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Review of LAT Accelerometers and Thermal Sensors

This review discusses the rationale, selection, and compatibility of the accelerometers and thermal sensors in the design of the Large Area Telescope (LAT) for the Gamma-ray Large Area Space Telescope (GLAST). The review also provides recommendations and updates to the LAT Instrumentation Plan.

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Review of LAT Accelerometers and Thermal Sensors

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  1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: LAT Accelerometer and Thermal Instrumentation Review Presented by Leonard Lee John Ku Jack Goodman

  2. Introduction Leonard Lee

  3. Purpose of Review (1) Review the rationale for the quantity and location of the LAT accelerometers shown in the current revision of the LAT Instrumentation Plan (LAT-TD-00890-02) – John Ku • Review the justification for the LAT thermal sensors (Flight and Test) with regard to the quantity and locations described in the LAT Instrumentation Plan – Jack Goodman (3) Provide redlines/comments if any to update the LAT Instrumentation Plan.

  4. LAT Accelerometer Review John Ku

  5. Items To Be Addressed • Compatibility with LAT Requirements • Purpose for Accelerometers • Selected Accelerometer Models • Sensitivity Requirements • Dimensions • Test and Flight Vacuum Compatibility • Outgassing issues • Compatibility with NRL • Facility capability: 32 Control, 300 Response • Connector Type: Voltage Output (BNC), or Charge Output (10-32 Coax) • Cable length • Accelerometer Locations by subsystem • ACD • TKR • CAL • Ebox • Mech • Grid • RMB • XLAT • RAD • SC Mount • Conclusions

  6. Compatibility with LAT requirements • Purpose for Accelerometers • Record acceleration vectors at key points on the integrated LAT such that natural frequency, transfer functions, and peak accelerations are captured • Natural frequency measurements provide insight into modes and shapes (phase) • Transfer functions (response divided by input) provide information on damping • Peak accelerations ensure the LAT and subsystems are not undertested • Accelerometer Models selected (Piezotronics brand) Model Validation Performance Verification 356M109 – Three Axis (12.0mm W X 7.0mm T) 355M64 – Single Axis (9.6mmW X 5.8mmT)

  7. Compatibility with LAT requirements • Sensitivity Requirements • Based on sine vibration pre-test analysis and accelerometer location optimization routines, 10mV/g accelerometers provide needed resolution to obtain the above requirements • Acoustic and shock environments demand higher frequency data acquisition; The accelerometers are compatible with high rate DAQ systems • Dimensions • Internal accelerometer placement must be carefully executed, as clearance is small. The accelerometers selected do not violate any dynamic clearance envelopes (to be confirmed when final locations are specified) • Test and Flight Vacuum Compatibility • Piezotronics has stated that these sealed accelerometers can withstand the vacuum of space without leaking or bursting • Outgassing issues • A detailed survey of all accelerometer types and associated cables has been performed to identify outgassing materials. Some problems have been identified, but steps are being actively taken to ensure no outgassing during TVAC

  8. Compatibility with NRL • Facility capability: NRL is easily able to handle the number of accel channels we are requesting • Vibration facility can handle 32 control accelerometers and 300 response channels • LAT sine vibration testing requires 49 total channels (control and response designations TBD, but only a few control channels are anticipated) • LAT acoustic testing requires 64 response channels • No LAT shock testing performed • Connector Type • Positive confirmation by NRL • Voltage Output accelerometers require BNC connectors • Charge Output accelerometers require 10-32 Coax connectors • Current accelerometers selected are ICP (Voltage) Type with BNC connectors, so they are compatible with NRL’s shaker • Cable length • Rough calculations show a 15 foot (~4.5 m) cable length requirement to allow routing from the LAT to NRL’s patch panel • When the cable routing is finalized, the cable lengths will be rechecked

  9. Accel Locations: ACD Subsystem • Nine Accels Requested • Grid 500599, X, Y & Z • Grid 500142, X • Grid 500353, Y • Grid 500202, Y • Grid 500021, Z • Grid 500043, Z • Grid 500045, X 500045 Bottom Edge Center of Panel 500353 500599 500043 500202 500021 500142

  10. Accel Locations: TKR Subsystem • Seven Accels Requested • Grid 309282, X • Grid 315085, X • Grid 308801, Y • Grid 315185, Y • Grid 301285, Z • Grid 307082, Z • Grid 324985, Z 301285 308801 309282 307082 324985 315185 315085

  11. Accel Locations: CAL Subsystem • Six Accels Requested • Grid 218623, X, Y & Z • Grid 230614, X, Y & Z 230614 218623

  12. 400580 404665 (PDU) 401182 400001 401618 401609 406023 (GASU) Accel Locations: EBOX Subsystem Seven Accels Requested Grid 400580, X & Z Grid 400001, X & Z Grid 401618, Z Grid 401182, Y Grid 401609, Z Two Accels Requested Grid 404665, Z Grid 406023, Z

  13. 750249 Attach Accelerometers to Clevis part of RMB 750232 103058 902227 750980 902264 904433 104216 Accel Locations: Mechanical Subsystem Two Accels Requested Grid 103058, Z Grid 104216, X Four Accels Requested Grid 902264, Y Grid 902227, Y Grid 904433, X & Y Twelve Accels Requested Grid 800565, X, Y & Z Grid 825565, X, Y & Z Grid 850565, X, Y & Z Grid 875565, X, Y & Z Three Accels Requested Grid 750232, Z Grid 750249, Z Grid 750980, Z

  14. SC Mount Accelerometer Locations and Overall Summary • Four three axis accelerometers are requested at the LAT side of the SC flexures. These accelerometers are removable prior to flight. • The 64 total accelerometers are broken down as follows: • ACD  9 fly-away provided by ACD • TKR  7 fly-away provided by I&T • CAL  6 fly-away provided by I&T • EBOX  9 fly-away provided by I&T • Mech  21 ground provided by NRL • SC Flexures  12 ground provided by NRL • 31 total Fly-away accelerometers • 33 total Ground (removable) accelerometers

  15. Conclusions • Design: Accelerometer models are compatible with LAT design and stayclears, and use flight qualified materials • Analysis: The current accelerometer instrumentation list reflects all needed channels to develop a validated finite element model and verify performance of the integrated LAT • Test: Accelerometers are compatible with NRL environmental facilities • Integrated LAT accelerometers have been specified and meet all design, analysis and test requirements

  16. LAT Thermal Instrumentation Review Jack Goodman

  17. LAT Thermal Flight instrumentation Refer To LAT Instrumentation Plan, Table No.1(Attached)

  18. LAT Thermal Test instrumentation Refer To LAT Instrumentation Plan, Table No.3(Attached)

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