I had been writing this for another site but it may be of interest here. I have updated it a bit to include some info on the American missile test and there are links to MSN reports on the Chinese test. While the low altitude of this test means much of the resultant debris will re-enter fairly soon the forces involved in this explosion will have lifted some debris into higher orbits - which would not have occurred if the satellite had been allowed to re-enter unmolested. Those of you who have read posts of mine before will probably have gathered I would be happier with no military satellites in space but I would concede that GPS is useful and that accurate satellite surveillance - post Gary Powers - helped control some of the wilder speculation by US hawks on the state of Soviet missiles putting a slight check on the arms race.
Kessler’s Syndrome
"Space," it says, "is big. Really big. You just won't believe how vastly hugely mindboggingly big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to space." The Hitchhikers Guide to the Galaxy.
The above not withstanding bits of it are more equal than others (with apologies to Orwell) and we (man) are endangering some of the bits that are most important to us. Which brings us to Kessler’s Syndrome; a runaway chain reaction involving space debris. I have written a short introduction in the box at the end with a number of links for greater detail.
If you are happy with the Jargon skip it, if not read it now.
Kessler’s warning relates to the LEO but with the importance of the GEO orbit the same could apply to both. If a satellite is hit - or worse still explodes - it may produce many high speed pieces of space debris, if there are enough satellites and other pieces of space junk in the vicinity a chain reaction can destroy all satellites in that orbital region and leave a dense debris field rendering any further attempts to enter orbit extremely hazardous. This could bar us from entering space for 1000s of years. Unlike criticality in a Uranium fission reaction - where 3 neutrons are released and at least one needs to impact with a fissile nucleus for the reaction to be sustained - here an impact could produce none or tens of thousands of debris pieces making it much less predictable. About a year ago China decided to hit one of their defunct satellites with a projectile in a test – this test doubled the debris field in that LEO orbital area (the NY Times has an excellent graphic showing how in just a few days this had distributed itself all around the globe. Also shows a Hubble solar panel with all of its hits - Links below). The US has now hit one of their failed spy satellites with a rocket. (They claim to prevent danger to humans from Hydrazine fuel but a quick look at N2H4 will show this as miscible with water, has freezing and boiling points similar to water and a 3-3-3 NFPA 704 rating so not exactly a major threat to survive re-entry nor to life on the ground if it does).
Is this syndrome imminent: probably not but the lead times are long and the orbital debris has a long half-life so it is important to ensure all new launches and satellites are designed to minimise the dangers and that our nations militaries are stopped from adding to the problem. When I say not imminent that is based on accidental initiation of the syndrome, the very high yield of fragments means the deliberate cascade initiation is not overly complicated for a power with the requisite missile technology who thought it was in their best interests to deny LEO to all. The IAA study, linked to in the first post, covers many of the simpler remedies (some are as simple as not painting satellites and rockets as paint is layered and brittle and can produce vast numbers of shards where a micrometeorite impact on metal won’t).
For an example of what not to do see The Westford Needles Project
Position Paper on Space Debris MitigationThe principles are all fairly simple ‘for every action there is an equal and opposite reaction’ so when a rocket goes up – or sideways - propellant is ejected at speed in the opposite direction. Getting a Kg of payload into orbit requires enormous amounts of energy and the higher the orbit the more energy required (Delta-v is a measure of the energy required to move from one state to another). The most popular orbits are low earth (LEO - because they are cheapest to achieve) and Geosynchronous/Geostationary (GES/GEO as they allow station keeping above a fixed ground position at a minimal fuel requirement). Kinetic Energy is calculated as the product of mass & velocity; in the absence of air resistance velocities are high, typically 10km/sec, at these speeds a 3mm particle would pack the same punch as a bowling ball at 100km/hr. The atmosphere has no clear top it just thins into space, 75% is within the first 11km and re-entry effects can be noticed from about 120km but to be totally clear of all atmosphere 10,000km is about right. A bodies gravitational effects are taken to act from it centre of gravity (in the earth’s case this is the middle of the core) and fall off in line with the reverse square law. The distance to the Earth’s surface is 6370km. From the surface LEO covers 160 to 2000km with GEO at 35,794km (other sites of interest: International Space Station ISS 500km, GPS 20,230, Hubble 589km)
Implementing Zero Debris Creation Zones
http://iaaweb.org/iaa/Studies/spacedebrismitigation.pdf
The Military Use of Space
http://www.parliament.uk/documents/upload/postpn273.pdf
US 'to shoot down spy satellite'
http://news.bbc.co.uk/2/hi/americas/7245578.stm
http://news.bbc.co.uk/2/hi/americas/7256741.stm
The military uses of space
http://www.parliament.uk/documents/upload/postpn273.pdf
Impact suspected for loss of Russian satellite
http://space.newscientist.com/articl...satellite.html
Debris Mitigation Improves, but More Work Urged
http://www.space.com/spacenews/archi...eo_013006.html
Geostationary Orbit Impact Detector (GORID)
http://esapub.esrin.esa.it/pff/pffv7n1/drov7n1.htm
Littered Skies (NY Times animation and graphic on debris damage & distribution)
http://www.nytimes.com/2007/02/06/sc...T_GRAPHIC.html
What I should have added was why this matters. My interest is largely in what we can learn about the universe (and earth) from space based instruments but more generally satellites are now critical for weather forecasting (and climate change data), transport (shipping, planes &, increasingly, road transport are ever more reliant on GPS - sextant futures might be a good investment), real-time news media are all satellite dependent and then there is the military ...
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