I have tried flying through the nebula near ESD but nothing happens.
I am Admiral Lower Half. One web source stated that I must "purchase" something from the c-store but I cannot find anything having to do with it?
The item you must claim for access to the Captain's Table is Secret Access Code. It will be in either the 'Items" or "Legacy Items" tab of the in-game C-Store. Claim the Access Code. And that should give your access to the Aenigma Nebula. (Assume you are a 400 days Vet or Lifetime Subber)