I got stuck in a traffic jam last night and stopped in a bookstore rather
than sit in traffic. I purchased the 3rd edition of the High Frontier,
and was reading in the parking lot that solar energy is 0.18 kW / m^2 on
the surface of the Earth whereas it is 1.4 kW / m^2 in HEO. The book said
this was a ratio of "almost 10", apparently proving that O'Neill could do
physics but not arithmetic ( I would say the ratio is closer to 7.78 ).
means to me is that available solar energy on the surface of the Earth is
equivalent to available solar energy in space at 2.79 AU from the Sun,
because energy intensity drops off as the square of the distance. This is
amazing because the first three clumps of asteroids in the Main Belt are
within 2.79 AU of the Sun ( c.f.,
http://cfa-www.harvard.edu/iau/plot/OrbEls01.gif ).
Thus, to the extent that solar energy ever becomes really viable on the
surface of the Earth, it also becomes viable deep into the heart of the
Main Belt. Pretty exciting stuff !!
(Not that we need to go to the Main Belt any time soon ... there's the Moon
and plenty of NEOs to keep us busy for the next 50 years or more. And
after the NEOs, the first big clump of asteroids occurs at 1.9 AU, where
solar energy would still be 0.39 kW / m^2, over twice as high as available
on the surface of the Earth. That first clump (the Hungarias) would keep
us busy for another 50 years.)
Ron Menich
>
> I got stuck in a traffic jam last night and stopped in a bookstore rather
> than sit in traffic. I purchased the 3rd edition of the High Frontier,
> and was reading in the parking lot that solar energy is 0.18 kW / m^2 on
> the surface of the Earth whereas it is 1.4 kW / m^2 in HEO. The book said
> this was a ratio of "almost 10", apparently proving that O'Neill could do
Note that it is a time averaged number, for example it includes the 50%
day/night cycle.
In some locations the ratio is 20:1
In polar regions in the long dark winter it is infinite.
Thus, to the extent that solar energy ever becomes really viable on the
surface of the Earth, it also becomes viable deep into the heart of the
Main Belt. Pretty exciting stuff !! In "The Millennial Project", Marshal Savage said something pretty close to "The Belt is not the dimly-lit realm of Orpheus that one might expect." I remember he compared the insolation at a Main Belt asteroid to that of a Scandinavian country.
Mike Combs
Taking the 7.78 time-averaged number and extending it, would it be
reasonable to say that the solar energy available in HEO is 7.78 * (1.5^2)
= 17.5 times as much as is available on the surface of Mars? (With --- as
you pointed out --- even much higher ratios possible depending on the
latitude on Mars under consideration.) ? Here, the 1.5 is the distance
of Mars from the Sun in AU. If so, that would mean that on a time-average
basis we would have
NEO 2000 SG344 1.46
HEO 1.4
high Mars orbit 0.62
Hungaria asteroid 0.39
surface of Earth 0.18
surface of Mars 0.08
The surface of Mars is resource rich, but it is very energy poor. No
wonder Zubrin relies on those nuclear reactors...
Ron Menich
Charles Radley
ssi_list@...
08/10/01 10:22 the Main Belt
AM
Please respond
to ssi_list
>
> I got stuck in a traffic jam last night and stopped in a bookstore rather
> than sit in traffic. I purchased the 3rd edition of the High Frontier,
> and was reading in the parking lot that solar energy is 0.18 kW / m^2 on
> the surface of the Earth whereas it is 1.4 kW / m^2 in HEO. The book
said
> this was a ratio of "almost 10", apparently proving that O'Neill could do
This number varies a lot depending on local conditions.
Note that it is a time averaged number, for example it includes the 50%
day/night cycle.
In some locations the ratio is 20:1
In polar regions in the long dark winter it is infinite.
> location time-avg available energy ( kW / m^2 )
> NEO 2000 SG344 1.46
> HEO 1.4
> high Mars orbit 0.62
> Hungaria asteroid 0.39
> surface of Earth 0.18
> surface of Mars 0.08
>
I should have stated something like, "high orbit around a typical Hungaria
asteroid". I didn't mean to imply the surface of the asteroid; sorry.
cfrjlr@...
Please respond the Main Belt
to ssi_list
In a message dated Fri, 10 Aug 2001 12:06:56 PM Eastern Daylight Time,
rmenich@... writes:
> location time-avg available energy ( kW / m^2 )
> NEO 2000 SG344 1.46
> HEO 1.4
> high Mars orbit 0.62
> Hungaria asteroid 0.39
> surface of Earth 0.18
> surface of Mars 0.08
>
I do not understand the number for the Hungaria asteroid, unless it is
sun-locked, i.e. rotates so that one face is always illuminated....?
> Thus, to the extent that solar energy ever becomes really viable on
> the surface of the Earth, it also becomes viable deep into the heart
> of the Main Belt. Pretty exciting stuff !!
the suns energy there is a few square meters of aluminium foil- it costs
very little. To do the same thing on earth requires energy storage.
Plants use solar energy on the earth because they have an efficient
energy storage technique (called 'carboydrates'). Humans energy
storage is much less developed at present.
> (Not that we need to go to the Main Belt any time soon ... there's the
> Moon and plenty of NEOs to keep us busy for the next 50 years or more.
> And after the NEOs, the first big clump of asteroids occurs at 1.9 AU,
> where solar energy would still be 0.39 kW / m^2, over twice as high as
> available on the surface of the Earth. That first clump (the
> Hungarias) would keep us busy for another 50 years.)
Not sure. Volatiles may be in the main belt, and rare elsewhere. The
main belt is far enough out that water stops subliming. That means that
we may be able to get our rocket fuels and nitrogen from there. Mars
is probably good for that stuff too but the delta-v to get to the
surface and back is roughly the same as going to the main belt
(guesstimate, it sounds about right).
Once you get enough mass from anywhere except the earth, going to other
places gets much easier. Twin stages of conventional rocket and ion
drive should be able to take you just about anywhere; if a little
slowly.
> Ron Menich
>
civilization?"