1. THERMAL CONTROL SYSTEM
MAXIM Pathfinder
THERMAL CONTROL SYSTEM
PRESENTATION
August 19, 1999
Wes Ousley
NASA/GSFC Code 545
(IMDC)

2. MAXIM Pathfinder Thermal System August 5, 1999
MAXIM mission thermal requirements can be accommodated with passive thermal control systems (blankets, heaters, heat pipes, thermo-electric coolers)
Optics module requires gradients to be minimized
Composite structure (near-zero CTE), sun side insulated
Radiators on anti-sun side control component temperatures
Detectors require fine temperature control near 170K
Thermo-electric coolers and heat pipes
Both modules require aperture sunshades to meet thermal requirements

3. MAXIM Pathfinder Thermal System August 5, 1999
Mission Requirements
Optics spacecraft:
Required pointing stability is 300 marcsec
Payload power dissipation is 259 Watts
Detector spacecraft:
Detectors require 170K temperature
Payload power dissipation is 313 Watts
Flyaway orbit eliminates earth effects
Both spacecraft point one side to the sun, +/- 5O
Allowable thermal deflection from off-pointing is severely limited

4. MAXIM Pathfinder Thermal System August 5, 1999
Thermal Design Features
Optical satellite
Pointing requirements dictate:
Mirror structure and spacecraft components must be thermally isolated
Mirror structure must be low-CTE composite to minimize deflections
Use of current flight spacecraft composite materials produces significant deflections
Thermal baffles required on front end (like AXAF) and back end (like C-X)
Heat pipes are required for spacecraft component temperature control
Radiators on anti-sun side easily accommodate power requirements
Radiators could be sized to reduce 30W prop heater power needs
Body-mounted solar array max temp would be about 100OC if fully populated

5. MAXIM ORBIT CONFIGURATION Detector Spacecraft Solar Array
(7 m^2, projected area)
Optic Spacecraft

6. MAXIM OPTIC SPACECRAFT (DIFFERENT VIEWS) Different views
of the Optic space-
craft
Spacecraft
Subsystem
This view: spacecraft subsystems removed

7. MAXIM Pathfinder Thermal System August 5, 1999
Thermal Design Features
Detector satellite
Detector requires a thermo-electric cooler to achieve 170K
Heat pipes transport TEC power and electronics dissipation to radiators
Radiator margins over 100% for spacecraft components and payload package
Hydrazine propulsion system heaters total 30 W (lines, tanks, valves, etc.)
Cold gas system would need no significant heater power

8. MAXIM DETECTOR SPACECRAFT Payload Fixed Solar Array (6m^2 shown)
Stowed
Orbit
Spacecraft
Spacecraft Subsystems are mounted in
this volume

9. MAXIM DETECTOR SPACECRAFT Detector Baffle Range Sensors Baffle
Detector / CCD/ QC Cryogenics
Payload Volume
Range Sensors
Enlarged View of Baffle
DETECTOR SPACECRAFT

10. MAXIM Pathfinder Thermal System August 5, 1999
Conclusion
Passive thermal control can accommodate instrument and spacecraft requirements.
Advanced composite structure required to meet pointing spec
Telescope and detector baffle systems will be challenging
Each spacecraft operational heater power totaled 30 watts
(for hydrazine prop systems)