TL;DR
When a space platform request only requests items from other platforms (not planet and not all) AND has a maximum (< inf) set it currently dumps cargo to planetary hub when i think it should not.The Topic is linked to this suggestion viewtopic.php?t=134822 as it tries to address similar issues but with a different or additional fix.
How i arrived here
I tried a simple thing: Send items by request from a Space Station to the Planet, but keep a minimum number on Station.Example: First space station that constructs science, should supply Planetary Base with overflowing Iron but keep a reserve for continued production.
The implementation of that idea has several issues. Even in [2.0] i can either:
- Set a space station request for Iron, but also limiting it.
- I now cannot enable automatic rocket requests, because it may waste Rockets on Iron. Can be mitigated by setting min amount to 0.
- I cannot limit Iron supply on Planet, in worst case resulting in Landingpad-Overflow
- Set a request for iron on landing pad
- Now i cannot guarantee space production as it may use all iron to fulfull the request
- I cannot coordinate different space station logistic hubs with that
Now with [2.1] arrived inter-space-platform-requests and i'm excited for a new idea:
I'll use a buffer platform like mentioned in the semi-recent FFF https://factorio.com/blog/post/fff-441
I set up everything like i imagine it should work and it does not:
- Buffer platforms in orbit for quicker transport turn around.
- Orbital assembling of space materials (such as Space platform foundation) to save on surface rockets.
- Landing pad requests items.
- Buffer station requests min X [no max set] of items only from other platforms. Inserters voids items to space if item_amount > X+threshold. (I would like it to enable supply of other stations for it to be also a space supply buffer, but do not as of now for simplicity)
- Any other platform or Ship in Orbit that want's to make use of the buffer is set to request the amount of item it wants to keep as min amount from other platforms and sets the max amount upon which it dumps items to other places in the same slider. They set no planetary request for those items. They enable supply of other stations.
What happens instead: Any other platform that overshoots it's target just dumps it's items directly into the planetary landing pad. This is frustrating because they completely circumvent the buffer station. And will still overflow the landing pad. That will happen even if the landing pad has no request set, or if the request is set to max=0 which will dump the items into it's trash-slots.
At least i can confirm that the Buffer station will adhere to landing pad requests, even if it has that request set from other stations on itself and it's minimum requirement are not yet met.
Current solution rant or Why this is important
The standard community (i asked in discord) solution seems to be "just use [2.0] method 1 and dump/void everything". But i would argue that is provably/empiricly wrong.The logistic problem i describe can appear as soon as the first space platform, long before we unlock the recycler or even Fulgora itself. While space has a voiding mechanic, Nauvis does not. The only reliable way to void overflow iron would be to limit oneself to ore (not plate) requests, detect an overflow, craft ore into plate and send that up to a second space station for voiding. At that point in the game there would be no way to effectively void carbon (if collection rate > burn rate on planet).
The other community answer is "you should not be overflowing iron anyway". And i would argue that assumption of player behaviour is out of place.
If you encounter the setting as early as i described you may soon fly to another planet, and have science stall for hours while exploring other places for the first time.
The last idea would be to try to automate requests with radar networking, memory cells and SR-Latches which would be way above the giving up threshold of your average player and also does not work for it's own reasons, see the linked suggestion in TLDR segment.
What i want to establish in this section: this issue is legitimately encounterable, confusing and has as of yet no viable automationable solutions.
Where do we go from here
I acknowledge that the first naive solution would be to set seperate requests in stations for each item for planetary and space requests.I tried that and found out that this basicly acts as an "from all" request with maximum values selected both requests min-max sliders.
I will asume that seperation of those request destinies would be technically difficult to implement.
That's why i propose this simpler fix: If a Space Platform has more items of a type than the maximum value of it's request from other stations and no planetary request for that item then exclude the landing pad from the list of valid recipients. I would like to see Stations with any request for that item with < maximum items of that type in cargo to be preferred in dumping cargo. If there are no other stations to dump to then the station should simply NOT send those items anywhere.

