This assignment is part of the DLC assignment Bring Down the Sky. You can start it by clearing the first fusion torch facility and talking to Simon as you exit, or by finding one of the bodies of the missing engineers - mostly like G. Mendel, who is near a shack just southwest of where the Mako will land on Asteroid X57.
When you land on X57, drive the Mako uphill to the southwest to find a shack (Survey Station 3), outside of which you’ll locate the body of G. Mendel and a Technician Kit. Search them to confirm G. Mendel’s demise to update this assignment.
In the southeastern corner of the operational area you’ll find Survey Station 1. Outside of the shack you can score a Secure Crate [Average], while inside you’ll find an Aid Station and the body of C. Hymes, one of the engineers Simon asked you to find. Doesn’t look like there’s going to be a happy end to this assignment.
Survey Station 2 can be found in the northwestern corner of the map. Search the shack there to find a Hardened Crate [Hard] and an Aid Station, then hit the Station Logs to find that the engineer here - R. Montoya - was a little more proactive than the other two. This isn’t necessarily a good thing, as three Defense Drones will swoop down and attack after you’re done with the logs.
After you dispatch the turrets (remember, Sabotage will render them temporarily harmless), search just east of the shack to find some footprints, which lead east. Get in the Mako and drive east until you find the body of R. Montoya.
When you find all three engineers, this assignment will end.