Jeff Findley wrote:
In article ,
says...
Yet, james Web was "assigned" to Arianne 5 in 2015, so there wouldn't
have been any recent discussions of it going on SLS.

That's because James Webb Space Telescope will be launched on an Ariane
5. The program is so expensive, NASA cut a deal with ESA to launch it,
no doubt in exchange for observation time on the telescope.

While NASA is the lead agency on JWST the project has AFAIK always
been based on having major contributions from European Space Agency[1]
and the Canadian Space Agency[2].

As an example, there's four main instruments and one of these provided
via NASA, one via ESA and one via CSA with the final being a
cooperation between NASA and ESA. And arguably the FGS (that keeps
JWST on target) that CSA provides is almost an instrument so one could
almost argue they provide "1.5" instruments each :-)

Also listed in the ESA document are the launch and "part of the
operations team" (I'm assuming both before launch and operationally
afterwards).

I expect that NASA is the biggest single contributor, likely even the
majority contributor but it's hard to find any real figures (and those
figures would by necessity be very fuzzy too).


parity error in my memory? or is SLS still planned to use one of its
limited rockets to launch a scientific payload to somewhere?

Europa Clipper, not JWST.

IIRC it's still supposed to be launched by SLS (by senate funding
requirement) because only SLS can send it in a direct trajectory to
Jupiter.

There's been some recent attempts to try to move this to a commercial
launcher instead to save (lots of) money with predictable blow-back
from the senate proponents for SLS.

I think these are merely trial balloons, preparing for if (or perhaps
when) Europa Clipper is getting close to being ready and SLS isn't,
the real discussion can take place because it'll be hard to dismiss as
"mere" speculations.

Apparently an expendable Falcon Heavy with a STAR 48BV? kick-stage can
do it with one gravity assist and Falcon Heavy and Delta IV Heavy can
do it with three gravity assists without a kick stage.

The three gravity assist version is going to be a lot slower than the
SLS direct trajectory (6-7 years vs 2-3 years depending on which
launch window used), the single gravity assist trajectory is clearly
going to be faster than the 3 assist one but I've not seen actual
timings on that trajectory.

1. https://sci.esa.int/web/jwst/-/45728-europe-s-role
2. http://www.asc-csa.gc.ca/eng/satelli...ntribution.asp