Orbits

To put an object into orbit around the Earth takes an impressive amount of power. You have to punch your way through the lower and thicker parts of the atmosphere, gradually change your direction from vertical to horizontal, and accelerate to a final speed of at least 17,500 mph.

http://justatinker.com/Future/images/delta-iv-profile-2x.png

But there are orbits, and then there are orbits. Let’s take a look at the possibilities.

Let’s start with the simplest case. Imagine a rocket launched into a circular orbit from the Earth’s equator, and aimed to go directly east.

http://www.yorku.ca/bartel/3250/f21/phys3250_2_orbit.pdf

Its ground track (its path on the surface of the Earth directly below the satellite’s trajectory) retraces the Earth’s equator.

But consider something launched into orbit from Cape Canaveral, at 28.4°N latitude. Because the orbit’s path is coincident with the Earth’s center, it doesn’t stay at that latitude. It is in an inclined orbit, traveling between 28.4° north and 28.4° south.

http://www.yorku.ca/bartel/3250/f21/phys3250_2_orbit.pdf

And because the Earth rotates toward the east, the satellite doesn’t return to the same spot one orbit later–its ground track shifts to the west. The diagram below shows the ground track and tracking station locations for the six-orbit flight of Sigma 7 on October 3, 1962, piloted by American Mercury astronaut Wally Schirra.

https://upload.wikimedia.org/wikipedia/commons/4/48/Mercury_Tracking_Network.png

To be able to look directly down on (at one time or another) ALL of the Earth’s surface, a satellite must be launched directly north or south in a polar orbit.

https://upload.wikimedia.org/wikipedia/commons/4/48/Mercury_Tracking_Network.png

Again, the Earth rotates under the satellite. A ground track for a satellite in a low polar orbit would look like this.

https://tsteinholz.github.io/polar-orbit/img/example_global_survey.jpg

When the Ariane 5 rocket carrying the James Webb Space Telescope into space lifted off, it did so from the Guiana Space Centre in French Guiana, only a little over 300 miles and five degrees north of the equator.

Google Earth

Why would you locate a spaceport in such a remote location? Launching from a location near the equator takes advantage of a velocity boost granted by the Earth’s rotation. The closer you are to the equator, the greater the boost. And the greater the boost, the less fuel required to reach your destination.

https://2.bp.blogspot.com/-FaOFmjIsYLU/XMFlZ4D31bI/AAAAAAAAA8E/xtGxxUOkAuYjISiuuf_Uw6o8wxXhLMBlACLcBGAs/s1600/earth.jpg

All of these examples assume a circular obit at relatively low altitudes, in the hundreds of miles. Things can get a lot more complicated when the orbits are elliptical, or much higher! For all the details, this excellent Wikipedia article is a good starting point.