STTS-Orbital: Trajectory Similarity Monitoring for Planetary Defense / Early Detection of Near-Earth Object Close Approaches from Short Observational Arcs

Current planetary defense monitoring systems — Sentry, Scout, CNEOS — detect close approach candidates by computing collision probability from orbit determinations that require weeks to months of observational arc to converge. We propose applying the State Topology and Trajectory Storage (STTS) framework to near-Earth asteroid orbital mechanics, asking a different question: does the current trajectory resemble trajectories that preceded confirmed close approaches? Applied to JPL Horizons orbital element histories for 973 confirmed Earth close approaches, STTS achieves V1 basin separation of 3.8x, V2 monotonic approach ρ = 0.631, and F1 = 1.000 95% CI: 0.998–1.000 on 795 held-out test objects (designation-level split). With 1,825-day trajectory histories, mean detection lead reaches 1,693 days (4.6 years) before close approach; 57.6% of objects are detected within 90 days of any point in their tracked history, and no object requires more than 665 days of history to trigger detection. The distribution is right-truncated at the 1,825-day window — the signal precedes the available data. Applied out-of-sample to asteroid 99942 Apophis, the framework produces a triage signal from 45 days of observational arc, 24.4 years before the 2029 flyby, using a corpus that contained no Apophis observations. As the Vera Rubin Observatory begins full operations, discovering an estimated 5 million new solar system objects, trajectory-similarity triage provides a computationally tractable method for prioritizing follow-up observations. The complete implementation uses JPL's public Horizons and CNEOS APIs with no authentication required.