Document two-body vs SGP4 propagation fidelity in ActorBuilder#214
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gomezzz merged 1 commit intoJul 6, 2026
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set_orbit creates an analytical Keplerian two-body orbit, so J2 and drag are unmodelled and propagated positions drift from real satellite trajectories over multi-hour horizons. Measured for a LEO/SSO actor seeded from an SGP4 state: 252 km at +3 h, 5,418 km at +72 h vs the TLE's SGP4 trajectory, while set_TLE matches SGP4 exactly. Add a fidelity note to the set_orbit docstring pointing TLE users to set_TLE, a cross-reference in set_TLE, and a matching N.B. in the README's orbit section. No behaviour change. Verified-by: pytest paseos/tests — 30 passed; 6 pre-existing env failures identical on unmodified tree Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Seems there is an issue with the CI, approving since only doc changes and should hence be fine. Thanks Tobias!
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Description
Summary of changes
ActorBuilder.set_orbitdocstring: it creates an analytical two-body orbit (no J2 / drag), so propagated positions drift from real satellite trajectories over multi-hour horizons; TLE users should preferset_TLE, higher-fidelity usersset_custom_orbit.set_TLEdocstring (propagates with SGP4, consistent with the model that generated the TLE).Motivation: we seeded a LEO/SSO actor (Sentinel-1C) via
set_orbitfrom its SGP4 state at epoch and measured divergence vs the TLE's SGP4 trajectory: 252 km @ +3 h, 485 km @ +6 h, 908 km @ +12 h, 1,856 km @ +24 h, 3,634 km @ +48 h, 5,418 km @ +72 h.set_TLEmatched SGP4 to 0.00 km in the same setup. Both behaviours are correct — this PR just makes the fidelity trade-off visible at the point of choice. Docs-only, no behaviour change.Resolved Issues
How Has This Been Tested?
pytest paseos/testsrun before/after the change: 30 passed, 6 failures pre-existing and identical on the unmodified tree in this environment (pykep/boost "bad lexical cast" + one thermal assert).Related Pull Requests
🤖 Generated with Claude Code