# INSPIRE-SAT 7, a Second CubeSat to Measure the Earth's Energy Budget and to Probe the Ionosphere
## 1 Introduction  
INSPIRE-SAT 7 is a scientific and technological pathfinder CubeSat mainly developed to measure the Earth's Energy (or Radiation) Budget (ERB) at the top-of-the-atmosphere (TOA) and to probe the ionosphere. INSPIRE-SAT 7 is a 2U CubeSat (11.5 \(\times\) 11.5 \(\times\) 22.7 cm) with a total mass budget limit of 3.0 kg and a power limit consumption of 3 W (orbit averaged power). INSPIRE-SAT 7 is a continuation of the UltraViolet and infrared Sensors at high Quantum efficiency onboard a small SATellite (UVSQ-SAT) programme [1]. UVSQ-SAT was successfully launched on 24 January 2021 by the Falcon 9 rocket, and represents the first French CubeSat measuring key scientific parameters (Outgoing Shortwave Radiation (OSR), Outgoing Longwave Radiation (OLR), Earth's magnetic field). The UVSQ-SAT CubeSat has been performing continuously ERB measurements since February 2021 [2]. In 2023, INSPIRE-SAT 7 will join its precursor satellite UVSQ-SAT in orbit to provide a global coverage of Earth observation with a shorter time span, and then replace UVSQ-SAT. The orbit selection is directly related to the scientific goals. It is necessary to take into account the constraints of the rules governing the space debris mitigation (international treaties, French space operation act), and the launch opportunities. The selected orbit is a Sun-synchronous orbit with a maximum altitude of 600 km and a local time at descending node (LTDN) of \(\sim\)09:30 h (vs. \(\sim\)21:30 h for UVSQ-SAT), which will result in an atmospheric reentry of the satellite within 25 years. INSPIRE-SAT 7 is planned to have a 2-years nominal mission lifetime, including the commissioning phase. The first objective of INSPIRE-SAT 7 is to improve the UVSQ-SAT technologies that are used to measure the ERB components and derive the Earth's Energy Imbalance (EEI), which is the difference between global mean solar radiation absorbed by the Earth system and thermal infrared radiation emitted to space by it. EEI results primarily from the increase in greenhouse gases levels and drives the global change. It is a crucial quantity for testing climate models and for the prediction of the future course of global warming. INSPIRE-SAT 7 will measure the incoming solar radiation (total solar irradiance (TSI)) and the outgoing terrestrial radiation (OSR and OLR) using 12 miniaturized Earth's radiative sensors (thermopiles with carbon nanotubes and optical solar reflectors). The second objective is to validate new technologies that help to characterize the state of the ionosphere for space weather studies and test an innovative approach based on the combined use of a ground-based High-Frequency (HF) transmitter and of a HF receiver onboard the INSPIRE-SAT 7 CubeSat. The attenuation of HF waves by the ionosphere crossing will be measured during the entire CubeSat trajectory, when it is visible from the ground transmitter. This kind of technology is important for monitoring the state of the ionosphere and, in particular, for wave propagation predictions. Indeed, multiple phenomena originating from the Sun or the lower of atmosphere can strongly disturb the ionosphere and wave propagation, even posing a threat to orbiting satellites in the case of powerful solar storms. The third objective of the INSPIRE-SAT 7 mission is to validate new technologies for other purposes. For instance, 14 photodiodes will be used to measure the TSI but also solar radiation in the ultraviolet range, whose variability directly impacts the ozone layer and the temperatures in the middle atmosphere. INSPIRE-SAT 7 will also operate the first Li-Fi (or Light Fidelity) module in orbit onboard a CubeSat. The aim is to demonstrate that light-based wireless communication is a credible alternative to traditional copper harnesses for small satellites. Finally, an amateur radio payload will be tested onboard INSPIRE-SAT 7. It is a complete 'open-source' bidirectional telemetry printed circuit board for CubeSat.