Ender wrote:Eh, his stuff is easily ignored by the fact he got the mass way off. Each fuel tank has the mass of the ship condensed into a small sphere. Find how many fuel takns are on the thing and adjust the calcs, and the thing should probably not go flying like he says. Besides the fact he left off the mass of the atmosphere in the thing.
The mass of the atmosphere is insignificant. Even if air fills the 90% of the DS CM declared as not solid, you only double the mass of the not-fuel component of the DS. This would produce only about an 8-9% decrease in the velocity after firing.
The fuel mass on the other hand is a different matter; because so much is required for firing, it dominates the DS mass by three orders of magnitude. I think CM assumed enough fuel for two blasts (the observed number of blasts), and I assumed enough fuel for one (the worst case). In the worst case, I found a final velocity of 70km/s, which is not really a problem. If the DS is 75,000km away from the Falcon when it arrives (as CM claimed Curtis Saxton found) and the Falcon arrives "near" Alderaan, then the DS would only have to travel at 70km/s for 18 minutes to achieve that setup (enough time that it would plausibly need more to get clear for a jump, not so much time that it would have gone when the Falcon arrived).
Besides all this, the interesting problem is not how the DS stayed put (if it did), but the level of resistance to the stresses of firing that it demonstrated, which was more exceptional, and does not depend on the mass of the station. The bulk acceleration does depend on the (fuel+structure) mass; obviously, increasing the fuel mass decreases the bulk acceleration but does not affect the forces acting on (and so stresses produced in) the DS. The acceleration would be inversely proportional to the number of shots (and so the stored fuel) the DS was capable of in total. To make the accelerations consistent with the millions of g that get quoted for an SD's resistance to tidal forces, the DS would have to be capable of between 10 and 10000 shots given CM's accelerations and minimum 10 shots with mine.
The biggest assumption in all these calcs is connected with mass; that the energy is provided through a maximally efficient annihilation reaction. Since at least some sources (most?) reckon that the energy comes direct from hyperspace, the kinematics of the DS are then modified.
Lets face it, the DS is all kinds of screwy. It goes to hyperspace when it's own mass should generate enough of a grav well for it not to. despite having a direct opening to space through the reactor, the Emperor's throne room did not depressurize. It causes ring explosions in some things, and doesn't cause them in others. It can hold enough tibanna gas to fire alot of DS shots even though there is nowwhere on the ship shown to hold that stuff. The thing gets shaken by TLshots. Not alot makes sense.
How much mass is required to prevent a hyperspace jump? Also, there are no obvious engines, despite repulsors only apparently being of use near planets and most ships in SW using obvious reaction drives.