A Carbon Fiber Reinforced Polymer (CFRP) optical bench has been developed for the Tunable Magnetograph instrument (TuMag) for the SUNRISE III mission. This mission is within the NASA Long Duration Balloon Program and it consists of 1-meter aperture telescope with three post-focal instruments to study the solar dynamics. One of them is TuMag: a diffraction-limited imager, a high sensitivity polarimeter and a high-resolution spectrometer. The composite material has been selected for the optical bench due to its lightweight, low sensitivity to thermal gradients and low coefficient of thermal expansion (CTE). Additionally, to the flight model optical bench, a breadboard model identical to the flight model has been manufactured including optical fiber Bragg temperature and strains sensors embedded in its upper skin. The goal is to demonstrate that the use of distributed fiber Bragg gratings (FBGs) can provide valuable information for strain and temperature mapping of an optical instrument onboard a payload, during its operation and its on-ground testing. Furthermore, surface mounted strain FBG sensors and thermocouples have been installed in the optical bench for intercomparison purposes. In this paper the results obtained for a thermal-vacuum test are presented. It consists of three thermal cycles with stabilization steps at 100ºC, 60ºC, 20ºC and -20ºC. The FBG embedded temperature sensors results have been compared with the surface mounted thermocouples; the FBG embedded strain sensor results have been compared to the surface mounted strain sensors.
The Tunable Magnetograph (TuMag) is one of the three post-focal instruments onboard SUNRISE III, a balloon-borne solar observatory aimed to the study of solar dynamics. TuMag is able to make Sun observations at three absorption solar lines: the Fe I lines at 525.02nm and 525.06nm, and the Mg I b2 line at 517.27nm. The spectral lines are scanned during the observation using a LiNbO3 etalon in double-pass configuration with a 65mÅ bandwidth. Additionally, to remove undesired orders of the Fabry-Perot interferometer, a narrow band filter with a ~1.5 Å FWHM is inserted in the optical path, and needs to be centered to the corresponding solar line. These filters feature high thermal sensitivity and incidence angle dependence. For this reason, they require a thermal stabilization of ±0.5°C and an angular position accuracy better than ±0.03 degrees. In order to switch between filters and hence the observation solar line, a Filter Wheel has been designed which comply with stringent thermal and mechanical requirements and it is presented in this work.
SUNRISE III mission is a one-meter aperture telescope onboard a balloon within NASA Long Duration Balloon Program. Three post-focus instruments are used for studying the Sun’s dynamics and magnetism, among which the Tunable Magnetograph (TuMag) is a tunable imaging spectropolarimeter. TuMag is a diffraction-limited imager, a high sensitivity polarimeter (< 10-3 ), and a high-resolution spectrometer ( ~ 65 mÅ). It will be able to study solar magnetic fields at high spatial resolution (~100 km on the solar surface). It will make images of the solar surface magnetic field after measuring the state of polarization of light within three selected spectral lines: the Fe I lines at 525.02 nm and 525.06 nm, and the Mg I b2 line at 517.27 nm. It will be sensitive to the solar vector magnetic fields and line-of-sight velocities, in the photospheric and chromospheric layers. TuMag will be the first solar magnetograph onboard an aerospace platform with the capability of tuning the solar line to be observed. In this paper the TuMag end-to-end tests carried out during the verification phase are described. These tests are performed to characterize and calibrate the instrument. Specifically, they determine the polarimetric and spectroscopic performances of the instrument as well as the image quality. The availability of a singular facility, an ISO6 clean room with a coelostat on the building roof, allowed the use of solar light during the verification campaign. This was key to a complete instrument verification due to the unique spectroscopic and polarimetric characteristics of solar light.
The Tunable Magnetograph (TuMag) is one of the three post-focus instruments onboard the SUNRISE III mission. It consists of a one-meter aperture telescope onboard a balloon within NASA Long Duration Balloon Program to study the solar dynamics. TuMag is a diffraction-limited imager, a high sensitivity polarimeter and a high resolution spectrometer. It will be able to study solar magnetic fields at high spatial resolution (~100km on the solar surface). It will make images of the solar surface magnetic field after measuring the state of polarization of light within three selected spectral lines: the Fe I lines at 525.02nm and 525.06nm, and the Mg I b2 line at 517.27nm. It will allow to be sensitive to physical quantities, and specifically to the magnetic fields, in the photospheric and chromospheric layers. TuMag will be the first solar magnetograph onboard an aerospace platform with the capability of tuning the solar line to be observed. TuMag consists of an Optical-Unit and an Electronic Unit to control it. The optical design is an optical relay of the telescope post-focal intermediate image where the light analysis is carried out in several stages. The polarization analysis is carried out with a polarization modulator based on Liquid Crystal Variable Retarders developed for the Solar Orbiter mission in operation currently. The spectral lines are scanned during the observation using a LiNbO3 etalon in double-pass configuration with a 65mÅ bandwidth. Additionally, to remove undesired orders of the Fabry-Perot interferometer, three narrow bandpass filters with a ~1.5 Å FWHM (Full Width at Half Maximum) are consecutively inserted in the optical path using a high precision and thermal controlled filter wheel. In this paper the optical, mechanical and thermal design of the TuMag optical unit is described as well as a brief summary of the results obtained during the manufacturing, assembling, integration and verification phases
The athermalized panchromatic imaging system (APIS) was the low-resolution refractive camera proposed by the Laboratorio de Instrumentación Espacial as a CubeSat payload. APIS flew on-board OPTOS CubeSat designed and developed by INTA using the methodology of European Cooperation for Space Standardization and space qualification tests. APIS had two main objectives: to analyze the performance degradation of commercial off-the-shelf (COTS) components due to space radiation and to verify in-flight functionality of the passive athermalization system. We summarize the design, manufacturing, and assembly integration and verification phases of the instrument, as well as the analysis of the radiation tests. Additional studies are included, such as thermal behavior, tolerances and sensitivity analysis, signal-to-noise ratio, and ghost images, as well as their implications during the design process. Three main goals were achieved during the mission lifetime: (1) the viability of a small refractive Earth observation camera on-board a CubeSat, (2) the validation for low Earth orbits of a passive athermalization system, and (3) the use of COTS elements, such as commercial glasses and detectors based on complementary metal–oxide–semiconductor technology, on a 2-year Earth observation mission.
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