How ISS
Tracking Works

The ISS moves around Earth roughly every 90 minutes, so a static marker would become outdated almost immediately. A tracker estimates the station position from fresh orbital data, then projects that 3D position down to a point on Earth called the sub-satellite point.

That point is what you see sliding across the map. It is not the place where the station is physically touching Earth. It is the location directly below the station at that moment.

On a flat map, the station path looks like a wave because Earth rotates below the orbit. The station follows a tilted orbital plane, while the planet keeps turning eastward. Put those together and the ground track shifts on each pass.

This is also why the station is visible from different places at different times. A good tracker needs the current orbit, the observer location, and the Sun angle to estimate useful viewing conditions.

JITM focuses on the two major crewed stations: the International Space Station and Tiangong. They are both in low Earth orbit, but they use different orbital inclinations, station architectures, and operational contexts.

Showing both stations in one monitor gives a quick sense of where human activity is happening above Earth right now.

The ISS does not sit still above one place. It travels at roughly orbital speed for low Earth orbit and completes many revolutions per day. Its altitude changes over time because the station experiences a small amount of atmospheric drag even hundreds of kilometers above Earth.

That is why station trackers often show altitude, velocity, and orbital period together. Altitude tells you how high the station is above the reference Earth surface. Velocity tells you how quickly it moves along its orbit. Period tells you roughly how long one orbit takes. Together, those three values make the moving dot feel less abstract.

Small differences between displays are normal. Trackers may update at different intervals, round values differently, or use slightly different source data. What matters for a public monitor is that the trend and position remain sensible and explainable.

Seeing a space station from the ground is not the same as knowing where it is. For a visible pass, the observer usually needs a dark enough sky while the station is still lit by the Sun. This is why many good passes happen after sunset or before sunrise.

A tracker can show the current ground point, but pass prediction needs more: observer location, elevation angle, station altitude, and sunlight geometry. A station can be directly overhead at noon and be impossible to notice with the naked eye. It can also be far from overhead but bright enough to spot at twilight.

For educational displays, the most useful first step is the live orbital context. Once people understand the moving path, visibility predictions become much easier to interpret.

Real-time does not always mean a direct live telemetry feed from the spacecraft. In a public web tracker, it usually means the display updates continuously using current time and recent orbital data. The position is calculated, not watched by a camera.

This is still valuable. A well-built real-time tracker lets users understand where the station is now, where it is heading, and what region of Earth is currently below it. For ISS and Tiangong, that creates a compact window into human activity in orbit.

The ISS is high above Earth, but it is not outside Earth's influence. The upper atmosphere is extremely thin at station altitude, yet it still creates drag. Over time, that drag slowly lowers the station's orbit. Without periodic reboosts, the station would gradually lose altitude.

A reboost raises the orbit using visiting spacecraft or station propulsion support. For a tracker, this means the station's orbital data must be refreshed over time. A model that was accurate before a reboost may become less useful after the orbit changes. This is one reason station tracking is a live-data problem rather than a one-time drawing problem.

For users, reboosts explain why altitude is not a perfectly fixed number. The station's height can vary within an operational band, and that variation is part of normal station life.

The ground point is the place directly below the station. It is useful, but it is not the same thing as the area that can see the station. A station hundreds of kilometers up can be visible from a wide region around its ground point, depending on elevation angle, sky darkness, clouds, and sunlight.

This distinction helps prevent confusion. If the tracker says the ISS ground point is over the ocean, observers on nearby coastlines may still see it. If the ground point is over land, many people under the path may still miss it because it is daytime, cloudy, too low on the horizon, or hidden by buildings.

A station monitor is best understood as orbital awareness. A pass predictor is the next layer, because it filters the orbit through a specific observer's location and local sky conditions.

Comparing ISS and Tiangong makes the concept of human spaceflight more concrete. Instead of treating "space station" as a single object, the user can see that different stations occupy different orbits, have different histories, and pass over different regions at different times.

It also helps users learn scale. Both stations are in low Earth orbit, so neither is parked above one country. They cross oceans, continents, day, and night repeatedly. Their motion is fast, but predictable enough for a web app to communicate clearly.

For Jewawud JITM, the value is not only the globe. The value is the combination: position, ground point, station identity, live UTC time, and educational context in one place.

A useful station tracker should answer the obvious questions quickly: where is the station, what is below it, how high is it, how fast is it moving, and what time is this data representing? If those answers are hidden behind too much decoration, the app becomes impressive but less educational.

Good visual design still matters. A 3D Earth view can make the orbit feel physical, while a clean telemetry panel makes the numbers readable. The trick is balance. The station should not disappear into effects, and the map should not become so busy that the path is hard to follow.

Share cards can extend this learning outside the app. When a user exports a station card with timestamp, location, altitude, and link, the card becomes a small public artifact that can bring new visitors back to the live tracker.

When a station tracker appears wrong, the problem is not always the 3D globe. A stale orbital data source, a browser clock that is off, a cached response, or a projection bug can all create confusing results. If the station marker and orbit line disagree, the app may be mixing coordinate systems or drawing a path from data that does not match the selected station.

Another common issue is day-night rendering. The station may be over daylight Earth while the share card or app background appears dark because the visual layer is decorative rather than physically tied to the Sun direction. For an educational tracker, that mismatch can confuse users. If the app shows sunlight, night side, or atmosphere, those visuals should support the data instead of contradicting it.

The best debugging habit is to separate data from presentation. First confirm the station's calculated latitude, longitude, altitude, and timestamp. Then confirm the marker uses that same position. Finally, check whether the visual scene is making a stylistic choice or accidentally implying a different physical condition.

Space tracking tools usually prefer UTC because it avoids local time confusion. The ISS does not care whether a viewer is in Jakarta, London, or New York. The orbit calculation needs one shared time reference, and UTC gives everyone the same clock.

Local time is still useful for human planning, especially for visible passes. But for a share card, telemetry record, or public screenshot, UTC is cleaner. It lets someone else compare the same moment later without guessing the viewer's timezone.

Does the ISS fly over every country? It covers a wide latitude band, but not the entire planet, because its orbit is inclined rather than polar.

Why does the ground track shift each orbit? Earth rotates underneath the orbital plane, so the next pass crosses a different longitude.

Is Tiangong tracked the same way? The display method is similar, but the orbit and station architecture are different.