# pg_orbit — Solar System Computation for PostgreSQL

## What This Is
A PostgreSQL extension that moves orbital mechanics inside the database — the way PostGIS did for geography. Native C extension using PGXS, 68 SQL functions, 7 custom types, covering satellites (SGP4/SDP4), planets (VSOP87 + optional JPL DE441), Moon (ELP2000-82B), 19 planetary moons (L1.2/TASS17/GUST86/MarsSat), stars, comets, Jupiter radio bursts, and interplanetary Lambert transfers.

**Current version:** 0.3.0 on branch `phase/solar-system-expansion`
**Repository:** https://git.supported.systems/warehack.ing/pg_orbit
**Documentation:** https://pg-orbit.warehack.ing

## Build System
```bash
make PG_CONFIG=/usr/bin/pg_config           # Compile with PGXS
sudo make install PG_CONFIG=/usr/bin/pg_config  # Install extension
make installcheck PG_CONFIG=/usr/bin/pg_config  # Run 13 regression test suites
```

Requires: PostgreSQL 17 development headers, GCC, Make.

### Docker
```bash
make docker-build   # Build standalone image (pg17 + pg_orbit)
make docker-test    # Smoke test the image
make docker-push    # Push to git.supported.systems registry
```

Image: `git.supported.systems/warehack.ing/pg_orbit:pg17`

## Project Layout
```
pg_orbit.control                # Extension metadata (version 0.3.0)
Makefile                        # PGXS build + Docker targets
sql/
  pg_orbit--0.1.0.sql           # v0.1.0: satellite types/functions/operators
  pg_orbit--0.2.0.sql           # v0.2.0: solar system (57 functions)
  pg_orbit--0.3.0.sql           # v0.3.0: complete extension (68 functions)
  pg_orbit--0.1.0--0.2.0.sql    # Migration: v0.1.0 → v0.2.0 (adds solar system)
  pg_orbit--0.2.0--0.3.0.sql    # Migration: v0.2.0 → v0.3.0 (adds DE ephemeris)
src/
  pg_orbit.c                    # PG_MODULE_MAGIC + _PG_init() (GUC registration)
  types.h                       # All struct definitions + constants + DE body ID mapping
  astro_math.h                  # Shared astronomical helpers + observe_from_geocentric()
  # --- Satellite (v0.1.0) ---
  tle_type.c                    # TLE custom type (I/O, binary, 15 accessors)
  eci_type.c                    # ECI position type + geodetic/topocentric types
  observer_type.c               # Observer type with flexible string parsing
  sgp4_funcs.c                  # sgp4_propagate(), _safe(), _series(), tle_distance()
  coord_funcs.c                 # eci_to_geodetic(), eci_to_topocentric(), ground_track()
  pass_funcs.c                  # next_pass(), predict_passes(), pass_visible()
  gist_tle.c                    # GiST operator class (&&, <->)
  # --- Solar System (v0.2.0) ---
  vsop87.c / vsop87.h           # VSOP87 planetary ephemeris (Bretagnon 1988)
  elp82b.c / elp82b.h           # ELP2000-82B lunar ephemeris (Chapront 1988)
  precession.c / precession.h   # IAU 1976 precession (Lieske 1979)
  sidereal_time.c / .h          # GMST calculation (Vallado Eq. 3-47)
  elliptic_to_rectangular.c/.h  # Orbital element conversions
  planet_funcs.c                # planet_observe(), planet_heliocentric(), sun/moon_observe()
  star_funcs.c                  # star_observe(), star_observe_safe()
  kepler_funcs.c                # kepler_propagate(), comet_observe()
  l12.c / l12.h                 # L1.2 Galilean moon theory (Lieske 1998)
  tass17.c / tass17.h           # TASS 1.7 Saturn moon theory (Vienne & Duriez 1995)
  gust86.c / gust86.h           # GUST86 Uranus moon theory (Laskar & Jacobson 1987)
  marssat.c / marssat.h         # MarsSat Mars moon theory (Jacobson 2014)
  moon_funcs.c                  # galilean/saturn/uranus/mars_moon_observe()
  radio_funcs.c                 # io_phase_angle(), jupiter_cml(), burst_probability()
  lambert.c / lambert.h         # Lambert transfer solver (Izzo 2015)
  transfer_funcs.c              # lambert_transfer(), lambert_c3()
  # --- JPL DE Ephemeris (v0.3.0) ---
  de_reader.h / de_reader.c     # Clean-room JPL DE binary reader (Chebyshev/Clenshaw)
  eph_provider.h / eph_provider.c # Provider dispatch, GUC, lazy init, frame rotation
  de_funcs.c                    # All _de() SQL function implementations
  sgp4/                         # Vendored SGP4/SDP4 (Bill Gray's sat_code, MIT license)
    sgp4.c                      # Near-earth propagator (period < 225 min)
    sdp4.c                      # Deep-space propagator (period >= 225 min)
    deep.c                      # Lunar/solar perturbations, resonance integration
    common.c                    # Shared initialization (Brouwer mean elements, Kepler solver)
    basics.c                    # select_ephemeris(), FMod2p()
    get_el.c                    # TLE parsing (parse_elements(), checksum)
    tle_out.c                   # TLE output (write_elements_in_tle_format())
    norad.h / norad_in.h        # Public + internal headers
    PROVENANCE.md               # Vendoring decision, modifications, verification
    LICENSE                     # MIT license (Bill Gray / Project Pluto)
test/
  sql/                          # 13 regression test suites
  expected/                     # Expected output
  data/vallado_518.json         # 518 Vallado test vectors (AIAA 2006-6753-Rev1)
docs/
  DESIGN.md                     # Architecture decisions, theory-to-code mappings
  Dockerfile                    # Starlight docs site (Astro + Caddy)
  package.json                  # Docs site dependencies
  astro.config.mjs              # Starlight configuration
  src/content/docs/             # MDX documentation pages
```

## Type System

All types are fixed-size, `STORAGE = plain`, `ALIGNMENT = double`. No TOAST overhead.

| Type | Bytes | Description |
|------|-------|-------------|
| `tle` | 112 | Parsed mean orbital elements for SGP4/SDP4 |
| `eci_position` | 48 | x,y,z + vx,vy,vz (km, km/s) in TEME frame |
| `geodetic` | 24 | lat, lon (radians), alt (km) above WGS-84 |
| `topocentric` | 32 | azimuth, elevation, range, range_rate |
| `observer` | 24 | lat, lon (radians), alt_m (meters) |
| `pass_event` | 48 | AOS/MAX/LOS times + max_el + AOS/LOS azimuth |
| `heliocentric` | 24 | x, y, z in AU (ecliptic J2000 frame) |

## Function Domains (68 total)

| Domain | Theory | Key Functions | Count |
|--------|--------|---------------|-------|
| Satellite | SGP4/SDP4 (Brouwer 1959) | `observe()`, `predict_passes()`, `ground_track()` | 22 |
| Planets | VSOP87 (Bretagnon 1988) | `planet_observe()`, `planet_heliocentric()` | 3 |
| Sun/Moon | VSOP87 + ELP2000-82B | `sun_observe()`, `moon_observe()` | 2 |
| Planetary moons | L1.2, TASS17, GUST86, MarsSat | `galilean_observe()`, `saturn_moon_observe()` | 4 |
| Stars | J2000 + IAU 1976 precession | `star_observe()`, `star_observe_safe()` | 2 |
| Comets/asteroids | Two-body Keplerian | `kepler_propagate()`, `comet_observe()` | 2 |
| Jupiter radio | Carr et al. (1983) | `jupiter_burst_probability()` | 3 |
| Transfers | Lambert (Izzo 2015) | `lambert_transfer()`, `lambert_c3()` | 2 |
| DE ephemeris | JPL DE440/441 (optional) | `planet_observe_de()`, `moon_observe_de()` | 11 |
| GiST index | Altitude-band approximation | `&&` (overlap), `<->` (distance) | 8 |
| Diagnostics | -- | `pg_orbit_ephemeris_info()` | 1 |

All functions are `PARALLEL SAFE`. VSOP87/ELP82B functions are `IMMUTABLE` (compiled-in coefficients). DE functions are `STABLE` (external file dependency).

## Body IDs

### Planets (VSOP87 convention)
| ID | Body | ID | Body |
|----|------|----|------|
| 0 | Sun | 5 | Jupiter |
| 1 | Mercury | 6 | Saturn |
| 2 | Venus | 7 | Uranus |
| 3 | Earth | 8 | Neptune |
| 4 | Mars | 10 | Moon |

### Planetary Moons (per-family indexing)
- **Galilean** (0-3): Io, Europa, Ganymede, Callisto
- **Saturn** (0-7): Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Iapetus, Hyperion
- **Uranus** (0-4): Miranda, Ariel, Umbriel, Titania, Oberon
- **Mars** (0-1): Phobos, Deimos

## Constant Chain of Custody

**The most critical design constraint.** TLEs absorb geodetic model biases — using wrong constants silently corrupts positions by kilometers.

### Rules
1. **SGP4 propagation**: WGS-72 constants ONLY (mu, ae, J2, J3, J4, ke)
2. **Coordinate output** (geodetic, topocentric): WGS-84 (a=6378.137km, f=1/298.257223563)
3. **TEME frame**: Only 4 of 106 IAU-80 nutation terms (matching SGP4's internal model)
4. **Solar system pipeline**: IAU 1976 precession, J2000 obliquity, GMST from Vallado Eq. 3-47
5. **Never mix**: WGS-72 propagation + WGS-84 output. No other combination.
6. **DE frame rotation**: DE positions (ICRS equatorial) pass through `equatorial_to_ecliptic()` at the provider boundary before entering the observation pipeline
7. **Same-provider rule**: Both target and Earth must come from the same provider in any geocentric computation (never mix DE target with VSOP87 Earth)
8. **DE AU consistency**: Verify DE header AU matches compiled-in `AU_KM` (149597870.7) at init time

### WGS-72 Constants (from Hoots & Roehrich STR#3, propagation only)
```c
#define WGS72_MU      398600.8            /* km^3/s^2 */
#define WGS72_AE      6378.135            /* km */
#define WGS72_J2      0.001082616
#define WGS72_KE      0.0743669161331734132  /* (min)^(-1) */
```

### WGS-84 Constants (coordinate output only)
```c
#define WGS84_A       6378.137            /* km */
#define WGS84_F       (1.0 / 298.257223563)
```

### Astronomical Constants
```c
#define AU_KM           149597870.7         /* IAU 2012 */
#define GAUSS_K         0.01720209895       /* AU^(3/2)/day */
#define OBLIQUITY_J2000 0.40909280422232897 /* 23.4392911 deg in radians */
#define J2000_JD        2451545.0           /* 2000 Jan 1.5 TT */
```

## JPL DE Ephemeris (Optional)

v0.3.0 adds optional JPL DE440/441 ephemeris support (~0.1 milliarcsecond accuracy) alongside the existing VSOP87 pipeline (~1 arcsecond). DE functions are separate `_de()` variants — existing VSOP87 functions are completely unchanged.

### Architecture

- **Clean-room DE reader** (`de_reader.c`): ~250 lines of C. Parses the JPL binary format, evaluates Chebyshev polynomials via Clenshaw recurrence. No GPL dependency (avoids Bill Gray's `jpl_eph`).
- **Per-backend lazy init**: Each PostgreSQL backend opens its own file descriptor on first `_de()` call. Never opens in `_PG_init()` (postmaster context). Safe for `PARALLEL SAFE`.
- **VSOP87 fallback**: Every `_de()` function falls back to its VSOP87/ELP82B equivalent when DE is unavailable.
- **STABLE volatility**: DE functions are `STABLE` (not `IMMUTABLE`) because output depends on an external file. Existing VSOP87 functions remain `IMMUTABLE`.

### GUC Configuration

```sql
-- Set the path to a JPL DE binary file (requires superuser)
ALTER SYSTEM SET pg_orbit.ephemeris_path = '/var/lib/postgres/de441.bin';
SELECT pg_reload_conf();

-- Check which provider is active
SELECT * FROM pg_orbit_ephemeris_info();
```

| GUC | Type | Default | Context |
|-----|------|---------|---------|
| `pg_orbit.ephemeris_path` | string | `''` (empty = VSOP87 only) | `SIGHUP` (superuser only) |

### DE Function Variants

Every `_de()` function mirrors an existing VSOP87 function:

| DE Function | VSOP87 Equivalent | Volatility |
|-------------|-------------------|------------|
| `planet_heliocentric_de()` | `planet_heliocentric()` | STABLE |
| `planet_observe_de()` | `planet_observe()` | STABLE |
| `sun_observe_de()` | `sun_observe()` | STABLE |
| `moon_observe_de()` | `moon_observe()` | STABLE |
| `lambert_transfer_de()` | `lambert_transfer()` | STABLE |
| `lambert_c3_de()` | `lambert_c3()` | STABLE |
| `galilean_observe_de()` | `galilean_observe()` | STABLE |
| `saturn_moon_observe_de()` | `saturn_moon_observe()` | STABLE |
| `uranus_moon_observe_de()` | `uranus_moon_observe()` | STABLE |
| `mars_moon_observe_de()` | `mars_moon_observe()` | STABLE |
| `pg_orbit_ephemeris_info()` | — | STABLE |

## Vendored SGP4/SDP4

Bill Gray's sat_code (MIT license): https://github.com/Bill-Gray/sat_code

Vendored into `src/sgp4/` from upstream commit `ff7b98957dfa2979700a482bde9de9542807293e`. The `.cpp` files were renamed to `.c` — the code is valid C99 with zero C++ features (no classes, templates, namespaces, exceptions, or STL). This eliminates the `g++` and `-lstdc++` dependencies.

Modifications from upstream are minimal and documented in `src/sgp4/PROVENANCE.md`:
- Renamed `.cpp` → `.c` (no code changes — already valid C99)
- Stripped Win32 `DLL_FUNC`/`__stdcall` decorators
- Removed `extern "C"` wrapper (now compiled as C)
- Removed unused SGP/SGP8/SDP8 model prototypes
- Added forward declarations (`-Wmissing-prototypes`)
- Changed bare `inline` to `static inline` for C99 compliance
- Added equation citations referencing STR#3 and Vallado Rev-1

All numerical logic is byte-identical to upstream. Verified against 518 Vallado test vectors (AIAA 2006-6753-Rev1).

## Testing

13 regression test suites via `make installcheck`:

| Suite | What it tests |
|-------|--------------|
| tle_parse | TLE I/O round-trip, malformed input rejection, all 15 accessors |
| sgp4_propagate | SGP4/SDP4, propagation series, tle_distance |
| coord_transforms | TEME-to-geodetic, TEME-to-topocentric, ground_track |
| pass_prediction | predict_passes, next_pass, pass_visible, min elevation filter |
| gist_index | `&&` overlap, `<->` distance, GiST index scan, KNN ordering |
| convenience | observe(), observe_safe(), tle_from_lines(), observer_from_geodetic() |
| star_observe | Star observation, IAU 1976 precession, heliocentric type I/O |
| kepler_comet | Keplerian propagation (elliptic/parabolic/hyperbolic), comet_observe |
| planet_observe | VSOP87 planets, sun_observe, moon_observe (ELP2000-82B) |
| moon_observe | Galilean/Saturn/Uranus/Mars moons, Io phase, Jupiter CML, burst probability |
| lambert_transfer | Lambert solver, lambert_c3, pork chop grid, error handling |
| de_ephemeris | DE function fallback to VSOP87, cross-provider consistency, error handling |
| vallado_518 | 518 Vallado test vectors (AIAA 2006-6753-Rev1), per-satellite breakdown |

## Error Handling Patterns

- `_safe()` variants (`sgp4_propagate_safe`, `observe_safe`, `star_observe_safe`) return NULL on error instead of raising exceptions. Use these for batch queries over potentially invalid data.
- SGP4 error codes: -1 (nearly parabolic), -2 (negative semi-major axis/decayed), -3/-4 (orbit within Earth, returns with NOTICE), -5 (negative mean motion), -6 (convergence failure)
- Pass prediction: propagation failures return -pi elevation (below horizon), shedding the failed timestep without aborting the scan.
- Input validation: same-body Lambert check, arrival-before-departure, invalid body_id, RA out of [0,24), negative perihelion distance.

## Documentation Site

**Live:** https://pg-orbit.warehack.ing

Starlight docs at `docs/` — 36 MDX pages covering all domains.

Sections: Getting Started, Guides (9 domain walkthroughs incl. DE ephemeris), Workflow Translation (Skyfield/Horizons/GMAT/Radio Jupiter Pro comparisons), Reference (all 68 functions incl. DE variants), Architecture (Hamilton's principles, constant custody, observation pipeline), Performance (benchmarks).

### Local Development
```bash
cd docs && npm run dev      # Dev server on :4321
cd docs && npm run build    # Static build to dist/
```

### Production Deployment

The docs site deploys to the `warehack.ing` VPS (`149.28.126.25`) which runs caddy-docker-proxy with wildcard DNS for `*.warehack.ing`.

**Deploy (or redeploy after changes):**
```bash
ssh -A warehack-ing@pg-orbit.warehack.ing
cd ~/pg_orbit
git pull origin phase/solar-system-expansion   # or the current branch
cd docs
make prod                                       # builds image + starts container
```

**First-time setup on VPS:**
```bash
ssh -A warehack-ing@pg-orbit.warehack.ing
git clone git@git.supported.systems:warehack.ing/pg_orbit.git
cd pg_orbit && git checkout phase/solar-system-expansion
cat > docs/.env << 'EOF'
COMPOSE_PROJECT_NAME=pg-orbit-docs
NODE_ENV=production
VITE_HMR_HOST=pg-orbit.warehack.ing
EOF
cd docs && make prod
```

**Makefile targets:**
- `make prod` — build + start production (Caddy serves static files)
- `make dev` — build + start dev mode (hot-reload, volume mounts)
- `make down` — stop containers
- `make restart` — stop + start production
- `make clean` — stop + remove volumes
- `make logs` — tail container logs

**Infrastructure:** Container `pg-orbit-docs` joins external `caddy` network. caddy-docker-proxy reads labels to auto-configure reverse proxy + TLS (Let's Encrypt via Vultr DNS challenge). TLS cert provisioning takes ~2 minutes on first deploy.

**Do NOT run the docs container locally** if also deployed on the VPS — competing ACME DNS challenges will corrupt each other's TXT records.

## Coding Style
- Standard PostgreSQL extension C style
- `ereport(ERROR, ...)` for user-facing errors, never `elog(ERROR, ...)`
- All memory via `palloc`/`pfree` (PostgreSQL memory contexts)
- Comments explain "why", not "what"
- No global mutable state — all computation from function arguments (exceptions: per-backend DE handle via `on_proc_exit`; 3 statics in vendored `deep.c` + 1 cache in `sdp4.c`, safe in PostgreSQL's fork model, never modified by pg_orbit)
- Every function handling SGP4 must check the error return code
- All functions marked `PARALLEL SAFE`
- DE functions: always fall back to VSOP87/ELP82B on any error

## Git Conventions
- One commit per logical change
- Branch per phase: `phase/solar-system-expansion`
- Tag releases: `v0.1.0`, `v0.2.0`
- Commit messages: imperative mood, no AI attribution