Using Reliability Optimization to Prevent Planetary Destruction

SUMMARY & CONCLUSIONSThis paper presents a thought-experiment case study in planetary defense, using asteroid 2024 YR4 as a reference scenario to illustrate how design-for-reliability (DfR) practices can be applied to a high-stakes, single-shot mission. Although subsequent observations have shown that YR4 is unlikely to impact Earth, the asteroid’s orbital dynamics and timeline provide an excellent framework for evaluating how fault tree analysis (FTA), redundancy allocation, and mission-level design trade-offs can optimize reliability in a kinetic impactor mission.A notional mission architecture was developed, consisting of a single impactor launched in 2028 on a direct intercept trajectory, with arrival near the asteroid in late 2028. The spacecraft design emphasizes simplicity and robustness, while still requiring critical systems such as propulsion, guidance and navigation, communications, power, and thermal regulation. A baseline fault tree was constructed with the top event defined as "failure to impact YR4 at the required geometry and velocity." Initial analysis showed that mission reliability is dominated by GN&C and propulsion, with power and thermal systems acting primarily through cascading failures.Reliability optimization was then addressed through targeted redundancy, including dual star trackers, multiple optical navigation cameras, cross-strapped thrusters, and dual-string power systems. FTA results demonstrate that relatively modest increases in system mass can yield significant reductions in failure probability, though trade-offs must be carefully managed. As discussed, "mass is mass" in terms of momentum transfer, but not all kilograms contribute equally to mission assurance: dense impact mass is guaranteed to reach the target, while fragile subsystems may not survive to deliver momentum efficiently. Thus, redundancy investment must balance increased reliability against structural robustness.Finally, mission-level redundancy was examined through the use of multiple launches. Modeling showed that fielding two or three impactors can reduce failure probability to very low levels—but only if common causes are properly addressed. Launching identical spacecraft on identical vehicles exposes the mission to shared risks, limiting the benefit of redundancy. By deliberately diversifying launch vehicles, spacecraft builds, or timelines, overall reliability is significantly improved. This counterintuitive lesson—that sometimes two "perfect" systems are less reliable than a mixed fleet—underscores the value of FTA in capturing dependencies and guiding design decisions.In conclusion, this study demonstrates that DfR methodologies, particularly fault tree analysis, can provide critical insights into how to optimize planetary defense missions. Beyond the specific case of asteroid 2024 YR4, the work illustrates how reliability engineering principles can help ensure that when the stakes are highest, humanity’s first line of defense is as robust as possible.