Why did Superman need a spaceship to travel to and from the remains of Krypton? Couldn he have flown?
Superman derives his powers from Earth’s yellow sun. His body acts like a solar battery, converting the yellow sun energy into his amazing powers. Being away in deep space means Superman’s powers would eventually run out without a source of yellow solar radiation. Therefore Superman wouldn’t be able to fly to and from the remains of Krypton under his own power. In other mediums (comics and recent cartoons), Superman can hold his breath for hours on end, a trip into the deep vacuum of space would not be possible for him unaided. Perhaps this reasoning also applies for the film version.