OBSERVATIONS FROM SCOTLAND 23 Feb 2009 GM1SXX
'So many choices, so few opportunities".
Satellites, orbits and space junk.
I've known about the 'official' graveyard orbit just beyond the Clarke belt for
many years, but today I read of a new 'graveyard' orbit, one at 800 Kms.
http://www.spacemart.com/reports/Collision_Possibly_Caused_By_US_Satellite_Crash_Into_Junk_Orbit_999.html
Some sources also claim that 700-1000Kms altitude is a 'burial orbit'.
I've never seen this particular definition before, and of course, the area
between 700-1000Kms has been used in the past for a fair number of satellite
missions, including amateur radio birds. It would appear that in
some quarters at least, this altitude range is also considered to be a graveyard
for space junk. Of course there is a load of other unwanted junk at
lower altitudes too, including those used for manned spaceflight. While it makes
some sense to place unwanted junk in an agreed higher orbit, none of it is
static, it's all headed downwards, at a rate depending on both
orbital altitude and solar activity, but I wonder how long it will take before
800, 700, 600, 500 400 & 300 Kms and all orbital altitudes in between are so
cluttered with junk as to be unusable?
Between 900 and 1000Kms, are quite a few dozen old Russian TOPAZ reactors, their
ejected fuel load, when the ejection process actually worked as planned, plus at
least tens of thousands of solid radioactive NaK (Sodium/Potassium mixture)
coolant droplets in orbit that currently cause problems for Gamma Ray astronomy,
as well as being a collision threat for any spacecraft going through that
altitude to elsewhere.
The ground based RADARS that track space junk can only 'see' objects over a
certain size. The US ODERACS experiment was used in the past to calibrate at
least one of these RADARS (Haystack), using accurately sized metal spheres
repeased into LEO, but I believe from memory the smallest things that are
routinely tracked by these RADARS are around the size of a grapefruit, and
in space junk terms, that's pretty big! Smaller objects, down to 3Cms *can* be
tracked but are often simply ignored. The JSC link below lists Haystack as being
able to 'see' objects down to 1Cm.
For sure, stuff is always coming down, and the rate of course is greater at
solar maximum but I do often wonder what the future will bring. Will a 'happy
medium' be reached between launch rates and decays, or will near-Earth space
simply become unusable. These has been speculation about another scenario, where
inter-debris collisions cause such a proliferation of small pieces of debris
that near space becomes unusable. I don't subscribe to that view.... yet,
but the future I'm sure will be interesting.
For amateur satellites, much below 600Kms, you really don't want to be.
Life expectancy will be limited, especially at solar maximum. 600-800Kms
circular is where you might want to be. If 800Kms is a graveyard orbit,
you don't want to be there. Ditto 900-1000Kms.
The inner Van Allen belt extends from around 650-10,000Kms and,if you go there,
of course, some radiation screening and perhaps a hardwired CMOS command system,
rather than an IHU might be advisable. CMOS seems to tolerate space
radiation better than some other logic families.
Unfortunately, for Molniya birds, this is *not* an option, because they require frequent attitude 'tweaks', to keep them Earth Pointing, so radiation screening and EDAC memory is used alongside known radiation tolerant components including CPU's. If you really want to ensure a long operational life, you don't want to fly through the Van Allen belts, but for Molniyas, there's no choice but to!
As scroungers of rocket payload space, the amateur radio satellite-builders have no clout, which means that if a launch can be secured at all, the injection orbit is fixed by the primary payload. That's only fair, since they are paying big bucks for the privilege. The builders of genuine amateur radio satellites, ones that have a useful function for the radio amateur on the ground, such as a linear or even an FM transponder also have to compete for launch space with University CUBESATS and other parties needing a launch.
In the last few years, the launch agencies have been demanding full commercial rates for launches of any type. In some respects, the Universities have an easier job than amateur satellite builders since they are better organised and have allocated funding.
73 Al.
GM1SXX
http://apollo.cnuce.cnr.it/rossi/publications/iaf97/iaf97_html.html
http://www.svengrahn.pp.se/trackind/RORSAT/RORSAT.html
http://www.fas.org/spp/guide/russia/military/sigint/rorsat.htm
http://www.fas.org/spp/military/program/track/fgan.pdf
http://orbitaldebris.jsc.nasa.gov/measure/radar.html
http://www.fas.org/spp/military/program/nssrm/initiatives/millhay.htm
http://www.cosis.net/abstracts/COSPAR04/00990/COSPAR04-A-00990.pdf
http://www.globalsecurity.org/space/systems/haystack.htm
73 AL.
GM1SXX