You're apparently seeking something on a planet, needing an SRV. I was a bit quick here.
Additional info for those who seek an USS in space:
System-map
Open system map after updating the mission, look for the mission icon in the system map, it will tell you which planet/object you need to get within the influence of to get the correct USS.
Object of influence
Look at the navigation MFD (left), you have the blue 'caret/diamond' at the end of a name in the list.
Where the blue diamond is, that's the object thats in your influence.