Webb Launch Mechanics: Tangential Speed Benefits?

[RobtO]

TL;DR

Why was Webb launched from French Guiana?

When I read about the launch location, it is explained that the French Guiana launch site was chosen because it is close to the equator, which means it started with a larger tangential speed than if it were launched from a US location. However, doing the numbers, I find that an initial tangential speed of 460 m/s only gives you about 2 m/s tangential speed at L2, while the orbital speed needed is 500 m/s. So the difference between 2 m/s tangential speed and 88% of that (from a US launch site) seems completely negligible, compared to the difficulty/danger of moving Webb to French Guiana. Is there something I'm missing here?

 

[anorlunda]

The Ariane rocket from the European Space Agency has a larger diameter for payload than any US rocket, and ESA is one of the partners in the JWST project. Ariane is launched from the ESA facility in French Guiana.

The Ariane performed admirably putting JWST into an unexpectedly precise trajectory. Because of that, estimates say that JWST's fuel will last for 20 years instead of 10 years.