collision#

Collision probability computation for conjunction assessment.

Compute probability of collision (Pc) between two space objects given their state vectors, position covariances, and hard-body radii. Implements the Foster 2D method (NASA CARA), Chan series expansion, and Alfano maximum Pc bound. Validates against the TraCSS CA verification dataset.

Installation#

Install with opam:

$ opam install collision

If opam cannot find the package, it may not yet be released in the public opam-repository. Add the overlay repository, then install it:

$ opam repo add samoht https://tangled.org/gazagnaire.org/opam-overlay.git
$ opam update
$ opam install collision

Usage#

let report_pc (cdm : Cdm.t) =
  (* Quick Pc from a CDM *)
  let pc = Collision.pc ~hbr:0.015 cdm in
  Fmt.pr "Pc = %e@." pc;
  (* Step-by-step: project to conjunction plane, then compute *)
  let enc = Collision.encounter_of_cdm ~hbr:0.015 cdm in
  let pc_foster = Collision.pc_foster enc in
  let pc_max = Collision.pc_max enc in
  Fmt.pr "Foster Pc: %e, Max Pc bound: %e@." pc_foster pc_max

API Overview#

type encounter -- Conjunction geometry in the encounter plane: miss_x, miss_y, sigma_x, sigma_y, hbr
encounter_of_cdm -- Project CDM conjunction geometry onto the conjunction plane
pc_foster -- 2D Pc via Gauss-Legendre quadrature (NASA CARA standard method)
pc_chan -- Pc via Chan series expansion
pc_max -- Upper bound: hbr^2 / (2 * sigma_x * sigma_y)
pc -- Convenience: project + Foster in one call
assess -- Full assessment from a CDM (returns assessment with all Pc methods)
risk_level -- Classify an assessment: Low, Medium, High, Critical
tca -- Refine time of closest approach from ephemeris arrays

Testing#

TraCSS verification dataset: Validated against 900K+ conjunction scenarios from the TraCSS CA Verification Dataset (spherical + SFSH screening volumes)
GMAT interop: Two-object conjunction scenario from NASA GMAT R2026a — ISS-like vs SSO-like on crossing orbits. Validates miss distance and relative velocity from OEM ephemerides. See test/interop/gmat/.

License#

ISC

Configure Feed