Objective

1. Introduction 7

NASA criteria is based on real-observation data from ERBE mission, based on measurements of Earth Radiation Budget Satellite (ERBS) and National Oceanic and Atmospheric Administration (NOAA) satellites from 1984 to 1987 [17]. Since then, many other satellites have been observing the Earth and acquiring data from the Earth Radiative Balance in order to study the global warming. The Clouds and Earth Radiant Energy System (CERES) have been collecting data for more than two decades and treating them with the aim of providing a global grid of radiative parameters [18]. This data is of free-access to the scientific community allowing for many other studies as the one developed in this Doctoral Dissertation. However, CERES is not the only available database. During the last years, free-access have been provided for a very wide range of satellite-data. Chapter 3 provides a summary of the data source used in this work for characterizing the albedo, the Outgoing Longwave Radiation (OLR), the solar irradiance, not only at the Top of the Atmosphere but also below, where the sky temperature, the air temperature and the wind speed, are also relevant parameters.

As previously pointed out, stratospheric balloon missions are becoming more and more relevant with time as suitable platforms for solar and exoplanets observation, technology demonstration, CubeSat pre-flight test or even student experimentation.

The IDR/UPM, has participated in SUNRISE mission since its first scientific fight in 2009 [19]. This mission consists on a solar telescope on board a Long Duration Balloon (LDB) with the objective of studying the structure of the magnetic field of the solar atmosphere [20]. In the last flight, SUNRISE III, the IDR was the group responsible for the thermal analysis and design at system level [21]. This is why the author firstly focused on the thermal environment characterization of stratospheric missions. He realized that the literature regarding this field was scarce and the methodology used by other missions could be considerably improved using real-data observations. In addition, regarding the ascent phase of this missions, only analytical studies were preformed without considering the influence of a very variable radiative environment [22, 23].

Therefore, the main objectives of this Doctoral Dissertation regarding the planetary thermal environment characterization for stratospheric balloon thermal analysis are the following:

• Study of the relationship between the system’s characteristics and the worst- cases for the float steady state thermal analysis.

• Development of a new methodology for selecting the worst-case conditions particularized to stratospheric balloon missions.

1. Introduction 9

• Parametrization of the potential worst-case condition in order to analyse the influence of the thermo-optical properties and the orientation of the considered instrument on board a LDB.

• Characterization of the thermal environment during the ascent phase of stratospheric balloons.

• Evaluation of the thermal influence of the balloon film on the payload.

• Development of a new methodology for the thermal analysis of the ascent phase of stratospheric balloon missions.

All of this has been performed using previous mentioned data, python [24] as the programming language and ESATAN-TMS for the thermal analysis. Chapter 4is focused on the "Planetary Thermal Environment" where firstly the methodology is explained and then, all the work is applied to the SUNRISE III mission. In a lower scale, TASEC-Lab [25, 26], which is a stratospheric experiment developed by UPM students and led by the author, was also analysed following the same approaches. It is also introduced and a comparison between flight data and the thermal analysis is shown.

Once defined the planetary thermal environment for stratospheric flight appli- cations, the author wanted to focus on the Low Earth Orbit thermal environment with the aim of reviewing the NASA criteria using a next generation of real-data and trying to update the methodology for a closer characterization of the thermal environment [27]. Other space agencies, as ESA through the European Cooperation for Space Standardization (ECSS) [28], recommends the use of these criteria due to its success in several missions since the nineties. However, they provide some warnings saying that "assumptions made are not valid for some cases". The main objective is focused on improving the existing criteria for accounting their limitations and adapting the selection methodology to the capabilities of the current software analysis tools. For this reason, the proposed methodology, based on time-dependent profiles instead of constant values for the thermal environmental parameters is then applied to the thermal analysis of small satellites [29]. Their low thermal inertia makes that their behavior under variable conditions cannot be completely analysed by the convectional criteria because they are considerably coupled to the thermal environmental variations.

Therefore, the main objectives of this Doctoral Dissertation regarding the Low Earth Orbit thermal environment characterization for space thermal analysis are the following:

• Study of the relationship between the orbital, environmental and system’s parameters.

• Development of a new methodology for the selection of the worst-case condi- tions based on time-dependent profiles.

• Adaptation of the proposed methodology to be used by current analysis tools.

• Application to the small satellites thermal analysis.

As done before, here, CERES data is analysed using python as the programming language together with ESATAN-TMS for the thermal analysis and General Mission Analysis Tool (GMAT) [30] for the orbit calculations. This methodology is presented in Chapter 5.

Conclusions and some guidelines for future works are drawn in Chapter 6 where the contribution of this Doctoral Dissertation to the current state of the field is discussed.

1.2.1 Literature production

In this dissertation, the content of Chapter 4 and Chapter 5 summarized different studies that have been already published in the literature. During the development of this Doctoral Dissertation, five articles have been published in major journals of aerospace engineering, in collaboration with other PhD. candidate researchers and professors of the Universidad Politécnica de Madrid.

• Arturo González-Llana et al. “Selection of extreme environmental conditions, albedo coefficient and Earth infrared radiation, for polar summer Long Duration Balloon missions”. In: Acta Astronautica 148 (2018), pp. 276–284

• David González-Bárcena et al. “Real data-based thermal environment defini- tion for the ascent phase of Polar-Summer Long Duration Balloon missions from Esrange (Sweden)”. In: Acta Astronautica 170 (2020), pp. 235–250

• David González-Bárcena et al. “Ascent Phase Thermal Analysis of Long Duration Balloons”. In: Acta Astronáutica 195 (2022), pp. 416–429

• David González-Bárcena et al. “TASEC-Lab: A COTS-based CubeSat- like university experiment for characterizing the convective heat transfer in stratospheric balloon missions”. In: Acta Astronautica 196 (2022), pp. 244–258

1. Introduction 11

• David González-Bárcena et al. “Selection of time-dependent worst-case thermal environmental conditions for Low Earth Orbit spacecrafts.” In: Submitted to Advances in Space Research (2022)

Furthermore, five more articles have been presented in prestigious congresses of the space sector,

• David González-Bárcena et al. “Parametric Worst Case thermal environment conditions selection for Polar Summer Long Duration Balloon missions”. In:

24th ESA Symposium on European Rocket and Balloon Programmes and Related Research. 2019

• David González-Bárcena et al. “Methodology for the thermal analysis of instrumentation in Long Duration Balloon missions”. In: 8th European Conference for Aeronautics and Space Sciences (2019). doi: 10 . 13009 /

EUCASS2019-323

• David González-Bárcena et al. “Challenges in the thermal analyses of the ascent and float phases of SUNRISE III”. in: International Conference on Environmental Systems. 2020

• Alejandro Fernández-Soler et al. “Thermal Analysis of SUNRISE III ascent phase”. In: International Conference on Environmental Systems. 2021

• David González-Bárcena et al. “The worst-case thermal environment parame- ters of small satellites based on Real-Observation Data”. In: International Conference on Environmental Systems. 2021