1. Thermal/Radiation Protection Upper Stage Satellite
Responsible Engineer: Jason LaDoucer

2. Purpose Protect payload (computer chip, vaccine)
Protect satellite instrumentation (computer system, sensors, fuel)
Protect structure of the satellite

3. Radiation Environment
Same orbit as ISS (340km). LEO(<1000km)
Radiation not a design driver since in LEO and within the inner Van Allen belt(>1000km)
Only radiation concern is UV

4. Thermal Environment
Majority of orbital period (90 minutes) spent on sunlight side (395K)
Dark light side reaches 173K

5. Passive Thermal Control Pros
No controls required and no input energy from the satellite
Based on geometry, insulation, coatings, fins, heat pipes
Cost effective, reliable, simple
Adequate for the duration (30 days) of the mission

6. Aluminized Mylar-Several Applications
Provides radiation, thermal, and impact protection
Aluminized, reflecting heat away (ε≈0.03)
Light weight (1.39 g/cc)
High strength (Typical E= 70 GPa)
Common material resulting in lower costs

7. Internal Thermal Control
Heat pipes
Tubular device with wick going from one end to another
Partially filled with ammonia
Heat is removed by ammonia evaporating at hot end causing vapor to condense at the cold end
Condensed fluid in the cold end then drawn back to the hot end by capillary action

8. Passive Thermal Control Cons
Only mode of heat transfer is radiation since no equipment to produce convection (fans)
Control of heat pipes requires a loaded gas reservoir or valve
If the ammonia in heat pipes too hot, the wick may become dry, making capillary action ineffective
Likewise, if the ammonia is too cold, the fluid will freeze
Heat pipes work differently in 0 g’s in the absence of free convection

9. Conclusion
For the mission requirements, Passive Thermal Control adequate for the payload
For the environment, Aluminized Mylar is a reliable material to protect against UV radiation, reflecting sunlight, and protection against micrometeoroids/space debris
Heat pipes will be adequate to equalize temperature in the interior of the satellite
Passive Thermal Control is reliable, simple, and cost effective saving time and money