... like I'm 5 years old
Imagine you're playing a game of catch. You toss the ball, and it arcs through the air before falling back into your hands. What if you could throw the ball so hard that even as it fell back towards Earth, it would keep missing and continue circling around? That's essentially what an orbit is. Satellites stay in orbit around the Earth because they are moving fast enough to keep falling towards the Earth, but their speed also allows them to keep missing it. They are falling, but also moving forward at the same time.
Picture a ball constantly falling towards the ground but also moving forward fast enough to keep missing it. That's what a satellite in orbit is doing.
... like I'm in College
Delving deeper into the physics behind orbits, it's all about the balance between gravity and inertia. Gravity is the force that pulls objects towards each other - in this case, the satellite towards the Earth. Inertia, on the other hand, is the property of an object to resist changes in its state of motion. In the case of a satellite, it wants to keep moving in a straight line at a constant speed.
When a satellite is launched, it is given a high enough speed (about 28,000 kilometers per hour) that as gravity pulls it towards Earth, its inertia keeps it from falling straight down. Instead, it falls around the Earth, creating an elliptical orbit. These two forces are constantly in balance, allowing the satellite to maintain its orbit.
Let's try to understand this with Lego bricks. Lay out a large, flat blue Lego baseplate - this is our Earth. Now, grab a small Lego piece to represent our satellite. If we throw our satellite straight, it will go off the baseplate - this is inertia. But gravity pulls it down. So, if we throw our satellite diagonally across the baseplate, it will keep falling towards it but also keep missing it, illustrating how a satellite stays in orbit.
Now, build a mountain with Lego bricks on one side of the baseplate. If the satellite passes over this, it might be pulled slightly towards the mountain, changing its path - this shows the effect of Earth's uneven gravity on a satellite's orbit.
To demonstrate station-keeping, imagine a gentle breeze (external forces like solar wind or atmospheric drag) blowing on your satellite, nudging it off its path. You'd need to give it a little nudge (using a thruster) to get it back on track. That's station-keeping in a nutshell.
... like I'm an expert
To an expert in orbital mechanics, orbits are more than a simple balance of gravity and inertia. The shape of an orbit is influenced by several factors, including the satellite's speed, its altitude, and the Earth's gravity. Orbits can be circular or elliptical, with the specific shape determined by the satellite's velocity and the direction of that velocity relative to the Earth's surface.
The Earth's gravity is not uniform; it varies with altitude and latitude, and is also affected by the distribution of mass within the Earth. These gravitational variations can cause a satellite's orbit to precess, or shift over time. Satellites require occasional adjustments, or "station-keeping," to maintain their intended orbits.