[dr_orpheus]

The closer to the equator that you launch the more of an advantage you get from the rotation of the earth. Your starting velocity is higher launching from the equator than from a point closer to the poles of the earth.

It is launching on an Ariane 5 rocket which has the launch facilities in French Guiana (for the reason I mentioned above).

Edit: Vandenburg is also even worse from this perspective because in order to launch out over the ocean, you are launching against the rotation of the Earth so you have to overcome that velocity. But Vandenburg is often used for polar orbits where the rocket launches almost due south from Vandenburg over the ocean.

[diveandfight]

ah, thanks for that. I wonder if this also explains why spaceports in the U.S. have tended to be located further south.

[dr_orpheus]

Yep, that is definitely one of the reasons.

The other significant reason for putting a spaceport further south is the inclination of the orbit (angle of the orbital plane to the equator) is limited by the latitude of the launch site (without a secondary maneuver after launch). So for example if you launch due east (which gives the most advantage of the Earth's rotation) from Cape Canaveral, which is at a latitude of ~28 degrees, you will end up in an orbit with a 28 degree inclination. Launching further North or south you end up with a higher inclination either way. So in order to get an inclination close to equatorial it is easiest to launch closer to the equator. Its a bit hard to visualize but this article has some good explanations [0].

[0] https://www.planetary.org/articles/3450