# UVSQ-SAT, a Pathfinder CubeSat Mission for Observing Essential Climate Variables
## Appendix A  
UVSQ-SAT consists of several subsystems such as the mechanical structure, the power subsystem, the thermal control subsystem, the attitude determination and control system (ADCS), the command and data handling subsystem (CDHS), the communication subsystem and the payload subsystem (ERS, DEVINS, and the 3-axis accelerometer/gyroscope/compass (TW sensor)). The UVSQ-SAT CubeSat structure is compliant with the CubeSat standard and is compatible with the ISIPOD or Quadpack CubeSat deployer. Two separation switches are part of the satellite structure. These ensure that the UVSQ-SAT CubeSat is inactive during launch and pre-launch activities. All UVSQ-SAT materials and coating selection, must be compliant with specific requirements such as total mass loss (TML) less than 1% and collected volatile condensable material (CVCM) less than 0.1%, according to guidelines for spacecraft cleanliness control (ESA-PSS-51 from European Space Agency). The Electric Power Supply (iEPS) is designed to support the power conversion, storage and distribution to the UVSQ-SAT CubeSat subsystems. The iEPS provides 3 max power point tracking (MPPT) for power conversion up to 25 W. This system would improve the amount of power supplied to the batteries of the CubeSat. The MPPTs make sure the attached solar panel cells are operated at a voltage that yields maximum power, which increases efficiency with respect to other EPS that use fixed point voltage for the solar panels. iEPS includes 2-batteries pack (22.5 Wh), which regulates the voltage to several outputs (3.3 V, 5 V, and unregulated battery line (6-8 V)) through multiple switchable and permanent power lines. Fully charged battery corresponds to 0% depth of discharge (DOD). Ideally, 30% DOD or less is recommended full time. UVSQ-SAT has 6 ISIS solar panels made up of 12 Azurspace solar cells at high efficiency (30% for beginning of life (BOL)), which allow a solar power conversion of up to 2.2 W per 1 U area in low Earth orbit. The UVSQ-SAT ADCS contains a set of 6 photodiodes located on the solar panels (coarse estimation of the Sun's direction) and a magnetorquer board (iMTQ) with 3 magnetic actuators in 3-axis for providing actuation of 0.2 Am\({}^{2}\) (for limit the tumbling, which typically will occur as soon as the CubeSat will be deployed). UVSQ-SAT does not have a system that allows a satellite pointing in a specific direction. The CDHS subsystem with the onboard computer (OBC) will process, distribute, command, store and format data (master of the I\({}^{2}\)C bus with the different platform subsystems and the payload, high storage capacity embedded with the two SD-cards, joint test action group (JTAG) interface for debugging, etc.). It consists of a motherboard (iOBC) and a daughterboard (DB). The iOBC electronic motherboard interfaces with the UVSQ-SAT daughter board (DB), which is a custom design for the UVSQ-SAT project. The daughterboard is used on the UVSQ-SAT platform for interfacing with the external sensors of the platform (6 temperature sensors and 6 coarse photodiodes) and for interfacing with the payload electronic board (8 general purpose input/output (GPIO) pins, serial peripheral interface (SPI) data line). There is also an interface system that allows among other things to connect the electronic boards between them using the 104-pin CubeSat kit bus (CSKB) connectors. Because of satellite tumbling and low power range, radio-communications are a challenge. UVSQ-SAT uses a VHF/UHF transceiver (TRXVU), which is a full-duplex VHF/UHF radio system. It offers an uplink capability of 9.6 kbps (FSK modulation) and a downlink rate of up to 9.6 kbps (BPSK modulation). The electronic board uses radio link layer protocol AX.25. The deployable antenna system contains two tape spring antennas of up to \(\sim\)60 cm in length in the case of VHF and two tape spring antennas up to \(\sim\)20 cm in length in the case of UHF. This antenna system is located at the bottom side of the UVSQ-SAT satellite along the Z direction (Figure 2).