## The Rods from God#

The Rods from God is an article about space-based weaponry.

The system would likely be comprised of tandem satellites, one serving as a communications platform, the other carrying an indeterminate number of tungsten rods, each up to 20 feet in length and 1 foot in diameter.

It's an interesting approach. Very heavy objects dropped from a very high altitude carry a lot of potential energy, which is then converted to kinetic energy, which is then used to destroy things.

I wondered though, where does that energy come from? We have to lift those rods into space. How much would it cost?

• What is the volume of each rod? The volume of a cylinder is `pi * radius2 * length` = `pi * 0.5ft * 0.5ft * 20ft` = `15.7 cubic feet`.
• What is the density of tungsten? Google tells me 0.7 pounds / cubic inch.
• What is the weight of each rod? First convert `15.7 cubic feet * (12 in/ft)3 = 27143 cubic inches`. Then multiply `27143 cubic inches * 0.7 pounds/cubic inch` and we get `19000 pounds`.
• What is the cost of tungsten? Google pointed me to a Reuters story suggesting prices are quoted in hundreds of dollars per ton. That means the tungsten in this rod should be fairly cheap (under \$5000).
• What is the cost of lifting something into orbit? This is harder to find; Google pointed at many different costs. The ad I got on that search led me to `spacetethers.com`, which gives `\$1000-\$2000 per pound`. Given that it's the military doing this, I have to take the upper estimate, and say that the cost is `\$2000/pound * 19000 pounds`, giving `\$38,000,000`.

I suppose \$38 million could be considered a “reasonable cost” to the military.

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