R.A.V.E.N. · Satellite Location

Earth is the only body in the series where the catalog is too large to hand-curate — Celestrak's active list currently runs past 16,000 objects, dominated by the ~10,700-strong Starlink shell. So instead of writing out orbital elements by hand we fetch the live TLEs (refreshed every two hours upstream), parse them with satellite.js, and run SGP4 in the browser. Every dot you see is one current TLE propagated to the current simulated time. The 16 catalogued entries below are the curated overlay: the astronomical platforms working observers actually point at. Three of them — TESS, INTEGRAL and Xihe — have no usable GP element set in the live feed and are listed but not rendered; their cards say so. Deep-space platforms at the Sun–Earth Lagrange points (JWST, Gaia, Euclid, Spektr-RG, ACE, DSCOVR, SOHO, Aditya-L1) are listed in the catalog but not rendered — SGP4 isn't valid at L1/L2 and they'd plot at fabricated positions.

Curated Astronomical Overlay

Twelve Earth-orbiting astronomical platforms with active or recently-active scientific operations. NORAD IDs listed; each card click flies the camera to that satellite's current SGP4 position. If a NORAD ID isn't in Celestrak's live response (sometimes happens with very new launches), the marker is hidden and the card flags it.

Lagrange-Point Astronomical Platforms

Catalog only — SGP4 propagation isn't valid at the Sun–Earth Lagrange points (1.5 million kilometres from Earth, dominated by Solar rather than Earth gravity), so these aren't rendered in the live map. Their state vectors come from JPL Horizons / mission DSN tracking.

How the Positions Are Computed

Live TLE pipeline

On page load, the browser fetches the current Celestrak GP catalog (group active) via the public HTTPS endpoint. Celestrak refreshes TLEs every two hours, so each visit gets data within that window. The TLE block is parsed by satellite.js into per-satellite SGP4 state structs (satrec). On every animation frame, each satrec is propagated forward by the elapsed simulated time and the resulting TEME-frame position is written into a single packed Float32Array driving a THREE.Points draw call.

SGP4

SGP4 is the analytic propagator that NORAD designed for TLEs, accounting for J2-J4 zonal harmonics, atmospheric drag, and lunisolar perturbations in a closed-form expansion. It's accurate to roughly a kilometre over a day for LEO targets, falling off for high-eccentricity or very-high-altitude orbits. We use it for every satellite in the catalog including GEO (where it's still fine) but exclude the L1/L2 platforms whose orbits are dominated by Solar gravity (SGP4 wasn't designed for that regime).

Earth rotation

Earth's body-fixed frame is rotated about its spin axis (= scene +Z) by the Greenwich Mean Sidereal Time of the current simulated instant — the standard GMST = 280.46061837 + 360.98564736629·(JD − 2451545.0) formula. SGP4 returns positions in TEME (an inertial-ish frame that differs from GCRF by sub-arc-second angles, negligible at rendering scale), so satellites and Earth surface line up correctly.

Classification

After parsing TLEs, each satellite is classified by its mean motion (rev/day): >11.25 = LEO, 1.5–11.25 = MEO/HEO, <1.5 = GEO. Note the bins are by mean motion, not orbit family: everything above ~26,000 km altitude falls in the GEO bin, including graveyard and high science orbits, while Molniya-class HEO (mm ≈ 2) files under MEO. Starlink is broken out separately (name match) because at ~7,000 entries it dominates the shell. Layer toggles let you isolate any class.

References

Hoots, F. R. & Roehrich, R. L. 1980 — Spacetrack Report #3: Models for propagation of NORAD element sets (canonical SGP4 reference)
Vallado, D. A. et al. 2006 — Revisiting Spacetrack Report #3, AIAA 2006-6753 (modern reformulation)
Celestrak GP catalog — live TLE data, refreshed every 2 hours
satellite.js — battle-tested SGP4 implementation
Petit, G. & Luzum, B. (eds.) 2010 — IERS Conventions (2010), Tech. Note 36 — GMST & reference-frame definitions
Weisskopf, M. C. et al. 2002 — Chandra X-ray Observatory overview, SPIE 4012
Gehrels, N. et al. 2004 — Swift gamma-ray burst mission, ApJ 611
Atwood, W. B. et al. 2009 — Fermi LAT instrument, ApJ 697
Gendreau, K. C. et al. 2016 — NICER on ISS, SPIE 9905
Ricker, G. R. et al. 2015 — TESS mission overview, JATIS 1
Harrison, F. A. et al. 2013 — NuSTAR mission, ApJ 770
Weisskopf, M. C. et al. 2022 — IXPE mission, JATIS 8
Yuan, W. et al. 2022 — Einstein Probe mission, Sci. Bull. 67

Entry III in the RAVEN Satellite Location series · v1 · 2026-05-13

Earth

Initialising

Earth-Centered Inertial · TEME (SGP4 native frame)

Layers

Clock

Camera Presets