While Mordred's hovercraft runs on manure, the saucer is advanced technology. It has a green fuel rod that has been broken. You need to get a replacement fuel rod. For the procedure, see the related question. Setting the coordinates, you will find that none of the planets is in range. Go to the moon mentioned on Mordred's missing journal page, at X-56 Y-52.
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You will use the saucer Excalibur to reach space, then build a spaceship on the Pewter Moon. (see related questions for how)
You do not get or use a bucket on Astro Knights Island.
Use the UFO. (The saucer Excalibur in the mud swamp past the mill.) To use it you need to find a fuel rod and the coordinates. Once you get to the Pewter Moon you can make a new spaceship. (see related questions)
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.
When you have recovered a fuel rod for the saucer, the instrument will let you use the X and Y dials to set the coordinates. But the planet coordinates the Queen gave you are too far away. You will need to use the coordinates from Mordred's missing journal page, which are X-56 Y-52. (see related question)
Park your Spaceship on top of the CastleTo leave Astro Knights Island (without completing the quest), return to Arturus on the planet Poptropica (X-56 Y-52), landing there and not on the Pewter Moon. Your spaceship will park on top of the castle.Shortcut to another Island (to play another island or an ad-game)To "quickly" leave Astro Knights Island, you can use the Haunted House. While previously it was free and now may not open, new users can buy it from the Store for 350 credits. Select it from your Store Items list, enter, and then leave. You should be at the Island Map, from which all current islands can be selected. When you are ready to resume the Astro Knights quest, return to the island by blimp and enter Arturus. Your spaceship will be parked on top of the castle and you can return to space with the same status as you had previously acquired.
You need a new green fuel rod and space coordinates to use the saucer Excalibur. (see the two related questions)
When Excalibur crashes on the moon, go right and talk to the worker. He will refer you to his boss, the manager at Astro Zone. Climb up and enter the store. The manager will let you use his holo-pad spaceship builder to get a new spaceship. (There is not much difference between the designs.)
To find the hovercraft on Astro Knights Island, you need to rescue the princess and receive the Coordinates Decoder. Once you have the decoder, you can use it to uncover the hovercraft's location on one of the planets. It's located on a frozen planet called Tundara.
Once you have replaced the fuel rod for the saucer Excalibur, you can go to the moon at X-56 Y-52. There you can get a new spaceship. Use it to go to the three planets and find the knights, who can help you battle the robot creatures.
* On Astro Knights Island, you must return to the planet Poptropica (X-56 Y-52) and land there. Your spaceship parks on top of the castle, and you can go left from there to reach the blimp.* On Time Tangled Island, use your time device set to the "Lab" setting, which is right outside Pendulum's lab on Main Street. Go left to reach the blimp.