Well if you consider MB's comment that the UAs use Morse for a reason then I think there are only two possibilities:
1) UAs were created by humans using some alien organic technology, origin unknown
2) UAs were created by aliens trying to communicate something to humans.
i don't think we yet have any evidence to prefer one, after almost two years they are still equally probable.
Those were pretty much the ones I had in my list too, but I think 1 is broader and is just generic human origins. Don't get me wrong, I think the one you've said is the most likely one of the set, but there's other options - they're created by human AI (still no clues what happened to them that I've seen), they're pure human creations but there's been a time-slip, they're pure human creations from some of the missing who have made rapid progress away from the main human bubble.
My money is on the UAs being human creations from cannibalised UPs:
- UPs use of symbols & non human reference points vs UAs use of morse & human system names
- UPs being completely unusual looking vs UAs looking half (head) unusual and half (tail) pretty normal tech-wise.
So why did we find UAs first and what's the deal with them and the UA shell?
Ok, here goes:
- Whatever's in Col 70 Sector FY-N C21-3 was found by humanity (which is why it's locked). UPs were either there or in the vicinity.
- The UPs transmission to Merope along with the Col 70 Sector FY-N C21-3 to Merope distance unit lead the powers to be to investigate Merope.
- Nothing was found, but there was obviously some significance to Merope
- It was assumed that the something would return to Merope at some point
- Realising the possibility of a threat, the Merope situation was put to use
- A hidden repeater was installed in Merope
- The UP was cannibalised with human tech to make the UA
- The UAs were distributed around Merope in the UA shell
Why cannibalise the UPs? Various reasons:
1. Concealing what was going on from humanity
2. Making use of advanced tech within the UP
3. Providing an anomaly as bait to get ships to stop and investigate the UA (at which point they would be scanned and their ships shape transmitted to the repeater station at Merope)
Why do it all? Early warning. Unrecognised ships spotted by the UAs would be the trigger. Where in the shell the alarm was triggered would also indicate the where the ship was coming from (assuming they were going towards Merope). Even if not heading to Merope, enough triggerings would give a general direction of approach.
Also UAs which were picked up would eventually be dropped (either intentionally or through the corrosive effects of the UA), providing a mechanism for tracking the ships.
What happens when certain ships trigger the alarm? Exodus, Warfleet/INRA activation, diplomatic missions, who knows?
Our interaction and interference with it all wasn't planned for - the advent of the FSD and widespread access to fast, long distance travel putting it all within easy access for most of humanity hadn't been anticipated. (Or possibly it was and the Antares incident was rigged to stop the take off of FSD tech.)
I could be talking absolute rubbish of course!
