Satellite Pass Tracker

Next Pass

{{ selectedSatelliteName }} {{ observerLabel }} {{ lookaheadLabel }} Min elev {{ minElevationLabel }}

Satellite search:

Search one satellite, then select the match used for pass prediction.

Satellite preset:

Pick ISS, Hubble, Tiangong, or NOAA starter; Custom leaves search text alone.

Observer location:

Enter decimal lat/lon and optional meters altitude, or use browser location.

Lat Lon Alt m

Lookahead:

Enter 1-168 hours; longer windows can reveal sparse targets.

hours

Start time:

Leave blank for now, or set a local timestamp for repeatable forecasts.

Min elevation: {{ minElevationLabel }}

Use 0-90 degrees; 10-20 degrees is a practical viewing filter.

Step size:

Use 5-120 seconds; 20-60 seconds balances speed and precision.

sec

Max passes:

Enter 1-50 qualifying passes to keep after elevation filtering.

passes

Manual TLE:

Paste line 1 and line 2, with an optional satellite name above them.

{{ satellitesSummary }}
#	Name	NORAD	TLE epoch
{{ row.rank }}	{{ row.name }}	{{ row.id }}	{{ row.epochLabel }}
No satellite matches are loaded Search above or pick a preset to populate the selectable TLE ledger.

#	Rise	Max	Set	Duration	Max elev	Rise az	Set az	Copy
{{ row.rank }}	{{ row.riseLabel }}	{{ row.maxTimeLabel }}	{{ row.setLabel }}	{{ row.durationLabel }}	{{ row.maxElLabel }}	{{ row.riseAzLabel }}	{{ row.setAzLabel }}
No qualifying passes are available Adjust lookahead, minimum elevation, or satellite selection and compute again.

{{ icsText }}

No calendar ICS is available

Compute at least one pass before copying or downloading calendar events.

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A satellite pass is the interval when an orbiting object rises above a local horizon, reaches its highest apparent point, and then sets again. For visual observing and radio planning, the useful window is often only a few minutes long. Direction, timing, and peak elevation decide whether the pass is practical from one specific site.

The same spacecraft can be well placed from one observer location and invisible from another. A pass forecast therefore needs three pieces together: an orbital element set, a ground location, and a time window. Without all three, the result may describe the satellite's orbit but not the opportunity from the user's sky.

Peak elevation is often the quickest quality signal. A high pass usually clears more local clutter and gives a longer useful view or tracking arc. A low pass may still be mathematically valid, but buildings, trees, terrain, haze, and antenna horizon limits can make it weak in practice.

TLE-based pass predictions are forecasts, not guarantees. Element age, maneuvers, propagation limits, local obstructions, weather, and illumination can all change the real-world outcome. For repeatable planning, use a saved element set, a fixed start time, and the same observer coordinates.

How to Use This Tool:

Choose a satellite source first, then define the observer and scan window before computing passes.

Use Satellite search or a Satellite preset when you want a current TLE. Use a name such as ISS or NOAA 19, or a NORAD ID when you already know the catalog number.
Enable Manual TLE only when you want to paste a saved two-line or three-line element block. Manual mode disables lookup and makes the run easier to reproduce.
Enter Observer location as decimal latitude, longitude, and optional altitude, or press My location when browser-provided coordinates are acceptable.
Set Lookahead. The accepted range is 1 to 168 hours, so a longer window can reveal sparse targets that do not pass soon.
Open Advanced when you need a fixed Start time, a stricter Min elevation, a different Step size, or a specific Max passes limit.
Click Compute passes. A successful run fills the Next Pass summary and the Pass Forecast Ledger. If no passes are found, lower the elevation filter or lengthen the lookahead window.
Select a row in Pass Forecast Ledger, then open Pass Elevation Profile to inspect the climb, peak, and descent. Use Calendar ICS only after confirming that the pass is worth scheduling.

Interpreting Results:

The main decision field is usually Max elev. It reports the highest angle above the local horizon during the pass. A higher value often means an easier visual pass and a stronger antenna geometry, although local site conditions still matter.

Rise, Max, and Set describe the pass timeline. Duration is the time between the rise and set crossings. Rise az and Set az are compass bearings at the horizon, not the full path shape. The chart is the better view when the path between those bearings matters.

Read the satellite match ledger before trusting a text search. Similar names, old spacecraft, and catalog duplicates can appear in broad searches. A preset or NORAD ID is usually safer for a known target.

A high pass does not prove that the object is visible to the eye or usable for radio. Illumination, transmitter activity, regulatory permission, local interference, and antenna gain are separate checks. Keep one backup pass if the first candidate is close to the horizon or directionally blocked.

Technical Details:

Pass prediction is topocentric, meaning the calculation is made from the observer's location rather than from the center of Earth. The TLE is propagated through the selected time window, each sample is transformed into local look angles, and elevation is compared with the horizon. Azimuth is normalized to a 0 to 360 degree bearing measured clockwise from north.

A pass opens when elevation crosses upward through 0 degrees and closes when elevation crosses downward through 0 degrees. The scan step finds the rough bracket, then the crossing time is refined inside that bracket. The highest point is refined by scanning the pass interval again with a smaller step. Very short events are discarded, and the remaining list is filtered by the selected minimum elevation.

Rule Core

The prediction path is deterministic once the TLE, observer, start time, lookahead, and step size are fixed.

Read the selected TLE from search, preset, NORAD lookup, or manual text.
Choose the scan start from Start time, or from the current local time if that field is blank.
Propagate the orbit every Step size seconds and convert each point into elevation and azimuth for the observer.
Open a pass at an upward 0 degree elevation crossing and close it at the next downward 0 degree crossing.
Refine rise and set times within the crossing brackets, then refine the maximum elevation inside the pass.
Discard passes shorter than 30 seconds, filter by Min elevation, sort by rise time, and keep up to Max passes.

Formula Core

The displayed duration, azimuth label, and cardinal direction are simple deterministic transformations of the pass times and bearings.

\begin{array}{rcl} d_{s} & = & round (\frac{t_{set} - t_{rise}}{1000}) \\ {az}_{\deg} & = & ({az}_{raw} + 360) mod 360 \\ k_{dir} & = & round (\frac{{az}_{\deg}}{45}) mod 8 \end{array}

Satellite pass inputs and bounds
Input	Accepted range or mode	Effect on the forecast
Observer latitude and longitude	Latitude -90 to 90, longitude -180 to 180	Defines the local horizon and look angles.
Observer altitude	-500 to 9000 m	Adjusts the observer height used in look-angle geometry.
Lookahead	1 to 168 hours	Sets the future scan window.
Min elevation	0 to 90 degrees	Filters out passes whose peak stays below the chosen clearance.
Step size	5 to 120 seconds	Sets the coarse propagation spacing before crossing refinement.
Manual TLE	Line 1 and line 2, with optional name line	Bypasses lookup and uses the pasted element set.

For example, a pass that rises at 22:37:34 and sets at 22:48:30 has a duration of 656 seconds after rounding. A raw azimuth of -20 degrees normalizes to 340 degrees, which maps to the N or NW sector depending on the nearest 45 degree bucket.

Comparability depends on the element set and the clock. A fresh lookup later in the day may return a different epoch, and leaving Start time blank makes each run start at a different moment. For stable comparisons, keep the same TLE text, observer coordinates, elevation filter, and explicit start time.

Privacy Notes:

Live lookup sends the search text or NORAD ID to a public TLE service. The observer coordinates are used in the browser for pass computation, charting, JSON, and ICS output. Manual TLE mode removes the lookup step and keeps the prediction path on the device.

The My location button asks the browser for coordinates and copies them into the form. Use manually entered site coordinates when exact repeatability or privacy is more important than convenience.

Worked Examples:

Planning a strong ISS pass

A user selects the ISS preset, enters a known observing site, sets Lookahead to 24 hours, and keeps Min elevation at 10 degrees. A pass with Max elev near 70 degrees is a strong candidate because it climbs well above most local horizon clutter. The rise and set azimuths tell the user where to begin and end the watch.

Using the elevation filter to remove weak passes

Raising Min elevation from 10 degrees to 25 degrees removes passes that never get much above the horizon. The result list may shrink, but the remaining rows are easier to plan around because each one clears the selected height threshold.

Repeating a forecast from a saved TLE

Manual TLE mode is useful when a user wants the same input on another device. Paste the name line if available, then TLE line 1 and line 2, set an explicit Start time, and keep the observer fields unchanged. That makes differences easier to trace because the element set and clock are fixed.

Fixing a failed manual paste

If manual mode reports that it needs at least two lines, or cannot find valid line 1 and line 2, the pasted text is incomplete or out of order. Paste both numbered TLE lines, with an optional name line above them, before computing passes again.

FAQ:

Does a listed pass mean I will see the satellite?

No. A pass means the propagated object rises above the mathematical horizon from your location. Visibility still depends on illumination, weather, local obstructions, and the satellite itself.

Why do pass times change later in the day?

Leaving Start time blank uses the current local clock, and a live lookup can load a newer element set. Use manual TLE plus a fixed start time when you need repeatable comparisons.

Can I paste a satellite name above the two TLE lines?

Yes. Manual mode accepts a line 1 plus line 2 pair, or an optional name line followed by those two numbered lines.

Why did the tool say no passes were found?

The object may not rise above your local horizon in the chosen window, or each pass may fail the minimum elevation filter. Try a longer lookahead or a lower elevation threshold.

What does Step size change?

It controls the coarse scan spacing before rise and set are refined. Smaller values make the initial search denser and can help difficult passes, but they also take longer.

Glossary:

TLE: A Two-Line Element set that describes an orbit at a specific epoch.
Epoch: The timestamp that tells when the element set was valid.
Elevation: The angle between the satellite and the local horizon.
Azimuth: The compass bearing to the satellite, measured clockwise from north.
Rise: The upward horizon crossing that starts a pass.
Set: The downward horizon crossing that ends a pass.
Maximum elevation: The highest elevation reached during the pass.

References:

A New Way to Obtain GP Data, CelesTrak.
Revisiting Spacetrack Report #3: Rev 3, AIAA and CelesTrak.
Orbital Coordinate Systems, Part II, CelesTrak.