The Temperature Shell Condition of Calibration Spacecraft at the Shadow Area of the Earth Orbit

Abstract

Сalibration spacecraft (CSC) is used to assess the energy potential of the radar channel of a ground-based complex for the motion control of space objects. A high precision spherical shell is one option for the geometric shape of such a CSC. The passive repeaters of signals and some types of reference reflectors have a shape of the same character. Along with the orbits close to the Arctic ones, said CSC may be in the circular and elliptical earth orbits, which have areas shaded by the Earth from the sun rays.We can assume that in the shaded area of the earth orbit the CSC shell is under temperature extremes only of the intrinsic radiation of the Earth surface, the intensity of which is substantially less than the intensity of the Sun heat radiation that reaches the near-Earth space. In this regard, one should expect a lower temperature of the shell in this area of the orbit as compared with its temperature in the sun-lit area. This will cause a significant change in CSC shell temperature within a period of its revolution around the Earth. Long-term cyclic change of the temperature condition of the CSC shell may restrict the resource efficiency of its material.As the shell material, is, usually, used a polymer film with several tens of microns in thickness, covered by a thin layer (a few nanometers of thickness) of deposited aluminum that is necessary to meet the CSC performance requirements. Following the CSC Earth orbital injection the shell takes a spherical shape due to the relatively low pressure produced by gas that fills it. In this case it is possible to obtain a spherical shell of a sufficiently large diameter, which is specific for the modern trends in deployment of large orbit transformable structures.To predict the health of the shell material resource is necessary to have information on the temperature distribution across its surface not only in the lit but also in the shaded area of the orbit. A quantitative analysis of the temperature condition of the CSC shell can be conducted through mathematical modeling, using its thermal model. The paper offers three stages to create such a model for a spherical shell as applied to the conditions in the shaded area of the orbit.At the first step for an arbitrary portion of the outer surface of the shell is determined a density of the incident-on-it intristic Earth's radiation on the premise that the angular distribution of intensity of this radiation according to directions obeys Lambert's law. Depending on the optical characteristics of the outer surface, part of this radiation is absorbed by the outer surface of the shell. The second stage builds a thermal model of a spherical shell, which establishes a pattern of redistribution of energy absorbed by radiation from its inner surface with regard a reradiation effect between the concave portions of the surface. Finally, the third stage uses the ratio of the local heat balance of a separate shell portion, which allows you to find the temperature of this portion, and then build the temperature distribution across the entire surface of the shell.

Keywords

• calibration spacecraft
• thermal model of the shell
• the steady state temperature