Q: If astronauts float in Earth orbit because they are “falling to earth,” why do astronauts experience zero gravity en route to the moon? (Phil Gartner, Benton, Louisiana)
The common situation for the astronauts is that in both cases they are in free fall, falling solely under the influence of gravity. When I was on the shuttle I was falling around the Earth, under its gravitational tug. Same for ISS astronauts today: they fall toward the center of the Earth, but their speed is such that their curved, falling path carries them around the curved surface of the Earth—they never hit the ground, fortunately.
The Apollo astronauts on their way to and from the Moon were still in an Earth orbit, still “falling around Earth.” When close to the Moon, they fell under its gravitational tug and entered lunar orbit, thus falling around our natural satellite in the same way. A Mars-bound spacecraft is actually falling around the Sun, in a solar orbit, until it encounters the gravitational field of the Red Planet. In each case, astronauts experience free fall.