Talk to the head mechanic at Astrozone and get a new spaceship. Then you can go to the planets on the Queen's coordinate list (jungle, fire, and ice planets).
you have to find the UFO in astro knights island.
When you are in the spaceship (solar system) view, click on the moon or planet you want to land on. To leave again, use the "launch" lever.
This means you have already completed the Arturus part of Astro Knights Island. Your spaceship should be parked on top of the castle if you return to the planet.
Saturn star moon
Yes, anytime you are back on the Pewter Moon.
When your on the moon just jump to the big building and he is inside.
press the moon button then figure out the combination
On the Pewter Moon, see the manager at AstroZone about replacing your ship.
get the fuel and put it in the rocket ship and put in 56 and 52.
You must enter the Astrozone building and swap your saucer for a new ship, which you build on the Holopad.
When the Excalibur crashes on the Pewter Moon, go to Astro Zone and the manager will arrange for you to have a new ship holographically constructed outside.
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)