The saucer Excalibur is in the mud to the right of the Mill. Use the hovercraft to reach it. It needs a new green fuel rod to replace the broken one, and you will need coordinates to enter into the ship's computer.
(see related questions)
Once you reach the Pewter Moon, Excalibur is wrecked and you need to swap it for a new ship at the Astro-Zone store. If this new ship loses its shield power, you can orbit the Pewter Moon to recharge the shield.
Once you fix the crashed saucer Excalibur, you can go to the pewter moon and build a new spaceship there. (see related question)
There is nowhere to enter a password. Fix the saucer and get the coordinates you need to fly it. (see related questions)
The saucer Excalibur is crashed in the mud swamp past the mill. If you fix it, you can reach the nearby Pewter Moon (X-56 Y-52), where you can build a real spaceship. (see related questions)
Get the hovercraft from the mill attic and fix the saucer that is crashed out in the swamp to the right of the mill. Once you set the coordinates to the Pewter Moon, you can travel there. You will build a new spaceship to travel to the three planets that the space knights have gone to. (see the related questions)
The missing journal page from Mordred's Journal tells you what space coordinates to travel to, but you still need a spaceship. Fix the saucer in the mud swamp past the mill. (see the related question)
you go to the dungeon with the owl
The first time, you have no choice. Fix the saucer and launch it (see the related question). Once you have a spaceship, you can land on Poptropica, the Pewter Moon, or any planet by clicking on it. (The exception is the ice planet, see related question)
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jump
The saucer Excalibur is crashed in the mud swamp past the Mill. If you can get to it and fix it, you can get to space. (You can get out to it with the hovercraft from the attic of the mill.) Fly it to the moon at X-56 Y-52. There you can build another spaceship to reach the other planets. (see related questions) *** If you leave Astro Knights Island from space, your spaceship will park on top of the castle.
Once you fix the saucer in the swamp, you only have enough fuel to reach the nearby Pewter Moon (X-56 Y-52). Once you are there, there are no particular types of spaceship that are much better to build, and you can go to any of the three planets in whatever order you want. (see related questions)
get the new one on the top of the roof in a shop with drunkards.