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Mechanical Systems

Mechanical Systems. Martin Nordby Stanford Linear Accelerator Center Stanford University GLAST LAT Mechanical Systems Engineer nordby@slac.stanford.edu. Mechanical Systems. Overview Mechanical Systems work breakdown and organization Parameters management Technical update

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Mechanical Systems

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  1. Mechanical Systems Martin Nordby Stanford Linear Accelerator Center Stanford University GLAST LAT Mechanical Systems Engineer nordby@slac.stanford.edu

  2. Mechanical Systems • Overview • Mechanical Systems work breakdown and organization • Parameters management • Technical update • Scheduling and milestones • Budget summary • Issues Outline

  3. Large Area Telescope (LAT) Design Overview Tracker Thermal Shield Anticoincidence Detector Grid Structure Calorimeter Electronics

  4. LAT Mechanical Layout Radiator mounts to SC Thermal/micro-meteorite shield (MLI and ceramic blankets) ACD Tracker Calorimeter Grid support structure (aluminum) Heat pipes on top and sides of Grid (aluminum) Spacecraft mount points (4x) Radiator (aluminum) LAT Model with Radiators and Subsystem Stay-Clears

  5. Mechanical Systems Work Breakdown • Mech Systems WBS maps to the three key functions of the subsystem • Mechanical Design Integration • 4.1.8.1 Management: SC interface development; materials • 4.1.8.2 Reliability and Quality Assurance • 4.1.8.3 Mechanical Systems Development: mech design, analysis • 4.1.8.4 Thermal Systems Development: thermal design, analysis • System-Level Hardware Development • 4.1.8.5 Thermal Control System • 4.1.8.6 Radiators • 4.1.8.7 Grid: development and fab of Grid support structure • LAT I & T Support • 4.1.8.8 Subsystem Integration and Test: verification testing • 4.1.8.9 LAT I&T Support • 4.1.8.A Mission I&T Support

  6. Mechanical Systems Organization

  7. Parameters Management: Mass • Mass estimate • Current estimates rolled up from subsystem details, supplied by subsystem engineers • Estimates updated quarterly • Reserve analysis from ANSI/AIAA G-020-1992 • Independent reserve analysis for Proposal supports AIAA estimating analysis • Analysis plans for controlled draw-down of reserve

  8. Review Threshold Current Estimate LAT Mass Budget LAT Mass (kg) TKR 487 CAL 1463 ACD 199 Mech 192 Elec 180 Other 0 Total2521 (Eff. Date: 18-Jan-01) Proposal SRR Feb-01 JOG PDR CDR PSR Budget (kg) 2600 2600 2725 2725 2850 2960 Estimate (kg) 2557 2572 2521 Date Nov-99 Sep-00 Jan-01 Aug-01 Aug-02 Oct-04 Threshold (kg)

  9. Parameters Management: Dimensions and Volume • Three sets of interface volumes being defined • Stay-clear dimensions: subsystem volume allocation managed by table and LAT stay-clear drawing • Integration allowance: the volume and access needed for subsystem integration • Operational stay-clear: region needed for expected static or dynamic motion (a.k.a.: gaps) • ICD’s will be developed for each subsystem, as information about the interfaces matures

  10. Key Requirements • Thermal • Total dissipated power (orbit average) < 650 W • 35 °C operational temp range (-10 °C to +25 °C) • Stiffness: first-mode natural frequency > 50 Hz • Stability: pointing error knowledge < 10 arc-seconds • Operations: point anywhere, anytime • Mass: total mass < 3000 kg • Volume: footprint and center-of-gravity constrained to dimensions in the SI-SC IRD

  11. Technical Status: Thermal-Mechanical Analysis • Analysis to understand thermal behavior of the LAT • Total power dissipated: 518 W • Heat pipes used for channeling heat to perimeter of LAT • Minimize transverse temperature gradients • Reduce peak temperature of the TKR • Steady-state analysis results • Heat conducted up to heat pipes • 40% of heat from Grid base • DT = 4 deg C • Grid bows due to gradients • +/-120 mm • Concave upward • TKR’s tip due to Grid bow • DX = 100 mm at topof TKR module • Angle = 42 a-sec • 1.5 mm gap closes by 100 mm 3/8” Heat pipes on sides held to 0 deg C ACD and SIU boxes in corners cause corner hot spots (5 C) Temperature Contour Plot of LAT(half-model, looking at symmetry plane)

  12. Technical Status: Dynamic Response to Launch • Investigating modes and deflections due to launch loads • 4- vs. 8-point mount to spacecraft • LAT stiffness from CAL, TKR • Dynamic motion of TKR • Modal analysis • Drum-head mode, F2 = 60.5 Hz • CAL bottom plate stiffens Grid • Spacecraft mount • 4 and 8-point mount resultsin same drumhead mode • 4-point support results in atwisting mode, F1 = 41.9 Hz • Structural analysis • 1.5 mm gaps between TKR modules close by 396 mm in 6.6 g loading • LAT analysis results used to size hardware for CAL mounting to Grid Drumhead modeF2 = 60.5 Hz • ggd49l5mod2

  13. Technical Status: Thermal Environment Analysis • Determining variations in environmental heat load and effect on the LAT • Extreme cases of orbital radiative heat load • Coupling of changes in external heating to internal LAT temperature • Performance requirements for the Radiators • On-orbit radiation analysis • Worst-case pointed-mode load change: 0 to 500 watts/orbit • Total heat dissipation needed • Generated by LAT: 650 W • Parasitic from SC: 10 W • Environmental load: 250 W (orbit averaged) • Using variable-conductance heat pipes (VCHP’s) on radiators to isolate LAT from external heat source (sun, earth) • Future work • Currently investigating scanning-mode heat load fluctuations for full range of beta angles • Dynamic thermal response of the LAT to variable heat loads on radiators

  14. Interface Design: Calorimeter and Tracker • Calorimeter interfaces • LAT analysis shows that CALbottom plates stiffen Grid • Analysis being used to sizeCAL tabs and hardware • Interlocking tabs leave gapsfor CAL, TKR cable routing • Tracker interfaces • Structural analysis showsthat 1.5 mm gap is adequate • Thermal analysis showsstatic tipping of TKR is OK,with dynamic analysis needed • Flexure support for TKR is being developed now • Accommodates thermal expansion mis-match and and distortion effects between CFC Tracker and aluminum Grid Underside View of LAT Grid

  15. Interface Design: ACD and Spacecraft • ACD interfaces • Modal analysis shows that ACD decoupled from TKR is adequately stiff • ACD structure deepened to carry loads • F1 = 118.3 Hz (top panel) • ACD electronics packaging around perimeter under investigation • Impact on LAT, Grid being evaluated • Spacecraft interfaces • Spacecraft mounting • 4-pt mount minimizes over-constraint • Will investigate alternate concepts to avoid first-mode twisting of LAT • Radiator stiffness and SC mount locations • Proposed 2-pt mount on SC sides • F1 = 77 Hz, with stiffened radiators • Will work with SC Study contractors ACD F1 = 118.3 Hz • acd4el1 • rad12l1mod1 F1 = 77 Hz for Stiffened Radiator with 2-Pt Mount

  16. 4.1.8 Mechanical Systems Schedule • Currently developing Mechanical Systems schedule • Scoping work • Identifying key milestones • Establishing linkages to other subsystems, especially I&T

  17. Mechanical Systems Milestones • Mechanical Systems Requirements Review 04/11/01 • Mechanical Systems PDR 05/23/01 • LAT Instrument PDR 08/06/01 • Engineering Model (EM) Grid Complete 05/10/02 • Mechanical Systems CDR 05/22/02 • LAT Instrument CDR 08/05/02 • Flight Grid Ready for Integration 10/01/03 • Flight Radiators Ready for Integration 08/15/03 • Radiator Thermal Balance Testing Complete 05/21/04

  18. Interim Mechanical Systems Cost Estimate* • Interim cost estimate based on Proposal cost estimate • Currently developing and checking grounds-up re-estimate Escalated k$ *DOE/NASA funding

  19. Issues • Static thermal behavior of the LAT understood; effects of dynamic changes being analyzed • Modelling dynamic changes in temperature, due to external environmental changes • Will work to characterize/specify expected internal dynamic power fluctuations • Investigating thermally isolating heat loads from back of CAL • LAT mounting to spacecraft • SC Accommodation Study includes a coupled-loads analysis to understand possible twisting modes of LAT • Will investigate 4-point and 8-point mounting options with SC contractors • ACD mass and new baseline design • System-level trades are underway • Working with ACD subsystem engineers to understand implications on mass and volume budgets for the ACD

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