Gregory Benford discusses the science behind two novels written with Larry Niven, Bowl of Heaven and Shipstar, in “Building the Bowl of Heaven” on Paul Gilster’s Centauri Dreams blog.

Physicist Leonid Shkadov first described in 1987 a stellar propulsion system made by putting an enormous mirror in a static, fixed position near a star. To stay there it had to balance gravitational attraction towards and light pressure away from the star, exactly—or else it would either fall into or away from the star. Since the radiation pressure of the star would be asymmetrical, i.e. more radiation is being emitted in one direction as compared to another, the excess radiation pressure acts as net thrust, so tiny that the Sun would, after a million years, have speed of 20 m/s, and have moved 0.03 light years—far less than its orbital speed around the galaxy, ~100 km/sec.

Surely we can do better, I thought back in the early 2000s. So I mentioned some ideas to Larry Niven, and eventually we wrote two novels about a different sort of stellar thruster — Bowl of Heaven and Shipstar.

Being shown how two masters of hard science fiction worked out a rationale for this spacecraft might be the modern equivalent of Leonardo Da Vinci opening his sketchbook and saying, “Here’s the latest thing I’ve been working on….”