1. Diverse background -- None of the starting planets can be the same (unless more than five players, in which case additional Energy).
Rational: In a game in which more than one ore/gold/rock world begins, the players with those are able to rapidly double (or triple/quadruple) up production of that material. Note that a single production at a factory of one of these commodities yields material sufficient for, in addition to the starting pack of one of every, building one new colony and one new ship. IOW, if two players begin with crushed-rock, you can expect to see two crushed rock productions as well as two builds early. In additional turns, the massive production disparity results in quick scoring of same-type cards from the players so blessed (they also play their other scoring cards, and pick choices which result in ties, and by doing so "flush" their scoring cards back to their hands) -- and the game is often over before the other players have a chance to do much. One recent game was over so quickly that almost half of the worlds remained uninhabited, and no one had more than three buildings.
2. Pirates of Catan -- A marauder from the Catan Galaxy preys upon Ad Astra. Trading is modified.
Rule change: All cards remain hidden during trading.
When a Trading action is revealed, the following occur in order:
* All players with ten or more (round down) goods cards lose half.
* The player of the card moves the pirate ship to a star system, where he steals one resource card (if any, random) AND one victory point (if any) from up to two players with planets there (the card and the victory point can come from the same player, or split).
(Effects of pirate presence: The productive capacity of the entire system the pirate ship occupies is -1 per planet (i.e., a spaceship and a colony together produce one, but either alone produces nothing). The scoring capacity of the entire system is likewise diminished, with all buildings and starships present worth -1, and the system is considered unoccupied when scoring systems.)
* Trade between players occurs. Variant: After the player who played the card finishes, each other player may (if able) trade ONE time with ONE other player (he made trade as much as he likes with that one player) and trade in sets of three-of-a-kind for single goods of his choice.
If you have the least victory points at the end of a round, you receive two goods cards of your choice. If you are in second-last place, you receive one.
4. Centenium -- a longer game
The game ends upon the completion of the round in which a player achieves 100 points, or the last unexplored world has been revealed. The player with the "42" alien artifact can win on a multiple of 42 (e.g., 84, 126, etc).