As an alternative to an asteroid that destroys your entire home planet if the game is lagging when it shows up, gatekeep new players with pirates that teach new players the basics of combat without setting any strict deadline.
-When you start, pirates are blockading your wormholes, so you can't leave until you destroy the pirate ships. Gatekeep warp behind destroying the blockade somehow. Either set home systems guaranteed to not have antiflux, or just block construction of warp ships until it's destroyed. This will let new players learn the basics of ship vs ship combat. Maybe someone on the planet assigns a mission to get rid of the blockade, and this person tells the player that their options include destroying the ships and capturing them.
-After you destroy the blockade, a nearby (3-5 wormhole jumps) pirate city starts regularly sending raids on your home city. Instead of conquering the city if you can't defend it, they just plunder goods/money or kidnap citizens. This will teach players how to build effective planetary defenses, without forcing them to start over when they inevitably fail the first attempt.
-To permanently stop the raids, you must capture or destroy the pirate city. This will teach new players how to siege and capture enemy cities.
Edit: Gate warp behind capturing the enemy city instead. Maybe say the pirates stole the warp blueprint or something.
-When you start, pirates are blockading your wormholes, so you can't leave until you destroy the pirate ships. Gatekeep warp behind destroying the blockade somehow. Either set home systems guaranteed to not have antiflux, or just block construction of warp ships until it's destroyed. This will let new players learn the basics of ship vs ship combat. Maybe someone on the planet assigns a mission to get rid of the blockade, and this person tells the player that their options include destroying the ships and capturing them.
-After you destroy the blockade, a nearby (3-5 wormhole jumps) pirate city starts regularly sending raids on your home city. Instead of conquering the city if you can't defend it, they just plunder goods/money or kidnap citizens. This will teach players how to build effective planetary defenses, without forcing them to start over when they inevitably fail the first attempt.
-To permanently stop the raids, you must capture or destroy the pirate city. This will teach new players how to siege and capture enemy cities.
Edit: Gate warp behind capturing the enemy city instead. Maybe say the pirates stole the warp blueprint or something.