Stabilize Earth module and fix satellite TLE handling

backend/app/core/satellite_tle.py

@@ -0,0 +1,116 @@
+"""Helpers for building stable TLE lines from orbital elements."""
+
+from __future__ import annotations
+
+from datetime import datetime
+from typing import Any, Optional
+
+
+def compute_tle_checksum(line: str) -> str:
+    """Compute the standard modulo-10 checksum for a TLE line."""
+    total = 0
+
+    for char in line[:68]:
+        if char.isdigit():
+            total += int(char)
+        elif char == "-":
+            total += 1
+
+    return str(total % 10)
+
+
+def _parse_epoch(value: Any) -> Optional[datetime]:
+    if not value:
+        return None
+    if isinstance(value, datetime):
+        return value
+    if isinstance(value, str):
+        return datetime.fromisoformat(value.replace("Z", "+00:00"))
+    return None
+
+
+def build_tle_line1(norad_cat_id: Any, epoch: Any) -> Optional[str]:
+    """Build a valid TLE line 1 from the NORAD id and epoch."""
+    epoch_date = _parse_epoch(epoch)
+    if not norad_cat_id or epoch_date is None:
+        return None
+
+    epoch_year = epoch_date.year % 100
+    start_of_year = datetime(epoch_date.year, 1, 1, tzinfo=epoch_date.tzinfo)
+    day_of_year = (epoch_date - start_of_year).days + 1
+    ms_of_day = (
+        epoch_date.hour * 3600000
+        + epoch_date.minute * 60000
+        + epoch_date.second * 1000
+        + int(epoch_date.microsecond / 1000)
+    )
+    day_fraction = ms_of_day / 86400000
+    decimal_fraction = f"{day_fraction:.8f}"[1:]
+    epoch_str = f"{epoch_year:02d}{day_of_year:03d}{decimal_fraction}"
+
+    core = (
+        f"1 {int(norad_cat_id):05d}U 00001A   {epoch_str}"
+        "  .00000000  00000-0  00000-0 0  999"
+    )
+    return core + compute_tle_checksum(core)
+
+
+def build_tle_line2(
+    norad_cat_id: Any,
+    inclination: Any,
+    raan: Any,
+    eccentricity: Any,
+    arg_of_perigee: Any,
+    mean_anomaly: Any,
+    mean_motion: Any,
+) -> Optional[str]:
+    """Build a valid TLE line 2 from the standard orbital elements."""
+    required = [
+        norad_cat_id,
+        inclination,
+        raan,
+        eccentricity,
+        arg_of_perigee,
+        mean_anomaly,
+        mean_motion,
+    ]
+    if any(value is None for value in required):
+        return None
+
+    eccentricity_digits = str(round(float(eccentricity) * 10_000_000)).zfill(7)
+    core = (
+        f"2 {int(norad_cat_id):05d}"
+        f" {float(inclination):8.4f}"
+        f" {float(raan):8.4f}"
+        f" {eccentricity_digits}"
+        f" {float(arg_of_perigee):8.4f}"
+        f" {float(mean_anomaly):8.4f}"
+        f" {float(mean_motion):11.8f}"
+        "00000"
+    )
+    return core + compute_tle_checksum(core)
+
+
+def build_tle_lines_from_elements(
+    *,
+    norad_cat_id: Any,
+    epoch: Any,
+    inclination: Any,
+    raan: Any,
+    eccentricity: Any,
+    arg_of_perigee: Any,
+    mean_anomaly: Any,
+    mean_motion: Any,
+) -> tuple[Optional[str], Optional[str]]:
+    """Build both TLE lines from a metadata payload."""
+    line1 = build_tle_line1(norad_cat_id, epoch)
+    line2 = build_tle_line2(
+        norad_cat_id,
+        inclination,
+        raan,
+        eccentricity,
+        arg_of_perigee,
+        mean_anomaly,
+        mean_motion,
+    )
+    return line1, line2