It can spawn in 3 places iirc. Barrens - where you 1st spawn into Mars Buried City - If you go left tunnel from spawn past the next group through the tunnel again to the next area. Scablands - from the spawn go right (all the way right) to the next area. When I was on the hunt for the warsat for the Sleeper Simulant quest I just did laps around Mars until it spawned. With less people on patrols now you might just have to pick a spot and wait for it to spawn.