As the size of spacecraft decreases, the contribution of the power subsystem to the overall spacecraft weight significantly increases. This paper will focus on describing a prototype solar array utilizing three promising technologies to significantly reduce weight, deploy with low shock, and increase packaging efficiency of the solar power system. These technologies are: Copper Indium DiSelenide (CIS) Thin-Film Photovoltaics, Smart Mechanisms Employing Shape Memory, and Multifunctional Structures.
Recent advances in shape memory alloy devices, ultralight composites, along with thin-film copper indium diselenide (CIS or CuInSe2) photovoltaics (PV), have shown the potential of providing solar array systems with overall array specific power of >100 W/kg. This results in solar arrays that are a factor of 5 lighter than the current state-of-the-practice, and a factor of 3 lighter than the state-of-the-art.
The synergistic merging of shape memory mechanisms, thin-film PVs, and lightweight structures technologies into an advanced lightweight solar array (LSA) can meet the requirements of the emerging generation of small satellites. This example approach utilizes the development of shape memory deployment fixtures, composite panels, and flexible thin-film PVs based on CIS technology.
Suspended within each panel of our prototype is a unique spring system that counteracts thermal expansion mismatch between the CIS blanket and the composite frame. This basic design approach will be used to scale-up to fabricate a 9-panel, 750 Watt protoflight array exceeding 100 W/kg.
The array will be exposed to environmental tests including thermal cycling, vibration, dynamic response, and deployment (functional) tests. This effort will qualify the array for use on a future spacecraft.
The teaming arrangement for this effort consists of the Defense Advanced Research Projects Agency (DARPA), Air Force Phillips Laboratory, NASA Langley, and Lockheed Martin Astronautics (LMA). LMA will integrate these technologies toward a LSA design that addresses the requirements of future spacecraft. LMA will also be responsible for the fabrication and testing of the system.
LMA has developed a large-area (30×30-cm) in-line, sequential CIS manufacturing approach amenable to low-cost PV production. A prototype CIS manufacturing system has been designed and built with compositional uniformity (Cu/In ratio) verified within ±4 atomic percent over a 30×30-cm area. CIS (non Ga containing) device efficiencies have been measured by the National Renewable Energy Laboratory (NREL) at 7% on a flexible non-sodium-containing substrate, and 10% on a soda-lime-silica (SLS) glass substrate.
Recent CIS effort has included Ga incorporation, with a goal of increasing the cell-level efficiency and modifying the bandgap to reduce module integration losses. Critical elements of the manufacturing capability include the sequential process selection, uniform large-area material deposition, and in situ process control. Details of the process and large-area manufacturing approach are also discussed and results presented.