High Emissivity Coatings for Arcjet Thrusters

The addition of a high emissivity coating to the radiating surfaces of an arcjet thruster has been explored as a means to improve arcjet performance. At arcjet nozzle operating temperatures, the emissivity of an uncoated tungsten nozzle is approximately 0.4. When coated with a material having an emissivity of 0.55-0.6, the nozzle temperature is reduced by 120C, due to enhanced radiative cooling. The proposed program will investigate potential emissivity coating with radiation coefficients up to 0.8-0.9. The use of such coatings can reduce nozzle operating temperatures, leading to longer anode life. Enhanced radiative cooling will also provide wider engine design latitude and improved operating power margins.