TuMag Optical Unit Thermal Control for a Stratospheric Balloon-borne Mission

Abstract

The Tunable Magnetograph (TuMag) is an imaging tunable spectropolarimeter designed to study solar magnetic fields at high spatial resolution. It measures the state of polarization of light at three selected spectral solar lines: the Fe I at 525.02nm and 525.06nm, and the Mg I b2 at 517.27nm. TuMag is part of the post-focal instrumentation of the SUNRISE III mission whose first launch attempt was carried out from Kiruna (Sweden) in July 2022. The correct science performance of the instrument is strongly determined by the thermal stability of critical subsystems during observations. Elements such as the polarization modulator based on Liquid Crystal Variable Retarders, the LiNbO₃ etalon used to scan the spectral lines, or the three narrow bandpass filters with a ~1.5 Å FWHM mounted on a filter wheel, are required to operate within a tight temperature set-point. TuMag Thermal Control System (TCS) will guarantee the correct operational temperature for the aforementioned sub-systems at the time that provides a cooling mechanism for the detectors and minimizes thermo-elastic deformations across the optical path. It combines active and passive strategies in an architecture that profits from the unit location within the balloon gondola, which leaves only its top surface opened to the outer space. The thermal environment of a stratospheric flight is similar to that in LEO and hence typically driven by radiation. However, the presence of a 5 mbar rarefied atmosphere is shown to have an undesired effect in the thermal control performance of some of the internal elements. This impact was assessed during the thermal ground testing with the fully integrated Optical Unit, prior to its delivery to the platform. The expected TCS performance is currently being compared to the real data retrieved during the brief SUNRISE III first flight.

Description

Alejandro Gonzalo, National Institute for Aerospace Technology(INTA), Spain
Manuel Reina, National Institute for Aerospace Technology(INTA), Spain
Antonio Sánchez, National Institute for Aerospace Technology(INTA), Spain
Ana Fernández-Medina, National Institute for Aerospace Technology(INTA), Spain
María Cebollero, National Institute for Aerospace Technology(INTA), Spain
Hugo Laguna, National Institute for Aerospace Technology(INTA), Spain
David Escribano, National Institute for Aerospace Technology(INTA), Spain
Alberto Álvarez-Herrero, National Institute for Aerospace Technology(INTA), Spain
ICES202: Satellite, Payload, and Instrument Thermal Control
The 52nd International Conference on Environmental Systems was held in Calgary, Canada, on 16 July 2023 through 20 July 2023.

Keywords

Thermal Control, Magnetograph, Balloon-borne, Rarefied atmosphere, Thermal testing, Thermal correlation, Flight data

Citation