PhotSat is a satellite mission aimed at exploring deep space through high-resolution imaging using advanced optical sensors. Utilizing a CubeSat platform, the mission seeks to obtain precise astronomical data at a low cost, leveraging miniaturized technologies that reduce complexity while maximizing observational capabilities. The platform is equipped with a high-performance optical system capable of capturing images in two spectral bands (visual and ultraviolet), making it possible to detect transient events such as exoplanets or variable stars. The preliminary design of PhotSat integrates an innovative data compression system based on a binary context-based arithmetic coder, ensuring the preservation of quality in crucial observations while optimizing bandwidth and storage usage. A comparative experiment was conducted with five state-of-the-art codecs, and the results show that the proposed codec outperforms the others in terms of compression efficiency. PhotSat establishes a significant precedent in the field of astronomy with CubeSats, serving as a proof of concept for the feasibility of low-cost scientific missions yielding high-quality results.