DiffOrb

DiffOrb is a differentiable, batchable Python framework for small-body orbit propagation, orbit determination, and Horizons-like ephemeris products.

Features

Key features:

• Native JAX with an object-oriented interface. DiffOrb exposes object-oriented, PyTree-compatible public objects for common astrodynamical workflows, while keeping the numerical core compatible with JIT compilation, vectorized execution, and automatic differentiation.
• Automatic differentiation support and usage. DiffOrb keeps its core computations differentiable and uses this capability internally, including residual Jacobians for differential correction, radar Doppler from the derivative of the converged delay model, and velocity or acceleration derived from SPK position interpolation.
• Batch computation and automatic broadcasting. DiffOrb supports scalar inputs and batch inputs. For batch inputs, public APIs support automatic broadcasting, including aligned evaluation and Cartesian-product grid evaluation. This allows one call to evaluate many targets, epochs, observers, states, or observations without user-written loops or multiprocessing code.
• Dense orbit propagation. DiffOrb propagates small-body states in BCRS as functions of TDB and returns dense trajectories over the solved time interval. The same trajectory can be reused by light-time iteration, optical reduction, radar reduction, and ephemeris-product generation.
• Composable orbit-determination and ephemeris-generation workflow. DiffOrb exposes the major stages from observations or supplied orbits to fitted solutions and prediction products as composable components, including observation loading, initial orbit determination, differential correction, outlier rejection, weighting policies, propagation, and observation modelling.
• Horizons-like ephemeris products. From a fitted or supplied orbit, DiffOrb can generate optical tables, radar tables, vector states, osculating elements, apsides, and close-approach products using shared propagation and reduction models.
• Reusable astrometric and astrodynamical infrastructure. DiffOrb provides reusable interfaces for epoch creation, time-scale and reference-frame conversion, Earth-orientation modelling, observatory position calculation, and SPK/DE ephemeris access. These are the same components used internally by the orbit-determination and ephemeris-generation workflow.

Documentation Coverage

• Time scales, Earth rotation, frames, states, sites, and orbital elements.
• Observation loading, optical debiasing, weighting, and measurement reduction.
• Force models, numerical propagation, and prediction products.
• SPK ephemeris access and ephemeris-backed body queries.
• Initial orbit determination, differential correction, outlier handling, and high-level orbit-determination workflows.

Suggested Reading Order

1. Start with Installation to install DiffOrb.
2. Read Concepts to understand the models and algorithms used by DiffOrb.
3. Use Guides to learn how to use the common DiffOrb APIs.
4. Use Workflows to learn how to use DiffOrb for real orbit-determination and ephemeris-generation tasks.
5. Use the API pages when you need exact arguments and return fields.

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.