I think the answer to your question is that:
There is chemical energy being produced (by the water) and that causes the base of iron to absorb the heat. Then when the heated base of the iron is placed onto the shirt, the heat flattens the wrinkles on it.
<span>Force is mass times acceleration, or F= m x a. This means an object with a larger mass needs a stronger force to be moved along at the same acceleration as an object with a small mass. </span>
The total gravitational force on the astronaut is greater in the second case. But the additional force is the attraction toward the planet. The force of attraction toward the moon is the same in both cases.
That's another interesting thing about gravity ... Nothing blocks it or shields against it. The strength of the gravitational force isn't affected by whatever may be between the two bodies.