Firstly, go to Larry's garage on the eastern area of the space map and find the quest giver by the broken down rocket ship.

The quest giver will then give you a blueprint, which then you will take to the cargo area under the Space mall.

Take the blueprint to a hydraulic press machine with a wobbly standing by it.
The wobbly will first want you to find 4 pieces of Aero steel and bring it back to the press.
Aero steel locations:

After putting the four aero steel pieces into the press, there should be a nose thin that comes out, take the nose fin and bring it back to the original quest giver.

After you turn in the nose fin, the quest giver will tell you that you need to bring them grease because it helps make the rocket ship fast. To find the grease head to the back of the space diner


In the back there is a hole with a bucket and a puddle of grease. Take the bucket and put it in the grease to collect it.

When you have collected the bucket of grease, take it back to the quest giver to finally be able to unlock the 'secret' rocket ship!