The Utopia Project rocket was an immense rocket. Its main purpose was to transport the last humans in the year 100 Trillion CE to the fabled planet of Utopia. Professor Yana and Chantho worked on the rocket, but stayed behind when the rocket finally launched. When the rocket landed, the humans found nothing but darkness. Presumably the other remaining outpost of humanity launched passenger rockets from their home worlds to Utopia as well, to make up six billion Toclafane.
The rocket used some kind of combusting fuel to power the engines, but due to its size an immense "foot" was required to get it off the ground. (DW: Utopia)