Group 1  Energy collection to bus:  SPS photovoltaics and module construction
Status: Document under construction
(Updated June 30, 1998)
A typical photovoltaic (PV) fabric now available and resembling what might eventually be used to fabricate an SSPS is a product called UltraFlex, a translucent high efficiency space rated PV fabric available from AEC Able Engineering. It is scheduled for flight  use by NASA in the near future. While this material is not today available in great quantity, serious consideration of an SSPS would presume a major investment in PV R&D and production facilities.
Currently attainable PV efficiencies  range just above 30%  Efficiencies are usually stated in BOL (Beginning Of Life) and EOL (End  Of operational Life). The highest "reasonable" efficiencies on the horizon would be about 30% at BOL, perhaps a bit higher and perhaps 20% at EOL (time for replacement) with a projected contracted cost of roughly $0.50/Watt for use at GSO. (More about this price range later.) Remember we are contracting for a long term many Gigawatt quantity, this price and quality is not something to buy at Walmart next month.  The average efficiency over a thirty year life we will project to be 25%. This involves no new technology, but only vastly upgraded and integrated manufacturing facilities, such as various PV manufacturers would greatly like to discuss ordering.

Efficiencies of 23% (Tecstar)  and 25 % (UltraFlex) are now available for space-qualified PV, although cost is a secondary consideration to performance for arrays powering communications satellites. Cost and weight would both be major considerations for an SPS.  Light weight UltraFlex uses a flexible proprietary nonorganic backing.  Might this backing one day be manufactured from lunar regolith?  Other PV choices are possible depending on your assumptions/expectations/familiarity with leading edge PV research and market expansion, see the SPSS cost calculator for other choices (coming).

Rectangles of UltraFlex type fabric 10 meters x 500 meters will be rolled into cylindrical packages 10 meters long and covered with a thin metal shell made of a light stiff material such as AlBeMet© used in several satellites already, including Iridium,or similiar alloys. These cylinders will be launched to the GSO staging or SPS assembly sites.

NOTE of interest:  Uni-solar has formed a joint venture, Sky Station, to operate hundreds of high altitude (21km - 70,000 ft)  balloons  to provide communications services over major cities. Each platform will use over a Megawatt of PV cells.  Uni-Solar says they will be the largest users now on the PV horizon. The average platform will be 157 m long and 62 m (203 feet) in diameter at the widest point.  United Solar owns 60% of Sky Station. They have received WRC approval to use the 47 GHz radio band, which one of the partners already has experience with. 

Light near earth receives about  1367 W/sq meter and so we expect to average 342 W/sq meter during the life of the fabric.
Related links from both - equally important - sides of the PV tracks the  high cost -space qualified  and the low cost - high volume markets are shown for further review:

Able Engineering       source of UltraFlex

PV Central site          great collection of commercial PV Links

United Solar Systems  Uni-solar

The general design of our power satellites will be patterned after the “Sun Disk” design in NASA’s “Fresh Look”. (picture http) This thin disk has one face always pointing at the sun and the back always dark. Power transmission from the many panels will be done by running cables on the satellite's back - shadowed - face to utilize it’s low temperature for high temperature superconducting (HTS) power cables, now commercially available. These cables require liquid nitrogen temperatures to maintain their superconductivity.

Some Prospective SSPW Modules:

Module 1.11 "Basic PhotoVoltaic panel design"
This baseline SSP design (described by the following variables) is like feathers, and will be combined to make the wings module, 1.12, which will be assembled into the full satellite structural description, 2.12. That full structure must have well known structural characteristics, although some of the variables listed below will not be necessary for module 1.11:

1. Panel Length, Width, Height
2. Mass(Kg)
3. BOL (Beginning of Life) PV cell efficiency
4. Environmental sensitivity (loss of efficiency over time, (by year)
5. Cell operating temperature (C)
6. Output Voltage and Amps/hr
7. Transportation cost to GSO (either from earth or the moon)
8. Are Lunar Fabricated Materials included ? This determines whether lunar base
  modules are evaluated.
9. Unit cost.  Whether this piece went through a lunar fabrication process involving
  many steps (represented only with this number)  or a "simple" earth supply.
10. Radiated energy at backplane
11. Engineering reliability
12. Maximum allowable stress (P)
13. Cross sectional area, (A)
14. Neutral axis position, (C)
15. Principle second moments of area, (I)
16. Equivalent Young's modulus (E)
17. Torsional rigidity, (GJ),
18. Period
19. Natural Harmonic Frequency
20. Stiffness
21. Maximum G load
22. Maximum G load axis (L,W, or H)
23. Minimum launch size package (Folded L, W, H)
CATIA or a similar tool, would be a likely vehicle for handling these parameters when the when they arrive, fully described  in 2.12. Some of these may not need to be stated for the smaller subassembly.

Module 1.12 "Solar Array Wings"
This module will get input variables from 1.11  (Module 2.11 is actually  Module 1.11)  Output variables flow to higher numbered modules 2.11 to  2.12, to 2.13, etc., After selecting a  basic module, like  1.11;  larger sub assemblies, or PV "wings", will be assembled from those basic elements to compose module 2.12, with the same or similar variables. These 2.11 modules take all their inputs from 1.1 (or 2.10)  and in turn output variables to module 2.12, below.