and these are the questions i come to the dope for 
Even the Death Star clearly makes hyperspace jumps. It can leap from annihilating Alderan to readying itself to wipe out a rebel base in little longer than the time it takes a ship that does the Kessel Run in mumle mumble to do the same.
The point about orbits is likely the key get out. The various Empire warships don’t orbit. They just loom. They can sit over a city at what is only a few miles altitude. And they arrive in loom mode directly out of hyperspace. The Death Star would reasonably have exactly the same ability. Except when the plot demands it can’t. Such as when wiping out a rebel base.
Control of the basics like local gravity inside spacecraft is clearly available to even the lowliest heap of junk. Thus control of the local field around any craft no big step. We can thus reasonably assume that there is no issue with differential forces on even the most gratuitously huge craft. Not unless the plot demands it that is.
So they use the Force?
“How do force fields generators work, anyway?”
“They contain very bored Jedi.”
“Sir, we have arrived in the Yavin system. The moon with the rebel base is currently on the other side of the planet. We are traveling in opposition to its orbit to bring it into view but it’ll be a while before we have a clear shot.”
“Why didn’t we come out of hyperspace over on the other side of the planet so we could shoot at the moon immediately? Presumably any technological society with the capacity for interstellar travel would have charts and systems for predicting the orbital positions of target bodies.”
“Yes sir, but (insert handwavey lore about Old Republic recordkeeping standards and sabotage by Rebel sympathizers combined with the mystical influence of nascent Jedi defenders and and and)”
“Oh, shut up, just tell me when we’re ready to fire.”
Nitpick: rappel, not repel.
You do pretty much have to presume some such handwave or literally astronomically bad luck, considering that the odds of it randomly coming out in just the right place for the rebel base to be in eclipse are really small. Either Force shenanigans or a secret Rebel actually being the Death Star pilot, basically, considering the necessary precison.
If they were really clever, they would have popped in above the plane of the system, so they could shoot down at the moon and make its orbital position around the planet irrelevant.
“Now they tell me.”
-Khan Noonien Singh
“Two-dimensional thinking.”
No they couldn’t. The Plotium makes that impossible.
Maybe I missed it above, but are there calculations for how long it takes for the tidal to pull a natural object inside the Roche limit apart?
Ha! How did I know that was going to happen?
Anyway, that’s not even exactly what they do, just described that way for brevity.
Thanks though!
To be fair, none of the major characters in any of the movies have been physicists, engineers, or anything of the sort (the closest we have are R2D2 and Chewbacca, neither of whom speaks English). If you ask most modern first-world Earthlings how their air conditioner works, they’ll tell you “I push the buttons on this little panel to set the temperature to 72”. If you ask most Star Wars denizens how their artificial gravity works, they’d tell you something similar.
Just a moment here - I can personally verify that Unobtanium does exist on Earth. It is well known that all spare parts for BSA motorcycles were manufactured from it, although some more uncommon parts were made from Ontheboatium. Research has not disclosed just what material was used in the expensive Replacement Smoke Kit for Lucas “Prince of Darkness” Wiring Harnesses.
I don’t know if anyone’s come up with calculations, but the time isn’t very long. It varies with what the natural object is made of. For icy objects it’s a faster than rocky objects.
We haven’t seen a whole lot of Solar System objects disrupted by tidal forces. Some comets that came especially close to the Sun have broken up, although those are probably due as much or more to the loss (sublimation) of the ice holding them together than just tidal force. The comet Shoemaker-Levy 9 broke up when it made an especially close pass near Jupiter. It wasn’t discovered until after that happened, at which point it was in about 20 main pieces and probably many more too small to see with telescopes. I can’t think of any other examples.
There is a hypothesis that Phobos, the moon of Mars, is the remains of a larger satellite that broke up when it reached the Roche limit. The idea is that most of the predecessor satellite was inside the limit and stayed in pieces, eventually to crash into the planet. But some small part, perhaps 10% or less, was outside the limit, so it recollected into a smaller satellite which we see today. In fact, they suggest that this may have happened more than once, each time leaving a much smaller satellite.
It seems to me that there’d be some better evidence for this if it did happen. A residual ring around Mars and/or a series of craters along the equator where the larger pieces landed.
Thanks. I hadn’t thought I’d seen anything about it. Makes the application to the Death Star even less meaningful.
“With all due respect, sir, who cares? We’ve got a moon-sized space station with a laser that blows up planets. They’ve got about a dozen single-pilot fighters. We can come out of hyperspace here, and blow them up ten minutes from now, or we can circle around the solar system to come in from the other side, and blow them up in thirty minutes. It’s not like there’s a single thing they can possibly do to stop us, so let’s just mop this up quick and break for an early lunch.”
"I am ashamed of you. They couldn’t hit an elephant at this dis
Plus, for the Empire, Evil Is Its Own Reward. The Emperor could have killed Luke at almost any time, but he dragged it out instead, just to torture Luke both physically and mentally. With the Death Star, they wanted the target to know it was coming. They wanted them to have long enough to experience the looming terror of being wiped out, but not long enough to do anything about it.
Remember, “Fear of this battlestation” was literally their entire strategy for maintaining control of the galaxy, right from the beginning.
Bumped.
This may also be of interest - a nifty AI short film.