Spoken like someone who's spent a bit too much time in KSP :)
There are more issues than just sheer mirror size in this case.
- Resistance to vibrations is a _major_ issue if the mirror is monolithic (as with HST) as opposed to segmented (as with JWST).
- The mirror also has to either be very resistant to extreme temperature changes (and the contraction that comes with it), or must be cooled before launch. For extremely large mirrors, the cooling assembly would add _tons_ of extra weight, since this would most likely be active/liquefied gas cooling, and the weight of the cooling medium alone would be significant in this case.
- Using a shape that's close to being a cylinder is great for cooling too, because cylinders have a very good surface area-to-volume ratio, which matters when you have to account for heat exchange. If memory serves, only ellipsoids are better (with spheroids being a better than ellipsoids, and spheres being ideal).
- The support structure for the mirror (the satellite fuselage proper) would probably have to fit in there too, at least for the first launch. That's not small, even though it can be made collapsible.
- All of the optical elements have to stay outstandingly precisely positioned within insanely tight tolerances. Any shifting could result in a lack of clarity, chromatic aberrations, or other issues, even if the mirror(s) aren't directly warped or damaged.
Even accounting for that, a fairing that's irregular around the long axis of the rocket is often undesirable. While it reduces (compared to the alternative), it can cause issues with rolling after launch, and introduces additional complexity.
There are more issues than just sheer mirror size in this case.
- Resistance to vibrations is a _major_ issue if the mirror is monolithic (as with HST) as opposed to segmented (as with JWST).
- The mirror also has to either be very resistant to extreme temperature changes (and the contraction that comes with it), or must be cooled before launch. For extremely large mirrors, the cooling assembly would add _tons_ of extra weight, since this would most likely be active/liquefied gas cooling, and the weight of the cooling medium alone would be significant in this case.
- Using a shape that's close to being a cylinder is great for cooling too, because cylinders have a very good surface area-to-volume ratio, which matters when you have to account for heat exchange. If memory serves, only ellipsoids are better (with spheroids being a better than ellipsoids, and spheres being ideal).
- The support structure for the mirror (the satellite fuselage proper) would probably have to fit in there too, at least for the first launch. That's not small, even though it can be made collapsible.
- All of the optical elements have to stay outstandingly precisely positioned within insanely tight tolerances. Any shifting could result in a lack of clarity, chromatic aberrations, or other issues, even if the mirror(s) aren't directly warped or damaged.
Even accounting for that, a fairing that's irregular around the long axis of the rocket is often undesirable. While it reduces (compared to the alternative), it can cause issues with rolling after launch, and introduces additional complexity.