Wednesday, 25 January 2017

Houston, we have a problem. Our satellites are playing chicken over the poles.

The more I read about satellites, the more it seems we’re missing the startlingly obvious: The satellite constellations we’re so proud of and have become so reliant upon are in real danger and may in future jeopardise anyone leaving or returning to the atmosphere safely. The story so far:
      Engineers realised that many functions which satellites need to perform (mapping, global positioning and communications) could be done better if the satellite holding those sensors was placed in a polar orbit. That would allow them to pass the equator at a different longitude on every orbit and cover the whole planet in a more efficient, regularised pattern. In the 1990s this was implemented with more than one satellite, co-ordinated groupings, to allow them to be used for the triangulation of positions on the ground and to increase the frequency of passes and updates because if you increase the number of satellites on the same path, you reduce the length of blind-spots between passes.

      Various constellations or flocks of satellites have since been launched, such as Iridium which has 66 active satellites and 6 spares on a low Earth polar orbit (485 miles) on 6 orbital planes will 11 active objects on each but still all converging at the poles. Other constellations include Globalstar, GPS, A-Tram and Walker Star.
      Some altitudes are now unavailable because of debris. Both China and the US have deliberately shot down satellites, to demonstrate that they can, which has left thousands of pieces of debris at those altitudes, travelling at over 17,000 mph (7.5 miles a second relative to the ground), at which velocity a sugar cube has the energy of a bullet. To avoid these bands of fragments that are too small to track, satellites have been placed into lower orbits, which means they expire sooner, which has led to more being placed.
      In February, the ISRO intends to release 103 satellites from a single mission. The ISRO also intends to gradually place 648 satellites over three years into low Earth orbit. In June 2016, Boeing announced their intention to place a constellation of either 1,396 or 2,956 (decision pending) new satellites up, at multiple inclinations, avoiding many high bands and including all of the popular polar tracks.
      If we have very high speed passes at similar low orbit altitudes at the poles, the reducing range of available clear pathways, and at the same time we are increasing the number in the flock, without unified coordination on the ground, with each increase in saturation the odds of a collision are shortening. If two satellites collide, the debris will destroy every satellite at that altitude, removing another safe and available altitude for satellites and forcing the over-saturation of yet another altitude as everybody switches to it. The remains and debris are also something that ground launches will have to fly through.

      From an insurance point of view, if an old satellite is left up and a new one hits it, who is to blame? I’ve read (in a fictional book but probably true) that there’s no international law to cover this. Usually, the polluter pays but the dead satellite can be tracked, so the owners of the active one have understood that and chosen to put theirs on the same altitude, convergence and inclination as a known hazard. We aren’t looking at just two satellites lost in a two satellite prang though. We’re risking all constellations using that altitude.
      On the positive side, there’s climate change. Really, it’s true, I’ve found something good to say about that. Increased solar activity and a weaker atmosphere causes debris to drop out of low and near Earth orbit much faster. Solar activity, the sun spot count, has been increasing through the last five years. If we stopped putting stuff up now though, would it take a century for all the debris to clear, even with increased solar pressure?
      I don’t think I’m sticking my neck out far by predicting there’s going to be a very serious satellite collision event in the next few years, which will make space exploration as a whole more difficult. For anyone insuring satellites, they should not think in terms of the price of replacing one unit, they should understand that a single bump between any two objects at that altitude will destroy the whole fleet for every company or state using that altitude, whether they are in a polar or equatorial orbit. I think the first crash will be over one of the poles because it’s a thirty lane crossroads with no traffic lights, they’ve got no brakes, they’re all going at full speed and business says we don’t have enough of them.
      They look so serene, don't they?


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