glast lat projectquarterly review of the glast/lat project, august 14, 2001 martin nordby1 glast...

GLAST LAT Project Quarterly Review of the GLAST/LAT Project, August 14, 2001

Martin Nordby

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GLAST Large Area Telescope:GLAST Large Area Telescope:

Mechanical Systems

Martin NordbyStanford Linear Accelerator CenterMechanical Systems Engineer

[email protected]

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope


Martin Nordby

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OutlineOutline

Issues and Recommendations from previous reviews

Technical status

LAT analysis

Structural analysis

Thermal Systems Analysis

Interface design

Technical issues

Schedule

Cost issues


Martin Nordby

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LAT Mechanical LayoutLAT Mechanical Layout

Thermal/micro-meteorite shield (MLI and ceramic blankets)

Radiator (aluminum)

LAT Model with Radiators and Subsystem Stay-ClearsLAT Model with Radiators and Subsystem Stay-Clears

Grid support structure (aluminum)

Spacecraft mount points (4x)

Radiator mounts to SC

Heat pipes on top of Grid (aluminum)

Anticoincidence Detector (ACD) surrounds TKR

Tracker (TKR) mounts to top flange of Grid

Calorimeter (CAL) inside Grid

Electronics (Elec) mounts to CAL bottom plates

Radiators mounts to Grid and Spacecraft (SC)


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Issues from May 2001 Quarterly ReviewIssues from May 2001 Quarterly Review

• Transient thermal behavior of the LAT– Issue 1: transient behavior is driven by LAT, Radiator, and SC

operating scenarios, none of which are well defined

– Action: GLAST operating scenarios being set and reflected in updated IRD; Radiator and LAT operating scenarios becoming understood

– Issue 2: transient response of LAT has never been modeled

– Action 2: transient response of LAT and Radiators fully modeled, and design of thermal control system updated as a result; More analysis in progress

• LAT—Spacecraft interfaces– Issue: design, structural and thermal interfaces are still immature

– Action: some progress during SC study; still an issue

• Grid prototyping– Issue: prototype testing must be done to validate FEA model details

– Action: prototyping thus far shows design carries >75% margin in CAL joint. Further CAL and Grid heat pipe prototyping underway


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Recommendations from the Feb 2001 ReviewRecommendations from the Feb 2001 Review

• Finish performance specifications by PDR– LAT-SP-00010 “LAT Performance Spec” revision in-progress to

reflect better understanding of operations and thermal requirements

– LAT-SS-00115-1-D4: Mechanical Systems Spec finished draft ready for approval by LAT project

– Missing: Mechanical Systems Level IV spec’s for Grid, Radiators, Thermal Control System being drafted now (drafts complete by PDR)

• Finish interface control documents by PDR– LAT-DS-00038-2-D3: LAT Instrument Layout

– LAT-SS-00273-1-D3: LAT-Cal Mech Interface Control Document

– LAT-DS-00233-1: CAL-LAT Interface Definition Drawing

– LAT-SS-00241-1-D2: LAT-ACD Mech Interface Control Document

– LAT-TD-00224-1-D1: LAT Thermal Design Parameters Summary

– LAT-TD-00225-1-D1: LAT Dissipated Power for Thermal Design

– LAT-TD-00227-1-D0: LAT Thermal Operations Assumptions

– Missing: TKR and Electronics Mechanical ICD’s (drafts complete soon after PDR)


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Structural AnalysisStructural Analysis

• LAT2 finite element model delivered• Modal analysis results

– Drum-head mode, F4 = 64.8 Hz

– IRD Requirement: > 50 Hz

• Structural analysis

– Bowing of Grid closes 2.5 mm gap between TKR modules by 0.39 mm

– LAT stiffness dependent on CAL bottom plate

LAT Distorted-Shape Axial Deflection LAT Distorted-Shape Axial Deflection Contour PlotContour Plot

Drumhead modeDrumhead modeF4 = 64.8 HzF4 = 64.8 Hz

-Back out bolt forces-Design joint, pick bolt

-Torque test-Tensile test-Validate FEA model with shear pull test

Detail of FEA Model at CAL MountDetail of FEA Model at CAL Mount

Tensile Test ofTensile Test ofCAL JointCAL Joint


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Thermal Systems DevelopmentThermal Systems Development

• TSS reduced thermal radiation model delivered• LAT on-orbit transient thermal model complete

– Used to characterize LAT performance due to varying environmental heat loads

• Radiator development– Detailed Radiator thermal model complete

– Design decisions:• Two thermally coupled 2.7 m2 Radiators on opposing Y-sides• Variable-Conductance Heat Pipes to regulate Radiator active area,

compensating for variations in heat loading• Active control system to operate VCHP’s and keep LAT

temperature stable to +/- 3 oC

– Detailed mechanical design and structural analysis just beginning• This is starting late, the result of delays in Radiator work start-up,

and needed changes to their thermal design• Planning to catch up to schedule this fall


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Thermal Systems Development (2)Thermal Systems Development (2)

• LAT steady-state thermal behavior – 650 W of dissipated power

– Grid bows 173 m due to temperature gradients

– TKR tips 22 arc-sec

– Requirement: 30 arc-min

• LAT performance due to +/- 3 oC swings in Radiator temperature– Transient temp gradients tip TKR’s

– Tipping: 3.7 arc-sec

– Req: max misalignment = 7 arc-sec

• Response to time-varying process power draw– TKR tip = 3.0 arc-sec for P = 68 W

– Req: tip < 7 arc-sec for P = 350 W

– Design mod: shunt electronics heat directly to Radiators Distorted-Shape Temperature Contour PlotDistorted-Shape Temperature Contour Plot

(red = hotter)(red = hotter)

Tip = 3.7 arc-sec

Temp Variation for 5.25 OrbitsTemp Variation for 5.25 Orbits(red = Rad interface, blue = CAL plate)(red = Rad interface, blue = CAL plate)

Tmin = -0.3 oC


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Interface DesignInterface Design

• CAL joint– Prototype testing underway: Grid, bolt, joint design strength OK Interface looks solid, with no surprises in view

• TKR interface– Flexure design in place and TKR is prototyping joint for EM tests Design looks good, but testing needs to resolve thermal, structural

questions (how to align flexures; affect of thermal gasket on structure)

• ACD– Conceptual design in place, thermal interface design in-progress Interface may need modification if ACD tile coverage is modified

• Spacecraft– Interface development held up due to export-control issues

– Legal hurdles recently cleared, and progress is now re-starting Will not be able to baseline an interface design with SC before PDR


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Technical Issues ListTechnical Issues List

• Spec’s and ICD’s– Issue: level 4 spec’s and ICD’s are not yet complete

– Response: expect completion of 90% of drafts by PDR

• Thermal systems development– Issue 1: Radiator design is immature for PDR

– Response 1: Contractor is ramping up on personnel to develop conceptual design

– Issue 2: Electronics thermal design is very immature

– Response 2: Handling thermal transients by shunting power to Radiator is being baselined. Planning EM test and analysis of this

• Spacecraft interface design– Issue: Design has not matured adequately for PDR

– Response: Export-control issues have been resolved, and progress is re-starting. We will miss PDR, but expect conceptual baseline by early CY2002


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Mechanical Systems ScheduleMechanical Systems Schedule

• Scheduling– Mechanical Systems schedule is being final-checked for baseline

• Check links to I&T• Find and resolve budget phasing discrepancies between budget

and cost-loaded PMCS schedule

• Status– In general, we have slipped with respect to the schedule

• Short staffing of budgeted positions• Late start of thermal contract

– Expect to make up schedule variances during EM development, since this program is being scaled back• New I&T Manager and Engineer will unload Mech Systems

personnel from double-duty work• Thermal contract in-place (possibly approved today)


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Cost IssuesCost Issues

• Budget vs proposal estimate– Current budget of $RYM8.5 is high by $RYM3.5

– Areas where cost grew• Corrections for lost system-level analysis, reserve, and overhead• Addition of EM test program, Qual. Grid test program

• Issues in investigating de-scoping options– Engineering model

• Current budget includes ~$700k for EM thermal-vacuum testing• We are planning to scale this back to a minimal EM program with

moderate additional risk

– Qual Grid• Qualification test of Grid and Radiators (thermal, mass models)• Budget includes ~$800k for Qual Grid fabrication• This reduces technical and schedule risk of qual testing flight

hardware at the end of the program

glast lat projectquarterly review of the glast/lat project, august 14, 2001 martin nordby1 glast...

Documents

lat issue

pdr latds

lat projectlatss

transient response of

lat operating scenarios

pdr latsp

thermal requirements

lat dissipated power