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Now
Object
—Az (deg)
—El (deg)
—AOS
—LOS
—Pass length
—Altitude
—Range
—Footprint (Ø)
—Footprint area
—Following pass
Object
—AOS
—LOS
—Pass length
—Object: —
UTC: —
Lat: —
Lon: —
Alt: —
Az: —
El: —
Rng: —
Dly: —
DopRx: —
DopTx: —
Instructions
Quick start
- Load Keps/TLEs: choose a TLE group and click Update Keps, or upload your own .tle file.
- Find an object: use the search box to filter, then pick an entry from the dropdown.
- Select: click Select to lock in the object (required before Start).
- Set your location: enter your observer Lat/Lon (or press Use device location), then click Apply.
- Set options:
- Time Window (hours): how far ahead the forecasts and plot time-axes extend.
- Min elevation (deg): horizon mask for “in view” and for the footprint overlay.
- Frequency (MHz): used for Doppler estimates (Tab 4).
- Run: press Start for live 1 Hz updates; press Stop to pause.
Typical workflows
- Where is it now? Select an object, set location, then check the telemetry line (top of each tab) and the live dot on the map (Tab 2).
- When is the next pass? Open Pass Metrics (Tab 3) to see AOS/LOS, pass length, and the polar view of the next and following passes.
- How will az/el/range change? Use Misc Metrics (Tab 4) for time-series plots across your chosen window.
- What’s the ground track? Use World Map (Tab 2) for the predicted track line and footprint (satellites only).
Controls & buttons
- Select: commits the dropdown selection (and resets the live loop).
- Clear: clears the selection, plots, and overlays.
- Start / Stop: toggles the live update loop (1 second cadence).
- Update Keps: fetches the selected public group from the server (no page refresh).
- TLE upload: replaces the satellite list with your file contents.
Good to know
- Times are shown in UTC (plots may use a Z suffix where relevant).
- The app supports both satellites (TLE propagation) and solar-system bodies (ephemerides).
- Some fields show
—when a value is not meaningful (e.g., footprint for non-satellite objects) or not computable at that instant.
Information
Common terms
- Subpoint (Lat/Lon): the point on Earth directly under the object (geodetic latitude/longitude).
- Azimuth (Az): direction along the horizon, measured clockwise from North (0°=N, 90°=E).
- Elevation (El): angle above the local horizon (0° at horizon, 90° at zenith).
- Range: line-of-sight (slant) distance from the observer to the object.
- AOS / LOS: Acquisition / Loss Of Signal — when the object rises above / falls below your Min elevation.
- Footprint: the area on Earth where the satellite is above Min elevation (satellites only).
Units
- Angles: degrees (°).
- Altitude: km (satellites); blank for bodies.
- Range: km.
- One-way light-time: ms (derived from range and c).
- Doppler: kHz (derived from range-rate and the entered frequency).
- Footprint diameter: km; footprint area: km².
Tab 1 — Long / Lat
- Two time-series plots show the predicted latitude and longitude of the subpoint over the selected window.
- Hovering a trace shows a marker at the hovered timestamp to make reading values easier.
- Latitude is constrained to [-90°, +90°].
- Longitude is shown in [-180°, +180°] (dateline wrap is handled in the forecast track).
Tab 2 — World Map
- The map shows the predicted ground track over the selected window.
- The light-blue dot is the current subpoint; for satellites, the yellow overlay is the current footprint at your configured Min elevation.
- The track line is split at the dateline to avoid “long wrap” artefacts.
- If you pan/zoom the map, the app stops forcing the default “cover” view until you reload.
Tab 3 — Pass Metrics
- This tab focuses on the next pass and the following pass as seen from your observer location.
- Polar plots: angle is azimuth; radius is drawn so the center corresponds to high elevation (near zenith).
- The Now dot appears when the pass is in progress.
- Info boxes list AOS, LOS, pass length, and (for satellites) footprint diameter/area.
Tab 4 — Misc Metrics
- Time-series plots for key topocentric quantities over the selected window:
-
- Azimuth and Elevation (deg).
- Range (km) and one-way delay (ms).
- Footprint area (km²) — satellites only.
- Doppler (Rx/Tx) (kHz): computed from range-rate and your entered frequency. Receding gives negative Rx Doppler (frequency drops); Tx is the opposite sign for pre-compensation.
- Plots are anchored so the left edge starts at “Now” when you open the tab or press Start.
Interpreting —
—is shown when no selection is active, when a value is not meaningful for the selected object type, or when the geometry does not produce a valid result for that timestamp.