At this point in the film Thanos has the reality stone.

As long as Thanos was aware of the fleet's arrival, I don't see how they could hurt him. Since it's been seen on screen that large ships exiting hyperspace make a noticeable sound, and even a ship only twice the size of an ISD could be seen from orbit, I'd bet he'd notice the Executor .

At that point, all he has to do is use the reality stone.

With the power stone backing it, there's really no telling what he can do, we see Thanos change the visible landscape for what appeared to be his entire surrounding and well out into space above the planet.

He does this at the collectors place in Knowhere too.

He's seen on screen changing blaster fire to bubbles several times... if his powers extend as far as they appear to in this scene (Which with the space stone at his disposal as well, I see no reason why not) it seems likely that every weapon aboard those ships or maybe even the ships themselves could be changed to something else... bubbles, bats, dust, thumb tacks, whatever he wanted...


I think the important thing to remember about Thanos in his fight on Titan is that he is clearly holding back. As soon as he lands he is confronted by the holder of the Time Stone. His goal isn't to vaporize his opponent, it's to get him to give up the stone. The whole fight he toys with them. Even when he almost loses the gauntlet, he doesn't drop the entire moon on them, he makes it rain meteors instead... just enough force to win.

I just don't see an orbital bombardment being effective against a guy that can change reality at will..