On Sep 26, 11:56*am, Michel wrote:
How Safe is Space? New Study Spotlights Anti-Satellite and Space
Debris Risks.http://www.spacesecurity.org/SSI2008.pdf

There are over 12,000 space objects registered with the UN, of this
total, 6,000 are still on orbit.

http://www.uni-koeln.de/jur-fak/inst.../workshop05/10

These are not a hazard, their orbital parameters are well defined.
Imagine 6,000 refrigerators tossed across the surface of the Earth-
they would be hard to find even let alone run into. Of course, all
objects are moving and sweeping out vast volumes of space - but the
volumes of space are vast as well.

The space between Earth's surface and geosynch orbit is over 40 times
the entire volume of the Earth itself. Cut into spheres every 10
meters the total surface area created is millions of times the surface
area of Earth - so we are in most cases talking about something the
size of a refrigerator or automobile - and only 6,000 of these in well
defined orbits.

What is of concern is the numbrer of tiny objects shed b these larger
objects over time, and their dispersal through this vast volume.

For example, there is a famous photo of a crack in the space shuttle
window created by collision with a tiny paint chip less than a
millimeter across, shed by a Gemini capsule in the 1960s.

There is a problem of detection, and a problem of what to do about it.

NORAD and later the Aerospace Command has high power radars that have
the capacity to track objects the size of a nut or bolt on orbit out
beyond GSO. Modern LIDAR - laser light distance and ranging - methods
can extend this down to the micrometer range. LIDAR can even be
switched to a higher power mode, involving laser sustained detonation
(LSD) - where a portion of the object is evaporated with laser energy
and then the vapor formed is detonated with laser energy providing a
controlled propulsive effect. A LIDAR / LSD combination in the 100 MW
range should be capable of sweeping out small objects like the paint
chip just described - in less than five years. A continuous sweeping
operation should be added to a dedicated survey to detect NEAs and
NEOs since the complement one another. LIDAR / LSD detects and sweeps
away - into lower orbit and eventually re-entry - all objects larger
than a millimeter and smaller than 10 centimeters - if limited to 100
MW..

For objects smaller than a millimeter - one sweeps them up physically
with a sweeper mechanism made of a thin sheet of material that absorbs
the materials in the size range desired. These sweepers avoid larger
objects altogether. Once the smaller objects are swept up into the
sweeper,solar wind and solar light pressure is used to bring the
sweeper down to burn up in the atmosphere..

Proposed Sweeper

PET plastic is 1.2 grams per cubic centimeter. An 8 micron thick
layer of this film masses 9.6 grams per square meter. 9.6 metric tons
per square kilometer.

Evacuated aerogel is 1 milligram per cubic centimeter. A foamed in
place aerogel that is 9.6 millimeters thick atop a PET film masses
another 9.6 grams per square meter - 9.6 metric tons per square
kilometer.

So, a 20 metric ton satellite with an 800 kg mechanism can take 19.2
metric tons of materials and fabricate 1 sq km 'sweeper' - a disk
1,128 meters in diameter.

10 such satellites launched into orbits every 2,800 km in altitude out
to GSO use light pressure to graduallly lose altitude- avoiding the
6,000 large objects - as they gradually descent - clearing out the
equatorial ploane.

A more agressive campaign involves 40 sweeper satellites in retrograde
polar at longitudes 9 degrees apart - precessing in a non-synchronous
way. When they precess 9 degrees they drop 10 kms due to solar
pressure. Starting at 30,000 km and dropping 20 meters per week - in
28 years - they will have evacuated every particle orbiting everywhere
above Earth out to 30,000 km.

The laser/lidar/lsd system, the 50 sweepers - constitute a total cost
of approximately $5 billion. There are 50 or so space launches per
year - a tax of $10 million per launch, would collect sufficient fees
to run this sort of operation.

This leaves the larger 6,000 objects of which 2,800 are non-
functioning.

Here, one only need make it legal for registered and certified
recovery operators to capture these objects return them safely to
Earth and sell them as collector items. Here the fee to collect each
object starts at $3 million - and collecting all of the non-
functioning satellites collects $8.4 billion. Assuming one launch
per collection attempt, another $28 billion is raised in per launch
fees.

In this way, at the present launch rate, sweeping operations may be
continued indefinitely - as well as surveys to watch out for NEAs and
NEOs.

NEAs and NEO capture for industrial development is another revenue
source, and another topic, though related.