Is Simplicity Golden? A Survey of Post-Launch Adaptation in Planetary Missions

The conventional wisdom in space systems engineering holds that simplicity is golden: systems should minimize complexity while meeting requirements. A simpler system is typically considered more robust and less prone to risk because it can be tested thoroughly and has fewer points of failure. While the core philosophy of this principle remains valid, we argue that the reality is more nuanced—particularly for planetary exploration missions, which face substantially greater uncertainties than Earth-orbiting missions. We investigated 10 past and ongoing missions that encountered unexpected situations and either successfully or unsuccessfully adapted to them: Galileo, Hayabusa, EPOXI, Deep Space 1, Juno, SMAP, OSIRIS-Rex, InSight, Mars 2020 Rover (Perseverance), and Ingenuity. Our study draws on a series of interviews with experts directly involved in these missions, as well as a review of relevant literature. We found that it is often departures from design minimalism—such as functional redundancy in sensing and actuation, subsystem interconnections, and onboard software flexibility—that enabled, or could have enabled, missions to adapt to anomalies and surprises. From these observations, we distilled five design principles for future planetary missions to enhance adaptability while keeping overall system complexity under control. Finally, we propose a concept of software-defined space systems (SSDSs), which is built upon the proposed design principles and can dynamically adapt physical behaviors in remote planetary environments.