Squad isn't done adding to Kerbal Space Program just because the game's protracted development is over... if anything, the studio is just getting started. The company has unveiled KSP's first expansion, Making History, and this is definitely represents more than your usual downloadable add-on. It earns its namesake from the ability to reenact real-life space missions (insofar as you can in a fictional universe, anyway), but the real highlight is the option to create your own missions. There's a simple "drag and drop" interface, Squad says, and you can throw players for a loop by introducing everything from arbitrary limits (such as fuel or time) to surprise events.
The pack logically includes new parts (including some inspired by US and Russian space programs) as well as a competitive scoring mode. There's even a personal parachute to save your crew if they have to bail in atmospheric flight.
There's no release date yet. However, you may be in for a surprise if you're used to the steady stream of free upgrades from KSP's testing days: Squad says the expansion will cost you money. While that's not very surprising (the developer can't coast forever on core game sales), that does mean that you'll have to keep shelling out to experience everything the Kerbin system has to offer.