A Comet with a Steering Wheel: Four Engines for an Interstellar Voyage
An icy rock is flying through the Solar System on an open trajectory — coming in from interstellar space, swinging around the Sun, and heading back into the dark.
A Spaceship Made from a Comet
A comet hurtling through space is a mountain of ice and dust that carries itself across the Solar System. If you mount small engines on such a mountain, it becomes a ship with its own fuel: gas from the interior can be vented through nozzles to change course.