The anti-gravity ray was a weapon, which could be used to fight against the Uvodni.
Sarah Jane Smith had one of these weapons at her attic. It came from an old Nadloon circus comedy cruiser that crashed in the Thames. Sarah Jane and her friends had recovered the cruiser from the Thames. Clyde Langer used the antigravity ray to fight off Uvlavad Kudlak, who was in the army of the Krulius and attacked him. (COMIC: Defending Bannerman Road)