It is true that the domino effect changes things we could not possibly forsee. The meteorite that slammed into Jupiter probably had no effect on it's mass, inertial rotation or elliptical path though. Why? Point One: Many scientists believe that Jupiter does not have an actual "surface", or if it does, only a very small core of solid metallic hydrogen. The meteroite would never cause an impact because it would simply "burn up" in Jupiter's very dense (and deep) atmosphere. Point Two: It was not really a meteorite but rather a comet that met its demise (Shoemaker-Levy). Comets are loosly compacted objects consisting mostly of empty space, dust and ice with hardly any mass. When this comet encountered Jupiter's gravitational pull, it broke apart into many smaller pieces. Point Three: The mass of this comet was miniscule compared to Jupiter's mass. Even an object the size of our moon would have little or no effect.
Explosions (such as volcanoes or atomic bombs) that happen on a planets surface do nothing to change it's orbit. The atmosphere will absorb most of the kinetic energy as friction, dissipating any "thrust" it could produce. An explosion in space could possibly change an orbit or cause a planet to "wobble", but most scientists agree that this would have to be a pretty big blast to cause any serious damage, especially with a planetary-sized object.
As for the thrust of UFO's, my explanation was theoretical in nature due to the description of the Power Source. The OFOpaedia description of Elerium-115 clears up some questions regarding anti-matter production. Here is a direct quote:
"This element has the unusual property of generating anti-matter when bombarded with certain particles. This creates gravity waves and other forms of energy. It is not naturally found in our solar system and cannot be reproduced."
So actually, gravity waves AND
anti-matter is produced simultaneously from the bombardment of E-115. In addition, the definition claims "certain particles" are used in the bombardment - NOT
Elerium-115. Therefore, one bombardment only uses one unit of this rare element, not 3 as I guessed.
With bombardments, we are talking about interactions between these "certain particles" and an atom
of Elerium-115. What I would like to propose is that one "UNIT" of Elerium-115 does not equal one atom
. Even one mole of Elerium (6*10^23 atoms) is a fairly small quantity to even handle! For now, let us just assume that one mole of E-115 = 1 "UNIT".
What this means is that one bombardment of E-115 by one particle produces one unit of anti-matter, gravity waves, and energy. The destruction of this anti-matter may produce 100 subatomic particles (just a guess). The equation of this reaction would be:
1 "Particle" + 1 atom Elerium -> 100 subatomic particles + Energy (including gravity waves). The weight of these subatomic particles would have to be less than the original weight of the E-115 due to conservation of mass and energy. The energy produced can be converted into a weight (or mass) by Einstein's famous equation E=mc^2.
More importantly, those 100 particles are moving at a high rate of speed each adding a small amount of thrust to the craft. Because these bombardments occur atom-by-atom the spacecraft should remain maneuverable even with many per second. Two, three, or even four engine spacecraft could fly easily by synchronizing the bombardments to occur at the same time.
So in short (yeah, right!) your supply of Elerium would not be depleted too fast if you think of the Units as moles. My Avenger used 3 units of Elerium for 2 hours of flight. If you convert this ratio to bombardments per second, the result is 2.5*10^20! Seems a little high for me, so my assumption that 1unit = 1mole must be too high. Anyhow, even if 1unit = .00000005mole you are still looking at a fairly high number. Let's say 10,000 atoms per second can be bombarded. If this is true than 1 Unit of Elerium = 24,000,000 atoms (or 2.4*10^7)! If everyone agrees that this rate is possible, then logically, you have to also agree that 1 unit = 24,000,000 atoms (ratios do not lie). This explains why craft do not suddnly run out of fuel in mid-flight!