System-Constrained Multi-Gravity-Assist Trajectory Design for Small Satellites

Small-satellite mission design requires joint consideration of trajectory geometry, launch conditions, propulsion capacity, spacecraft mass, and operational lifetime. This study presents an integrated preliminary-design workflow combining Lambert-grid exploration, cascade filtering, and differential-evolution refinement, followed by encounter and spacecraft screening. The workflow is illustrated using Earth–Venus–Mars–Earth, Earth–Moon–Earth–Moon, and Earth–Venus–Earth–Vesta mission contexts. Launch-provided injection is separated from onboard manoeuvre requirements, and the optimization objective is identified as an energy-and-encounter-matching surrogate. An analytical assessment of 20 spacecraft–propulsion configurations shows that increasing the assumed total correction allowance from 0.10 to 0.40kms−1 reduces capacity-compliant configurations from 18 to 15. For a fixed 1538-day benchmark, increasing the assumed 3.5-year microsatellite lifetime by approximately 20.3% removes its lifetime-only exclusion. A 5 kg Nano R3 configuration requires approximately 16.50 days of ideal powered operation to deliver 100ms−1, illustrating the distinction between propellant capacity and manoeuvre-time feasibility. The results show that the candidate configuration set depends materially on the adopted screening assumptions. The framework uses patched-conic dynamics and ideal propulsion screening; independent trajectory reconstruction, stochastic robustness assessment, and finite-thrust verification remain outstanding.