The orbital path of the International Space Station (ISS) may appear confusing at first glance, but it follows a predictable pattern determined by its inclination and the rotation of the Earth. The ISS orbits the Earth in a near-circular orbit with an inclination of approximately 51.6 degrees.
As the Earth rotates beneath the ISS, the path of its orbit traces out a sine wave-like pattern when viewed from a fixed reference frame on the ground. This is because the Earth's rotation causes the ground track of the ISS to shift slightly with each orbit. The ground track is the path on the Earth's surface directly below the orbiting spacecraft.
The inclination of the ISS's orbit is responsible for the apparent north-south movement. The orbit is inclined relative to the equator, which means that during each orbit, the ISS crosses different latitudes. It reaches as far north as about 52 degrees latitude and as far south as about 52 degrees latitude, covering a significant portion of the inhabited Earth.
However, the ISS does not cross over the exact geographic North or South Poles during its orbit. The orbit is designed to maximize coverage of populated areas on Earth, and passing over the poles would provide limited access to these regions.
So, while the ground track of the ISS may appear to change direction in a sine wave pattern, it is a result of the combination of Earth's rotation, the ISS's inclination, and its continuous orbit around the Earth.