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Thermal control materials of different types are being used on the spacecraft for temperature control viz. Thermal control tapes, Thermal control paints, Anodised surfaces and Optical solar reflectors. This paper covers the measurement of emittance at different temperatures on various Optical Solar Reflectors ( OSR ) both rigid and flexible types. The rigid OSRs evaluated are OCLI - USA, PPE - UK and ISRO - INDIA. The flexible OSR is from SHELDAHL - USA. The emittance of the OSRs were measured in the temperature range 223K - 373K using steady state calorimetric method. Measurements were done on a square sample with OSRs affixed on each face. The sample has a built in heater and an evacuated low temperature radiation receiver is used for the test environment. Experimental results, temperature dependence of the total hemispherical emittance relation for each of these OSRs and error estimation are presented in this paper.

The total hemispherical emittance of different Thermal Control Coatings viz. Chemglaze Black Paint Z-306, 3M Black Paint, ECP-2200, Whittakar White Paint APA-247 4 and Astral Aluminium Paint PSG-173 being used in different spacecrafts for thermal control purpose were measured in the temperature range 115K-375K using steady state calorimetrie method. Measurements were done on a disc shaped sample with built in heater and an evacuated low temperature radiation receiver is used for the test environment. Experimental results and error estimation are presented here. The results indicate that the emittance increases with increase of temperature for all the coatings. Along with the experimental results, temperature dependence of the emittance relation for each of these coatings is also presented. Facilities and measurement technique used here are capable of providing the results better than ±3.0 % at the lowest temperature of the measured temperature range.

Measurement of thermal emittance of hardanodized coating on aluminium sample at different temperatures from −80°C to +100°C has been made using steady state calorimetric method. The measurement sample consists of two aluminium circular discs hardanodized on all surfaces except on assembly contact areas. A thin circular heater was sandwiched between the discs. The assembled sample was suspended inside a vacuum chamber with LN2 cooled shroud and maintained at different temperature levels using electrical power. The thermal emittance of the sample is determined from the sample equilibrium temperatures and from the elect rical power input. An error estimation has been performed, it shows a maximum uncertainty of ±3.3% on the emittance.