Reference

Python / C++ API

The compiled module is imported as from arlamx_v2 import cpp (it wraps arlamx_cpp). Vectors are numpy arrays of length 3, and quaternions are scalar-first [q0, q1, q2, q3].

Simulator

p = cpp.SimParams(); p.gsi = "cll"; p.lunisolar = True
sim = cpp.Simulator(p)
sim.load_gravity(path) -> bool      sim.load_wmm(path) -> bool      sim.load_spice([kernels]) -> bool
sim.set_panels(n (N,3), A (N,), c (N,3))
sim.set_mass(m); sim.set_inertia_diag([Ix, Iy, Iz]); sim.set_inertia(I 3x3)
sim.set_atmosphere(rho, T, m_bar, chi=None)       # chi: 7 mole fractions He,O,N2,O2,Ar,H,N
sim.set_atmosphere_end(rho, T, m_bar, chi=None)   # linear interpolation over the next step
sim.set_mode("point" | "detumble" | "prescribed")
sim.set_cmd_frame("inertial" | "flow" | "flowB" | "flowS"); sim.set_nav(r, v); sim.clear_nav()
sim.set_srp_scale(s); sim.set_wind(w_N)
sim.set_controller(cpp.MRPFeedback); sim.set_quat_controller(cpp.QuaternionFeedback); sim.set_bdot(cpp.BDot())
sim.set_dipole_max(m_max); sim.set_rods(axis (N,3), dmax (N,)); sim.set_rod_gates([bool]*N)
st  = sim.reset(r, v, sigma, omega)                # dict r, v, sigma, omega, t
out = sim.step(q_cmd)                              # dict, see Architecture → StepOut
sim.get_state()                                    # r, v, sigma, omega, t, C_BN, sun_N, eclipse, altitude_km
sim.params(); sim.gravity_loaded(); sim.wmm_loaded(); sim.dipole_max(); sim.rod_gates()

Force-model kernels

Function	Returns
`sentman(theta, s, Tw_Ti, alpha_E=1)`	(C_p, C_τ) for one plate
`cll(theta, s, Tw_Ti, alpha_n=1, alpha_t=1)`	(C_p, C_τ), Walker atomic-O row
`spacecraft_aero(n, A, c, v_rel_B, rho, T, m_bar, T_w, alpha_E=1, one_sided_ref=True, gsi="sentman", alpha_n=1, alpha_t=1, chi=None)`	dict F, tau, Cd, Cl, A_ref
`coefficients_only(...)`	same, per unit q
`panel_srp_optical(n, A, c, sun_hat_B, ca, cs, cd, eclipse=1, pressure=0)`	(F, τ). pressure 0 → P_SR.
`panel_srp_force_torque(n, A, c, sun_hat_B, eclipse=1, pressure=0, Cr=0)`	(F, τ), cannonball
`earth_rad(n, A, c, nadir_B, r_m, cos_sun, p_sun, sol=(ca,cs,cd), ir=(ca,cs,cd))`	(F, τ)
`gg_torque(I_diag, r_B, mu)`	τ_gg

Orbit, frames, ephemeris

Function	Notes
`accel_twobody(r, mu)`, `accel_j2(r, mu, Re, J2)`, `accel_j3(...)`	closed forms
`GravityHarmonics().load_ggm(path, max_degree=20)`, `.accel_ecef(r, deg)`, `.mu()`, `.Re()`, `.J2()`	SH model
`accel_third_body(r_sat, r_body, mu_body)`	point-mass perturbation
`sun_unit_analytic(jd)`, `sun_dist_au(jd)`, `moon_analytic(jd) -> (r_hat, r_m)`	analytic ephemerides
`eclipse_cylindrical(r, s_hat, Re)`, `gmst_rad(jd)`, `ecef_to_geodetic(r) -> (lat, lon, h)`, `sma_from_rv(r, v, mu)`	geometry helpers
`propagate_f32_samples(r0, v0, offsets_s, dt_s=30, bc_inv=0, rho0=3e-12, alt0_m=4e5, h_scale=6e4, a_srp=0, sun_hat=None)`	onboard FP32 forecast

Attitude and control

Item	Notes
`mrp_to_dcm, mrp_shadow, mrp_rate, mrp_compose, mrp_error, mrp_angle`	MRP algebra
`quat_mul, quat_conj, quat_unit, quat_normalize, slerp_clip, quat_to_mrp, mrp_to_quat, dcm_to_quat`	quaternions (Hamilton, scalar first)
`MRPFeedback`, `QuaternionFeedback`	`kp, kd, max_body_rate, proper`; `set_inertia_diag`, `set_max_torque`, `compute(...)`
`BDot`	`gain, dt, max_dipole`, `dipole(B)`, `reset()`
`apply_magnetorquer(tau, B, m_max)`, `saturate_dipole`, `apply_rods(tau, B, axis, dmax, on)`, `rods_allocate(m, axis, dmax, on)`	magnetic allocation
`WMM().load(path)`, `.field_ecef(r, year)`, `dipole_field_ecef(r)`	field models

Constants

MU_WGS, RE_WGS, OMEGA_EARTH, J2_GGM, K_B, P_SRP_1AU

Main Python modules

Module	Entry points
`env.py`	`ArlamxV2Env`
`physics.py`	`load(name\|path\|dict, overrides)`, `validate`, `apply_to_params(params, cfg, ...)`, `msis_version`
`atmosphere.py`	`query_msis(alt_km, lat, lon, dt, f107, ap, version, return_species)`, `jd_to_datetime`
`geometry.py`	`load_mesh`, `load_geom`, `write_geom`, `simplify_sides`, `projected_area`
`sail_optics.py`	`PRESETS`, `apply_optics(params, name)`
`session.py`, `train.py`, `train_v12.py`, `sweep.py`	sessions, `train_one`, `build_model`, `train_run`
`decay_run.py`	`coe_to_rv`, prescribed decay
`config.py`	`load`, `merge`, `load_reward`, `pin`, `snapshot`