[adventured]

The launch partner/platform wasn't chosen recently and it's part of what ESA is providing as a partner in the program.

"In exchange for full partnership, representation and access to the observatory for its astronomers, ESA is providing the NIRSpec instrument, the Optical Bench Assembly of the MIRI instrument, an Ariane 5 ECA launcher, and manpower to support operations. The CSA will provide the Fine Guidance Sensor and the Near-Infrared Imager Slitless Spectrograph plus manpower to support operations."

https://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Par...

[khuey]

"not recently" is underselling it a bit. ESA agreed to launch it before Falcon 9 (let alone the Heavy version) had ever flown.

[rrss]

It looks like it was even before Falcon 1’s first success.