Saturday, May 2, 2009

The inverse square law and long thin sausage balloons with internal skeletons

Our balloon could end up quite an interesting shape. If we are going to sterilise it with UVC LEDs then we want to make it as long and thin as possible. Why? Well, the intensity of UVC light at the balloon's surface from an LED in the centre of the balloon falls off with the square of the radius of the balloon - so if we can half the diameter of the balloon we boost our intensity fourfold. A normal balloon is essentially spherical at altitude, presumably to minimise the surface area, and hence the weight, of the canopy. But sterility is our overwhelming priority. Can we make a long thin balloon that can still lift its own weight to high altitude? Either way it will start looking rather like a Zeppelin - or a Skylon. The Skylon would be a better analogy, pointing straight up as our balloon will.
How do we work out the buoyancy of our balloon at a given altitude anyway? Any buoyancy experts out there?
One difference from a zeppelin though is that our balloon can have internal structures but no hoops, plates etc on the skin. We need all the parts of the skin to be illuminated, without any dead zones, by the UVC.

Something else to save weight perhaps - don't have lots of LEDs, have a few, and move them around. Imagine a central pole within the canopy which is extendable (maybe an adapted telescoping car aerial? Do they still do those??), or has a pulley mounted on it perhaps. This allows a UVC LED to be moved back and forth along the entire inside length of the balloon, illuminating its entire surface with a germicidal dose of UVC - eventually...

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