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Observer ?

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Adjust coordinates, height, elevation mask, or a longer search window.

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Next passes?

Next 21 days
Calculate an AOS to list upcoming passes here.

AOS results ? 24-hour format

UTC AOS
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Observer AOS
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AOS azimuth
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Max elevation
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Observer timezone
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Pass duration
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Map · Select observer point

Observer ISS position Visibility footprint Radio footprint Pass path
Location changed. Press Calculate next AOS to refresh, or undo back to the last calculated location.
Pass simulation?
Sim time:—
ISS elevation
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ISS azimuth
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Distance
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Local time
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Range rate
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Doppler shift
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RX tune
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TX tune
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Approx only: positive range rate means the ISS is moving away. RX tune estimates received downlink; TX tune estimates ground transmit pre-correction for uplink.
View or edit TLE

These are the active orbital data. Editing them switches to Manual and clears previous pass results. Use the source selector above to return to stored data.

Data source and AOS calculation method
Orbital data sources
SpaceOpsLab stores ISS data from Space-Track, CelesTrak and AMSAT. Auto selects the valid stored TLE with the newest orbital epoch; ties prefer Space-Track, then CelesTrak, then AMSAT. Selecting a provider uses only that provider.

Source switches and Reload stored data read the SpaceOpsLab database; they do not request an upstream refresh. Fetch time records when SpaceOpsLab retrieved a TLE. Epoch is the time represented by its orbital elements.

A warning appears when the epoch is more than 48 hours old, or the stored fetch is more than 6 hours old or unknown. These are freshness indicators, not accuracy guarantees. Changing orbital data clears earlier calculations.

Sources: Space-Track · CelesTrak · AMSAT.
High-level method
1. Convert the selected observer location into geodetic coordinates.
2. Convert the observer start date and start time into UTC.
3. Use the entered TLE with satellite.js (SGP4 propagation) to step the ISS forward in time.
4. At each step, compute the ISS look angles from the observer: azimuth, range, and elevation.
5. Detect the first time when elevation crosses above the chosen elevation mask angle. Observer height is included in the observer geodetic position, but the mask remains the actual acquisition threshold.
6. Refine that crossing with a binary search to get the result down to about the second.
Readable formulas
Observer → geodetic: latitude, longitude, height
TLE + time → ISS position: SGP4 propagation
ISS position → look angles: azimuth, elevation, range
AOS condition: elevation(t) crosses above elevation mask
Advanced math view
r_eci(t) = SGP4(TLE, t)
Use the TLE and the SGP4 orbit model to estimate where the ISS is at time t in an Earth-centered inertial frame.
r_ecf(t) = ECI_to_ECF(r_eci(t), GMST(t))
Rotate that ISS position into the Earth-fixed frame, so it lines up with the rotating Earth and ground locations.
ρ(t) = r_ecf(t) - r_obs,ecf
Find the line-of-sight vector from the observer on the ground to the ISS by subtracting the observer position from the satellite position.
[az(t), el(t), range(t)] = LookAngles(ρ(t), φ_obs, λ_obs, h_obs)
Convert that line-of-sight vector into the observer-friendly values: azimuth, elevation, and slant range.
AOS = first t such that el(t) ≥ el_mask and el(t-Δt) < el_mask
The AOS is the first moment when the ISS elevation rises above the selected elevation mask. Height is already included in the observer position used for the look-angle calculation.
The page uses coarse stepping first, then a binary search on the bracketed crossing interval:
if el(t₁) < el_mask and el(t₂) ≥ el_mask, then AOS ∈ [t₁, t₂]
Once the code finds a time window where the elevation goes from below the mask to above it, the true AOS must be somewhere inside that interval.
repeatedly bisect interval until desired time precision is reached
The interval is halved again and again until the AOS time is refined down to roughly second-level precision.
ISS radio frequencies
Common ISS amateur-radio frequencies for planning and listening. Always confirm the current active mode before transmitting or relying on a pass. Anyone can receive, only licensed operators can transmit.
Use Uplink Downlink Mode / notes
Crew voice / ARISS school contact — 145.800 MHz FM Listen on the public downlink for scheduled ARISS contacts or occasional crew voice activity.
FM voice repeater 145.990 MHz FM, PL/CTCSS 67 Hz 437.800 MHz FM Worldwide cross-band repeater when enabled.
APRS / packet VHF 145.825 MHz 145.825 MHz 1200 baud AFSK AX.25 packet digipeater when active.
APRS / packet UHF 437.825 MHz 437.825 MHz UHF packet/APRS mode may be active during testing or station mode changes.
SSTV — 145.800 MHz or 437.550 MHz Event dependent. Check ARISS SSTV announcements before a pass.
HamTV — 2395.000 MHz Specialist S-band receive setup required; status varies.
Reference links: ARISS contact/listening info · current ARISS station status.
Location lookup methods
This shows which service produced the visible Location name beside the grid square. The page asks the SpaceOpsLab geocode API for a nearby place name. The grid square itself is calculated locally in your browser.
Last service used
Not used yet
Resolved place
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Detail
Waiting for observer location
Date & Time Format (ISO 8601)

This tool displays dates and times using the ISO 8601 international standard in the format:

YYYY-MM-DD HH:MM:SS

For example:

  • UTC: 2026-07-16 16:51:15
  • Observer: 2026-07-17 02:51:15

ISO 8601 is an international standard published by the International Organization for Standardization (ISO) and is widely adopted throughout the aerospace, satellite operations and scientific communities.

Why ISO 8601?

  • Eliminates ambiguity between DD/MM/YYYY and MM/DD/YYYY date formats.
  • Sorts naturally into chronological order.
  • Widely used by organisations including NASA, the European Space Agency (ESA), satellite operators and observatories.
  • Commonly used in satellite tracking software, mission planning systems, APIs, databases and engineering applications.
  • Easy to copy into spreadsheets, databases, programming languages and AI tools for further analysis.

Using a consistent international standard helps ensure that ISS pass predictions, ARISS schedules, mission documentation and technical correspondence all refer to exactly the same date and time, regardless of a user's location or regional settings.

Tip: If you need to present dates in another format, such as 16/07/2026 02:51 AEST, the ISO 8601 values displayed by this tool can be converted while preserving the original timestamp.

Notes: this page uses satellite.js for propagation and a Leaflet map canvas. Times are shown as UTC and observer time. Optional custom time rows can be added for other timezones.