On Thursday, September 12, 2019 at 1:15:38 AM UTC-4, JF Mezei wrote:
On 2019-09-11 19:41, Alain Fournier wrote:
Both the James Webb Space Telescope and SLS are scheduled for 2021.
https://jwst.nasa.gov/content/about/launch.html
Launch Date
Webb will launch in 2021.
Launch Vehicle

The James Webb Space Telescope will be launched on an Ariane 5 rocket.
The launch vehicle is part of the European contribution to the mission. ...

This isn't just a question of wanting the Telescope up there to do
needed work, it is also a question that Ariann 5 being retired in 2022,
so there is much motivation to get it launched in 2021. (The decision to
laujch on Arianne 5 was taken in 2015 from what I read, so SLS has been
out of the loop for quite some time now).

Maybe Ariane 6 will be available by then.