The solar probe shield/antenna materials characterization Original Research Article

This paper describes the development process used to select the shield/antenna material satisfying the design requirements of the Solar Probe mission that will encounter a flux at perihelion equivalent to an intensity of 3000 times greater than that at the Earth. A joint U.S.–French testing program was devised that would screen samples of carbon–carbon to determine the fabrication process that would produce the best thermal-optical and thermal-mechanical properties, lowest mass loss, and acceptable RF properties for temperatures up to 2400 K during shield operation. The thermal optical properties are emphasized since these determine the operating temperature and mass loss of the shield and are the most uncertain. The U.S. optical testing program relied on two facilities. The first facility used a high intensity halogen lamp to heat the sample. The temperature data were used in a heat balance equation to determine the solar absorptance/infrared emittance (α/ϵ) ratio given the known heat flux input. The emittance of the samples was determined, independently, by another specially calibrated facility that used Joule heating of the samples and measured the temperature by remote pyrometry that had been precisely calibrated. The French testing utilized a precisely designed chamber facility at the CNRS 1000 kW Solar Furnace at Odeillo Font-Romeu and the data collected there are sufficient to identify the thermal-optical properties of the materials, as well as their mass loss characteristics at high temperatures including the principal carbon vapor species evolved.