Don't forget - due to the speed of light it takes 5-10 hours to get feedback on if the square illuminated, but maybe more because you don't know exactly how long you'll need to wait.
And there's uncertainty in whether your measurement is accurate.
And there's a background of other illuminated squares that can interfere with your readings.
And you're spinning while this is going on.
And the target square is continually moving. You might have just missed it.
That's smaller than I expected. To convert that into human scale sqrt(500 million) = 22360, in millimeters that's around 22 meters (72 ft).
So if we had a square wall 22 meters by 22 meters we could paint a grid of 1 mm by 1 mm squares on it and end up with around 500 million squares.
Then we'd need to stand there in front of the wall with a laser pointer and shine the laser at each individual square and check the light bouncing back at us.