# Design and Validation of a U-Net-Based Algorithm for Star Sensor Image Segmentation
## 4 Discussion
### Small Satellite Mission Proposal  
The payload will be able to process camera images up to 10 Hz. This would be good both for AD and RSO detection functions. It will have a total weight not higher than 330 g, a total power consumption not higher than 2 watts with a total volume lower than 0.3 U. It can be installed both on Cubesats and micro satellite platforms, and once in orbit, it can work without any limitations of pointing except for the luminosity conditions: Sun, Moon and Earth to be avoided within the FOV.
* The orbit: The RSOs spatial and mass distribution is strictly related to the former space activities and the collisions and fragmentation of orbiting objects. Several studies have described and modeled the debris evolution during the years, showing that LEO is the most densely populated region around the Earth, especially in 600-800 km altitudes with high inclinations [49]. For this reason, the onboard SST mission will be focused on LEO debris detection at a 600-800 km altitude range, and the orbit selection will be constrained by the sun illumination. To guarantee the correct detection functioning, the optical sensor (on-board camera or star sensor) cannot be oriented against the Sun. Figure 18 shows possible sun-illumination conditions. In particular, \(d_{s_{i}t_{i}}\) represent the target directions, with \(s_{i}\) denoting the observer satellite and \(t_{i}\) one of the debris elements. Satellite \(s_{2}\) cannot detect target \(t_{2}\) because it is backlit, while the sun illumination allows for a correct detection of target \(t_{1}\) by satellite \(s_{1}\). Another limiting factor to be considered is the presence of the Earth in the FOV, because of the consequent reduced FOV of the optical sensor. To guarantee the visibility of the target by the observer, the vector \(\hat{d}_{s;t_{i}}\) cannot cross the Earth. Finally, to ensure the same sun-illumination condition during the mission, the best candidate orbits for object detection are the Sun-Synchronous Orbits (SSOs). In particular, the dawn-dusk orbits can ensure a continuous and constant utilization of the optical sensors, while the noon/midnight orbits are not recommended for this kind of application due to the possibility of having eclipses. Due to all these considerations, the selected orbit for the mission will be a circular dawn-dusk SSO with a height of 700 km.
* The purpose: Detection of RSO populations in the LEO region will be with an onboard optical sensor and an AI-based image segmentation routine.
* The Validation: The satellite will be equipped with an attitude control system (ACS) capable of orienting the SAGITTA boresight direction in the along-track direction and anti-Sun direction to maximize the time the RSOs spend inside the FOV. Ground commands will be sent to the platform to schedule the pointing operation to switch between these two targeted directions. An input image will be stored together with the corresponding mask for validation purposes during a test phase. Once on the ground, the raw image will be processed and compared with the onboard produced mask. A match score based on Precision, Recall and F1 indices will be used to assess the correctness of the onboard payload routine. During normal operation, the payload will be responsible for the provision of the attitude for the onboard platform. The platform will be equipped with a reliable and independent attitude determination module to compare the payload outputs in term of quaternion.  
The mission intended to be proposed has as a goal the detection of space debris in LEO. The payload will be mounted onto a 3U Cubesat, where an entire unit will be dedicated for our payload.