in which man is virtually completely out of the loop except in a monitoring role. The lightweight, flexible solar arrays which represent the best of today's technology are very similar in concept to those which will be necessary for the SPS application. The major differences lie in weight and cost of the blankets. TheJightest blanket available in today's designs are 0.95 Kg/M? (0.20#/ft2) and cost $20K-$40K/M2. The blankets for the SPS must weigh on the order of .4 Kg/M2 (0.08#/ft2) or less and cost 1/500 to 1/1000 as much as today's cheapest space quality solar arrays. The only way to achieve this level of cost reduction (given an inexpensive solar cell) is through an automated continuous process. This process will be more akin to newspaper printing than today's production techniques. The process will employ rolls of substrate material moving continuously through the various processes with a finished product coming out in a package suitable for launching to the SPS assembly site. The basic construction of the blankets is shown in Figure IV-B-l-b-4. The concept involves a patterned interconnect (conductor) system of aluminum or copper (or other suitable material) laminated between two thin layers of Kapton. A pattern of holes in the top layer of Kapton will expose the interconnect pattern. The solar cells will be laid onto the upper Kayton layer and welded through the hole pattern to the interconnect. Via this method the cells are electrically and mechanically attached to the blanket, no cell to substrate adhesive is needed. Finally, the cells will be covered with a plastic material (e.g., FEP Teflon or similar material) either singly or in groups. Solar Cells The solar cells used in the reference configuration are wraparound contact cells; i.e., both positive and negative contacts are on the back side of the cell. With this type of cell several benefits are realized. 1) The whole top of the cell can be covered with the cell cover with no gap for the looped top interconnector. 2) Both positive and negative contact welds can be made simultaneously and 3) all inspections (manual or automatic) are performed from the back side. Such cells as these have been in development for several years. They were, in fact, the baseline solar cell on JSC's large space station solar array (1970-73) as well as MSFC's SEPS array. The solar cells in the reference system design are very thin in order to reduce basic blanket weight. Current production solar cells are from 200 pM (8 mils) to 300 pM (12 mils). The cells in the SPS reference are 100 PM (4 mils) in thickness and might possibly be as thin as 50 pM (2 mils). In today's production methods it is extremely difficult to manufacture a cell of 100 pM thickness. Breakage of cells this thin would be very high with today's hand manufacturing. Most probably a high volume, automated production system could cope with the thin cells since machines can be programmed for a more delicate touch than can a human being.
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