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Astrodynamics and Spacecraft Toolkit. Features fast orbit prop, celestial precession, CCSDS parsing, RF parsing, fits image parsing, and more!

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## Astronomical and Spacecraft Toolkit Written in Zig

**Featuring the fastest CPU based open source SGP4/SDP4 propagator**

| Orbital Mechanics | Spacecraft Ops | Astronomy |
|-------------------|----------------|-----------|
| SGP4/SDP4 propagation | CCSDS packets | FITS parsing |
| TLE & OMM parsing | VITA49 packets | WCS coordinates |
| Orbital maneuvers | Attitude determination | Star precession |
| Force models (J2-J4, drag, SRP, third-body) | CSPICE ephemeris | Celestial bodies |
| Dormand-Prince 8(7) integrator | Monte Carlo sims | |

### Performance

Sub-meter accuracy validated against reference implementations. Automatically dispatches between SGP4 (near-earth) and SDP4 (deep-space) based on orbital period. Uses SIMD (AVX512/AVX2) to process 8 satellites simultaneously, with multithreaded constellation propagation across all available cores.

#### Single-Threaded (1.2M propagations, single satellite)

| Implementation | Props/sec | Speedup vs python-sgp4 |
|----------------|-----------|------------------------|
| **astroz** | **30.8M** | **11x** |
| Rust sgp4 | 5.1M | 1.8x |
| heyoka | 3.8M | 1.3x |
| satkit | 3.5M | 1.2x |
| python-sgp4 | 2.8M | 1x |

#### Multi-Threaded Constellation (13,478 satellites × 1,440 times)

| Implementation | 1 Thread | 16 Threads |
|----------------|----------|------------|
| **astroz** | 37.7M/s | **303M/s** |
| heyoka | 15.7M/s | 155.6M/s |
| Rust sgp4 (rayon) | 4.4M/s | 47.9M/s |
| satkit | 3.5M/s | 3.5M/s |
| python-sgp4 | 2.7M/s | 2.7M/s |

*Benchmarked on AMD Ryzen 7 7840U (16 threads). All implementations using their optimal configurations (SIMD, pre-allocated outputs, batch mode).*

Uses SIMD (AVX512 for 8-wide, AVX2/SSE for 4-wide) with multithreaded time-major iteration. Validated against Vallado AIAA 2006-6753 reference vectors (< 10m position error, < 1µm/s velocity error). Set `ASTROZ_THREADS` environment variable to control thread count (defaults to all available cores).

The [Cesium visualization example](examples/README.md) propagates the entire active satellite catalog (~13,000 satellites) at interactive rates. **[Try the live demo →](https://attron.github.io/astroz-demo/)**

### Validated Accuracy

Force models and propagators are validated against reference implementations:

| Component | Reference | Tolerance |
|-----------|-----------|-----------|
| SGP4/SDP4 propagation | python-sgp4 | < 100m position |
| J2 RAAN drift | Vallado analytical | < 1% |
| Hohmann transfer ΔV | poliastro | < 0.1% |
| Orbital periods | Analytical | 1e-10 relative |
| Two-body energy | Conservation law | 1e-10 over 100 orbits |

Run validation tests: `zig build test`

With CSPICE enabled (for high-precision ephemeris): `zig build test -Denable-cspice=true`

### Python

Only supports **Linux x86_64** and **macOS ARM64** (Python 3.10–3.14):

```bash
pip install astroz
```

#### python-sgp4 Compatible API (Recommended)

Drop-in replacement for [python-sgp4](https://github.com/brandon-rhodes/python-sgp4) with transparent deep-space (SDP4) support. Just change the import for instant speedup:

```python
# Before                                    # After
from sgp4.api import Satrec, jday      →    from astroz.api import Satrec, jday
```

| Your Code | python-sgp4 | astroz | Speedup |
|-----------|-------------|--------|---------|
| `sat.sgp4()` loop | 1.3M/s | 2.5M/s | **2x** |
| `sat.sgp4_array()` | 2.7M/s | 15M/s | **5x** |
| `SatrecArray.sgp4()` | 3M/s | 290M/s | **100x** |

See [migration guide](bindings/python/README.md#migrating-from-python-sgp4) for optimization tips.

```python
from astroz.api import Satrec, SatrecArray, jday, WGS72
import numpy as np

# Single satellite (same syntax as python-sgp4)
line1 = "1 25544U 98067A   24127.82853009  .00015698  00000+0  27310-3 0  9995"
line2 = "2 25544  51.6393 160.4574 0003580 140.6673 205.7250 15.50957674452123"
sat = Satrec.twoline2rv(line1, line2, WGS72)

jd, fr = jday(2024, 5, 6, 12, 0, 0.0)
error, position, velocity = sat.sgp4(jd, fr)

# Batch propagation (270-330M props/sec with SIMD)
sat_array = SatrecArray([sat1, sat2, ...])  # List of Satrec objects

# Single time point (scalars)
e, r, v = sat_array.sgp4(2460000.5, 0.5)

# Multiple time points (arrays)
jd = np.full(1440, 2460000.5)
fr = np.linspace(0, 1, 1440)
e, r, v = sat_array.sgp4(jd, fr)  # (n_sats, n_times, 3)

# Skip velocities for 30% faster propagation
e, r, _ = sat_array.sgp4(jd, fr, velocities=False)
```

#### High-Level API

Convenience functions for common workflows:

```python
from astroz import propagate, Constellation
import numpy as np

# Load and propagate - automatically optimized for maximum performance
positions = propagate("starlink", np.arange(1440))  # 1 day at 1-min intervals
# shape: (1440, num_satellites, 3) in km, ECEF coordinates

# With options
from datetime import datetime, timezone
positions = propagate(
    "starlink",
    np.arange(1440),
    start_time=datetime(2024, 6, 15, tzinfo=timezone.utc),
    output="geodetic",  # "ecef" (default), "teme", or "geodetic"
)

# With velocities
positions, velocities = propagate("starlink", np.arange(1440), velocities=True)

# For repeated propagation, pre-parse to avoid overhead
c = Constellation("starlink")
positions = propagate(c, np.arange(1440))
```

#### Orbital Mechanics & Numerical Propagation

```python
from astroz import hohmann_transfer, propagate_numerical, EARTH_MU, EARTH_J2, EARTH_R_EQ

# Hohmann transfer: LEO to GEO
result = hohmann_transfer(EARTH_MU, 6778, 42164)
print(f"Total ΔV: {result['total_dv']:.3f} km/s")

# Numerical propagation with J2 perturbation
state = (6778.0, 0.0, 0.0, 0.0, 7.668, 0.0)  # [x,y,z,vx,vy,vz] km, km/s
times, states = propagate_numerical(
    state, 0.0, 86400.0, 60.0, EARTH_MU,
    j2=EARTH_J2, r_eq=EARTH_R_EQ,
)
```

Also available: `bi_elliptic_transfer`, `lambert`, `orbital_velocity`, `orbital_period`, `escape_velocity`. See [Python README](bindings/python/README.md) for full details.

### Usage

- Add `astroz` as a dependency in your `build.zig.zon`.

```sh
zig fetch --save https://github.com/ATTron/astroz/archive/<git_tag_or_commit_hash>.tar.gz
#or
zig fetch --save git+https://github.com/ATTron/astroz/#HEAD
```

- Use `astroz` as a module in your `build.zig`.

```zig
const astroz_dep = b.dependency("astroz", .{
    .target = target,
    .optimize = optimize,
});
const astroz_mod = astroz_dep.module("astroz");
exe.root_module.addImport("astroz", astroz_mod);
```

- Propagate any satellite — the `Satellite` type auto-selects SGP4 or SDP4:

```zig
const astroz = @import("astroz");

var tle = try astroz.Tle.parse(tle_string, allocator);
defer tle.deinit();

const sat = try astroz.Satellite.init(tle, astroz.constants.wgs84);
const result = try sat.propagate(60.0); // minutes from epoch
const pos = result[0]; // [x, y, z] km
const vel = result[1]; // [vx, vy, vz] km/s
```

### Examples

#### Spacecraft Operations

- #### [Force Model Propagation](examples/maneuver_planning.zig)
  Composable force models (TwoBody, J2) with the Dormand-Prince 8(7) adaptive integrator. Shows `ForceModel.wrap()` and `Composite` for combining perturbations.

- #### [Constellation Phasing](examples/constellation_phasing.zig)
  Sun-synchronous orbit design and constellation plane separation using J2-induced RAAN drift.

- #### [Orbit Orientation Determination](examples/simple_spacecraft_orientation.zig)
  Calculate spacecraft attitude and orientation.

#### Orbital Mechanics

- #### [Planet Transfer & Mission Planning](examples/transfer_propagation.zig)
  Demonstrates interplanetary transfers with mission planning (Hohmann vs Bi-Elliptic comparison) and trajectory propagation.

- #### [Orbit Maneuvers](examples/orbit_maneuvers.zig)
  Comprehensive example showing TLE-based orbit propagation with various maneuver types: impulse, plane change, and phase change.

- #### [Monte Carlo Simulation](examples/simple_monte_carlo.zig)
  Statistical analysis for mission planning with uncertainty.

- #### [Propagation](examples/propagation.zig)
  Analytical orbit propagation using SGP4/SDP4 with TLE input. Demonstrates direct SGP4 usage, the modular propagator interface, and the unified Satellite type that auto-dispatches between SGP4 and SDP4.

- #### [SPICE Propagation](examples/spice_propagation.zig)
  High-fidelity LEO propagation with SPICE-updated Sun/Moon ephemeris. Combines TwoBody + J2 + SRP + third-body perturbations with real-time position updates.

- #### [Cesium Satellite Visualization](examples/README.md) — **[Live Demo](https://attron.github.io/astroz-demo/)**

Interactive 3D visualization of the entire near-earth satellite catalog (~13,000 satellites) using Cesium. Features multithreaded SGP4/SDP4 propagation at ~300M props/sec, constellation filtering, search, and satellite tracking.

#### Telemetry & Data Handling

- #### [Parse Vita49](examples/parse_vita49.zig) / [with Callback](examples/parse_vita49_callback.zig)
  VITA Radio Transport (VRT) packet stream parsing.

- #### [Parse CCSDS](examples/parse_ccsds.zig) / [with File Sync](examples/parse_ccsds_file_sync.zig)
  Parse CCSDS space packet protocol from files.

- #### [Create CCSDS Packet](examples/create_ccsds_packet.zig) / [with Config](examples/create_ccsds_packet_config.zig)
  Generate CCSDS packets for telemetry.

#### Astronomy & Astrometry

- #### [Generate Image from FITS File](examples/parse_fits_file.zig)
  Parse and render FITS astronomical image data.

- #### [Precess Star Coordinates](examples/precess_star.zig)
  Calculate stellar precession to a target epoch.

- #### [Calculate WCS from TLE](examples/wcs.zig)
  Compute World Coordinate System values from orbital elements.

[ci-shd]: https://img.shields.io/github/actions/workflow/status/ATTron/astroz/ci.yaml?branch=main&logo=github&label=CI&labelColor=black
[ci-url]: https://github.com/ATTron/astroz/blob/main/.github/workflows/ci.yaml
[cd-shd]: https://img.shields.io/github/actions/workflow/status/ATTron/astroz/cd.yaml?branch=main&logo=github&label=CD&labelColor=black
[cd-url]: https://github.com/ATTron/astroz/blob/main/.github/workflows/cd.yaml
[dc-shd]: https://img.shields.io/badge/click-F6A516?logo=zig&logoColor=F6A516&label=doc&labelColor=black
[dc-url]: https://attron.github.io/astroz

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