GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby1 Mechanical Systems Martin Nordby Stanford Linear Accelerator Center Stanford University GLAST LAT Mechanical Systems Engineer Martin Nordby Stanford Linear Accelerator Center Stanford University GLAST LAT Mechanical Systems Engineer

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby2 Mechanical Systems  Overview  Mechanical Systems work breakdown and organization  Parameters management  Technical update  Scheduling and milestones  Budget summary  Issues Outline

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby3 Large Area Telescope (LAT) Design Overview Grid Structure Calorimeter Tracker Anticoincidence Detector Electronics Thermal Shield

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby4 LAT Mechanical Layout Thermal/micro-meteorite shield (MLI and ceramic blankets) Radiator (aluminum) LAT Model with Radiators and Subsystem Stay-Clears Grid support structure (aluminum) Spacecraft mount points (4x) Radiator mounts to SC Heat pipes on top and sides of Grid (aluminum) ACD Tracker Calorimeter

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby5 Mechanical Systems Work Breakdown Mech Systems WBS maps to the three key functions of the subsystem Mechanical Design Integration – Management: SC interface development; materials – Reliability and Quality Assurance – Mechanical Systems Development: mech design, analysis – Thermal Systems Development: thermal design, analysis System-Level Hardware Development – Thermal Control System – Radiators – Grid: development and fab of Grid support structure LAT I & T Support – Subsystem Integration and Test: verification testing – LAT I&T Support –4.1.8.AMission I&T Support

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby6 Mechanical Systems Organization

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby7 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 –Independent reserve analysis for Proposal supports AIAA estimating analysis –Analysis plans for controlled draw-down of reserve

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby8 LAT Mass Budget LAT Mass (kg) TKR487 CAL1463 ACD199 Mech192 Elec180 Other0 Total2521 (Eff. Date: 18-Jan-01) Review Threshold Current Estimate ProposalSRRFeb-01 JOGPDRCDRPSR Budget (kg) Estimate (kg) DateNov-99Sep-00Jan-01Aug-01Aug-02Oct-04 Threshold (kg)

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby9 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 Instrument Outside Dims (m) WidthHeight Gap between TKR stay-clears Module pitch Instr. max dim SI-SC IRD stay-clear square C.G. of instr off Grid bottom TKR SSD size TKR module stay-clear CAL CsI Logs (W x H x L) CAL Module stay-clear ACD ACD stay-clear inside dim ACD outside dimension Thermal Blanket outside dims Top of Therm Blank from Grid Grid Outside dim of Grid

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby10 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

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby11 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  T = 4 deg C –Grid bows due to gradients +/-120  m Concave upward –TKR’s tip due to Grid bow  X = 100  m at top of TKR module Angle = 42 a-sec 1.5 mm gap closes by 100  m 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)

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby12 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, F 2 = 60.5 Hz –CAL bottom plate stiffens Grid –Spacecraft mount 4 and 8-point mount results in same drumhead mode 4-point support results in a twisting mode, F 1 = 41.9 Hz Structural analysis –1.5 mm gaps between TKR modules close by 396  m in 6.6 g loading –LAT analysis results used to size hardware for CAL mounting to Grid Drumhead mode F2 = 60.5 Hz ggd49l5mod2

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby13 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

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby14 Interface Design: Calorimeter and Tracker Calorimeter interfaces –LAT analysis shows that CAL bottom plates stiffen Grid –Analysis being used to size CAL tabs and hardware –Interlocking tabs leave gaps for CAL, TKR cable routing Tracker interfaces –Structural analysis shows that 1.5 mm gap is adequate –Thermal analysis shows static 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

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby15 Interface Design: ACD and Spacecraft ACD interfaces –Modal analysis shows that ACD decoupled from TKR is adequately stiff ACD structure deepened to carry loads F 1 = 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 F 1 = 77 Hz, with stiffened radiators Will work with SC Study contractors rad12l1mod1 F1 = 77 Hz for Stiffened Radiator with 2-Pt Mount ACD F1 = Hz acd4el1

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby Mechanical Systems Schedule Currently developing Mechanical Systems schedule Scoping work Identifying key milestones oEstablishing linkages to other subsystems, especially I&T

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby17 Mechanical Systems Milestones Mechanical Systems Requirements Review04/11/01 Mechanical Systems PDR05/23/01 LAT Instrument PDR08/06/01 Engineering Model (EM) Grid Complete05/10/02 Mechanical Systems CDR05/22/02 LAT Instrument CDR08/05/02 Flight Grid Ready for Integration10/01/03 Flight Radiators Ready for Integration08/15/03 Radiator Thermal Balance Testing Complete05/21/04

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby18 Interim Mechanical Systems Cost Estimate* Escalated k$ *DOE/NASA funding Interim cost estimate based on Proposal cost estimate Currently developing and checking grounds-up re-estimate

GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb , 2001 Martin Nordby19 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