Shroom Man 777 wrote:But hey, it's in space, and its weapons yield is measured in kilotons according to these guys, and unless the atmosphere significantly degrades the weapons range
The Earth's atmosphere
does provide a measure of protection against kiloton-level events.
NewScientist wrote:On 8 October an asteroid detonated high in the atmosphere above South Sulawesi, Indonesia, releasing about as much energy as 50,000 tons of TNT, according to a NASA estimate released on Friday. That's about three times more powerful than the atomic bomb that levelled Hiroshima, making it one of the largest asteroid explosions ever observed.
However, the blast caused no damage on the ground because of the high altitude, 15 to 20 kilometres above Earth's surface, says astronomer Peter Brown of the University of Western Ontario (UWO), Canada.
This 50 kiloton energy release
shook some people up on the ground but apparently did little noteworthy damage.
The
average density of air at sea level is ~1.29 kg/m^3, about half that at an altitude of around 5 km. So there's a fairly decent air mass between Earth and space, I calculate about 9.68 tons over every m^2 of land area. Depending on the properties of TIE weapons fire I'd say it's quite possible if they tried to shoot at cities from space most of the energy would end up harmlessly heating up a lot of high altitude air.
Bakustra wrote:Didn't we just have a thread where we pointed out how difficult it would be to move an asteroid from the Belt to Earth? The required energies were on the level of sterilizing the surface.
If you're talking about the thread I'm pretty sure you're talking about the asteroid being used as an example there (
16 Psyche) is a monster over 200 km across that has something approaching 1% of the total mass of the asteroid belt and is one of the 10 most massive main belt asteroids. If it were to impact Earth with a velocity of a mere 1 km/s the resulting explosion would be the better part of 3000 teratons, or almost 30 times the estimated energy of the impact that wiped out the dinosaurs. Throwing 16 Psyche at Earth would be horrible overkill to destroy civilization. It's also a main belt asteroid, so it would require a high delta V to reach Earth, and the calculation was for a transfer to Earth orbit which would require slowing it down on arrival whereas if you were using it as a projectile obviously you would have to do no such thing.
A much more sane choice for a projectile would be the near-Earth asteroid
Eros, which is something like 1/10,000th 16 Psyche's estimated mass and according to
PERMANENT could reached from Earth orbit with a delta V of under 2 km/s (ergo it would probably take similar delta V to move it onto a direct collision course), as opposed to the 8-10 km/s needed for asteroid belt to Earth transfer orbits.
Doing some quick napkin calculations with the numbers cited for ANH (covering hundreds of thousands of km in minutes, which would imply several hundred to thousand km/s) and assuming TIEs have a mass in the ton range they might have a total potential KE in the ballpark of 2 X 10^15 joules. Imparting a delta V of 2 km/s to Eros would require roughly 1.2 X 10^22 joules, a difference of approximately 7 orders of magnitude. So just going by that it's doubtful they could do it, although that's hardly a thorough analysis.
Edit: by the same estimate a TIE doing a suicide run into Earth might get you a boom in the low megaton range (a few tons at 2000 km/s - a speed at which 100,000 km could be covered in 50 seconds).