Can you advance sensor even on top of a rock?

Advanced sensors grants a free action before you reveal your maneuver dial.

Here's what the rules say about obstacles and free actions:

A ship can perform free actions even if it skipped its “Perform Action” step due to overlapping an asteroid obstacle or another game effect.

Rules Ref Page 12

and this

A ship can still perform free actions even if it moved through or overlapped an obstacle, as long as the ship is not stressed.

Rules ref page 14

In other words, yes.

addendum.

the only exception would be if you attempted to use Adv Sens to perform a boost or barrel roll action and the movement template overlaps the obstacle

Can you advance sensor even on top of a rock?

you cau

unless

1. you are stressed (so no actions, free or not)

2. you have some crit that prohibits you to perform actions

3. you are ionized (and as scuh don't assign a dial)

4. your action cannot be done. boost\barrelroll template overlaps an obstacle or your final position overlaps something