Death by Satellite

Posted on by

The Upper Atmosphere Research Satellite (UARS) is on its way down after 20 years zipping by at 375 miles above our heads.  As the bus-sized satellite breaks up parts will reach earth and NASA reassuringly tell us that there is only a 1 in 3,200 chance that anyone will be hit.  Given being hit by a piece of satellite is likely to be painful and most likely terminal, I wonder if I should be worried.

With a world population of 6,963,070,0291, that is around one in a trillion chance that I will die from UARS this year.  Given the annual risk from asteroid impact or shark attack is around one in in 2 billion2, that sounds quite good for UARS (but must buy that shark repellent from Boots).

Of course, it is a bit unfair comparing the UARS that has been up there for 20 years spinning round the world like frenzy, with more mundane day-to-day risks like crossing the road.  For air travel they take into account the distance travelled and aim for safety factors around 1 accident (but with a lot of people in the aeroplane) every hundred million flying miles and achieving a figure about 10 times better than that3.

At 375 miles the UARS will have been orbiting at 7.55978 km/s4, so travelled 2.9 billion miles in the last 20 years.  That means it is causing one death in 10 trillion miles travelled … five thousand times safer than air flight, 120 million times safer than car travel5, and around million times safer than bicycle6.  I must cancel my KLM ticket home and get one by satellite.

  1. World population of 6,963,070,029 at 5:14 UTC (EST+5) Sep 19, 2011 according to US Census Bureau World Population Clock [back]
  2. Scientific American, “Competing Catastrophes: What’s the Bigger Menace, an Asteroid Impact or Climate Change?“, Robin Lloyd, March 31, 2010 [back]
  3. Wikipedia Air Safety page quotes different, but close numbers: 3 deaths per 10 billion passenger miles, one death in 20 billion passenger miles and 0.05 deaths per billion passenger kilometers.[back]
  4. CalcTool Earth Orbit Calculator[back]
  5. Based on UK figures of 3,431 deaths per year (US NHTSA) and 26.7 billion miles driven in the UK per year (Admiral Insurance).[back]
  6. Wikipedia Air Safety statistics[back]