Answer
Both s/he and the ship are "falling" in the gravitational field of the Earth.
Work Step by Step
An astronaut in orbit is accelerating, because the ship orbits in a circle. The force of Earth's gravity is the net force, and is just enough to keep the astronaut moving in a circle.
The astronaut feels weightless because there is no normal force exerted by a weighing scale (as discussed in Chapter 9).
