Space Junk                   Observations from Scotland March 2006        Allan Copland GM1SXX

You probably don't give it a second thought. You may not even be aware of it, but several hundred miles above your head there is a growing problem.... Space Junk.

Its difficult to place an accurate figure on what's up there because the RADARs that track objects in space can't see things smaller than a grapefruit.  Of the items that are big enough to monitor, major data sources place their number at over 7500 and growing rapidly.

The larger items are dead satellites, old rocket parts, kick motors, abandoned nuclear power sources, and the general detritus of the space business.  In LEO and MEO there are lots of these items as can be seen in the animation.   This growing aerial junkyard is a threat to both manned and unmanned spacecraft.  The good news is that the larger items can be (and are) tracked by RADAR. It has been known on several occasions for manned spacecraft to take action to avoid space junk.  Although the possibility for a collision during a launch is real, it is still considered to be fairly small.

 The Geostationary arc although busy is in a somewhat better state. Operators usually reserve some propellant at the end of life of a spacecraft that can be used to move a dying satellite out of the arc into a 'graveyard' parking orbit

In addition to the thousands of large items in orbit, there are tens or hundreds of  thousands (some say millions) of smaller items.  The small items are a real problem.   At around 1000Kms there are a great number of small fragments, most likely the result of sodium-potassium  (NaK) coolant leaking out of abandoned radio-isotope thermal generators (RTGs) used by Russian RADAR Ocean Reconnaisance Satellites (RORSATS).  These RADAR satellites needed a lot of power and used the heat of radioactive decay to produce electricity using thermocouples heated by liquid sodium coolant.  Collisions with space debris have leaked liquid sodium droplets into space which then solidified into bite sized chunks of debris.

Other debris in Earth orbit results from explosions of spent rocket stages. Over one hundred such events have been noted.  In the past, some rocket bodies were deliberately exploded to protect technology although this practice has now ceased.

The above debris noted does not include the many smaller parts discarded in the course of a normal mission. These include nuts and bolts, springs and other parts used to deploy satellites plus various shrouds and covers that are discarded.

If this all sounds rather worrying, there is a problem that is potentially even worse.  There are huge numbers  of very small pieces of debris in Earth orbit.  Paint flakes are a noteworthy example.  Rocket bodies and spacecraft are painted with protective coatings. In time under the effect of severe solar UV and thermal cycling, paint flakes off, breaks loose to join the swarms of other junk.  When the US space shuttle started flying in 1981, it was noted that the windows were sustaining considerable damage.  Much of this damage was from very small paint flakes striking the glass.  The worst case scenario for a paint flake hit is 'head-on' at 11 MILES PER SECOND. The result is severe damage to glass and other surfaces.   Other spacecraft have been damaged by paint flakes and its almost inevitable that any LEO bird will suffer degradation of its solar arrays by this mechanism.   The Surrey Space Technology satellite CERISE was damaged by a hit from space junk.

In the collisions mentioned above we are assuming VERY small pieces of debris doing the damage. A single flake of paint may not seem like much, but it can do a great deal of damage.  A somewhat larger item the size of a grain of rice, can do considerable damage.  You'd rather not think about what a 'head-on' collision with something metallic the size of a garden pea might do.

The space junk issue is a serious problem for the industry and although the pace of rocket launches has slowed somewhat in recent years, many launches carry multiple payloads.  This problem won't simply go away.   Its bad and getting worse.

It should be interesting to see how this problem will be addressed in future.

Many launch agencies now carry  a little extra propellant in order to deliberately de-orbit spent stages that would otherwise go into orbit with the payload(s). This is very commendable.   Boost stages go into orbit with payloads and there is no obvious means to reverse that process.   Newer and more durable painted coatings could possibly help the paint-flake problem.   It should be possible by design to reduce the number of small parts ejected during satellite deployments.

GM1SXX will be watching the space business with some considerable interest to see what transpires over 'litter control' in space.

73 Al.  GM1SXX

A particular interest of mine is the RORSATS and their 'leaky radiators'   Read more at...

http://www.ilr.ing.tu-bs.de/forschung/raumfahrt/spacedebris/en/index.html

http://www.loyola.edu/dept/politics/intel/cosmos954.pdf

http://www.svengrahn.pp.se/trackind/RORSAT/RORSAT.html

http://www.astronautix.com/project/rorsat.htm

htthttp://www.space.com/news/mystery_monday_040329.html

http://www.daviddarling.info/encyclopedia/R/RORSAT.html

http://www.svengrahn.pp.se/trackind/RORSAT/RORSAT.html#NaK

http://apollo.cnuce.cnr.it/~rossi/publications/aquila/node19.html

http://www.space4peace.org/ianus/npsm2.htm#2_2

http://www.i-depth.com/P/o/ow00412.frm.czech1.msg/21026.html

http://www.esa.int/spacecraftops/ESOC-Article-art_print_friendly_1100182720509.html

http://www.newscientist.com/article.ns?id=dn4882

http://www.aas.org/~light/sdpa.pdf