No calculations are required. If gravity in the space shuttle is equal to 0.5, then I would weigh 37.5 N and feel practically weighless.
Gravity does decrease as the distance away from earth increases.
Therefore the result of the equation becomes less and less meaning that gravity is decreasing. Thus, astronauts in space and all object floating in space will feel weightless. The asronauts feel weightless because the certripital force acting on them is not as strong. So therefore the force of gravity, so to speak, is less out there. No the astronaut feels weightless because both it and the space shuttle are actually both accelerating as in free-fall due to the force of gravity which is the only force acting upon the space shuttle.