Global Cooling

On May 3, 8:05 pm, PcMan wrote:
"Ken S. Tucker" wrote innews:9935470d-e386-4022-b
:

On Apr 18, 7:14 am, John Hampson wrote:
Hi,
Does anyone know if a ballistic trajectory exists directly from the
Moon’s surface to the Earth-Sun L1 Lagrange point? I’m interested
to
know if it’s possible to eject material from the surface of the Moon
so that it reaches L1 at near zero velocity before dispersing. I
would also like to know for how long each month these trajectories
exist, from where on the Moon’s surface (the far-side I assume) and
for how long the material would lie between the Sun and Earth.
I’m interested to see if Moon dust could be used to reduce sunlight
reaching Earth in the event that global warming is not controlled.
The low gravity, absence of atmosphere and plentiful supply of dust
on the Moon may make this possible, providing trajectories exist and
the technology can be developed.
If trajectories do exist then the problems with implementing a
project will be formidable: establishing a base and infrastructure
might be the easy part. Accelerating massive quantities of dust to
the required velocity (2.5km/sec) will pose huge technical problems.
I’m also interested to know what impact the solar wind might have o
n
small particles and if the dust might require grading or processing
beforehand.
I suspect many members of this group will be appalled at what I’m
suggesting, given the implications it has for space pollution. I
trust it should be obvious that no one would attempt such a crazy and
costly project except in the most dire circumstances when all
reasonable alternatives had failed. Because most of the dust will
disperse over time the process is arguably reversible, however some
dust could remain in stable orbits around the Earth and Moon leading
to a long term problem. In the worst case converting global warming
into an ice age!
Regards
John Hampson

Nature has recently provided a sort of yard stick as to dust quantity
effects on climate,
http://expo.edu.ph/pinatubo/index.html

That seriously affects the DVI, (Dust Veil Index),
http://www.geo.mtu.edu/volcanoes/vc_...cano_climate.h
tml

Personal experience: In 1991 we were wintering in central
Ontario, and normally used ~6 cords of wood / year, with
1 cord back-up and 250 gallons of heating oil emergency
reserve if the woodstove malfunctioned.
We ended up burning 9 cords that winter.
Daily high's stayed below -20F to 0F for weeks.
By putting a fist at arm's length in front of the day-time Sun,
the dust was quite apparent in the sky region around it.
Regards
Ken

Lets throw some numbers at this problem:
* How to get from lunar surface to earth-sun L1.. trivial
A linear boost of some 2.6 km/s will do the job, taking about a month to
get there, at very low resultant velocity.
* How much dust will you need?
To block just ONE PERCENT of sunlight, you need to block some 1.35
million square kilometers.
Assuming you grind down your regolith to about cement-dust scale (10 nm
grain size), you will need some 53 million metric tons. In addition, at
this dust size, solar radiation pressure is quite significant, imparting
some 250 m/s of acceleration per day. If you plan your trajectory well,
you could have your dust linger in a usefull region for up to a week, so
you only need to be able to sling 200 million tons of material delivered
per month. Not too practical.
Increasing the dust particle size fixes your solar pressure problem, but
increases the initial mass required as the cube of the particle size..
1mm grains would be stabile, but mass required is some 4.6e12kg

For comparison: the cooling effect caused by mount Pinatubo's eruption
ejected some 500 million tons of dust and, more significant to the
cooling issue, some 20 million tons of SO2. The earth's
gravity+atmosphere neatly contains this material from scattering, until
normal weather effects wash them from the air, which takes some months.

Conclusion: If you want to block the sunlight from reaching earth
surface, you need to keep your solution close to earth. On or just above
the surface, like volcanoes do, or at most in LEO where you have control
over its location. And given the sheer mass required for any meaningfull
shading, space is just not an option.

Good post. I think your conclusions are correct.
Though the idea of using lunar materials propelled
from it's surface is always interesting, such as,
http://en.wikipedia.org/wiki/Mass_driver

Part of the idea floated in Project Constellation is
to use the Moon as a springboard to Mars and
beyond, and I've read a few ideas on the subject
that seem borderline sci-fi, or economically harsh.

Backup to 1975, and consider the state of the
PC (personal computer), and there was a lot of
hand waving and maybe's, then 25 years later,
from a toy to a mammoth industry.
The Moon might be like that.
Ken

In article ,
PcMan writes:
To block just ONE PERCENT of sunlight, you need to block some 1.35
million square kilometers.

OK. (This assumes a grain blocks its geometric area, but it actually
blocks a factor of two more because of scatttering, but we won't
worry about that.)

Assuming you grind down your regolith to about cement-dust scale (10 nm
grain size), you will need some 53 million metric tons.

But I don't get this. The area is 1.35E12 m^2, and the area of one
grain is 8E-17 m^2, so the number of grains needed is 1.7E28. Each
grain has a volume of 5E-25 m^3 and (at density = 3 g cm^-3) mass of
1.6E-27 kg for total mass 27000 tonnes. What am I doing wrong?

Whether this (if correct) is small enough to make the idea feasible,
I don't know.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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