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, 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.