difforb 0.1.0

Differentiable small-body orbit computation and orbit determination with JAX.

DiffOrb

DiffOrb is a differentiable, batchable Python framework for small-body orbit propagation, orbit determination, and Horizons-like ephemeris products. It is built on JAX and keeps the main numerical objects compatible with automatic differentiation, JIT compilation, and vectorized execution.

Documentation: Read the DiffOrb documentation

Features

• Native JAX with an object-oriented interface.
• Automatic differentiation support and usage.
• Batch computation and automatic broadcasting.
• Dense orbit propagation.
• Composable orbit-determination and ephemeris-generation workflow.
• Horizons-like ephemeris products.
• Reusable astrometric and astrodynamical infrastructure.

Installation

DiffOrb requires Python 3.11 or later.

python -m pip install difforb

Download the EOP parameter file, observatory list, and optical debiasing model:

python -m difforb.data install all

Verify the downloaded data:

python -m difforb.data status

Quick Start

Propagate a small body and query its state from the dense trajectory:

from difforb.body import SmallBody
from difforb.core import BCRS, State, Time
from difforb.dynamics import DynamicSystem
from difforb.integrator import NumericalIntegrator
from difforb.spk import set_default_ephemeris

set_default_ephemeris("/path/to/de441.bsp")

t0 = Time.from_tdb_date(2025, 1, 2)
t1 = Time.from_tdb_date(2025, 2, 15)
t_query = Time.from_tdb_date(2025, 1, 20)

state0 = State(
    tdb=t0.tdb(),
    pos=[1.685775738339898, -1.336388854313325, -0.2144927004440800],
    vel=[0.008995712853117517, 0.006985684417802803, 0.004020851173846060],
    frame=BCRS,
)

force_model = DynamicSystem.from_standard_system().build_force_model()
integrator = NumericalIntegrator(method="IAS15", tol=1e-12)

body = SmallBody.create(state0).propagate(t0.tdb(), t1.tdb(), force_model, integrator)
state = body.state(t_query.tdb(), frame=BCRS)

print(state.frame.name)
print(state.pos)
print(state.vel)

License

DiffOrb source code, documentation, and DiffOrb-maintained bundled data files are licensed under the Apache License, Version 2.0. Data files downloaded from external sources are still governed by the original providers' terms.