I'm a fan of Star Wars, and I've read a bunch of different science looks at the elements of Star Wars. I might expand on this at some point and do a video explaining it.
I just heard yet another person complain about how "those little torpedoes fired into that little hole caused a space station the size of a small planet to blow up" and "well why didn't the empire cover the hole" and "why didn't the rebels fly around space so they wouldn't have to fly through the trenches?"
1. You obviously haven't read up on the science behind the explosion of the death star. That was an exhaust port that lead right to the main reactor of the ship's power source. In our universe, it's essentially the equivalent of 100 nuclear reactors, and that was the equivalent of 100 nuclear reactors simultaneously blowing up. 100 nuclear reactors could destroy the Earth, it wouldn't have any trouble blowing up a space station that's a little larger than our moon. The torpedoes aren't what blew up the death star, they are what set off the chain reaction in the reactor that blew up the death star. It only takes 1 neutron to blow up a uranium atom, and there's a lot of neutrons in a small torpedo.
2. It wasn't covered because, as I said, it's an exhaust port. You can't cover an exhaust port without damaging and ultimately destroying the thing that's emitting the exhaust. Also, an exhaust port has to be at least a certain dimension for it to be effective, otherwise it's only slightly less useless than if it wasn't there in the first place. That hole was as small as they could get it without being bad.
3. With this in mind, the empire realized how glaring of a weak spot this is, and is why they protected it heavily presumably at all times. If the rebels made a full on frontal assault, it would be suicide because the empire would be ready for them. They had the top guards on the front line, and had the lesser guys on the back where the rebels made their attack. They weren't fighting the top guys initially. Notice how it isn't until much later do the rebels start losing pilots. Top guys right there. If you actually think about the science and tactics of star wars, that "plot hole" makes a lot more sense.