See it run - a worked example, 100% in this browser tab
What it is
Browser-native satellite orbit propagator. Paste a NORAD two-line element set (TLE) and get the TEME-frame position and velocity (km, km/s) across an ephemeris window, an ephemeris table, a 3D orbit track drawn over a reference Earth, and a JSON export. Add a second TLE for a conjunction assessment - closest-approach distance and time by coarse grid then golden-section refinement. Near-earth SGP4 is implemented faithfully from Vallado (AIAA 2006-6753); deep-space objects (period >= 225 min) are detected and reported honestly rather than propagated with the wrong model. Deterministic, entirely client-side, wall-time shown on every run.
Honest scope
Deterministic and citation-backed: every figure is exact arithmetic or a cited rule. Any year- or jurisdiction-indexed value is a confirmable input, never an eternal hardcode. This is a computation tool, not professional (legal, tax, medical, or financial) advice - confirm against the controlling authority for your context.
Authorities cited
D. A. Vallado, P. Crawford, R. Hujsak, T. S. Kelso (2006). Revisiting Spacetrack Report #3. AIAA/AAS Astrodynamics Specialist Conference, AIAA 2006-6753. The reference SGP4/SDP4 implementation and the SGP4-VER verification cases. https://celestrak.org/publications/AIAA/2006-6753/
F. R. Hoots and R. L. Roehrich (1980). Spacetrack Report No. 3: Models for Propagation of NORAD Element Sets. The original SGP4/SDP4 specification and TLE format.
WGS-72 gravity constants (mu = 398600.8 km^3/s^2, R_e = 6378.135 km, J2 = 0.001082616, J3 = -0.00000253881, J4 = -0.00000165597). SGP4 mean elements are fitted in this model; SGP4 must propagate in it.
T. S. Kelso, CelesTrak. TLE format documentation and current element sets. https://celestrak.org/
Run it on your own data
Open it inside GDBS to save runs to Sandbox, attach results to a Worklog case, or share through a Gate client portal - all in the browser, nothing uploaded to anyone’s cloud.