Ancient Ruins Mission for Guardians?

I got this mission and I am unsure what to do next.

Is it a one time only? Does it prompt Thargoid attacks? I am brand new to the game and I just started accessing engineers.

It gives me 3 weeks to do it so I have a feeling it is a whopper.
 
That is good to know. I want to check it out, but maybe I'll do it at a later time.
There are actually 2 - from different stations in Meene. The first is possible - most cannot even get the goods to start the second one. No rush, and probably worth looking at the online guides if you do try them - they're not designed to be solo'ed.

o7
 
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