BALBOA Thermal Analysis – TVAC Experiment and Flight Test

The BALBOA (BALloon‑Based Observations for Sunlit Aurora) project is a pathfinder mission to explore auroral imaging in sunlight, aimed at enabling new advances in science, such as dayside auroral N-S conjugacy and dayside-to-nightside auroral causality/correlation. Given that solar wind‑magnetosphere‑ionosphere coupling is initiated on the dayside, the BALBOA science addresses the fundamental questions of the auroral dynamics in dayside and global coupling. The science payload consists of four large FOV InGaAs cameras, whose combined FOV covers 240° in azimuthal and 52° in vertical direction centered at the gondola. Each camera and its support system are enclosed in a pressure vessel (PV) to ensure a required working environment. The PV is equipped with optical baffles to eliminate the stray light and the reflected light from the balloon and Earth albedo. The BALBOA thermal analysis is one of the mechanical keys to ensuring the instrument functions well during the flight, i.e., to establish a thermal scheme so that the camera and computer work in the required operations temperature. There are two types of approaches to understanding the overall thermal solution. The most common one is the CAD software simulations. Although they comprehensively describe the heat flow, temperatures, and temperature gradients, they can be costly and time-consuming. Additionally, thermal-vacuum (TVAC) testing is necessary to validate the modeling with the system operating. Besides, thermocouple loggers or dataloggers are efficient tools that work in many thermal conditions, especially for small dimension and scale instruments. We used this approach for establishing the BALBOA thermal model and proved it is an efficient method for our instruments. We installed a data logger to measure the PV internal temperatures and pressure from eight channels. After a series of experiments and tests inside TVAC and outside in sunlight, the thermal model uses Mylar and Mesh tape to cover the PV ~50% of the surface that is exposed to sunlight. Such shielding ideally keeps the PV warm in a cold environment and cool in a warm environment to maintain the operation temperature. A full-payload flight test is scheduled for August 2022 to validate this design. We will report the thermal test results at the meeting.