Answer: J) the size of the moons orbiting the planet
Explanation: The least important factor in the design of a spaceship that will visit another planet is the size of the moons orbiting the planet (J). While the size of the moons may be interesting for scientific study, it has less direct impact on the design and functionality of the spaceship compared to factors like the mass of the planet (F), the distance from Earth to the planet (G), and the surface temperature of the planet (H).