Insurance: Space junk presents novel case

The talk has all been about why no one should worry. But now NASA and the US Department of Defense (sic) is admitting that there are reasons to be concerned about the risks arising from a falling satellite.

First, some facts:

1. This is no surprise: the UARS (as it is known) has been redundant since 2005. It has been in a steadily declining orbit for some time. But it is a low-orbit satellite and was initially falling slowly so it does not "burn up on re-entry." Even so, no plan has been made to try to spin it off into space or any other technique to prevent its fall to earth. NASA stopped updating its UARS web page on 18 November 2005: http://uars.gsfc.nasa.gov/www_root/homepage/uars-science/Weekly_Status/Weekly_Status_111805.html. That page shows that there was a "burn" planned for 1 December 2005 to adjust the orbit.

2. It's heavy. This is no spaceframe and tin-foil contraption. It weighs (on earth) six tons. That's almost the equivalent of three Rolls-Royce Ghost motor cars, not something one wants landing on one's head.

3. It's moving fast: about five miles per second. Let's put that into perspective. At the UK's near-walking pace motorway speeds of 70mph, we are travelling at 0.194 miles per second. At Monza, the fastest F1 cars were doing around 216mph. That's 0.060mph. The speed of sound (remember the one-elephant, two elephant... test for how far away is by counting the time from seeing the flash of lightning to hearing the bang of thunder?) is one mile in five seconds (give or take a bit for atmospheric conditions).

4. There is a maximum 20 minute warning of the main "hit" site. The speed and the lack of clear understanding of how the satellite will move as it goes through different atmospheric strata means that the crash site cannot be identified until it stops wobbling and gets a fixed trajectory: think yellow triangles in Angry Birds: once you tap to set its direction, then you know where it's going. Unfortunately, no one has a "tap" function for this thing.

5. When it crashes, if it hits land, it will create a crater. That will spew dust and debris into the air. There are no public predictions for how much or how high because there are so many variables. But there is some information on how the thing itself will fragment. NASA warn that sharp metal (and other substances) pieces might be strewn over an area as large as 500 miles. Unfortunately, despite being scientists, NASA have not been very clear as to what "500 miles" means. is it a 250 mile radius or an area of 500 square miles (which isn't very big: the square root of 500 is only 22.36).

6. The potential crash area is potentially massive. 57 degrees north to 57 degrees south with no clear idea on east/west numbers. This covers an area from northern Europe to the southern tip of Africa - and more than half the world's population, including all of the world's most densely populated cities.

7. Some pieces will be big: NASA estimate that the largest will be 300 pounds - the weight of the fabled gorilla that those in trouble are said to carry on their backs. Coincidence? Maybe.

8. There is no official word of the likely ecological effects of the crash. Of course, this will depend on exactly where and on what it crashes. If it hits water, it will cause waves but not a tsunami-style devastation. If it hits sand, then some of its force will be dissipated in soft sand - but hard sand will not absorb so much. There is, also, no official word on whether the debris would interfere with commercial flights. But what can be said with total certainty is that, no matter where or what it lands on, it will not cause a dust storm such as wiped out the dinosaurs. It's big, but not that big.

9. The force with which it will hit will be phenomenal. Not to be seeking controversy, is is relevant to point out it will be significantly greater than the force of a plane hitting New York's Twin Towers of the World Trade Centre. Although its weight is less, the speed more than makes up for it. The question will not be whether it will cause great damage but how random that damage will be. For example, it will be moving so fast that, depending on angle (which will not be vertical) it may scythe through whatever it hits before being itself destroyed on the next thing, or the next... .

10. Insurers will, potentially, be on the hook for thousands of millions of dollars of property claims to say nothing of the life assurance, medical insurance and, even, travel insurance. The insurance industry faces a significant burden - and the chances of a successful re-claim against NASA or anyone else are close to zero.

Within the area concerned, there are large areas of light or close to zero habitation and large areas of ocean and other water. Even so, 1:3,200 seems short odds when, according to recent figures, Earth's population will reach 7,000 million on 31 October this year.

NASA say that in 50 years of space exploration, no one has ever been injured by falling space junk. The tendency is to think that each event reduces the odds of that continuing but, of course, each event is unique and not part of a series so the odds are not affected by previous activity.

No time has been announced for when UARS is likely to start to be visible - in part that is for the same reasons that it is not known where it will fall. Sky watchers will be out in force hoping to catch the first glimpse and to calculate its likely landing place.

Don't bother. twenty minutes isn't very long.