Oribitals

How big should you make a ring-shaped orbital to get a 24-hour day?

Centrifugal acceleration a = v^2 / r

9.8 m / s^2 = v^2 / r

v = 1 rev / day = 2 * pi * r / 86400 s

9.8 m / s^2 = (2 * pi * r / 86400 s) ^ 2  / r

 = 5.289 * 10 ^ -9 * r

r = 1,853,078,528.45 m =~1.85 million km.

Yep, Banks got it about right.