Complete “The Purge,” the final story mission of the Artemis Path, the main campaign of No Man’s Sky.
Own a Planetary Settlement to start the quest, “A Trace of Metal,” which involves creating a Sentinel Companion and upgrading your Minotaur mech.
Warp to a desolate system.
It doesn’t not automatically trigger and more information is not thoroughly explained. Watch YouTube videos on the subject. You will need to destroy a Dissonance Resonator… on a dissonant planet to get the echo locator. You know the big walking machine with a tall purple winky. Also, you may need to kill 2-3 before the Echo Locator drops. After you get the locator you ‘should’ be able to use it on the same planet. However, if it doesn’t activate (not automatic… inventory press ‘E’) then find another dissonant system. Some have stated it has to be a pirate dissonant system but I don’t think that’s true.
Note that it is best to get a new multi-tool IMO as it has some good features not sure are possible on a normal multi tool. Also, you can get more than one Echo locator so if you don’t like that multi-tool then you can always keep on going to new camps.
Finally, one place I got way confused was after finding the interceptor, it requires a brain. You will get a similar item that says brain but isn’t the correct part. Press E on it and it will scan for a monolith station. This non standard MS will convert your item to the correct needed item. FYI, you must be in the interceptor to further the mission. You’ll need to do a number of things in it. If you have a freighter you can have multiple ships so don’t freak about losing your precious. The tech in the interceptor doesn’t seem good enough to keep long term, but it’s standard weapon is way more powerful that the standard ship weapon (upgrades notwithstanding). Good luck!
You also have to have visited a harmonic camp, you'll know if you have already if you have the aeron turbojet backpack. It took me forever to find out but this was the first video I came across that explains it:
The harmonic camp part is what threw me off, because I didn't get the drop to find that off the miner things (the dissonance resonator) when I got my sentinel interceptor ship. So all those videos and guides were talking about doing something at a location I didn't know how to access.
You have to kill dissonance resonators until you get the drop that has "echo" in the name, and use that drop to get the coordinates to a camp.
So you're not just looking for the mirrors you need to get your sentinel interceptor ship(s). You need to get the "echo" drop too, and I don't think you get both from one mob, you'll have to kill multiple until you get your drop.