albert.y.lin@aero.org 6/27/05

Problem Statement The CRATER Telescope must: Hold three pairs of thin-thick detectors Hold two samples of TEP Be configured to meet geometry for science mission Hold interface circuit boards Subject to: Positive stress margin for all environments Minimum first fundamental frequency Weight constraints of overall instrument

Telescope Requirements Mechanical Requirements Design Details Overview Telescope Requirements Mechanical Requirements Design Details Trade Studies

Telescope Requirements From Level 2 Mission Requirements Document 32-01205 Section Requirement 3.1.1 Pairs of thin (approximately 150 micron) and thick (1000 micron) Si detectors 3.2.1 0.030” thick aluminum wall on both ends of the telescope 3.3.1 A-150 TEP of 27 mm and 54 mm in length 3.5.1 30 degree FOV zenith, 80 degree nadir All requirements incorporated into model

Telescope Geometry All Requirements Met Pairs of thin (~150 micron) and thick (~1000 micron) Si detectors used 0.030” thick Aluminum on top and bottom apertures A-150 TEP of 27 mm and 54 mm in length 30 degree FOV Zenith 80 degree FOV Nadir

Telescope Requirements Mechanical Requirements Design Details Overview Telescope Requirements Mechanical Requirements Design Details Trade Studies

Mechanical Requirements From Environments, 431-RQMT-000012 All components must have positive stress margin with an appropriate factor of safety used for the material analyzed Requirement Description Levels 3.1.2 Net cg limit loads Superceded by Random Vibration 12 g 3.4.2 Sinusoidal Vibration Loads Frequency: 5-100 Hz Protoflight/Qual: 8g Acceptance: 6.4g 3.5 Acoustics Enclosed box without exposed thin surfaces OASPL Protoflight/Qual: 143.0 dB OASPL Acceptance: 140.0 dB 3.6.1 Random Vibration See next slide 4.2.1 6.0 Minimum Fundamental Frequency Minimum > 35 Hz Recommended > 50 Hz Will not provide FEM model > 75 Hz

Random Vibration Random Vibration will drive most of the analysis For resonances in the Random Vibration Spec, Miles’ Equation shows 3 sigma loading on the order of 100-150 g

Stress Margins Load levels are superceded by random vibration spec Factors of Safety used for corresponding material (MEV 5.1) Metals: 1.25 Yield, 1.4 Ultimate Composite: 1.5 Ultimate Margin of Safety = (Allowable Stress or Load)/(Applied Stress or Load x FS) – 1 Description MS yield MS ultimate Bolt Interface Loading +2,662 +5,615 Detector Boards brittle +18.6 Silicon Detector* +31.5 TEP Clamp +0.91 +1.21 All components have positive Margin of Safety *Assumes an ideal 3-point mount, to be discussed later

First Fundamental Frequency First Fundamental Frequency at 1,410 Hz Much greater than 75 Hz frequency where the FEM model will not need to be supplied

Telescope Requirements Mechanical Requirements Design Details Overview Telescope Requirements Mechanical Requirements Design Details Trade Studies

Design Overview Telescope is assembled using card guides for the circuit boards and screws for the TEP holders

Overall Dimensions Weight = 2.7 lbs

How to Mount TEP Limited Material Properties information on A-150 TEP Need to mount TEP to account for Minimal deformation of material during assembly Allowance for thermal contraction 20 lbs preload to withstand random vibration Springy Clamp Cross Section TEP Solution: Oversized mounting hole to allow for radial thermal expansion with a thin, springy clamp to hold in TEP. With differential thermal contraction at -40°C, spring still pushes with 7.4 lbs force

Mounting Detectors Detectors mounted using three point mounts on circuit boards to minimize stress caused by circuit board vibration Further investigation needed for the effectiveness of the three point mount interface Thin Detector Wires strain relieved away from mount to minimize stress from vibration Thick Detector on Underside

Purging and Venting Purge Inlet Purge and Vent Outlet Detector Mounts suspended above circuit board allows for gaps that equalize pressure

Telescope Requirements Mechanical Requirements Design Details Overview Telescope Requirements Mechanical Requirements Design Details Trade Study

Trade Study A limitation to the current design is the uncertainty of the detector mounting scheme in minimizing the effects of circuit board vibration An alternative design is to clamp the detectors in a stiff structure and decouple it from the circuit board using cables The detectors are tested at the manufacturer in a similar configuration but there are issues with using Rigiflex cables ?

Telescope – Mechanical Albert Lin

Backup Slides

Bolt Interface Loading Assuming worst-case loading at 1410 Hz fundamental frequency 3 sigma load = 125 g A286 CRES Bolts at Interface Worst Case Bolt Mechanical Engineering Design, by Shigley RP-1228 NASA Fastener Design

Detector Board Resonance First Mode: 1237 Hz Total nodes: 60546 Total elements: 33546 COSMOSWorks 2005

Detector Board Stress Using Miles Equation, assume Q = 15, FS = 1.5 3σ g loading = 133g Max Stress = 1,527 psi MS ultimate = 45,000 psi / (1.5 * 1,527 psi) - 1 = 18.6

Thin Detector Analysis Assuming Detector is mounted on an ideal 3 point mount, the silicon behaves linearly, and Q = 15 Fundamental Frequency = 1795 Hz, which yields 3 sigma load of 111g Margin of Safety = (17,400 psi / (1.4 * 382 psi) – 1 = 31.5

TEP Thermal Contraction Analysis of Beryllium Copper clamp TEP CTE assumed to be same as polyethylene, 77.8 μin / in-°F During launch, temperature is ~70°; TEP clamp exerts 20 lbs to resist vibration During cold survival mode at ~-40°, TEP clamp still exerts a preload of 7.4 lbs. The preload is lower due to the relative thermal contraction All stress margins are positive

Sensitivity Analysis Preceding calculations used a nominal Q of 15 This table shows how the 3 sigma g-loads vary with Fundamental Frequency and Q Most structures have Q between 10 and 20

Factors of Safety Used

Material Properties MIL-HDBK-5J 1 1 1 2 3 MIL-HDBK-5J Silicon as a Mechanical Material, Proceedings of the IEEE, Vol 70, No. 5, May 1982, pp 420-457 Boedeker Plastics via www.matweb.com