What could a space telescope with a main mirror area of 825m2 see? What would be its capabilities compared to current telescopes?

[OneQuestionGuy]

Hi, I'm not really Astronomy enthusiast, I'm rocket enthusiast. If this post doesn't belong here or if it is in wrong section I apologize, please tell me I will delete it. I've created this account to ask one question:

I've been wondering what kind of cargo could fully take advantage of the SpaceX Starship. And the biggest thing that came to my mind was large mirror space telescope, so I did a little bit of googling and found out that the biggest mirrors are about 8.4 meters in diameter, which is almost exactly the inside diameter of the Cargo Starship. Meaning that one or multiple Starship lunches could theoretically assemble a space telescope in the same configuration as James Webb Space Telescope made form 18 hexagonical mirrors each 8.4 meters in diameter. One mirror would have area of about 46m2, that is 825m2 for the entire telescope. My question is what would telescope like be used for? What would be it's capabilities? (I know basically nothing about telescopes so practical examples are welcome. For example: "It could directly image planets around other stars." etc.)

Thank you for your answers.

[Nik271]

Such big telescopes usually don't operate in the visual range of light, but let's assume your hypothetical telescope does. Take green light which has wavelength of about 500nm. The Rayleigh limit of resolution of a mirror with 32m diameter is then about 4mas (.004 arcsecond). Suppose there is a super bright planet around a distant star orbiting it at a distance of 1AU. From 1 parsec 1AU distance will look as 1 arcsecond (this is basically the definition of a parsec). So this telescope can resolve the planet from the star from a distance of about  1/.004= 250 parsecs or 800 light years. Not bad  However this assumes that the planet is of comparable brightness as its star which is ridiculous. In practice the planets will be 20-30 magnitudes dimmer and this is where it gets tricky, you need an image sensor with enormous dynamic range and very little light spill over the neighbouring pixels. Can it be done? Perhaps for nearby stars.

In practice planets are spotted from gravitational wobbles of their stars or from transits across the disc resulting in slight dimming of the light of the star. This is far more effective than direct imaging and large Earth based telescopes can manage it too, no need to go to space for that. James Webb will work in infra red to study very distant and very red-shifted light and this is why it needs to be in space, to avoid Earth's infrared cloud. 

Still it will be  exciting to be able to image through a 30 meter telescope in space

Edited April 9, 2021 by Nik271
corrected the parsec calculation

[Merlin]

The Russians are planning to build rockets capable of  lifting 200 tonne payloads. So, there could be some  impressive space telescopes  launched in coming years.