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Old 09-28-2017, 07:19 PM   #5
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: [Spaceships] [Space] Firing an Azrael-class world-killer at a planet's moon

Originally Posted by Michael Thayne View Post
If it helps to clarify, though, I'm interested in situations with relatively close-in moons, like Mars' phobos. Couldn't the debris from that do a lot of damage?
Total energy, assuming the math is correct: ~1.8e+23J.
Mass of phobos: ~1e+16kg
If we figure 1e+23J is used to create fragments, that's 1e+7J/kg, or an expansion velocity of 4.5 km/s. That exceeds the orbital velocity of Phobos, so some of it is gonna hit Mars (most of it is gonna go off into deep space and never be seen again). Figure around 10^15 kg of pieces hit Mars at 6 km/s (18 MJ/kg). Total energy reaching Mars: 1.8e+22J, or about a tenth as much as the original weapon.

Not great, but significantly less dangerous than a direct hit, and a lot harder to direct (you can aim the ship at stuff you want to die, such as cities; you can't aim fragments of moon). If I were gonna use an Azrael, I'd probably design it to turn into shrapnel, 10% of its mass as shrapnel across an area of 100 million square kilometers will flash the upper atmosphere and result in a ground level thermal pulse of about a megajoule per square meter, which will set the entire hemisphere on fire and kill everyone exposed to the sky. Use the remainder on harder targets.
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Last edited by Anthony; 09-28-2017 at 07:30 PM.
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