Satgen 223  SpaceGuard and SpaceWatch    by GM4IHJ             3rd July 93
BID of this msg is SGEN223  Please use that BID if you retransmit the msg

At GM4IHJ two HF receivers tuned to 29.358 and 29.408 MHz listen for sub
horizon transmissions from RS10 and RS12. At least twice a week , A very
sudden loud transmission of a perfect RS signal gets immediate attention ,
only to have it fade as quickly as it came after a few seconds. The
signals characteristics are "pure" meteor scatter = marked doppler and
deep selective fading. Normally the satellite heard is within 1500 kms of
the GM horizon, as would be expected for normal meteor scatter
propagation, but sometimes the satellite is at much greater range from UK
suggesting propagation via a medium much higher than normal ms 60 to 90
kms.
Remembering an incident a few years back when a meteoric body , literally
skimmed across the top of the atmosphere of Western Canada and then went
back into space again, I decided to do a search of recent literature. I
got quite a surprise , when I found how much study is going on in this
field.
Once again Science is following Science Fiction. In Arthur Clarke's
Rendezvous with Rama , Chapter 1 is titled SPACEGUARD. Well Spaceguard now
exists as a NASA programme which uses wide angle sky photos taken by
astronomers doing other studies ( Comet and Supernova patrols etc ) The
photos which would previously have simply been stored are now scanned for
the tell tale tracks with which asteroids moving with high angular
velocity near earth, reveal their presence.
In a parallel study called Spacewatch , the University of Arizona is
automatically scanning the night sky for the signatures of these near
earth visitors. Whilst a group in Australia are doing a search of pictures
taken by the UK Schmidt telescope. The combined results are startling.
Nature 24 June 93 carries two letters which sum up some of the results so
far. In a paper called "Explosions of small Spacewatch objects in the
Earth's atmosphere". There is an introductory list of these objects, which
the paper suggests are numerous enough to perhaps produce a 20 kiloton
explosion at the top of the atmosphere, every year.
The paper then points out that as most of these objects circa 50m in diam
or less, are made of lightweight materials, we on the surface are unlikely
to notice them - Although there have been 3 well reported  bigger events
this century, ( Tunguska, Sikote-Aline and Revelstoke)
A second letter in Nature reports findings from the Arizona Spacewatch,
which has identified more than 40 of these NEOs Near Earth Objects. Some
are less than 50 m in diameter but the curious thing about them all is
that they have very low orbital eccentricities. This latter point suggests
they are not from the familiar asteroid belt betwixt Mars and Jupiter, but
that, they have their origins much nearer Earth, perhaps as debris from
Lunar surface asteroid strikes, or residue from Earth Trojans - a
postulated group of debris material at the earth's 60 degree Lagrangian
points. No one has ever positively seen anything at these earth points but
we know they exist in the equivalent positions in Jupiters orbit, as a
sort of gravity balance, used asteroid, parking lot.
Perhaps it is time we Radio Amateur took note and listened now and again
for the radio events which would accompany a hit or near miss from one of
these objects . Meteor pings from "position accountable satellites" should
permit sorting out these events from ordinary MS. 73 de GM4IHJ @ GB7SAN