Lily Beesley, University of Birmingham; Phineas Whitlock, University of Warwick; Gruffudd Jones, University of Birmingham; James Blake, University of Warwick; Nina Maric, University of Birmingham, Rhea Space Activity; Leah-Nani Alconcel, University of Birmingham
https://doi.org/10.64861/INPV6617
Keywords: SDA, light curve, simulation, characterisation, software
Abstract:
Photometric observations of resident space objects (RSOs) provide a remote means of characterising their physical properties, attitude, and rotational state. As space situational awareness (SSA) and space domain awareness (SDA) become increasingly critical amid a growing orbital population, the ability to rapidly and accurately interpret photometric signatures is of growing importance. Synthetic light curves can support this effort, enabling the characterisation of RSO operational state, physical geometry, surface material properties, and attitude, as well as the production of labelled datasets for training machine learning architectures for automated RSO characterisation and monitoring. Critically, these datasets can be produced over timescales far shorter than observational campaigns and under controlled conditions that may be difficult to replicate through observation alone. Despite their growing importance, existing light curve simulators are either not publicly available or rely on simplified models that limit their utility for realistic SSA/SDA applications._x000D_
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We present SatLight, an open-source Python package for high-fidelity synthetic light curve generation of RSOs. Built on the Blender Python API, SatLight constructs a scene containing a model of the RSO, solar and Earth illumination sources, and the observer’s perspective._x000D_
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To replicate the perspective of a distant observer, SatLight employs orthographic ray casting in which rays are cast with parallel observing vectors across each screen co-ordinate, thus removing geometric foreshortening. For each point where the ray intersects the object surface, the surface normal and hit location are used to evaluate the bidirectional reflectance distribution function (BRDF) at that point for a given illumination angle. SatLight includes a library of common BRDFs suitable for typical spacecraft surface materials, and also supports user-supplied BRDF definitions. _x000D_
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Currently accepted object geometries imported via standard .obj and .stl file formats allow accurate representation of the complex structures of operational spacecraft and debris objects. For any 3D objects in the .obj format, complementary material files (.mtl) are not currently supported; material properties are instead specified via user-selected BRDFs._x000D_
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To the authors’ knowledge, SatLight also represents the first publicly available light curve simulation code to implement self-shadowing. Self-shadowing is implemented by casting a secondary shadow ray from each hit point toward the sun direction, with occluded points contributing zero flux. The reflected radiance at each surface element is scaled by the projected area of that element, summed over all illuminated surface elements, and scaled by the inverse square of the observer distance. Light curves are output in either monochromatic flux or AB magnitude._x000D_
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The incident solar flux defaults to the standard solar constant of 1360 W m-2 but can be specified by the user to match the bandpass-integrated solar irradiance of a given observing instrument. Earthshine irradiance is also incorporated by discretising Earth’s surface with an albedo of 0.3 at each point. _x000D_
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SatLight aims to provide the tools necessary for advanced light curve analysis, including RSO fingerprint generation for feature extraction, component failure analysis, and improved determination of rotation state and attitude. By also enabling rapid generation of large, labelled reference datasets, SatLight can support the training of machine learning models for automated classification systems. Additionally, SatLight offers capabilities for brightness mitigation analysis to reduce the impact of satellite constellations on astronomical observations._x000D_
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The capabilities of SatLight are demonstrated across three representative RSO scenarios: a tumbling rocket body, a geostationary satellite bus with tracking solar panels, and a Starlink v1.5 transit. These cases provide diverse surface reflectance properties, object geometry, and illumination conditions relevant to real observing scenarios. The fidelity of SatLight is then assessed through comparison of simulated light curves against measured data, demonstrating that the key photometric features are reproduced by the simulation._x000D_
Date of Conference: September 15-18, 2026
Track: Satellite Characterization