Visualizing Orbits

Why do satellite orbits look like a weird sine wave?

Satellites don't actually orbit like a wave; all orbital motion can be modeled as an ellipse (or some other conic section). The distortion is caused by mapping its orbit from a round body to a flat surface. The same sort of distortion can be seen on maps that depict Greenland as being larger than South America. You can see this in the graphic as the circular orbit gets flattened.

Why do satellites always orbit West to East?

Short answer: Because that's the direction the Earth rotates.

Long answer: By taking advantage of our existing rotational speed, it takes less time and energy to get into orbit. At the equator, our rocket is already moving at 465 meters per second (m/s) just sitting on the ground. That's 465 m/s less that has to be produced by the rocket's engines. If we wanted to launch in the opposite direction (due West), the engines would have to produce an additional 930 m/s to both cancel out the Earth's rotation AND get it back up to our original but opposite speed.

What's really cool is that every body in our solor system (planets, moons, asteroids, comets, etc) orbits West to East and every planet rotates West to East (except Uranus which is on a horizontal axis).

Why do we want to launch rockets close to the equator?

This is a two-fold answer.

• First off, launching closer to the equator allows us to take greater advantage of the Earth's rotational momentum. If you set the direction to due East (90°), the velocity savings decrease as the initial latitude moves away from the equator.
• Secondly, it offers the greatest possible range of orbits. Because the Earth rotates below, a circular orbit (as depicted) is primarily characterized by its inclination (the angle of deflection between the equator and the orbit). Thus, the available orbits are limited by the range of inclinations determined by its launch latitude. By launching at the equator, we have access to the full range of inclinations which fall between 0° and 90°. Launching at 30'N limits this range to between 30° and 90°

So why doesn't every country launch at the equator? Again this is a two-fold answer

• First and foremost: politics. Because of things like national pride and sovereignty, countries will always prefer to launch within their own borders. However, they will still seek to make this location as close to the equator as possible. This is one of the primary reasons NASA launches most of its rockets from Florida. Even so, international projects, like the ISS, are put into higher than necessary inclinations so that they are accessible to more countries.
• Sometimes, you just don't need access to those low inclination orbits. The US military launches many of its rockets from Vandenberg AFB in Central California. Surveillance and mapping satellites are usually put into high inclination orbits (called polar orbits) because it allows them to orbit above a larger portion of the Earth's surface as the Earth rotates below them. Also, satellites launched into polar orbits do not benefit from the Earth's rotational momentum, so it matters less where they are launched from.

Note: This graphic uses a perfectly circular orbit (constant altitude/speed) around a perfectly spherical Earth. In reality, the actual physics are a bit more complicated, but the underlying concepts are the same.