ssmichael1 · ssmichael1 · Aug 31, 2026 · Aug 30, 2026 · Aug 30, 2026 · Aug 30, 2026
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
@@ -137,6 +137,11 @@ jobs:
           path: astro-data
           enableCrossOsArchive: true
           key: satkit-data-${{ hashFiles('data/manifest.json') }}
+          # On a manifest change the exact key misses; seed from the newest
+          # older cache so EOP/SW survive a CelesTrak outage (the download
+          # step then verifies/updates the manifest files, and the refresh
+          # step updates EOP/SW when CelesTrak is reachable).
+          restore-keys: satkit-data-
 
       - name: Download Satkit Data
         if: steps.cache-satkit-data.outputs.cache-hit != 'true'
@@ -232,6 +237,11 @@ jobs:
           path: astro-data
           enableCrossOsArchive: true
           key: satkit-data-${{ hashFiles('data/manifest.json') }}
+          # On a manifest change the exact key misses; seed from the newest
+          # older cache so EOP/SW survive a CelesTrak outage (the download
+          # step then verifies/updates the manifest files, and the refresh
+          # step updates EOP/SW when CelesTrak is reachable).
+          restore-keys: satkit-data-
 
       - name: Download Satkit Data
         if: steps.cache-satkit-data.outputs.cache-hit != 'true'

diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
@@ -45,6 +45,9 @@ jobs:
         with:
           path: astro-data
           key: satkit-data-${{ hashFiles('data/manifest.json') }}
+          # Seed from the newest older cache on a manifest change, so EOP/SW
+          # survive a CelesTrak outage.
+          restore-keys: satkit-data-
 
       - name: Download satkit data (manifest-verified)
         if: steps.cache-astro-data.outputs.cache-hit != 'true'

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
@@ -72,6 +72,9 @@ jobs:
           path: astro-data
           enableCrossOsArchive: true
           key: satkit-data-${{ hashFiles('data/manifest.json') }}
+          # Seed from the newest older cache on a manifest change, so EOP/SW
+          # survive a CelesTrak outage.
+          restore-keys: satkit-data-
 
       - name: Download Satkit Data
         if: steps.cache-satkit-data.outputs.cache-hit != 'true'

diff --git a/.gitignore b/.gitignore
@@ -38,3 +38,18 @@ site
 docs/images/*.svg
 # GMAT scripts kept by tests/gmat/generate.py --keep-scripts
 tests/gmat/scripts/
+
+# Python tooling caches
+.mypy_cache/
+.ruff_cache/
+dist/
+
+# Jupyter checkpoints (docs/tutorials notebooks)
+.ipynb_checkpoints/
+
+# proptest failure artifacts (counterexamples get pinned as named tests instead)
+proptest-regressions/
+**/*.proptest-regressions
+
+# scratch scripts stay out of commits
+/scratch/
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -2,6 +2,12 @@
 
 Only recent releases are listed. Older entries are in this file's git history (`git show vX.Y.Z:CHANGELOG.md`) and on the [GitHub Releases](https://github.com/ssmichael1/satkit/releases) page.
 
+## Unreleased
+
+### Changed
+
+- `update_datafiles()` no longer downloads files that are compiled into the library: the IERS tables and gravity models are `default: false` in the manifest (still pinned and fetchable by name), and the unused `leap-seconds.list` (nothing ever read it — the runtime leap-second table is a compiled-in constant) is removed from the manifest entirely. The only static download left is the JPL ephemeris, alongside the daily EOP / space-weather / solar-cycle refreshes ([#163](https://github.com/ssmichael1/satkit/pull/163))
+
 ## 0.21.2 - 2026-08-30
 
 ### Changed

diff --git a/data/README.md b/data/README.md
@@ -48,15 +48,18 @@ All manifest URLs must be `https://` (validated on load).
 |---|---|---|---|---|
 | `linux_p1550p2650.440` | 102.3 MB | JPL | DE440 (Park et al. 2021). US Government work, public domain. Origin URL verified byte-identical | ephemeris (default) |
 | `lnxp1900p2053.421` | 14.0 MB | JPL | DE421 (Folkner et al. 2009). US Government work, public domain. `default: false` — fetched only by name (e.g. the conda package ships this one) | ephemeris |
-| `tab5.2a.txt`, `tab5.2b.txt`, `tab5.2d.txt` | 171 / 137 / 9 KB | IERS | IERS Conventions (2010), TN 36, Tables 5.2a/b/d. Freely redistributable. Origin URLs verified byte-identical | core |
-| `EGM96.gfc` | 5.6 MB | ICGEM (GFZ) | EGM96, Lemoine et al. 1998, NASA GSFC/NIMA — US Government work | core |
-| `JGM2.gfc`, `JGM3.gfc` | 118 / 215 KB | ICGEM (GFZ) | JGM-2 (Nerem et al. 1994), JGM-3 (Tapley et al. 1996), NASA GSFC / UT CSR — US Government work | core |
-| `ITU_GRACE16.gfc` | 1.8 MB | ICGEM (GFZ) | Akyilmaz et al. 2016, GFZ Data Services, **CC BY 4.0** — keep the file's header block, it carries the attribution | core |
-| `leap-seconds.list` | 11 KB | IERS / IETF | Public data. Reference only: the runtime leap-second table is compiled in | reference |
-
-`tier` is informational today: `core` = small files needed for frames and
-gravity, `ephemeris` = the large JPL files, `reference` = not read at runtime.
-Phase 2 (below) would embed the `core` tier in the binary.
+| `tab5.2a.txt`, `tab5.2b.txt`, `tab5.2d.txt` | 171 / 137 / 9 KB | IERS | IERS Conventions (2010), TN 36, Tables 5.2a/b/d. Freely redistributable. Origin URLs verified byte-identical. `default: false` — embedded byte-identical in the binary | core |
+| `EGM96.gfc` | 5.6 MB | ICGEM (GFZ) | EGM96, Lemoine et al. 1998, NASA GSFC/NIMA — US Government work. `default: false` — embedded to degree 70 | core |
+| `JGM2.gfc`, `JGM3.gfc` | 118 / 215 KB | ICGEM (GFZ) | JGM-2 (Nerem et al. 1994), JGM-3 (Tapley et al. 1996), NASA GSFC / UT CSR — US Government work. `default: false` — embedded to degree 70 | core |
+| `ITU_GRACE16.gfc` | 1.8 MB | ICGEM (GFZ) | Akyilmaz et al. 2016, GFZ Data Services, **CC BY 4.0** — keep the file's header block, it carries the attribution. `default: false` — embedded to degree 70 | core |
+
+`tier` is informational: `core` = the small files frames and gravity need
+(embedded in the binary since Phase 2, below — which is why their manifest
+entries are `default: false`: pinned and fetchable by name, but pointless to
+download while evaluation is capped at degree 40), `ephemeris` = the large
+JPL files. The only `default: true` entry — the only file
+`update_datafiles()` downloads besides the daily refreshes — is the DE440
+ephemeris.
 
 ## Files deliberately excluded
 
@@ -71,6 +74,10 @@ Phase 2 (below) would embed the `core` tier in the binary.
   daily, so they are never pinned: `update_datafiles()` fetches them from
   CelesTrak every run via the manifest's `refresh` list.
 - **`sw19571001.txt`** — an orphan on the old bucket; nothing reads it.
+- **`leap-seconds.list`** — nothing reads it: the runtime leap-second table
+  is a compiled-in constant (`src/time/instant.rs`). It was pinned
+  (`tier: reference`) through 0.21.2 and remains an asset on the immutable
+  `data-v1` tag, but the manifest entry is gone.
 - **`predicted-solar-cycle.json`** — fetched directly from NOAA/SWPC by
   `solar_cycle_forecast::update()`; not a bundle file.
 
@@ -89,8 +96,7 @@ gh release create data-v1 --repo ssmichael1/satkit-data --latest=false \
   --notes "Static data files pinned by satkit's data/manifest.json (sizes and SHA-256 there). Sources and licences: see data/README.md in ssmichael1/satkit." \
   "$D/linux_p1550p2650.440" "$D/lnxp1900p2053.421" \
   "$D/tab5.2a.txt" "$D/tab5.2b.txt" "$D/tab5.2d.txt" \
-  "$D/EGM96.gfc" "$D/ITU_GRACE16.gfc" "$D/JGM2.gfc" "$D/JGM3.gfc" \
-  "$D/leap-seconds.list"
+  "$D/EGM96.gfc" "$D/ITU_GRACE16.gfc" "$D/JGM2.gfc" "$D/JGM3.gfc"
 ```
 
 (`lnxp1900p2053.421` can be fetched first with

diff --git a/data/manifest.json b/data/manifest.json
@@ -7,7 +7,8 @@
     "URL order per file: GitHub release asset, then the origin server when it serves byte-identical bytes, then the legacy GCS bucket (transitional).",
     "SATKIT_DATA_URL, if set, is a base URL tried before all of these.",
     "Regenerate with tools/make_manifest.py; see data/README.md.",
-    "Deliberately excluded: msis21.parm (NRLMSIS 2.1 licence is academic/non-commercial), EOP-All.csv / SW-All.csv (CelesTrak asks that its compiled files not be mirrored; fetched at runtime via `refresh`), sw19571001.txt (orphan). See data/README.md."
+    "Deliberately excluded: msis21.parm (NRLMSIS 2.1 licence is academic/non-commercial), EOP-All.csv / SW-All.csv (CelesTrak asks that its compiled files not be mirrored; fetched at runtime via `refresh`), sw19571001.txt (orphan), leap-seconds.list (nothing reads it; the runtime leap-second table is compiled into src/time/instant.rs). See data/README.md.",
+    "default: false = pinned and fetchable by name, but skipped by update_datafiles: the IERS tables are embedded byte-identical, and the full gravity files add nothing while evaluation is capped at degree 40 (the embedded copies carry degree 70)."
   ],
   "files": [
     {
@@ -49,7 +50,7 @@
       "source": "IERS",
       "license": "IERS Conventions (2010), Technical Note 36, Table 5.2a (X series); freely redistributable",
       "tier": "core",
-      "default": true
+      "default": false
     },
     {
       "name": "tab5.2b.txt",
@@ -63,7 +64,7 @@
       "source": "IERS",
       "license": "IERS Conventions (2010), Technical Note 36, Table 5.2b (Y series); freely redistributable",
       "tier": "core",
-      "default": true
+      "default": false
     },
     {
       "name": "tab5.2d.txt",
@@ -77,7 +78,7 @@
       "source": "IERS",
       "license": "IERS Conventions (2010), Technical Note 36, Table 5.2d (s + XY/2 series); freely redistributable",
       "tier": "core",
-      "default": true
+      "default": false
     },
     {
       "name": "EGM96.gfc",
@@ -90,7 +91,7 @@
       "source": "ICGEM-GFZ",
       "license": "EGM96 (Lemoine et al. 1998, NASA GSFC/NIMA) as distributed by ICGEM; US Government work",
       "tier": "core",
-      "default": true
+      "default": false
     },
     {
       "name": "ITU_GRACE16.gfc",
@@ -103,7 +104,7 @@
       "source": "ICGEM-GFZ",
       "license": "ITU_GRACE16 (Akyilmaz et al. 2016, GFZ Data Services doi:10.5880/icgem.2016.006), CC BY 4.0",
       "tier": "core",
-      "default": true
+      "default": false
     },
     {
       "name": "JGM2.gfc",
@@ -116,7 +117,7 @@
       "source": "ICGEM-GFZ",
       "license": "JGM-2 (Nerem et al. 1994, NASA GSFC / UT CSR) as distributed by ICGEM; US Government work",
       "tier": "core",
-      "default": true
+      "default": false
     },
     {
       "name": "JGM3.gfc",
@@ -129,20 +130,7 @@
       "source": "ICGEM-GFZ",
       "license": "JGM-3 (Tapley et al. 1996, NASA GSFC / UT CSR) as distributed by ICGEM; US Government work",
       "tier": "core",
-      "default": true
-    },
-    {
-      "name": "leap-seconds.list",
-      "size": 10665,
-      "sha256": "14b4faab51b1885680a704744863bda8b5728a0f0a5e07a15c8469532318b305",
-      "urls": [
-        "https://github.com/ssmichael1/satkit-data/releases/download/data-v1/leap-seconds.list",
-        "https://storage.googleapis.com/astrokit-astro-data/leap-seconds.list"
-      ],
-      "source": "IERS",
-      "license": "IERS/USNO leap-second list; public data. Reference only: satkit's runtime leap-second table is compiled in",
-      "tier": "reference",
-      "default": true
+      "default": false
     }
   ],
   "refresh": [

diff --git a/docs/getting-started/datafiles.md b/docs/getting-started/datafiles.md
@@ -26,7 +26,7 @@ Two caveats on "offline". Frame transforms need Earth-orientation parameters as
 
 - **EOP-All.csv** — Earth orientation parameters. This includes $\Delta UT1$, the difference between $UT1$ and $UTC$, as well as $x_p$ and $y_p$, the polar "wander" of the Earth rotation axis. This file is updated daily with most-recent values at [celestrak.org](https://www.celestrak.org) (which repackages the IERS Bulletin A / finals series) and carries IERS predictions roughly six months ahead. For dates beyond the file, the last entry's values are used (constant extrapolation) — see [EOP coverage](#eop-coverage) below.
 
-- **leap-seconds.list** — Downloaded by `update_datafiles()` for reference only. The UTC↔TAI leap-second table that `satkit` actually uses is compiled into the library (current through the most recent leap second, 2017-01-01, when UTC began lagging TAI by 37 s); this file is not read at runtime, and a future leap second will require a new `satkit` release. The table is transcribed from [IERS Bulletin C](../guide/references.md#bulletinc); UTC and leap seconds are defined by [ITU-R TF.460-6](../guide/references.md#itu460).
+- **Leap seconds** — not a file: the UTC↔TAI leap-second table is compiled into the library (current through the most recent leap second, 2017-01-01, when UTC began lagging TAI by 37 s), and a future leap second will require a new `satkit` release. The table is transcribed from [IERS Bulletin C](../guide/references.md#bulletinc); UTC and leap seconds are defined by [ITU-R TF.460-6](../guide/references.md#itu460). (Releases through 0.21.2 also downloaded a reference `leap-seconds.list`; nothing ever read it, and it is no longer fetched.)
 
 ## Where satkit looks for data, and where it writes
 
@@ -116,7 +116,7 @@ data bytes.
 Sources and attribution: DE440 / DE421 — JPL (Park et al. 2021; Folkner et al.
 2009), US Government work; `tab5.2a/b/d.txt` — IERS Conventions (2010), TN 36;
 EGM96, JGM-2, JGM-3 — NASA GSFC (public), via ICGEM; ITU_GRACE16 — Akyilmaz et
-al. 2016, GFZ Data Services, CC BY 4.0; `leap-seconds.list` — IERS/IETF. The
+al. 2016, GFZ Data Services, CC BY 4.0. The
 Earth-orientation and space-weather files are fetched from CelesTrak on every
 update and are not pinned (they change daily). The full table, with licences,
 is in `data/README.md`.
@@ -139,13 +139,19 @@ a CI job, or a machine that will later be offline:
 
 ```python
 import satkit as sk
-sk.utils.update_datafiles()   # ephemeris + full-degree gravity files + IERS tables + EOP/SW, verified
+sk.utils.update_datafiles()   # ephemeris (verified) + EOP/SW + solar-cycle forecast
 ```
 
 Files already present with the right hash are skipped; the space-weather and
 Earth-orientation files are always refreshed. `update_datafiles(dir="...")`
 writes somewhere else; `overwrite=True` re-downloads even verified files.
 
+The IERS tables and gravity models are **not** downloaded — they are compiled
+in (the tables byte-identical, gravity to degree 70, identical results at the
+degree-40 evaluation cap). The full-degree `.gfc` files remain pinned in the
+manifest and hosted on the `data-v1` release; drop one into a search
+directory and it takes precedence over the compiled-in copy.
+
 ### The optional `satkit-data` bundle
 
 `pip install satkit[data]` installs the `satkit-data` package (~110 MB: the

diff --git a/docs/getting-started/installation.md b/docs/getting-started/installation.md
@@ -21,7 +21,7 @@ To provision everything up front (a Docker image, a CI job, a machine that will
 
 ```python
 import satkit as sk
-sk.utils.update_datafiles()   # ephemeris + IERS tables + gravity files + EOP/SW, verified
+sk.utils.update_datafiles()   # ephemeris (verified) + EOP/SW + solar-cycle forecast
 ```
 
 ### Offline and air-gapped use

diff --git a/python/satkit/utils.pyi b/python/satkit/utils.pyi
@@ -27,19 +27,17 @@ def update_datafiles(**kwargs) -> None:
     manifest. Files already present with the right hash are skipped.
 
     Notes:
-        - Files include:
-            - ``EGM96.gfc`` :   EGM-96 Gravity Model Coefficients
-            - ``JGM3.gfc`` :    JGM-3 Gravity Model Coefficients
-            - ``JGM2.gfc`` :    JGM-2 Gravity Model Coefficients
-            - ``ITU_GRACE16.gfc`` : ITU Grace 16 Gravity
-            - ``tab5.2a.txt`` : Coefficients for GCRS to GCRF conversion
-            - ``tab5.2b.txt`` : Coefficients for GCRS to GCRF conversion
-            - ``tab5.2d.txt`` : Coefficients for GCRS to GCRF conversion
-            - ``SW-ALL.csv`` : Space weather data, updated daily
-            - ``predicted-solar-cycle.json`` : NOAA/SWPC solar cycle forecast (~5 years of predicted F10.7)
-            - ``leap-seconds.list`` : Leap seconds (UTC vs TAI); reference only — the runtime table is compiled in
-            - ``EOP-All.csv`` : Earth orientation parameters, updated daily
+        - Files downloaded:
             - ``linux_p1550p2650.440`` : JPL Ephemeris version 440 (~ 100 MB)
+            - ``EOP-All.csv`` : Earth orientation parameters, updated daily
+            - ``SW-All.csv`` : Space weather data, updated daily
+            - ``predicted-solar-cycle.json`` : NOAA/SWPC solar cycle forecast (~5 years of predicted F10.7)
+
+        - The IERS nutation tables (``tab5.2a/b/d.txt``) and the gravity
+          models (EGM96, JGM2, JGM3, ITU_GRACE16 — to degree 70) are compiled
+          into satkit and are not downloaded. A full-degree gravity file or an
+          updated IERS table placed in the data directory still takes
+          precedence over the compiled-in copy.
 
         - The space weather and earth orientation parameters files are updated
           daily and will always be downloaded regardless of the overwrite flag

diff --git a/python/src/mod_utils.rs b/python/src/mod_utils.rs
@@ -21,19 +21,18 @@ use anyhow::Result;
 ///     dir (str): Target directory for files.  Uses ``datadir()`` if not specified
 ///
 ///
-/// Files include:
-///
-/// * EGM96.gfc :: EGM-96 Gravity Model Coefficients
-/// * JGM3.gfc :: JGM-3 Gravity Model Coefficients
-/// * JGM2.gfc :: JGM-2 Gravity Model Coefficients
-/// * ITU_GRACE16.gfc :: ITU Grace 16 Gravity Model Coefficients
-/// * tab5.2a.txt :: Coefficients for GCRS to GCRF conversion
-/// * tab5.2b.txt :: Coefficients for GCRS to GCRF conversion
-/// * tab5.2d.txt :: Coefficients for GCRS to GCRF conversion
-/// * SW-All.csv :: Space weather data, updated daily
-/// * leap-seconds.list :: Leap seconds (UTC vs TAI); reference only, the runtime table is compiled in
-/// * EOP_All.csv :: Earth orientation parameters,  updated daily
+/// Files downloaded:
+///
 /// * linux_p1550p2650.440 :: JPL Ephemeris version 440 (~ 100 MB)
+/// * EOP-All.csv :: Earth orientation parameters, updated daily
+/// * SW-All.csv :: Space weather data, updated daily
+/// * predicted-solar-cycle.json :: NOAA/SWPC solar cycle forecast
+///
+/// The IERS nutation tables (tab5.2a/b/d.txt) and the gravity models
+/// (EGM96, JGM2, JGM3, ITU_GRACE16 — to degree 70) are compiled into
+/// satkit and are not downloaded. A full-degree gravity file or an updated
+/// IERS table placed in the data directory still takes precedence over the
+/// compiled-in copy.
 ///
 /// Static files are fetched per the compiled-in data manifest
 /// (`data/manifest.json`): `SATKIT_DATA_URL` mirror first if set, then the

diff --git a/src/utils/manifest.rs b/src/utils/manifest.rs
@@ -476,6 +476,10 @@ mod tests {
             m.entry("msis21.parm").is_none(),
             "NRLMSIS 2.1 licence forbids redistribution"
         );
+        assert!(
+            m.entry("leap-seconds.list").is_none(),
+            "nothing reads it; the runtime leap-second table is compiled in"
+        );
         // Refresh files must not be pinned.
         assert!(m.entry("EOP-All.csv").is_none());
         assert!(m.entry("SW-All.csv").is_none());
@@ -488,9 +492,12 @@ mod tests {
                 e.name
             );
         }
-        // The default set includes the DE440 ephemeris but not DE421.
-        assert!(m.entry("linux_p1550p2650.440").unwrap().default);
-        assert!(!m.entry("lnxp1900p2053.421").unwrap().default);
+        // The only default download is the DE440 ephemeris: everything else
+        // pinned here is either embedded in the binary (IERS tables,
+        // gravity to degree 70) or an alternative (DE421), kept fetchable
+        // by name but not worth downloading on every install.
+        let defaults: Vec<&str> = m.default_files().map(|e| e.name.as_str()).collect();
+        assert_eq!(defaults, ["linux_p1550p2650.440"]);
         assert_eq!(embedded().data_version, m.data_version);
     }