That seems like it would be very difficult. For a telescope mirror you want a very good surface finish, and that's one thing that 3D printing does very poorly.
The polishing process could be done differently. If you could print the specific parabolic shape, that could save a lot of time hogging out. Although slumping might work better if surface ends up smoother. Im not sure of the annealing process might go.
The parabola of a telescope mirror generally deviates from a sphere by tens of micrometers at best. Figuring happens after grinding and after polishing. Slumping is neat, but I've heard from the grognards that they can shatter if the temperature changes too quickly.
There's a few combined-process setups coming out these days that use 3D printing as a first pass and then machine the print in-place before sintering etc. which saves a ton of setup and fixturing time.
Yes! This is exactly what I had in mind. Sintering (thanks for the term) combined with this 3D printing technique could still make the process faster and lead to more consistent results.
Now that’s I think about it, one could in theory use the exact same process for plastic-polymer lenses too, albeit at lower temperatures (better).