(a). Yes, if the spaceship is large enough then the astronaut will definitely detect the Mars gravity.

(b). Gravitational force is inversely proportional to the square of the distance whereas, Tidal effects are inversely proportional to the cube of the distance. So as the distance between the earth and moon is smaller than the distance between earth and sun, the moon will have a greater influence on the earth’s tidal waves.

(a) Can an astronaut feel gravity in a large spaceship?
Gravity in a Shuttle Orbiting Mars
An astronaut in a shuttle orbiting Mars cannot feel gravity. This is because the shuttle is in a state of free fall, just like the astronaut. Therefore, the astronaut and the shuttle experience the same acceleration due to gravity and there is no relative motion between them. As a result, the astronaut feels weightless and cannot detect gravity.

Gravity in a Large Spaceship
If the astronaut was traveling in a very large spaceship, he would have detected gravity. This is because the spaceship would have a large mass and would generate a gravitational force. Therefore, the astronaut would experience a gravitational force and would feel weight. However, the magnitude of the gravitational force would depend on the mass of the spaceship and the distance between the astronaut and the center of mass of the spaceship.

(b) Why does the Moon affect the tidal waves more than the Sun?
The Sun's Gravitational Force on Earth vs. the Moon's
The Sun's gravitational force on Earth is greater than the Moon's. However, the Moon affects the tidal waves much more than the Sun. This is because the Moon is much closer to Earth than the Sun and its gravitational force is more concentrated. The gravitational force of the Moon causes the tides to rise and fall on a regular basis.

The Effect of the Sun on Tidal Waves
The Sun also affects the tidal waves, but its effect is less pronounced than the Moon's. This is because the gravitational force of the Sun is spread out over a larger area than the Moon's. In addition, the Sun's gravitational force is counteracted by the centrifugal force of the Earth's rotation. This means that the Sun's effect on the tides is only about half as strong as the Moon's.

Conclusion
In conclusion, although the Sun's gravitational force on Earth is greater than the Moon's, the Moon affects the tidal waves much more than the Sun due to its closer proximity and more concentrated gravitational force.