Mechanical Analysis

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Mechanical Analysis
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Mechanical Analysis Subtopics

• Mechanical analysis of frame.
• Mechanical analysis of dewar vacuum housings.
• Mechanical analysis of dewar flexure
• Provided by Quartus
• Thermal analysis of dewar.
• System weights and c.g.

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Mechanical Analysis of Frame

• Stress/Deflection of frame due to gravity vector
  changes.
• Stress/Deflection of gantry crane fixtures during
  handling.

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Stress/Deflection of Frame MountStress 17100
psi (sf10) Deflection 0.040
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Stress/Deflection of PintelStress 1778 psi
(sf100) Deflection0.003
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Stress/Deflection of Clevis PinStress 6947 psi
(sf26) Deflection 0.003
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Vacuum Pressure Effects on Instrument

• MOS dewar lid stress/deflection analyzed because
  of the presence of weight reducing milled
  pockets.
• MOS dewar entrance window
• Wall thickness of camera dewar shell reduced for
  easier handling in the lab.

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Vacuum Pressure Effects on MOS DewarStress 3149
psi (sf11) - Deflection 0.043
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MOS Dewar Window Stress and Deflection Stress
610 psi (sf8) - Deflection 0.001
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Vacuum Pressure Effects Camera Dewar Stress 5574
psi (sf6) Deflection 0.053
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Thermal Analysis of Dewars

• Cold plate stress
• Stress in cold plate due to CTE mismatch with
  g-10 tube.
• Heat loads in dewars.
• MOS Dewar
• Camera Dewar
• Cooldown
• Cryo-cooler cooling power.
• Cooldown time.
• Warm-up time

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Stress of Cold Plate Due to G-10 Support Ring

• Large diameter g-10 tube support system imparts
  stress on the cold plate due to the differing
  thermal contraction coefficients.
• Stress at operating temperature (65K)
• cold plate lt1000psi in tension (35 Safety
  factor)
• G-10 ring10,000psi (10 Safety factor)

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Stress of Cold Plate Due to G-10 Support Ring
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MOS Dewar Heat Loads

• Steady state heat loading
• Passive shield (250K) 20.10 Watts
• Resulting energy balance heat load at a
  temperature of 250K.
• Active shield/Cold plate (100K) 24.70 Watts
• Conduction from the g-10 support and wires.
• Optical and passive shield radiation.
• Active loading
• Active loading
• Cryo-motor operation.

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Camera Dewar Heat Loads

• Steady state heat loading
• Passive shield (245K) 21.50 Watts
• Resulting energy balance heat load at a
  temperature of 245K.
• Active shield/Cold plate (65K) 22.70 Watts
• Conduction from the g-10 support and wires.
• Optical and passive shield radiation.
• Array (77K) 0.340 Watts
• Array power.
• Optical radiation.
• Active loading
• Active loading
• Cryo-motor operation.

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Cooldown

• Cooldown calculation
• Utilized the pre-cool loop to get the cold mass
  to 100K
• Equivalent aluminum thermal mass calculated for
  each dewar.
• MOS Dewar 60 kg
• Camera Dewar 90 kg
• Cooling power at 5-10K increments of the
  cryo-cooler from 150-77K determined from the
  CTI1050 and CTI1020 literature.
• Parasitic heat load into the dewar and thermal
  resistance of the cooling straps at each
  temperature increment were subtracted from the
  cooling power of the coldhead.
• The integrated specific heat of the cold mass at
  the incremental temperatures multiplied by the
  cooling power provides the time to cool the
  system the increment in temperature.

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Cooldown cont.

• MOS Cooldown calculation
• Utilized the pre-cool loop with CTI 1020 to get
  the cold mass to 140K
• 300 Watts ave. min.continuous from LN2
• 100 Watts continuous from CTI
• Time to 140K 5 hrs.
• Camera Cooldown Calculation
• Utilized the pre-cool loop with CTI 1050 to get
  the cold mass to 140K
• 300 Watts ave. min.continuous from LN2
• 100 Watts continuous from CTI
• Time to 140K 8 hrs.
• Time to 65K 20.2 hrs.
• Total time to operation 28.2 hrs.

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Warm-Up Time

• The dewars will be equipped with cartridge type
  heaters mounted on the cold plate to assist in
  warming to ambient. The heaters provide 380
  watts of power to the camera and 760 watts to the
  MOS and are thermostat controlled to prevent
  overheating.
• Camera warm-up time 10.1 hrs. (if necessary)
• 90 kg eqv. thermal mass (77-300K) 153.3 J/g.
• MOS warm-up time 3.1 hrs.
• 60 kg eqv. thermal mass (100-300K) 142.4 J/g.

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Motor Performance

• Stepper-motor warm torque (max) 150 mNm (21.1
  oz-in) at 600 rpm.
• Stepper-motor cold torque (max) 280 mNm (39.4
  oz-in) at 600 rpm.
• Max. motor torque to drive mechanisms
• Grism 35 mNm (4.9 oz-in) at 420 rpm.
• Motor test at 77K showed the required motor
  output to drive the mechanisms to be 12.5 of the
  motors maximum value.
• Testing under mock observatory situation (30 sec.
  on-300 sec. off, 60 min. integration) showed no
  measurable rise in surface temperature of motor
  or heat loading to the cryogen.
• Motors turned off when not used.

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System Weights

• Frame Weight
• Dewar Weight
• Thermal Enclosures Weight
• Ballasts

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Frame Weight

• Material 500A Steel
• Frame steel size 2X2X1/4 tubing (5.59
  lbs/ft)
• Main frame total weight 498 kg.
• C.g. z -1.162m (symmetrical about z-axis)
• C.g. measured with solid model

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Instrument Weights

• Camera Dewar
• Weight 416.6 kg
• C.g. (x,y,z)m 0.10,-.021,-1.26
• Spacer Mount
• Weight 113.7 kg
• C.g. (x,y,z)m -.01, -0.03, -0.70
• MOS Dewar
• Weight 479 kg
• C.g. (x,y,z)m -.02, 0.01, 0.26

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Ballasts

• Material 500A Steel
• Ballast size 3.5x3.5 (44 lbs/ft)
• Ballast Qty 4 (1 each corner (variable))
• Total Weight 200lbs

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Total Weights and C.G. of System

• Total frame weight 1094lbs (main frame only)
• Total dewar weight 2206lbs (MOSCameraSpacer)
• TE 1 480lbs
• TE 2 450lbs
• Ballast weight 200lbs (variable in
  quantity/position)
• Total 4400lbs (2000 kg)
• C.G. Z -1000mm
• Above values were determined using 3D AutoCAD,
  FEA, or actual weight measurements.

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Mechanical Risks

• Mechanism operation (binding, stalling,
  repeatability)
• Operate mechanisms in test dewar for fast
  turnaround.
• Lens mounting
• Test sample mounts in test dewar.
• Deflection
• Quartus and UF independent analysis.
• Room for additional bracing
• Alignment to telescope
• Use of proven mounting components
• System
• Copy previously proven components when possible.

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Summary

• UF proposes to build an instrument that meets the
  requirements of the FPRD and is delivered on
  time.
• Use known and verified mechanical components.
• Improved manufacturing techniques.
• Use of an outside vendor (Quartus) for the
  deflection analysis.
• In-house liquid cryogen test dewar for fast turn
  around mechanism testing.