ISS Live Tracker: How It Works
The International Space Station orbits about 400 km up at roughly 28,000 km/h, completing a circuit every 90 minutes. It is bright enough to see with the naked eye from most of the inhabited world, and knowing where it is makes that possible.
The orbit in numbers
| Property | Value |
|---|---|
| Altitude | ≈ 400–420 km |
| Speed | ≈ 27,600 km/h (7.66 km/s) |
| Orbital period | ≈ 93 minutes |
| Orbits per day | ≈ 15.5 |
| Inclination | 51.6° |
| Crew | Typically 7 |
The 51.6° inclination means the station passes over everything between roughly 51.6° north and south — which covers the large majority of the world's population. It was chosen so that launches from Baikonur in Kazakhstan could reach it, a decision made when the programme became an international partnership.
Why the orbit decays
At 400 km there is still a trace of atmosphere, enough to produce measurable drag. The station loses altitude continuously — around 2 km a month — and is periodically reboosted by a visiting spacecraft's engines. Without reboosts it would re-enter within a couple of years.
Drag varies with solar activity: an active sun heats and expands the upper atmosphere, increasing density at orbital altitude and accelerating the decay. Reboost schedules follow the solar cycle for this reason.
Seeing it
The station is often the third-brightest object in the sky, after the sun and moon. It appears as a steady bright point moving steadily across the sky over two to five minutes, with no flashing lights — which is what distinguishes it from an aircraft.
Three conditions must coincide:
- The station passes over your location.
- It is dark where you are — shortly after sunset or before sunrise.
- The station is still in sunlight, which it is at that altitude while the ground below is dark.
This is why visible passes cluster in the hour or two after dusk and before dawn. In the middle of the night the station is in the Earth's shadow and invisible.
Sixteen sunrises a day
Circling every 93 minutes, the crew experiences a sunrise and sunset roughly every 45 minutes — about 16 of each per day. The station runs on Coordinated Universal Time, and crew quarters are darkened for a scheduled sleep period, since the natural light cycle is useless for the purpose.
Weightlessness is continuous falling
The common misconception is that there is no gravity at that altitude. Gravity at 400 km is about 90% of its strength at the surface. The station and everyone in it are in free fall — moving sideways fast enough that they keep missing the Earth as they fall toward it. Weightlessness is the sensation of falling, not the absence of gravity.
Its future
The station has been continuously occupied since November 2000, the longest uninterrupted human presence in space. Partner agencies have committed to operations into the early 2030s, after which a controlled deorbit is planned over a remote area of the Pacific. Several commercial stations are in development to succeed it.
Position data is calculated from published orbital elements and is accurate to within a few kilometres. Visible pass times depend on your exact location, local horizon and weather.