# Presentation: 033296

## MAXIM Periscope Module

**Thermal**
**Rob Chalmers**
**25 April 2003**

## 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

## Materials

**	****Requirements for extreme dimensional stability demand the use of materials with extremely low CTE. Some candidates:**
**Material****	****	****	****	****	****CTE**
**ULE****TM**** (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**

## Thermal Design Concept

**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**

**MAXIM Thermal Requirements appear similar to the LISA Instrument, and the design approach is similar:**

## Thermal Design Concept

**Thermal “Pre-Collimators” at Entrance and Exit Apertures**

**Thermally-Isolating**
**Kinematic Mounts**

## Temperature Stability

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

## Mirror Transient Response

**Mirror Transient Response**

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

## Temperature GradientsThermal Influence of Aperture on Mirror Gradients

**Temperature Gradients****Thermal Influence of Aperture on Mirror Gradients**

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

**0°C aperture (assumed)**

**21°C enclosure (assumed)**

## Summary, Recommendations & Future Work

**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.**

## 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.**

## 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

## LISA Thermal Design (2 of 5)

**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 (f=1e******-4******)***

- Radiation Conduction

## 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**

**SPACE**

**STRUCTURE**

- 13.6 W 14.8 W

- 24.3 W 23.5 W

- 8.3 W  10.1 W

- INPUT FROM S/A 40.0 W 34.6 W

**ELECT. BOXES**
**154.2  W**

**RADIATOR**

- 27.2 W 26.3 W

**Y TUBE. **

- 7.2 W  6.7 W

- 3.1 W  2.9 W

- 16.0 W  15.6 W

- 116.4 W  113.7 W

- 146.2 W 142.7 W

## LISA Thermal Design (4 of 5)

**SPACE**

**Y-TUBE   4.3 W                 INT. POWER**

- 42.3 W 41.4 W

**RADIATOR**

- 2.7 W    2.6 W

**OPTICAL BENCH  (2.9 W of internal power)**

- INPUT FROM STRUCTURE & ELECT BOXES      26.3 W / 25.2 W

**SHIELDS**

**INTERIOR**

- 1.3 W  1.2 W

- 0.24 W  0.22 W

- 15.8 W  15.8 W

- 0.06 W  0.06 W

- 0.11 W  0.11 W

- 0.02 W  0.02 W

- 2.30 W  2.26 W

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

- * Interior includes everything except optical bench and thermal shield

- *

## LISA Thermal Design (5 of 5)

**Two driving thermal requirements:  **
- Stability of optical path of the cavity (30 Hz/√Hz) * at 10-3 Hz
- 60 x 10-6 K/√Hz 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/√Hz
- Assuming 3 x 10 -8 CTE and 0.3 meter Optical Bench results in 1.98 x 10 -14/√Hz
- Varied the power dissipation on the optical bench by 5.6 uW / √Hz
- Results  showed fluctuations were 2 x 10 -5 K/√Hz at 1 x 10-3 Hz.
- At 3 x 10 -3 Hz → 4 x 10 -6 K/√Hz (estimate)
- (3 x 10-8/K) (4 x 10 -6 K/√Hz)= 1.2 x 10-13 /√Hz x 2.8 x 10-14 Hz = 34 Hz/√Hz