SDN-AP propagator (space-data-network-modules, propagator/sdn-ap)
Copyright 2026 Edgesource Corporation

Licensed under the Apache License, Version 2.0 (LICENSE).

Not covered by that license:
- src/sgp4_core.inc and src/model.inc: derived from David Vallado's SGP4 (companion
  code for Fundamentals of Astrodynamics and Applications), which the author
  distributes freely with no license stated. These files are not covered by the
  Apache-2.0 license of this package.

The module compiles, from this repository, pinned by SHA-256 in build.mjs:
- ERFA (Essential Routines for Fundamental Astronomy), BSD-3-Clause, derived with
  permission from IAU SOFA (higherpop/third_party/erfa); its license is carried
  as LICENSES/ERFA.txt and dist/LICENSES/ERFA.txt.
- NRLMSISE-00, the C port by Dominik Brodowski, public domain
  (third_party/nrlmsise00).
- The EGM96 geopotential to degree and order 70, NASA GSFC and NIMA, public
  (propagator/ffm/lib).
- The Jacchia 1970 density table, SAO Special Report 313, Table 6, transcribed
  in src/j70_table6.inc.

The build reads, from SDNAP_HAC_ROOT, pinned by SHA-256 and refitted into tables
(README, "Build data"; tools/fetch-build-data.mjs fetches and verifies them):
- GRGM660PRIM, NASA GSFC GRAIL gravity, PDS Geosciences Node, public.
- NAIF moon_pa_de440_200625.bpc and de440s.bsp, NASA JPL NAIF, public.

spec-vectors/vectors.json holds element sets made for the specification and
the states and intermediate quantities that the unmodified US Space Force
Sgp4Prop library returns for them, run as a black box. The library is not in
this package; it is used and its outputs redistributed under the USSF open
source agreement (propagator/sgp4-xp/third_party/ussf-sgp4/AGREEMENT.txt).