"Super-reflectors will need some tweaking. I don't think 0.95 reflective layers are too much to ask, but it'll need cooling to avoid melt-down at a photospheric perihelion. Perhaps the energy needed to ablate the shield can be increased by mixing things in the ice, thus slowing the ablative mass-loss and reducing the total mass. Multi-layers of reflector in the ablative?"

When I began thinking about it, I was thinking of having ice on the outside of ship [and not worry about the losses from evaporation or do something to hinder that loss.
Mid way thru looking the numbers, I realized ice by itself wasn't anywhere near enough. And besides the water would get so much energy it could be used as good rocket propellent.
So, putting the ice in some tank or container so one could use the water to make steam, was the next part of the evolution.
But returning to the idea of having ice on the outside and perhaps a mixture or coating of material could be an option in addition. You could just spray it on the outside of the ship- paint it with say a meter of so of ice and a mixture or coating.
From a design point of view, doing that could like add solid booster to the Shuttle- you can make up the difference- allowing one to use a few inches to meters of the stuff depending upon what you actually needed.