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.