Ground sites & access passes
To predict satellite passes in the Orbit Visualizer, add a ground site with your latitude, longitude, and an elevation mask, then run the Access tab. You get each pass's AOS/LOS times, duration, maximum elevation, and azimuths — downloadable as CSV.
Quick start
- Add a satellite with a fresh TLE — e.g. Load from Catalog → ISS (ZARYA). Catalog objects use SGP4, which is what makes the pass times meaningful.
- In the sidebar's Ground Sites section, click Add Ground Site. Fill in Name, Latitude (°), Longitude (°) (east-positive), Altitude (km), and Elevation mask (°) — the mask defaults to 10° — then click Save.
- Press A to open the Analysis panel and switch to the Access tab.
- Check the objects to include, pick your Site and a Span (6 / 24 / 48 hours free), and click Run. The scan starts at the current scenario time.
- Read the pass table (details below). Tick Local time to convert the UTC timestamps, or click Download CSV to export.
Worked example
This link loads a ready-made scenario — the ISS (SGP4) plus a Kennedy Space Center ground site (28.5729° N, 80.649° W, 10° mask) — via a scenario permalink (the s parameter). Then open the Access tab and click Run:
▶ Open the ISS + Kennedy Space Center example
The embedded ISS TLE is from December 2025, so the computed pass times are a workflow demo, not tonight's schedule. For real predictions, load the current ISS TLE from the catalog first.
Reading the pass table
Each row is one pass of one object over the selected site. The columns, exactly as shown in the app:
| Column | Meaning |
|---|---|
| Object | The scenario object, with its color swatch. |
| AOS | Acquisition of signal — when the object rises above the site's elevation mask. UTC by default; the Local time checkbox switches to your browser's timezone. |
| LOS | Loss of signal — when it drops back below the mask. |
| Dur (s) | Pass duration in seconds. |
| Max El (°) | Maximum elevation reached. Higher = closer and easier to observe; a 10–20° max pass hugs the horizon. |
| Az AOS / Az Max / Az LOS | Azimuth (degrees from north) at rise, at maximum elevation, and at set — i.e. where to look, and which way the pass sweeps. |
Above the table the app restates the run configuration (site, mask, span, object count); below it, the honesty disclaimer for every propagator involved in the run.
CSV export
Download CSV exports the table with header comments recording the site (name, latitude, longitude, altitude, mask) and the time system (UTC), followed by one row per pass with the columns object, propagator, aos_utc, los_utc, duration_s, max_el_deg, az_aos_deg, az_max_deg, az_los_deg.
Free and Pro limits
The free plan includes 1 ground site and access spans of 6, 24, or 48 hours. ExoAtlas Pro raises these to 10 sites and spans up to 336 hours (14 days) — the Span selector's 7 days (Pro) and 14 days (Pro) options.
Accuracy & model notes
Passes are computed with each object's selected propagator — with SGP4 and a fresh TLE the times are real-world useful; with two-body or J2 they are geometry exercises. The app prints the applicable disclaimer under every results table; for SGP4 it reads: “SGP4/SDP4 (Vallado reference algorithm). Operational TLE propagation; accuracy degrades with TLE age (≈1–3 km at epoch, growing per day).” See propagation models for what each model omits, and the validation page for the verification behind SGP4.
Timing precision: the scanner samples elevation every 30 seconds, brackets each mask crossing, and refines AOS/LOS by bisection to ±0.5 s, with a parabolic refinement of the maximum-elevation point. Look angles are topocentric; Earth-fixed positions use the app's documented GMST rotation (no polar motion).
Related
Mini-FAQ
What elevation mask should I use?
10° (the default) is a sensible general-purpose horizon for visual observing and most antennas. Use a higher mask if your site has obstructed sightlines, or lower if you have a clear horizon and want every marginal pass.
Why do my pass times differ from other trackers by a few seconds?
Different tools use different TLE epochs, masks, and refinement tolerances. This app refines AOS/LOS to ±0.5 s against its own SGP4 solution — differences beyond that usually mean the other tool used a different (often fresher or older) TLE.