Radiation in Space and Its Control of Equilibrium Temperatures in the Solar System

ABSTRACT The problem of determining equilibrium temperatures for reradiating surfaces in space vacuum was analyzed and the resulting mathematical relationships were incorporated in a code to determine space sink temperatures in the solar system. A brief treatment of planetary atmospheres is also included. Temperature values obtained with the code are in good agreement with available spacecraft telemetry and meteorological measurements for Venus and Earth. The code has been used in the design of space power system radiators for future interplanetary missions. INTRODUCTION In the design of space power system radiators for missions within the solar system one of the main input variables is the space environmental temperature, also referred to as the equilibrium space sink temperature. The purpose of this report is to derive a procedure for determining space sink temperatures in the solar system. The environmental conditions within the solar system are controlled by the energy and particle outflow from our central type G star, popularly referred to as the “Sun”. A total of nine satellites, called planets, orbit the Sun, which is located at a focal point of each of the planetary elliptical orbits of varying eccentricity, ranging from 0.0068 for the almost circular orbit of Venus to 0.25 for the highly elliptic orbit of Pluto. The eccentricity for the Earth’s orbit is 0.0167, which implies that at closest approach to the sun, or perihelion, the sun-to-Earth “semi-minor” radial distance is 147.5 million km, while at aphelion the semi-major radial distance is approximately 152.5 million km. The distance outward from the sun to “Earth”, its third orbiting planet, is thus an average of 149.6×10