When Krypton was believed to de destroyed , it was initially thought that the people in Krypton were not so advanced in many fields. Jor El had just began to take interest in space travel when Krypton / Crypton was destroyed. The rocket was probebly the first testing space ship . But in latter versions it was suggested that Krypton was inhabitted by the most advanced civilizations in the world , but they them selves reduced their advancement in several reguards. The prohabiited the space trravelling technologies themselves. A very idiotic thing indeed. But in an alien planet where things were quite different , it may not be idiotic at all. Instead of controlled space trevelling attempts they hapazadly imposed a ban on the entire technology. This does shew that after the imposed ban there was an illegal attemt by Jor El to re-invent the tecnology all by himself , that is why he had to began every thing from the very beginning. So all he could to was no re-make a premative form of rocket or space ship which could go against the super gravity of Krypton.
This is an evidence that this Space Ship which is still called as rocket can not be one of the most advance space ships of Krypton.
An Example of an advance space ship. Even Kryptonians did not know Flying Saucers and UFO etc. How ever from Krytonians must have very advanced UFOs or Space Ships before they probebly destroyed each one of them. Perhapas Krypton was sentenced to Destruction on the day they imposed a complete ban on space trevellings.