(This question has been migrated from the SciFi StackExchange.)
"A radiation sail can be made very thin and light. Based on the current state of material sciences, we can make a sail of about fifty square kilometers and limit the mass to about fifty kilograms. That should be big enough." The speaker was a Russian expert who had once directed a failed solar sail experiment.
The good news was that the area of the radiation sail could be shrunk to twenty-five square kilometers, and with even more advanced materials, the mass of the sail could be reduced to twenty kilograms.
That's a mass of just one kilogram per square kilometer, or one gram per 1000 square meters, or one milligram per square meter. This immediately struck me as implausible... but I'm not sure.
I googled up this student report from circa 2014, which says:
For far-term missions, a value of 1 g/m² is required.
There is also ongoing research on [...] nanotubes [...] it could produce sails of ADD less than 0.1 g/m², 50 times smaller than that of a Mylar sail.
But that's still 100 times more massive than the 0.001 g/m² quoted by Death's End's "Russian expert."
Is a 0.001 g/m² solar sail
plausible by "near future" standards? (This part of Death's End is set in Year 1 of the Crisis Era, i.e. "201X".)
at least possible for a spacefaring civilization to achieve (in say the 24th century)?
unlikely or impossible, for fundamental physical reasons?
a translator's error? (If someone could show that the original Chinese said "fifty thousand square meters" instead of "fifty square kilometers," or something like that, then that would be a perfectly relevant and upvoted, if out-of-universe, answer.)