## 1 Introduction  
UVSQ-SAT is a nanosatellite designed to observe the Sun and the Earth, mainly for observing essential climate variables. It allows, among other things, measurements of the solar radiation reflected by the Earth or outgoing shortwave radiation (OSR) and of the outgoing longwave radiation (OLR) at the top of the atmosphere (TOA). A detailed description of the UVSQ-SAT mission and its satellite is given by [PERSON] et al. (2020) [1]. The main technical and scientific goal is to implement an agile demonstrator allowing to perform measurements of the Earth's radiation balance at the TOA. The UVSQ-SAT mission will allow to validate the principle of several miniaturized technologies as a first step to accurately measure the Earth's energy imbalance (EEI) with a constellation of small satellites. Regarding the educational objectives, the UVSQ-SAT program seeks to promote the transmission and valorization of scientific and technical knowledge through the innovation. This one feeds the creation of value and allows the implementation of technological breakthroughs and the associated risk-taking, the \"NewSpace\", and technology transfer. Developed from 2017, UVSQ-SAT is based on a CubeSat architecture [2; 3], which represents a satellite format defined in 1999 by the California Polytechnic State University and Stanford University (USA). UVSQ-SAT was developed and implemented by LATMOS and its INSPIRE international partners. The INSPIRE consortium was formed in 2015, with the objectives of developing small satellites to perform science missions, building a project-based learning curriculum for space science and engineering, and establishing a supporting network of ground stations. UVSQ-SAT/INSPIRESat-5 fully meets these objectives. A representative mockup of the UVSQ-SAT satellite is provided in Figure 1 left. Before being launched into space, a test campaign of the UVSQ-SAT CubeSat was carried out from August to October 2020. It typically involves several mechanical tests, electromagnetic compatibility (EMC) tests, calibration and performance tests, thermal vacuum and thermal balance tests, magnetic tests, and end to end tests. The satellite has been fully tested with French facilities (Figure 2) at LATMOS, at the Plateforme d'Integration et de Tests (PIT) of the Observatoire de Versailles Saint-Quentin-en-Yvelines (OVSQ), at French space agency (CNES), and at the Office National d'Etudes et de Recherches Aerospatiales (ONERA). A successful mechanical testing campaign of the UVSQ-SAT CubeSat was mandatory to get a launch clearance. It involved quasi-static testing (t  
Figure 1: (**Left**) Representative mockup of the UVSQ-SAT satellite. (**Right**) Transporter 1 mission (SpaceX) with 143 commercial and government satellites on-board, including UVSQ-SAT. Credits: SpaceX. a static load of 15 g to simulate the acceleration of the launch vehicle), shock testing, as well as random vibration (test levels are shown in Figure 3 left). Random vibration was carried out to simulate the loads of the upper stages of the SpaceX Falcon 9 launcher and is the most severe test. Before and after each random axis test run, a resonance search (Figure 3 right) was done with a frequency sweep of low-level sinusoidal vibrations to characterize main resonant modes of the UVSQ-SAT CubeSat, to determine if the tests loads have changed the mechanical properties of the CubeSat (first eigenmode close to 418 Hz), and to show possible deficiencies. Thermal bakeout was mandatory (+60 \({}^{\circ}\)C) for outgassing volatile materials of the CubeSat. A thermal vacuum cycling test (temperatures profile given in Figure 4) was also carried out to simulate the temperature conditions in orbit and to demonstrate that the CubeSat is able to survive, without loss of integrity or functionality. After performing all performances and environmental tests with success and confirmation of frequency coordination, UVSQ-SAT was ready to go in space.