Ryan Malloy
70420c3b4f
Add Universal Variable Lambert solver for computing transfer orbits between any two planets. Enables pork chop plot generation as SQL: SELECT dep_date, arr_date, lambert_c3(3, 4, dep_date, arr_date) FROM generate_series(...) dep CROSS JOIN generate_series(...) arr; New functions: - lambert_transfer(dep_body, arr_body, dep_time, arr_time) → RECORD Returns C3 departure/arrival (km^2/s^2), v_infinity (km/s), time of flight (days), and transfer orbit SMA (AU). - lambert_c3(dep_body, arr_body, dep_time, arr_time) → float8 Convenience: departure C3 only, NULL on solver failure. The solver uses Stumpff functions for unified elliptic/parabolic/hyperbolic handling, with Newton-Raphson iteration and bisection fallback. Each solve is sub-millisecond; PARALLEL SAFE for batch computation. All 11 regression tests pass.
61 lines
1.8 KiB
C
61 lines
1.8 KiB
C
/*
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* lambert.h -- Lambert transfer orbit solver
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*
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* Solves Lambert's problem: given two position vectors and a
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* time of flight, find the orbit connecting them.
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*
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* Uses the Universal Variable formulation with Stumpff functions,
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* handling elliptic, parabolic, and hyperbolic transfers uniformly.
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*
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* Reference:
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* Bate, Mueller & White, "Fundamentals of Astrodynamics" (1971)
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* Battin, "An Introduction to the Methods of Astrodynamics" (1999)
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* Curtis, "Orbital Mechanics for Engineering Students" (2014)
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*
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* All units: AU, days, AU/day. Gravitational parameter is Gauss's
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* constant squared (k^2 = GM_sun in AU^3/day^2).
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*
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* Thread-safe: no static mutable state.
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*/
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#ifndef PG_ORBIT_LAMBERT_H
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#define PG_ORBIT_LAMBERT_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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/*
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* Result of a Lambert transfer orbit solution.
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* All velocities in AU/day.
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*/
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typedef struct lambert_result
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{
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double v1[3]; /* departure velocity vector (AU/day) */
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double v2[3]; /* arrival velocity vector (AU/day) */
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double sma; /* semi-major axis (AU), negative for hyperbolic */
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int converged; /* 1 if solver converged, 0 otherwise */
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} lambert_result;
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/*
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* Solve Lambert's problem.
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*
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* r1[3]: departure position (AU, heliocentric ecliptic J2000)
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* r2[3]: arrival position (AU, heliocentric ecliptic J2000)
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* tof_days: time of flight in days (must be > 0)
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* mu: gravitational parameter (AU^3/day^2), use GAUSS_K2 for Sun
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* prograde: 1 for prograde (short way), 0 for retrograde (long way)
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* result: output lambert_result
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*
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* Returns 1 on success, 0 on failure.
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*/
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int lambert_solve_uv(const double r1[3], const double r2[3],
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double tof_days, double mu, int prograde,
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lambert_result *result);
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#ifdef __cplusplus
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}
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#endif
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#endif /* PG_ORBIT_LAMBERT_H */
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