Galaxy Explorer is a variant of Galaxy with a several subtle differences which significantly alter play strategy: limited knowledge of the galaxy, battle resolution, partial tech, and an expanded command set.
Galaxy Explorer limits each player's knowledge of the galaxy (planets, races, tech levels, and hostile ships) to what is actually observed. One of the unique features of Galaxy Explorer is that the galaxy is not revealed in total to the player at the start of the game, instead the player's knowledge of the galaxy grows as he explores the galaxy - meeting and interacting with newly discovered races, colonizing planets, and improving his own technology levels.
Another unique feature of Galaxy Explorer is the way battles are handled. In Explorer, all firing is simultaneous - rather than the sequential combat used by most galaxy variants. This means that every ship fires in combat resulting in much bloodier battles as well as occasional battles with no survivors.
The partial tech features provided by Galaxy Explorer enable players to more efficiently control their ship production and upgrades. Ships can be built at lower tech levels - possibly building more ships than normal; ships can be upgraded using just enough effort to complete the impending mission.
In addition to these features Explorer also incorporates features found in other variants including a wraparound map, double-blind mailing system, and a more balanced galaxy-generation algorithm.
Galaxy Explorer turn reports are generally not compatible with standard report reading tools though conversion utilities do exist and there are several tools which have been developed explicitly for Explorer.