WF/PC-I Radiator History

• WF/PC-I Radiator
  
  
  • Painted at Jet Propulsion Laboratory (JPL)
  • Pre-flight thermal measurements made by JPL
  • Post-flight thermal measurements made by GSFC
• Thermal Control Paint
  
  
  • Name: YB-71 White Paint
  • Pigment: Zinc Orthotitanate (ZOT)
  • Pigment Supplier: IIT Research Institute (IITRI)
  • Binder: Potassium silicate (PS-7)
  • Binder Supplier: Sylvania Electric Products Company
• Painting Completion Date
  
  
  • End of August 1985

• Solar Absorptance [alpha(s)]
  
  
  • Gier-Dunkle Instruments Inc. Solar Reflectometer Model MS-251 was used to measure pre-flight reflectance.
    
    
  • JPL records indicate that the [alpha(s)] values were influenced by the curvature of the surface and separation of 0.5 inch between the ZOT surface and the instrument used for measurement.
    
    
  • Inspection (witness) sample painted along with the radiator. The sample measured an [alpha(s)] value of 0.19 prior to vacuum bake. The inspection sample measured an [alpha(s)] value of 0.17 after vacuum bake.
    
    
  • The flight radiator was vacuum baked prior to solar absorptance measurements.
    
    
  Normal Infrared Emittance [epsilon(n)]
  
  
  • Gier-Dunkle Instruments Inc. Infrared Reflectometer Model DB-100 was used to measure pre-flight normal emittance.

  • Pre-flight inspection sample measured within specifications of greater than or equal to 0.85.

• Chassis Electronics Subassembly (Bay5)
  
  
  • ZOT paint was chipped at right center edge of panel approximately 0.5 inch and at the left edge of the panel.
    
    
  • Some difficulty was incurred during repair of ZOT surface.
• Paint Thickness
  
  
  • Measured 0.0068 inch.
    
    
  • Inspection sample measured within safe limits per specification requirements (0.003 to 0.006 inch).

• Solar Absorptance [alpha(s)]
  
  
  • AZ Technology Laboratory Portable SpectroReflectometer (LPSR) 200 was used to measure post-flight reflectance.
    
    
  • The instrument touched the surface of the ZOT paint during reflectance measurements.
    
    
  • The radiator was measured at GSFC on February 22, 1994.
    
    
  • The radiator was measured again at JPL on August 10, 1994.
• Normal Infrared Emittance [epsilon(n)]
  
  
  • Gier-Dunkle Instruments Inc. Infrared Reflectometer Model DB-100 was used to measure post-flight normal emittance.
    
    
  • Normal emittance measurements were only performed by GSFC on February 22, 1994.

• Stains were still present after the ZOT paint was sanded and cleaned with ethyl alcohol. It appears that stains penetrate through the paint material.
• JPL suspects that the source of discoloration is the epoxy Eccobond 57C used in the installation of the saddle when it was riveted to the radiator.
• Chemical analysis of the stains by NASA-GSFC Materials Branch have not been completed due to instrument failure.
  
  

• Due to the unsuccessful search by JPL to locate the inspection samples of the ZOT paint applied to WF/PC-I, a direct comparison between pre-flight and post-flight thermal values cannot be made.
• Pre- and post-flight measurements cannot be directly compared due to the differences in the method and the instrumentation used to measure the [alpha(s)] values.
• Assuming JPL pre-flight [alpha(s)] value from the inspection sample is representative of the pre-flight radiator's [alpha(s)] values, it appears that there is an increse in [alpha(s)].

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