TL;DR
Be able to "sell" large quantities of various items (ie: circuit boards, etc.) by launching them into space, in exchange for asteroids full of ore being directed to crash down to the planet, creating new ore patches.What
A player should be able to send large quantities of produced items (the higher the item, like blue circuits, the drastically more they're worth) up on the rocket into space, to be sold on an interplanetary marketplace. There are obviously various things that this marketplace could then offer (further research upgrades, and stuff) but the simplest idea would be for the service of de-orbitting an asteroid full of ore down to the planet's surface. You could designate a location and the asteroid would crash down, creating a new ore patch at that location. Depending on the price paid, the accuracy of the impact could vary (and it would destroy everything nearby so gotta be careful not to hit your own base). Also based on price would be the size, richness, and purity of the ore. Getting a 100% iron patch would be much more expensive than accepting one mixed with iron and copper. Etc.Why
Factorio's fun tends to run out in the late game when you have a big giant factory and everything is backed up because you don't have the demand for production anymore. For example, you may invest heavily in a huge production line to create lots of Speed III modules, but once you have all your buildings equipped with them, they become relatively useless and just back up until there is no more space on your belts. By creating an outlet for ANY of these items by massively sinking them into something, like a space based economy of some sort, you allow the player to continue producing ANY items at any rate and still having a use for them. This means that well into the late game you can keep your entire factory producing as much as possible because even if the items are needed, there is always somewhere for them to go. Attaching a running total to this "sunk" resource value acts kind of like a "score" for players to aim for high scores etc.Lore-wise, the entire concept of Factorio is (I believe) you are supposed to be a front runner sent to prepare the planet for colonization by creating infrastructure, subduing the locals, etc. What better way to signal that than to start exporting valuable goods off the planet back to where ever you are from.
Additional Details
These are just some of my additional thoughts on the idea, though the core of it is already outlined. I would have different classes of items such as Infrastructure (belts, inserters, factories, etc.) as well as Products (different circuit boards, ammo, even cars and tanks, etc.) that could maybe be used for different types of services (asteroid ore patches, research, etc.). Within those classes, the items would have different values depending on how far up the production tree they are. Copper wire should not be worth very much, but blue circuits should be worth a ton, etc. This value could then be used to spend on asteroids like mentioned above, but also on research to identify better asteroids, improve the aim of the crash sites, etc. The prices could vary dynamcially based on random chance and events, and supply and demand so you can't just flood the "best" product. For example, a shortage of green circuits in the offworld market place could drive their price sky high. If there is a way to connect the current prices to the circuit network you could then build a system that would sell things when prices of a product reach a certain threshold, etc.But you want to avoid making it a linear relationship because then it will just become a simple equation of "if its profitable right now, launch; otherwise wait" (and we are back to backing up the factory). Instead, if you make it all about the quantity being sold, then green circuits may become profitable when you launch/sell at least 100k of them together, but when there's a shortage, that drops to 50k or whatever. That way you are always launching them. Now whether there's a staging area in space and you send parts up constantly then sell them when you have enough for it to be worthwhile from your staging area (which would involve creating and sending up staging area storage, research related to this etc.) or if you need to research larger and larger cargo vessels for the rocket and larger ones require more rocket fuel for launch, etc. is a toss up. Maybe allow for both even.
EDIT:
Instead of having ammo grouped in with the intermediate products, you could have Weapons (including ammo, guns, rockets, etc.), then the Infrastructure (buildings, inserters, belts, etc) and the Intermediate Products. Each would be "currency" toward different types of services. This then means that there is much more incentive to build out the different kinds of weapons and ammo. Usually I build one (Uranium bullets for example) and ignore the rest (shotguns, flame throwers, cannon shells). Depending on the game I choose differently but I've never had a game where I automated the production of all the ammo types.
. Ofc this would require that there are some relevant new items/buildings that require those high-end components in the first place.