Resolve space-based observatories via JPL Horizons (Closes #55)#377
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Spacecraft observatory codes (HST, JWST, WISE, ...) have no MPC parallax constants, so layup could only place them if the user supplied an explicit ADES per-observation position; otherwise the fit raised ValueError. Port the spacecraft obscode -> NAIF-id map from the Rust `spacerocks` project and query the JPL Horizons vector API for the observer's geocentric state when no position is given. - New `utilities/special_observatories.py`: the 9-entry SPACE_OBSERVATORIES map + `query_horizons_geocentric()`. Asks Horizons for a geometric (VEC_CORR=NONE), geocentric (CENTER=@399), ICRF-equatorial state in km/km-s (OUT_UNITS=KM-S) -- i.e. layup's internal moving-observer units -- and parses the CSV vector table. Epochs are batched (one request per spacecraft). - `populate_observatory()`: in the no-parallax-constants branch, route a space-based obscode without a usable ADES position to Horizons, caching the geocentric position + velocity under the same per-epoch key #147 uses, so `_barycentric_moving_observatory` adds Earth's barycentric state to it. A user-supplied ADES position always takes priority. - `obscodes_to_barycentric()`: prefetch/warm the cache for all space-based epochs up front, one batched HTTP call per spacecraft. Tests: pure-logic (map, JD conversion, CSV parser, HTTP client with the network mocked) run everywhere; LayupObservatory integration tests (ephem-gated, HTTP mocked) cover the Horizons path, the ADES-override priority, batching, and the end-to-end barycentric placement. Cross-checked live against Horizons (HST: |r|~6916 km, |v|~7.6 km/s). The existing moving-observer test switched from C51 to the roving code 247 (C51 is now Horizons-resolved). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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See comment re-Geocentric vs Barycentric queries
#377) Per the #377 review discussion (kjnapier/matthewholman): document why we query the geocentric spacecraft state (reproducible offset against a physical body vs the ephemeris-dependent barycenter) and flag the residual ~meter-level geocenter-realization mismatch as a known limitation for very high precision work (e.g. space-based occultations). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Okay thanks for adding that comment, looks good to me
This was referenced Jul 2, 2026
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Closes #55. Scoped in #55 (comment).
Spacecraft observatory codes (HST, JWST, WISE, ...) have no MPC parallax constants, so layup could only place them when the user supplied an explicit ADES per-observation position; otherwise the fit raised
ValueError. This ports the spacecraftobscode -> NAIF-idmap from the Rustspacerocksproject and queries JPL Horizons for the observer's geocentric state when no position is given.What it does
utilities/special_observatories.py— the 9-entrySPACE_OBSERVATORIESmap +query_horizons_geocentric(). Asks Horizons for a geometric (VEC_CORR=NONE), geocentric (CENTER=@399), ICRF-equatorial state in km / km·s⁻¹ (OUT_UNITS=KM-S— layup's internal moving-observer units), and parses the CSV vector table. Epochs are batched (one request per spacecraft).populate_observatory()— in the no-parallax-constants branch, a space-based obscode without a usable ADES position is routed to Horizons; the geocentric position + velocity are cached under the same per-epoch key Read in and use user provided observatory velocities in layup orbitfit #147 uses, so_barycentric_moving_observatoryadds Earth's barycentric state to it. A user-supplied ADES position always takes priority.obscodes_to_barycentric()— pre-pass warms the cache for all space-based epochs, one batched HTTP call per spacecraft.Design decisions (per the issue)
CENTER=@399) — drops straight into the existing Read in and use user provided observatory velocities in layup orbitfit #147 "geocentric + add Earth" path; no new downstream code.Scope boundaries: roving (
247/270) and occultation (275) codes stay ADES-supplied (not Horizons-resolved).Validation
test_tno_validation(real HST data) still passes — confirmed no-op, since its fixture supplies ADES positions (which keep priority).Tests
Pure-logic tests (map, JD conversion, CSV parser, HTTP client with the network mocked) run everywhere.
LayupObservatoryintegration tests (ephem-gated, HTTP mocked) cover the Horizons path, the ADES-override priority, request batching, and end-to-end barycentric placement. No test touches the network.The one existing-test change swaps the generic moving-observer code
C51→ the roving code247intest_moving_observatory_coordinate_cache(sinceC51is now Horizons-resolved, it no longer exercises the "ADES position required" error path).🤖 Generated with Claude Code