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Comment by qikInNdOutReply | Hacker News Reader

The problem is that planetary civilization is inherantly fragile to those living up outside the gravity well. Every depressed belter asteroid-trucker with a balistics computer, can throw a garbage can at earth or mars at speed and end planetary civilization.

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I think you're confusing reality with science fiction.

Rods from god are roughly as powerful as nukes, which is bad but a single nuke wouldn't end planetary civilization. If the belters were able to throw things at relativistic speeds you'd have a problem, but there's also no stealth in space so it's feasible to monitor space traffic around a large planet and deflect anything incoming, be it a projectile launched from longer range or an untrusted, uninspected, shady-looking belter ship.

The "rod from space" just need to deflect the orbit of an already existing large asteroid doesn't it?

Which would hopefully be detected in time to "solve" the problem, but still... ;)

"just" is doing a lot of work there. It's a pretty serious engineering effort to move rocks around the solar system and unless you have unlimited-energy future tech, you're probably stuck with the current paradigm of nudging things slightly to take advantage of convoluted gravity assists and small time windows to move things about. It'd be a very slow and predictable weapon that we already watch for.

Anything small enough will just burn up in the atmosphere and big stuff will be easy to detect, even at the boost stage as the initial orbit change might take weeks or months possibly.

Orbitals at predictable orbits and surfaceinstallations on airless bodies might be more in danger though. There even a well targeted fast crowbar might do quite some damage.

I think rods from gods is oversold. The classic version of this is a "telephone pole of tungsten", or something along the lines of a 6 meter long cylinder, 0.3 meters across, which works out to 0.42 cubic meters of tungsten, which would be just over 8000 kilograms. If you do the math, rods coming in at orbit speeds are barely worth talking about; the actual rods from god USAF proposal had these tungsten telephone poles starting in orbit and impacting the ground at merely 3 km/s, equivalent to 11 tons of TNT.

Faster then: the kinetic energy of such a mass moving at 12 km/s, faster than escape velocity, would be 'only' 137 tons of TNT, approximately 1/15th of the 2020 Beirut explosion. Even if you throw the rods into the ground at a blistering 50 km/s, that only gives you the equivalent kinetic energy of 2.4 kilotons of TNT, or 1/6th of the Little Boy nuclear bomb.

Then there are the terminal effects; such a tungsten rod is basically an oversized armor piercing dart like tanks shoot at each other. It will drive itself straight into the ground and most of the rod's kinetic energy will be spent pulverizing bedrock and itself. Such a weapon would be great for taking out bunkers, but I think very wasteful for any other purpose.

> It will drive itself straight into the ground and most of the rod's kinetic energy will be spent pulverizing bedrock and itself. Such a weapon would be great for taking out bunkers, but I think very wasteful for any other purpose.

Wonder if it could be precision enough for non-military applications? eg possibly faster for deep geothermal drilling than using the existing surface based borehole drilling approach.

For military applications though, it'd wonder if such a rod (or small sequence of them) could be effective when striking geological fault lines. eg the San Andreas Fault line

Aka the old "use the terrain" approach.

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