On Astro Knights Island, the name Excalibur is given to the flying saucer that is crashed in the mud swamp to the right of the Mill. You can recover the hovercraft from the mill attic to reach it.
The equivalent to the "sword" Excalibur is the Golden Key, which is locked in a crystal stone on the Giant Asteroid (X-11 Y-82). To draw the Key from the stone, you will need all three Space Knights, so you must first defeat all three planets (ice, jungle, and fire).
(see related question)
The saucer Excalibur is crashed in the mud swamp to the right of the Mill.
The saucer Excalibur, one of the attacking craft, has crashed in the mud swamp to the right of the Mill.
It is half-buried in the mud swamp right of the mill. (see related questions)
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 fuel rod powers the saucer Excalibur. The hovercraft runs on manure.
You do not get or use a bucket on Astro Knights Island.
When you get a replacement for it, it automatically snaps into place. (see the related question)
On the saucer Excalibur, you must enter coordinates before the ship will launch. (see related question)
There is no treasure chest on Astro Knights Island.
Reach and repair the saucer Excalibur in the mud swamp past the mill. (see related questions)
The hovercraft will carry you over the mud swamp to reach the crashed saucer Excalibur. (see related question)
You will use the saucer Excalibur to reach space, then build a spaceship on the Pewter Moon. (see related questions for how)