## 2 Scientific Objectives and Requirements  
### Scientific Objectives  
One of the objectives of the UVSQ-SAT mission is the study of the Earth's energy budget (ERB) and its energy imbalance [1]. Climate is largely determined by its energy balance at the top of the atmosphere, which regulates the overall energy content of the Earth system, i.e., the atmosphere and ocean (IPCC, 2013). The system is heated by the absorption of incoming solar energy (shortwave) and is cooled by terrestrial infrared emission (longwave) to space. Almost 30% of the incoming solar energy is not absorbed  
Figure 4: Profile of the UVSQ-SAT thermal vacuum cycling tests carried out in September 2020. Figure 3: (**Left**) Random vibration profile was run in three orthogonal axes, referred as X, Y, Z. (**Right**) Resonance search carried out on UVSQ-SAT before and after each random run (September 2020). but reflected back to space. Human activities have led to increased levels of heat-trapping greenhouse gases (GHGs) in the atmosphere, with a decrease in the amount of terrestrial radiation that can escape, resulting in an Earth energy imbalance. As a result, the Earth system is heating up. The most obvious sign of this is the long-term increase in global surface temperatures, which increases outgoing terrestrial infrared emission and thus tends to restore the Earth's energy balance. However, as illustrated by the apparent slowdown in global surface warming observed between 1998 and 2012 (\"climate hiatus\"), global average surface temperature, with its large decadal internal variability, is certainly not the most appropriate indicator of the EEI and associated energy accumulation in the Earth system [4]. Since the EEI drives climate change, its continuous monitoring has been identified as a fundamental diagnostic for analyzing climate variability and anticipating future changes. Closing the Earth's energy balance is considered a key step to further improve our understanding of global climate change [5]. Ideally, the EEI should be measured continuously from space. To date, existing satellite instruments have not been able to measure solar and terrestrial radiative fluxes with sufficient accuracy to directly determine the absolute value of the EEI on their own, although measurements of relative changes in the EEI are much more reliable [6; 7; 8]. Note that determining EEI requires very accurate global radiative measurements because EEI results from the difference of several terms (incoming solar energy, reflected incoming solar energy, outgoing terrestrial infrared energy) that are two orders of magnitude higher than EEI. For this reason, satellite radiative flux data are often anchored in some way to ocean heat content data, as most of the excess energy does not accumulate at the surface or in the atmosphere, but is absorbed by the oceans [5; 8]. Although ocean heat content is considered a better indicator of EEI, its global assessment remains challenging, mainly due to insufficient and inconsistent data coverage, and uncertainties in global scale extension [9; 10]. Overall, this lack of accurate satellite measurements of EEI is a major problem because climate change is primarily a perturbation of the Earth's energy balance. In addition, satellite measurements of solar and terrestrial energy fluxes also represent critical constraints and benchmarks for the evaluation and improvement of climate models, including their representations of the radiative effects of clouds and aerosols (IPCC, 2013). Earth's radiation budget data are therefore a key source of information for distinguishing external from internal climate variability and for assessing the sensitivity of climate to different forcings (including volcanic eruptions, solar variability, and anthropogenic aerosols). EEI determination represents a complex problem where the first relatively detailed balances of the energy exchanges of our planet and its atmosphere were published in 1997 by [PERSON] and [PERSON] [11]. An update of the ERB was completed by [PERSON] et al. [12] in 2012.