# Deciding optical factors between a refractive and reflective space telescope optics as a function of aperture? (visible light)

Reading Yale News' Lighting a path to Planet Nine:

To detect objects that are otherwise undetectable, Rice and Laughlin employ a method called “shifting and stacking.” They “shift” images from a space telescope — like moving a camera while snapping photos — along pre-defined sets of potential orbital paths. Then they “stack” hundreds of these images together in a way that combines their faint light.

They used Transiting Exoplanet Survey Satellite (TESS) data presumably more for it's large number of exposures of a given field than each camera's 10 cm effective aperture.

Apart from mechanical and materials aspects such as (but not limited to) mass, thermal management and radiation and meteorite damage, what optical performance considerations would to into choosing between a refracting and a reflecting space telescope for a given diameter aperture?

A camera lens like TESS' can have many more optical surfaces than a reflecting telescope. The cross-sectional image of TESS' camera shows seven elements and therefore 14 surfaces that can be optimized for near diffraction-limited resolution over a wide field of view, whereas even the Vera C. Rubin Observatory (LSST) has only three reflecting and four refracting surfaces.

Refracting glass surfaces can also be smoother than aluminum on glass surfaces at the nanoscale, reducing haze and scattered light which can impact limiting magnitude especially if there are bright objects nearby.

Question: What are the deciding optical factors between a refractive and reflective space telescope optics in visible light as a function of aperture, apart from mechanical and materials aspects such as (but not limited to) mass, thermal management and radiation and meteorite damage?

Related:

From What causes these cross-shaped artifacts in TESS' first images? (the answer is interesting if you like CCDs)

• But perhaps the optical factors aren't the deciding ones... I mean there's no chance of launching a 6.5m diameter lens. And the TESS image qiuality is awful. – ProfRob Oct 28 '20 at 12:27
• Well yes, the PSF is something horrible like 20 arcseconds cross. That can't be down to the optics. – ProfRob Oct 28 '20 at 15:19
• @B--rian thanks but the question is about equipment that produces and records astronomical images, and not about any one particular system, so yes photography and no tess. Since you are good at tag usage guidance perhaps the tag definition could be updated to include space telescopes? – uhoh Mar 23 at 10:15
• @B--rian I have "(visible light)" in the title and "space telescope optics in visible light" in the body specifically to keep the scope narrow. One could include near IR and UV, cuts don't have to be exactly at 400 and 700 nm, but answers should be about this wavelength range. Also, cooling is not really about the optics per se. I'm primarily interested in spectral response, multiple reflections, scattered light, diffraction, small-angle scattering and haze from optical surface nano-roughness, chromatic effects... – uhoh Mar 23 at 10:34
• Thanks for (a) defining your wave-length range, and (b) for the general clarification. It is a bit clearer now, what parameters you are after. I guess you are well aware of en.wikipedia.org/wiki/… - I did not consider the bubbles inside lenses a problem, or lense stability in general. – B--rian Mar 23 at 10:43