They haven't decided. There are three options they are looking at for the launch.<br /><br />http://www.jwst.nasa.gov/Launch/index.html<br /><br />I personally doubt that Congress will allow NASA to launch it on the Ariane however.<br />
Last I heard - which was about a year ago - was that it was going to be launched on an Ariane 5. <br /><br />- The NASA website indicates that it could be any of an Ariane 5, a Delta IV or an Atlas V.<br /><br />- The Northrop Grumman site indicates an Ariane 5<br /><br />- The ESA site indicates an Ariane 5<br /><br />My money is on the Ariane 5, if the JWST ever launches
The JWST is a combined NASA, ESA and Canadian Space Association project. I'm not sure what the relative shares are - often the investment levels of the various partners changes over the course of these long contracts in line with changes in their domestic politics.<br /><br />If the ESA is carrying some of the costs, I'm sure they're going to expect some of the work. It's likely that they will pay for the launch, and strongly push the Ariane 5.
"If the ESA is carrying some of the costs"<br /><br />ESA is paying for more than half (and more than NASA notably) from what has been said. In fact ESA was rather annoyed when NASA decided it be called Webb without their consent. <div class="Discussion_UserSignature"> <p>-Ben</p> </div>
I'm guessing there may have been some doubt about the integrity of the launch vehicle. The design would require an Ariane 5-ECA. Perhaps NASA is keeping options open until the Ariane 5-ECA is thoroughly proven, which will soon be the case.
It already has. The first ECA flight never made it to test; the first stage engine malfunctioned and the rocket was destroyed.<br /><br />But ECA was finally tested earlier this year (X-TAR) and was successful.<br /><br />Had to look that one up to check. <div class="Discussion_UserSignature"> <p>-Ben</p> </div>
To elaborate, it's not the IUS that's forbidden, it's the Centaur. There had at one time been plans to put Centaurs in the Shuttle's payload bay, with the IUS being sort of a temporary solution until the neccesary alterations were made to the Shuttle. (Centaurs run on LH2/LOX, so they need special accomodations. IUS is solid-propellant, and thus much simpler.) But this was already fading by the time of STS-51L, partly because of the complexity, and then the loss of Challenger was pretty much the final nail in the coffin. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>
It is not the particular launch vehicle that concerns me. It is that this telescope is going to go out some 1 million miles then open up in a very complicated way and supposedly work. I remember the hubbles' early problems far too much to just sink my faith in something that can not be repaired if something goes wrong. And we all know that in deep space probes and other human efforts all too often something does go wrong!!<br /><br />This IS my main concern here, but of course my concerns are just the concens of a retired aerospace worker who very much supports such efforts, and fully hopes that everything is going to go corrrectly from the beginning.<br /><br />While I am a very patriotic American, I am an even more patriotic human being resident of planet Earth, so I really don't care who launches human efforts in space, I just want them to go correctly!!!