Within the context of scientific planetary missions – characterized by multi-instrument systems with demanding operational timelines – there is a need for more detailed, system-level analyses grounded in simulation rather than simplified analytical sizing methods. Growing accessibility and proficiency in high-level programming are shifting the paradigm from monolithic software solutions to bespoke script-based analysis in the spacecraft systems engineering process.

This thesis, conducted within the ESA EnVision project team at ESTEC, presents the development, implementation and evaluation of PAS3: a Python toolkit for Accessible SPICE-based Spacecraft Simulations. PAS3 streamlines the creation of ad-hoc, simulation-backed models for discipline-specific analysis, for any planetary mission in its implementation phase. It integrates Andrew Annex’ SpiceyPy, a procedural wrapper of NASA/JPL’s NAIF SPICE toolkit, inside an object-oriented framework extending its accessibility to non-developers. The toolkit was used to develop models for EnVision’s attitude, instrument and platform thermals, and power generation, as well as an interactive web-based 3D mission visualization.

PAS3 is an open-source package under the Permissive European Space Agency – ESA Software Community Licence and is available on the European Space Software Repository.

The search for extra-terrestrial life has long fascinated humanity, with Enceladus, one of Saturn's moons, emerging as a prime candidate due to hydrothermal activity and methane detected in its South Pole plumes by the Cassini mission. The ELMO orbiter is designed to explore Enceladus, searching for biosignatures, mapping its surface, and relaying data from two hopper vehicles deployed on the Saturnian moon. Carrying five scientific payload instruments, the orbiter must meet strict constraints, including a total mission cost of $750 million USD and compatibility with the Ariane 64 launcher. The spacecraft provides 6000 m/s Delta-V through a two-stage design: a main orbiter (3400 m/s) and a kick stage (2600 m/s). It also features an 85 m^2 solar array for power generation and a dual-band communication system to handle high data acquisition requirements (15% of operations time).

The lightweight truss structure, made of low-density composites, incorporates MLI for thermal regulation and multiple radiation-shielded electronics vaults. The fixed high-gain antenna ensures efficient Earth communication at Ka, X, and S bands. Weighing 13400 kg at launch, ELMO's innovative design cannot comply with the launch requirements, and it is therefore advised to perform further studies to re-evaluate the mission.