Observation

Thanks to BinkUncia from the playstationtrophies.org forum
(https://bit.ly/2VcDg3e)

This achievement is missable

Here is my 100% Achievement Guide for Observation (Including ALL 85 Collectibles)

This achievement can be obtained when you are on the Alternate ship.
You will play through a bit of the story until you

After that, you need to go back through the ship while Emma opens hatches for you.
Eventually you will be lead to UN-01 (The main room where we got the Base Of Operations Achievement earlier).

From here, look directly up and you will see a hatch called "UC 01/02 Hatch".. Get Emma to open that up for you and you will see a long pod type of thing. This is Alternate SAM, but just beyond this you will see a floating body.
Go up to it and interact with it, and as it is in the achievement name, its Alternate Emma that is dead.
Achievement unlocks.

Go to 2:03:25 to see where and how this unlocks.

Hope This Helps!