astroz is an astrodynamics and spacecraft toolkit with a fast SGP4/SDP4 propagator at its core.
| 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 |
|
SGP4 (near-earth) or SDP4 (deep-space) is picked per satellite from its orbital period. Satellites are propagated 8 at a time with SIMD (AVX512, or AVX2/SSE at 4 wide), and constellations are split across threads in time-major order. ASTROZ_THREADS sets the thread count; the default is every available core.
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 |
Measured on an AMD Ryzen 7 7840U (16 threads), each implementation in its fastest configuration (SIMD, pre-allocated outputs, batch mode). The scripts for astroz, Rust sgp4 and python-sgp4 are in benchmarks/ (see the Justfile).
The Cesium visualization example propagates the whole active catalog (about 13,000 satellites) at interactive rates. There is a live demo.
Accuracy
What the test suite checks (zig build test):
| Component |
Reference |
Tolerance |
| SGP4 |
Vallado AIAA 2006-6753 vectors |
10 m position, 1 mm/s velocity |
| SDP4 (GPS, GEO, HEO) |
python-sgp4 |
10 m position |
| SGP4 over one day |
python-sgp4 |
100 m position, 0.1 m/s velocity |
| J2 acceleration |
Analytical |
1% |
| Two-body propagation |
Analytical Kepler |
1 m after one orbit |
| Two-body energy |
Conservation |
1e-10 relative over 100 orbits |
CI also checks the Python bindings against python-sgp4 to within 1 m.
With CSPICE enabled: zig build test -Denable-cspice=true
Python
Wheels are published for Linux (x86_64, arm64) and macOS (arm64), Python 3.10 to 3.14:
pip install astroz
astroz.api follows the python-sgp4 API and also handles deep-space (SDP4) satellites:
from astroz.api import Satrec, jday, WGS72
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)
The Python README covers batch propagation, the high-level propagate/screen API, orbital mechanics helpers and numbers for migrating from python-sgp4.
Usage
Requires Zig 0.17.0.
- Fetch the package so it gets recorded in your
build.zig.zon. Pin a release tag or commit for reproducible builds, or follow the latest main:
# pinned to a tag or commit
zig fetch --save https://github.com/ATTron/astroz/archive/<tag-or-commit>.tar.gz
# latest main
zig fetch --save git+https://github.com/ATTron/astroz
- Wire the
astroz module into your compile step in build.zig:
const astroz = b.dependency("astroz", .{ .target = target, .optimize = optimize });
exe.root_module.addImport("astroz", astroz.module("astroz"));
- Propagate a satellite.
Satellite picks SGP4 or SDP4 for you:
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
Run them all with zig build example, or only compile them with zig build build-examples.
Zig
-
sgp4.zig: TLE and OMM parsing (including six-digit catalog numbers), SGP4 one time and eight at once with SIMD, Satellite picking SGP4 or SDP4, and the Earth-fixed position.
-
constellation.zig: a mixed near-earth and deep-space constellation propagated in batches, then screened for close approaches with Screening.
-
numerical_propagation.zig: one orbit propagated with two-body (RK4 and Dormand-Prince 8(7)), with J2, and with J2, solar radiation pressure and Sun/Moon gravity. Uses SPICE ephemeris when built with -Denable-cspice=true after zig build fetch-kernels.
-
spacecraft.zig: impulse, plane change and phase change maneuvers and how they change the orbit, then attitude propagation.
-
mission_design.zig: Earth to Mars by Hohmann and bi-elliptic transfer, the transfer propagated, and Monte Carlo statistics on it.
-
packets.zig: building and parsing CCSDS packets and parsing a VITA 49 stream.
-
astronomy.zig: star precession and reading a FITS image into a PNG.
Python
- python_sgp4.py: the python-sgp4 compatible API.
- constellation.py: loading a constellation from CelesTrak or a TLE/OMM file, propagating to Earth-fixed and geodetic coordinates, and screening it for close approaches.
- orbital_mechanics.py: circular-orbit numbers, Hohmann and bi-elliptic transfers, Lambert’s problem and numerical propagation with J2.
- Cesium visualization (live demo): the active catalog propagated and rendered in Cesium.
评论