How Do You Shoot Down A House?

This was one of those utterly random five-year-old questions, really. I have no idea what triggered it at all. We were in the car last night, and I was talking to my wife, and he just tosses this question out: “How do you shoot down a house?”

“You mean, like a flying house?” I ask, trying to parse this question.

“No! How do you blowed a house up?”

So I [i]think[/i] he’s talking about demolitions. So, let’s look into it.

The Demolition Planning chapter fo The Architect’s Handbook of Professional Practice, Update 2006 gives three primary categories of building demolition: mechanical demolition, implosion, and special demolition. Mechanical demolition is the type of demolition that uses excavators fitted crushing and shearing tools.

excavator

Not all of the excavators are the huge ones, though. Small excavators are used for for interior demolitions. But the process is generally the same. The machines knocks down or pull down walls, cut trough metal, break up concrete foundations, and so on.

Implosion is the use of “highly specialized explosives to undermine the supports of a
structure so it collapses either within its own footprint or in a predetermined path”.

implosion

This demolition method is generally used for tall buildings or specialized structures like cooling towers and steel mills and bridges.

Special demolition is a catch-all category that requires ” specialized handheld
tools for cutting, chipping, drilling, and breaking small amounts of materials”. These tend to be smaller projects, like cutting a hole through concrete to install a door or window. The sledgehammer is a popular mental image for the type of tool used, but it’s far more likely to be a one or two man hydraulic or pneumatic tool these days.

Clearly, to “blow up” most houses, you likely wouldn’t blow them up at all. You’d approach it with mechanical demolition, and tear the house apart with a mechanical excavator or a bulldozer. You can read about some of the specific details here, but in brief you probably need to do the following:

  • Get a permit.
  • Have the house inspected for hazardous materials.
  • See if the house can be deconstructed (i.e. have parts salvaged intact) rather than just destroyed.
  • The big machines arrive and wreck the joint.

Clearly, that’s the serious answer to the question. For laughs, though, let’s see what it would take to make a house fly so that you could actually try to shoot it down. Be aware that everything past here is ludicrous and involves giant rockets.

According to HandCrafted Homes, a company that makes modular homes, they estimate 35 – 45 pounds per square foot for a ranch style home (depending on the specific model), plus 1,500 pounds for rigging. The Seattle Times Ask the Expert column came up with an estimate of 200 pounds per square foot for a single-level home, 275 for a two level home, and 350 for a three level home.

Picking a random home in my area, I found a single level 2,800 square foot house. HandCrafted Homes would estimate that at (40 * 2,800) + 1,500 = 113,500 pounds. The Seattle Times would estimate that at 200 * 2,800 = 560,000. Since it isn’t a modular home, let’s go with the heavier one – 560,000 pounds, or 280 tons. That’s big, but not undoable – it’s only (only?) about 50 tons heavier than an Airbus A340-500, an aircraft that is big but hardly the biggest in the world. So we could fly that thing. And most fighter interceptors and many shoulder-fired anti-aircraft missiles could shoot it down.

But let’s crank this up a notch and put it on a huge rocket and launch this house into Earth orbit. Turning to WolframAlpha, we’ll plug the details into the Tsiolkovsky rocket equation.

…wait. The what, now?

The Tsiolkovsky rocket equation, also known as the ideal rocket equation, is a formula that describes how rockets work. A rocket has to lift the mass of the payload plus the fuel, but it expends fuel and gets lighter as it moves. So, this equation works out how the changing mass impacts the velocity of the rocket.

So, with that in mind, back to our rocket and WolframAlpha. The rocket needs a final speed of 7.8 kilometers per second to hit low earth orbit, so assuming effective exhaust velocity of 5 kilometers per second the total mass of the loaded rocket is 1,335.3 tons. To achieve escape velocity, we’ll need a 2,855.2 ton rocket. Which seems big, right? But for comparison purposes a Saturn V – the rocket that sent men to the moon – weighed 2,520 tons and could lift 155 tons to low earth orbit.

saturnv-3_0

Why could it lift less than the house rocket? Because it was a real rocket with mass outside the fuel and the payload. Also, I have no idea what the effective exhaust velocity of the Saturn V was.

Let’s get crazier and put my house in orbit. I live in a condominium, with a total of 24 units on three floors. The condos run about 1,200 square feet each, so that’s 10,080,000 pounds or 5,040 tons. WolframAlpha and Tsilokovsky tell us that we’d need a 24,035 ton ideal rocket to get my condo building into low earth orbit, and a 51,393 ton rocket to achieve escape velocity.

NOw, could we shoot down a rocket heading for LEO or excape velocity? According to Air&Space, the answer is yes, in theory at least, but it’s really, really hard.

So cheer up. Your house might be vulnerable to interceptors if you have it on wings. But if you’re heading for [i]space[/i], you’re probably safe.

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