(a) No, the gravitational force is a long-range force and we cannot escape from it.
(b) Due to the small space ship, the force of attraction between the earth and the ship is too less, the astronaut cannot detect gravity. If the size of the space station is very large, the magnitude of the gravity will also become appreciable and hence he can hope to detect it.
(c) Generally, the gravitational force of attraction between two bodies is directly proportional to their masses and inversely proportional to the square of the distance between them. The gravitational force between the sun and the earth or between the moon and the earth varies inversely to the square of the distance. But due to the very large mass of the sun, the gravitational force on the earth due to the sun is about 7x10 times the force due to the moon on it.
The tidal effect varies inversely as the cube of the distance. Therefore, though the mass of the moon is quite small as compared to the mass of the sun, yet the tidal effect of moon's pull is very large (as compared to that due to the sun) due to small distance between moon and earth.