Planetary and low orbit thermal environment for space thermal design

Abstract

The thermal environment characterization is one of the main steps to be done when facing the thermal analysis of space systems. They are usually analysed using worst-case values, which define the extreme conditions that can drive the system to its maximum temperatures. If the system is analysed under these conditions, temperatures during its whole life would be between these limits. However, it is important to well define the thermal environment in order to both get an appropriate design and to avoid oversizing the thermal control subsystem. The criteria developed by NASA for selecting the worst-case parameters has been widely used for years in several space missions. However, these criteria has not evolved since 1994 when first Earth radiation budget data were available. Nowadays, there are many data sources that can be used instead in order to deal with some limitations of the NASA criteria. In addition, the current computing capabilities allow for more complex analysis that can improve the thermal analysis and design of these systems. In this work, firstly, NASA criteria has been adapted to the thermal analysis of stratospheric balloon missions. This kind of missions have some differences with regard to the space ones, which makes necessary to perform a particularized analysis. Once at the floating altitude, convection is negligible in most cases but not during the ascent phase when it should be considered together with other parameters. In addition, the residence time over a point on the Earth surface is much higher than for a satellite. This makes necessary to focus the analysis on the geographic area where the flight is going to be, and to limit the data to the epoch when they can be performed. A complete thermal environment characterization based on real-observation data has been developed in order to define the worst-case analysis for both the float and ascent phases. This methodology has been applied to real missions such as SUNRISE III and TASEC-Lab. Secondly, NASA criteria for selecting the worst-case thermal environmental parameters in Low Earth Orbits has been reviewed with the aim of identifying its limitation and proposing a new methodology. It is common to analyse satellites from a thermal point of view by identifying worst-case orbits with constant values for the thermal environmental parameters. This method has been successfully used for years but small satellites or low massive parts need a reconsideration since they are more coupled to variations in the thermal environment. Here, worst-case time-dependent profiles are proposed in order to obtained more precise analysis based on a particularized characterization.