Whenever settlement of the outer solar system is discussed in this ng, it’s always assumed that it will be done using fusion power to provide energy, with an “edge of sunlight”, beyond which solar photovoltaics which cannot be used, around 3 A.U.
The edge of sunlight, commonly put at 3 A.U., could possibly be extended to hundreds of times that by using extremely thin mirrors to concentrate the attenuated solar light. The mirrors could be aluminum a few tens of atoms thick, and an array of flat mirrors could be aimed with a support structure to focus this for useful solar energy and/or light.
To supply 1 gw. of electrical power at earth orbit using the best photovoltaic cells available (~ 30% conversion efficiency), an area of 2.38 x 10^6 square meters is required. For getting the same electrical power at distances further from the sun, an area of mirrors is required amounting to
Area = A_e x Distance^2 / E
where
A_e = area at earth orbit = 2.38 x 10^6 m2
Distance = distance in A.U.
E = efficiency factor based on the reflectivity of the mirror,
and how well the light reflected hits the photovoltaics
due to possible aiming problems or mirror deformation.
and
Mass = Area x T x M_sp x Factor_s
where
Mass = entire mass of mirror system (kg)
T = thickness of mirror (m)
M_sp = mass density of mirror material (kg/m3)
Factor_s = factor for extra mass required for the support structure
for the mirrors.
Using an efficiency factor of 50%, a thickness of 40 nm, a mass density of 5 gm/cm3 (= 5000 kg/m3) (I don’t know the density of aluminum off-hand so I used this), and a support structure factor of 2, one gets
distance area required mass required
(A.U.) (m2) (kg)
orbit of Pluto 35 5.83 x 10^9 2.33 x 10^6
current outer
edge of the Kuiper belt 70 2.33 x 10^10 9.32 x 10^6
furthest orbit of Sedna,
inner edge of the Oort cloud 900 3.86 x 10^12 1.54 x 10^9
These could be made from chunks of aluminum only 10, 16, and 83 meters across respectively.
Problems erosion of the mirrors by dust and meteorites damage by the solar wind and/or cosmic rays reflectivity being obscured by dust particles or organic matter collecting on the surface solar sail effect which makes the mirror system(or what it is attached to) move manufacturing the huge mirrors in the first place
Solutions?
Give the mirrors a static charge so they might have net mass collecting capability instead of mass loss.
Attach the mirror system to its space settlement and orient it so that the settlement slowly spirals down toward a more desirable location closer to the sun.
Other possibilities
Instead of using mirrors, use photovoltaic cells themselves. Assumes an extremely cheap way of manufacturing them of course.
Have mirrors with a reflector made from organic materials (if there are any), which would make it lighter than an aluminum one and from more common organic elements. Or make a concentrating lense instead of a mirror.
Have there been any studies done on this subject? I think it’s very worthwhile looking at, given how much time and trouble we’ve had getting controlled fusion power to work. Also a space settlement out there in the Kuiper belt might want to save their deuterium for more useful things like propulsion, self-defense, etc.