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.
- 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]
- Scientific American, “Competing Catastrophes: What’s the Bigger Menace, an Asteroid Impact or Climate Change?“, Robin Lloyd, March 31, 2010 [back]
- 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]
- CalcTool Earth Orbit Calculator[back]
- 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]
- Wikipedia Air Safety statistics[back]