Reaction Penetrating Metal Sheet I'm writing a novel set 28 years in the future in which the protagonist attempts to manipulate a communications satellite by directing a swarm of nanorobots (or possibly micro-robots, depending on plausibility).

An initial wave of nanorobots is tasked with creating a path, such as a tunnel, through the satellite's casing so that a second wave can enter.

Inspired by real-life nanotechnology that delivers chemotherapy drugs only to leukemia cells, I thought to have each nanorobot carry a tiny amount of super acid, each depositing its payload onto the same spot of the metallic hull of the satellite. My thinking is that the vacuum of space would carry off the product of metal + acid, leaving fresh metal for the next microrobot to attack.

Is it plausible to erode a narrow path through metal in this manner? What acids would be well-suited to the task? How would I go about calculating the order-of-magnitude number of nano-robots needed to complete a path through a given thickness of (let's say) aluminum?
Depending on the material that the casing is made out of, you could have a mercury or gallium payload.  They both are capable of significantly weakening the structures of some metals (such as aluminum).  See the following video of gallium weakening a coke can.  Mercury can also weaken the structure, especially in conjunction with gallium as seen here.  Mercury will form an amalgam with aluminum and significantly weaken it, as will gallium.  You might conceivably have nanobots bring a payload of the two metals to weaken the structure, especially since they are not nearly as reactive with other things.

Unfortunately, this would only work if the structure you are trying to damage is primarily aluminum, but might give a starting place for non-acidic solutions.