Thermal Control

1
Thermal Control

• simple analysis
• detailed analysis
• control methods

2
Simple Analysis

• spherical cow approach
• simplify geometry

thermal inputs (internal)
approximate spacecraft
thermal output
3
Radiative Heat Transfer

• In steady-state, Qin Qout energy/time
• qin energy/area/time
• from solar flux (?S 1.35kW/m2 at Earths
  distance from Sun)
• Qin ? ?SAexposed Qinternal (?
  absorptivity)
• Qout qoutAtotal
• Stefan-Boltzman Law qout ??T4
• ? emissivity

4
Example

• Qinternal 100 W.
• Atotal 4? r2, with r 2 m.
• dist. from Sun 1.25 au
• 1.87?108 km
• 0.88 ? 0.90
• Aexposed 0.5 Atotal 25.1 m2
• Qin 100 W. 0.88?SAexposed(R?/R)2
• 19184 W.
• Qout ??T4Atotal
• ? T 294.2 oK 21 oC 70 oF

r
Aexposed
internal sources
Atotal
5
Detailed FE Analysis

• Consider individual internal components
  (placement and thermal properties) and external
  geometry
• TRASYS -- builds input file for SINDA
• SINDA calculates temperatures of components

6
Control Methods

• Passive
• MLI (multi-layer insulation)
• surface coatings
• louvers
• heat pipes
• Active
• electric heaters
• thermal fluid loops

7
Design Procedure

• Develop list of requirements
• min/max temperatures that components can tolerate
• special thermal rqts for some instruments?
• Estimate worst case hot/cold conditions
• Initially, use simple steady-state analysis
• Later, use FE analysis
• Select and size thermal control method(s)