MAXIM Periscope Module

1
MAXIM Periscope Module

• Thermal
• Rob Chalmers
• 25 April 2003

2
Thermal Requirements

• Temperature Stability (tens of mK)
• Optical Bench
• Mirrors
• Temperature Gradients (TBD)
• Mirrors
• Optical Bench
• Thermal Settling Time
• Minimize recovery time following operation of
  Mirror Actuators

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Materials

• Requirements for extreme dimensional stability
  demand the use of materials with extremely low
  CTE. Some candidates
• Material CTE
• ULE (Corning 7972 premium grade) 0.0 0.10 x
  10-9/K
• Zerodur 0.0 0.10 x 10-6/K
• Invar 2.0 x 10-6/K

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Thermal Design Concept
MAXIM Thermal Requirements appear similar to the
LISA Instrument, and the design approach is
similar

• Passive design with multiple nested thermal
  regions
• Optical bench highly isolated from instrument
  housing
• Instrument housing highly isolated from
  spacecraft thermal influences
• Low emittance (gold) thermal shields provide
  radiative isolation between regions
• Exotic conductive isolation (Kevlar suspension or
  similar) may be required to achieve required
  thermal stability
• Temperature-controlled thermal pre-collimators
  around entrance and exit apertures

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Thermal Design Concept
Thermally-Isolating Kinematic Mounts
Thermal Pre-Collimators at Entrance and Exit
Apertures
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Temperature Stability

• MAXIM stability requirements and baseline
  thermal design approach are similar to LISA
• (see backup charts)

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Mirror Transient Response

• 1.5 Watts applied to center of 5 x 20 x 2 cm ULE
  mirror for 10 seconds

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Temperature GradientsThermal Influence of
Aperture on Mirror Gradients
0C aperture (assumed)
21C enclosure (assumed)

• An aperture slit at 0C induces mirror
  temperature gradient of approx. 20 mK
• Heated thermal pre-collimator reduces gradient
  to near zero.

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Summary, Recommendations Future Work

• Passive thermal design is a feasible approach
• benign thermal environment
• very low power dissipation within the optics
  module
• infrequent operation of mirror actuators
• Choice of materials for mirrors and optical bench
  greatly influences temperature stability and
  gradient requirements.
• Need for extreme thermal isolation between the
  stable optics and the relatively unstable
  spacecraft will be a challenge to structural
  design.
• Required analytical precision may test limits of
  existing thermal software. At these levels,
  machine-dependent round-off errors can be
  significant. Validation of analytical results by
  comparing different solution methods and
  convergence criteria is recommended.

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Backup Charts
MAXIM Thermal Requirements appear similar to the
LISA Instrument. The following charts provided by
Hume Peabody are taken from a presentation of the
LISA thermal design.
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LISA Thermal Design (1 of 5)

• Overall philosophy
• Minimize radiative and conductive heat transfer
  to the optical bench and gravitational reference
  sensor
• Minimize temperature fluctuations across the
  optical bench and gravitational sensor
• Extremely stable power system
• Orbit provides a stable thermal environment
• Two sources of heat solar input and electronics
• Three zones of thermal isolation are used in
  series
• Zone 1 Solar input ?SA ?Structure
• Zone 2 Structure and electronics ? Y-Tube
• Zone 3 Y-tube ? Optical bench and gravitational
  reference sensor

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LISA Thermal Design (2 of 5)

• Key design features
• Solar cells are mounted on thin CFRP face sheets
  with insulating foam in between
• Low conductance standoffs mount solar arrays to
  the Al honeycomb top plate
• Top plate is gold-coated

Energy flow values represent steady-state
hot/cold cases (f1e-4)
Radiation Conduction
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LISA Thermal Design (3 of 5)

• Y- Tube constructed from CFRP
• Electronics mounted with low conductance feet
• Stable electronics power
• Radiator rejects structure and electronics heat

146.2 W 142.7 W
SPACE
RADIATOR
116.4 W 113.7 W
27.2 W 26.3 W
24.3 W 23.5 W
13.6 W 14.8 W
ELECT. BOXES 154.2 W
STRUCTURE
INPUT FROM S/A 40.0 W 34.6 W
8.3 W 10.1 W
7.2 W 6.7 W
16.0 W 15.6 W
3.1 W 2.9 W
Y TUBE.
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LISA Thermal Design (4 of 5)
RADIATOR
INPUT FROM STRUCTURE ELECT BOXES 26.3 W /
25.2 W
SPACE
42.3 W 41.4 W

• Gold thermal shield between Y-Tube and optical
  bench
• Optical bench made from ULE
• Stable power dissipation

2.7 W 2.6 W
1.3 W 1.2 W
2.30 W 2.26 W
Y-TUBE 4.3 W INT. POWER
SHIELDS
15.8 W 15.8 W

INTERIOR
0.06 W 0.06 W
0.02 W 0.02 W
0.24 W 0.22 W
0.11 W 0.11 W
OPTICAL BENCH (2.9 W of internal power)
Interior includes everything except optical
bench and thermal shield
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LISA Thermal Design (5 of 5)

• Two driving thermal requirements
• Stability of optical path of the cavity (30
  Hz/vHz) at 10-3 Hz
• 60 x 10-6 K/vHz fluctuations across GRS housing
  at 10-4 Hz. (derived from radiometric effect,
  thermal radiation pressure)
• RAL modeled the payload and spacecraft (Astrium)
• Varied electronic power by 1 at 10 -4 Hz
• Results showed that Optical Bench fluctuations
  are 6.5 x 10 -5 K
• Assuming 3 x 10 -8 CTE and 0.3 meter Optical
  Bench ? 5.85 x 10 -13 change in length.
• Varied the solar input by 0.3 at 10 -4 Hz
• Results showed that fluctuations at the Optical
  Bench were 2.2 x 10 -6 K/vHz
• Assuming 3 x 10 -8 CTE and 0.3 meter Optical
  Bench results in 1.98 x 10 -14/vHz
• Varied the power dissipation on the optical bench
  by 5.6 uW / vHz
• Results showed fluctuations were 2 x 10 -5 K/vHz
  at 1 x 10-3 Hz.
• At 3 x 10 -3 Hz ? 4 x 10 -6 K/vHz (estimate)
• (3 x 10-8/K) (4 x 10 -6 K/vHz) 1.2 x 10-13 /vHz
  x 2.8 x 10-14 Hz 34 Hz/vHz