Right now is more or less the worst possible time to plan out a new space telescope. There's one simple practical reason, the JWST hasn't been launched yet. Onc

Right now is more or less the worst possible time to plan out a new space telescope. There's one simple practical reason, the JWST hasn't been launched yet. Once it has then that'll end it's budget dominance and if it succeeds then it'll hopefully start to pump some fresh air back into the space science community, after having sucked most of it up for the past decade with its cost-overruns and schedule slips. But far more important than that are the drastic changes coming to space launch. Reusability is on the horizon, and innovative launch concepts are being tested. Almost assuredly launch capabilities and launch prices 10 years from now will be very different. And that is the primary driver of cost and program complexity when it comes to orbital space telescopes. High launch costs means that spacecraft need to eek out the utmost performance from within tight payload margins, that raises cost. It means there's no room for contingencies like backup missions, which raises the stakes. And because the cost and stakes are so high that means the vehicle has to be over-engineered so that it has a very high probability of completing its primary mission, which further increases cost. Even though launch doesn't end up being the majority of mission cost, it still has an enormous impact on it. In a decade or so it may be possible to launch payloads at somewhere between half to 1/10th of current costs. Which opens up a whole new vista of opportunities and changes the local cost/benefit maxima sharply. It will likely be possible to build, launch, and operate a Hubble-class telescope for less than a billion dollars, perhaps only a few hundred million dollars. That makes it more feasible to test innovative designs, it makes it easier to launch a fleet of similar or identical telescopes to increase science throughput, and it makes it feasible to simply replace failed telescopes. That may very well change the way we design and build spacecraft, relying more on extra mass instead of bleeding-edge over-engineering to provide longevity and reliability. But it'll also provide new insights into orbital telescope design, instrumentation, as well as abundant new science data, all of which will inform next generation telescope design, likely leading in different directions from the designs and budgets we would choose today.