# UVsq-Sat NG, a New CubeSat Pathfinder for Monitoring Earth Outgoing Energy and Greenhouse Gases
## 3 Description of the Uvsq-Sat NG Space-Based Mission
### Description of the Uvsq-Sat NG Satellite and Its Payloads
The scientific objectives of the mission require a satellite capable of accurately pointing to an observation area. Furthermore, Uvsq-Sat NG must possess both agility and swiftness to rapidly align itself with the target area. This is important, especially during calibration phases (atmospheric corrections), where it will be necessary to rapidly observe a target area (Nadir, Earth's limb) from various angles. These calibrations will also require rapid payloads data acquisitions to mitigate the satellite's motion effect (\(\sim\)6 km s\({}^{-1}\)). These various objectives led us to implement a complex ADCS system to meet our requirements. The UVsq-Sat NG ADCS subsystem is tasked with precisely determining and managing the satellite's orientation or attitude in space. It can achieve an absolute pointing error of 0.1 degrees or even higher precision, along with an attitude knowledge error of 0.05 degrees, in accordance with the mission's requirements. Several elements contribute to ensuring this performance. The essential components of this subsystem encompass an ADCS OnBoard Computer, a Star Tracker OnBoard Computer, sensors (Uvsq-Sat NG photodiode, Fine Sun Sensor, Uvsq-Sat NG magnetometer, Star Tracker, LATMOS Inertial Measurement Unit (IMU) with its gyroscopes and magnetometers), and actuators (Reaction Wheel, iMTQ with magnetorquers), as shown in Figure 1. Coarse and Fine Sun Sensors are used to detect the Sun's direction, contributing to determining the satellite's orientation with respect to the Sun. Magnetometers measure the local magnetic field, assisting in establishing the satellite's orientation in relation to Earth's magnetic field. Gyroscopes are utilized to measure angular rates, furnishing insights into changes in the satellite's attitude. The Star Tracker is used for star identification and tracking, allowing for the determination of the satellite's orientation relative to known star positions. The IMU combines accelerometers and gyroscopes to furnish precise attitude information. Magnetic Torquers create torque by interacting with Earth's magnetic field, allowing for controlled adjustments in orientation. Reaction Wheels employ spinning wheels to generate angular momentum, enabling controlled rotations with precision. Figure 2 depicts the general control loop of the UVsq-Sat NG ADCS. At its core, the fundamental International Geomagnetic Reference Field (IGRF) and Simplified General Perturbations 4 (SGP4) models, which have demonstrated their effectiveness in flight, are utilized for magnetic field modeling and accurate orbit propagation, aiding in predicting a satellite's trajectory over time by accounting for various gravitational perturbations and forces. In advanced high-performance platforms such as Uvsq-Sat NG (utilizing a Global Navigation Satellite System (GNSS) and a Global Positioning System (GPS) antenna), models are substituted with GNSS inputs for position, velocity, and timing. Attitude Determination relies on a sophisticated Unscented Kalman Filter that leverages non-linear dynamics and fuses sensor information from all available sources, enabling optimal estimations of spacecraft attitude and angular rate. Attitude Control employs a range of controllers, including B-dot, magnetic-only pseudo three-axis control, and a quaternion-feedback Proportional-Integral-Derivative (PID) controller. These functionalities are accessed through specific operational modes, facilitating initial spacecraft detumbling, magnetometer-based angular rate estimation, comprehensive attitude and angular rate estimation, and three-axis control directed towards inertial and rotating reference frames. The Two-Line Element set (TLE) is commonly used for tracking and predicting the orbits of satellites.