The Space Sword was Sailor Uranus' talisman that was sealed within her pure heart. She could use the sword to perform her attack Space Sword Blaster, which was her most powerful attack in the anime.
In the anime, when the sword was brought together with the other talismans, the Deep Aqua Mirror and the Garnet Orb, it produced the Holy Grail. In the manga, Sailor Uranus already had the weapon when she first appeared, and instead of summoning the Holy Grail, the talismans summoned Sailor Saturn.
In the anime, the sword's blade was red, and was often concealed with a jewel-decorated sheath. The handle of the sword was golden. The Space Sword in the manga was silver, and the blade was much longer than it was in the anime. In the Sailor Moon musicals, the Space Sword had the same appearance as in the anime, but its blade was silver, and did not have a sheath to cover it.
The three talismans were based on the three imperial treasures of Japan. The sword was said to represent valor.