{
  "schema": "system-state-atlas/science-profile-2",
  "status": "experimental project convention; not an IAU standard or a certified navigation service",
  "profile_id": "usst-tcb-j2000/1",
  "coordinate_time": {
    "scale": "TCB",
    "epoch": {
      "julian_date": 2451545.0,
      "scale": "TCB"
    },
    "value": "elapsed coordinate seconds since the declared TCB epoch",
    "formula": "USST = (JD_TCB - 2451545.0) * 86400",
    "not_a_local_proper_clock": true,
    "tdb_relation": {
      "LB": 1.550519768e-08,
      "T0": 2443144.5003725,
      "TDB0_seconds": -6.55e-05,
      "source_id": "iau-tdb"
    }
  },
  "stored_state": {
    "time_compatibility": "TDB",
    "origin": "Solar System barycenter, Horizons 0",
    "axes": "ICRF",
    "position_unit": "km",
    "velocity_unit": "km/s",
    "corrections": "NONE; geometric simultaneous-coordinate states",
    "rescaled_to_TCB": false,
    "TCB_label_does_not_relabel_dynamics": true
  },
  "display_coordinates": {
    "solar": "heliocentric state difference in J2000 ecliptic axes",
    "obliquity_arcsec": 84381.448,
    "local": "east, north, up at declared WGS84 geodetic site",
    "azimuth": "clockwise from true north; undefined for vertical direction",
    "solardian": "heliocentric spherical display; radius/c in seconds as a length notation",
    "polar_longitude": null,
    "origin_longitude_and_latitude": null,
    "gaze": "unit direction transformed by rotations only"
  },
  "data_modes": [
    {
      "id": "jpl-horizons-2026-6h-r1",
      "file": "horizons-2026.json",
      "start": "2026-01-01T00:00:00 TDB",
      "end": "2027-01-01T00:00:00 TDB",
      "targets": 11,
      "retained_samples_per_target": 1461,
      "method": "exact retained samples or cubic Hermite interpolation; no extrapolation",
      "earth_target": 399,
      "moon_target": 301
    },
    {
      "id": "jpl-table1-transcription-2026-09-23",
      "file": "approximate-elements.json",
      "range": "2000\u20132049",
      "method": "low-accuracy fitted Keplerian elements with rates and numerical derivative",
      "earth_proxy": "Earth\u2013Moon barycenter, target3",
      "moon_unavailable": true
    }
  ],
  "earth_attitude": {
    "bias_precession": "IAU2006 Fukushima\u2013Williams",
    "nutation": "ERFA-derived IAU2000B with P03 adjustment",
    "sidereal_rotation": "ERA + IAU2006 GMST polynomial + truncated equation of equinoxes",
    "eop": "earth-orientation-2026.json; linear interpolation; prediction flags retained",
    "without_eop": "UT1=UTC and polar motion=0, explicitly marked unavailable/assumed",
    "not_applied": [
      "celestial-pole dX/dY",
      "length-of-day rate correction",
      "light-time",
      "aberration",
      "gravitational deflection",
      "refraction",
      "terrain",
      "sensor calibration"
    ]
  },
  "utc": {
    "TT_minus_TAI_seconds": 32.184,
    "TAI_minus_UTC_2026_seconds": 37,
    "announcement": "IERS Bulletin C72, no leap at end December2026",
    "later_epochs": "37seconds held as an explicitly labeled projection",
    "TT_to_TDB": "NAIF naif0012 periodic approximation; separate numeric comparison report",
    "leap_second_label": "not representable by browser Date; explicit 23:59:60 rejected"
  },
  "galactic": {
    "center_icrs_degrees": [
      266.4051,
      -28.936175
    ],
    "solar_distance_kpc": 8.122,
    "solar_height_pc": 20.8,
    "solar_velocity_galactocentric_km_s": [
      12.9,
      245.6,
      7.78
    ],
    "convention": "Astropy v4.0 parameter set pinned; not absolute velocity",
    "measured_star_catalog_included": false,
    "galaxy_drawing": "illustrative structure; not a star catalog or integrated Galactic orbit"
  },
  "proposed_units": {
    "solartation": "NAIF pck00011 solar reference grid rotation; 360/14.18440 TDB days",
    "solorbitron": "Sun barycentric trajectory descriptor; no fixed period adopted",
    "SSD": "no duration adopted",
    "system_year": "no exact Galactic calendar unit adopted"
  },
  "uncertainty_rules": [
    "Never equate display precision with measured accuracy.",
    "Held-out interpolation discrepancies compare one interpolation scheme to the same provider's samples, not independent physical observations.",
    "Numerical comparison with ERFA at selected epochs is not a guarantee at every epoch or a physical error bar.",
    "Imports declare their provider; a valid schema does not authenticate the provider or validate physical truth.",
    "Preserve epoch, origin, axes, units, body IDs, source hashes, source models, interpolation status, and degraded-mode flags in exports."
  ],
  "id": "system-state-atlas/2.0"
}