Galaxian 3 is a game in the Galaxian series and the introduction of the UGSF. It has two sequels(Galaxian 3:The Rising of Gourb, and Galaxian 3: Attack of the Zolgear)
The UGSF has started moving forward. They have started colonizing galaxies other then our own, but in their latest attempt to colonize Area 0088 they have been attacked by a mysterious mechanical race. They have dubbed the aliens UIMS or Unidentified Intellectual Mechanical Species. And kept tabs on them. They later found out that the UIMS had been working on a secret gravitic weapon known as the "Canon-Seed". Knowing that this creation could graviticly crush a planet in seconds they dispatched Dragoon to deal with the threat.
Galaxian 3's general gameplay revolves around blasting a proton canon at different targets. The game has three levels, each one vastly different. The game supports a multiplayer capability, where several other players can be involved in the game. (Anywhere between 4 and 21 depending on the port.) The simple goal is to destory every enemy, and every other object as fast and efficient as possible before the game ends.
StarBlade was originally going to be merly a single player Galaxian 3. But over development it became it's own game. However it kept several UIMS enemies, and the involvemnet with the UGSF. But it no longer had the Dragoon, instead we gun on board GeoSword. The relation to the UGSF and the fact that the UIMS were introduced here, makes StarBlade a spin-off of sorts.