you can cheat. masked with dithered opacity mask. you only get a 50/50 transparency in cheap mode, but it’s something, not nothing. lowest possible shader complexity for glass. and it’s rather stable, depending how much bloom and stuff you shoehorn into it. i mean the bloom flicker is upto how small your sun is and…
… how lowres the raytrace is rendered? i got a lil close up there. i can see the coarse pixels and “reconstruction”. it’s fine tho. it’s performant. 
usually metals are a lil rough and glass a lil dirty. not 100 percent smooth.