 Basking in its warm rays, nature seeks out the sun's inexhaustible power. This nuclear reactor burns 4 million tons of hydrogen every second, creating an unmatched source of energy. While ancient observers worship the life-giving rays of this day star, modern science has taught us to harness its power. This superstar is essential to life on Earth, as well as to one of man's boldest ventures. Space Station Freedom. 196,000 photovoltaic cells will collect energy to power this laboratory and indeed become the solar connection. But it states, Canada, Japan and the European Space Agency have come together to build freedom. Responsibility for the entire electric power system, known as Work Package 4, rests in Cleveland, Ohio at the NASA Lewis Research Center. The power collection system is being developed by the solar array branch of the photovoltaic power module division. Design of Space Station began in 1984. Now it's pencils down. Time to build and test the actual flight hardware. In the summer of 1991, for the first time anywhere in the world, an array of cells and structural components were tested together in the simulated low-Earth orbit environment of tank 5 in the Electric Propulsion Laboratory. Funding from NASA's Office of Safety and Mission Quality and the Work Package 4 project office allowed engineers to develop and design a high-fidelity plasma generation and diagnostic system. The intent? To test the electrodynamic reaction between the photovoltaic system, the structure, and the plasma. A nitrogen cold wall was attached to a test fixture to regulate temperature of the test article. The cage design allowed for quick installation and removal of hardware from the vacuum tank. A light bank of 252 DED lamps was built to provide illumination equal to one-third of the sun's intensity. Spherical probes measured the current voltage profile to determine plasma density. In preparation for the test, an engineer checks to ensure that illumination is falling evenly on each solar cell. The cells 8 mm thick and 8 cm square are the largest ever used in space. The cells are welded to a flexible printed circuit which is insulated from the outside environment. The cell edges remain exposed. 16,400 individual cells are grouped into blankets, 110 feet long by 15 feet wide. Each blanket is protected by and deployed from a blanket box. Underwater testing was conducted by Lockheed Corporation, aiding engineers in improving deployment techniques of the blanket box. From the beginning of life on earth and now in space, nature has relied on the sun. These sunflower seedlings track the sun morning till night. Technology imitates nature. Once freedom's wings are attached to the truss, alpha and beta gimbals will enable them to track the sun during orbit, 60 minutes in sunlight and 30 minutes in eclipse. While in sunlight, the six wings will collect light and convert it directly to electric current. At the same time, 304 nickel-hydrogen battery cells will be charged to provide power while freedom is in earth shade. When the sun is set and energized, the solar arrays will supply more than 56 kilowatts of conditioned power to the user, the most power ever used in space. Solar energy will supply power for experiments, research projects, housekeeping functions, and life support systems. However, these can come crashing to a halt in the harsh environment of space. Micrometeors can damage freedom structure, contamination can degrade its power, and an invisible gas known as plasma can cause arcing. Why is that a threat? The potential effects of such arcing was studied by the photovoltaic power module division. The threat that plasma poses to the space station freedom was examined here in tank 5 during the plasma interactions test. The objectives of this test were to investigate on a systems level the possibly detrimental effects of the space plasma on the photovoltaic system as well as on the structures that make up space station freedom. We also wanted to investigate the effectiveness of a possible mitigation strategy, that is a plasma contactor. For hardware, we used two fully populated photovoltaic panels in combination with a variety of anodized aluminum structures which were there to simulate various structures on the space station freedom. The solar array circuit that we had was capable of generating 160 volts at almost one amp under test illumination conditions. We used the voltage that was generated on the solar array to drive the potential of the aluminum piece to a voltage that would be quite close to what it would be seeing went on orbit. The combination of the largest aluminum panels and the photovoltaic circuit was approximately one 490 second the scale of the space station freedom and therefore allowed us to get the very first large scale test of plasma environment interactions with space station type hardware. Our data capture system was designed to return information in three specific areas. Current collection, floating potential and arc transients as well as to give us information on key environmental parameters like temperatures and the plasma potential. Concern for the possible detrimental effects of arcing on the space station freedom led us to plan and conduct this plasma interactions test so that the program office could assess the risks and develop engineering solutions. We looked to the space environments effects branch here at Lewis for a more detailed description of the low earth orbit plasma environment and its potential impacts. Contrary to popular belief the space station freedom will be orbiting not in empty space but in the upper reaches of the earth's atmosphere. The upper reaches of the atmosphere are mainly atomic oxygen and this atomic oxygen gets ionized by the ultraviolet radiation from the sun. The ultraviolet radiation splits the atomic oxygen atoms up into an ion and electron and in the altitudes that space station will be flying there will be something like a million electrons and ions per cubic centimeter that is flying through. This space plasma as we call it is going to be important in terms of interactions between the space station and its surroundings. First of all what will happen if the arcing does occur? One of the things is it can cause tiny holes in the anodized surface and change its properties. In particular it could change the thermal properties of the surface so that it wouldn't maintain the right temperature. In addition the material that comes off during these arcs will deposit somewhere else on the space station. The solution to the possible arcing problem on space station we think is a device called a plasma contactor. Mike Patterson of the Space Propulsion Technology Division explains his group's involvement with the test. Here at NASA Lewis at the EPL facility tank 5 our organization provided support for the plasma interactions test for the space station freedom solar array. One of the critical aspects of conducting that experiment was to provide a simulation of the low earth orbit space plasma environment. And to do that we provided holocaust plasma sources to generate a quiescent low density low electron temperature space plasma environment. We used a number of holocaust plasma source devices optimized for operation to provide a low electron temperature and a very uniform plasma to engulf the solar array to simulate the low earth orbit environment. The plasma contactors have been developed previously for specific mission applications on specific spacecraft primarily for science. This is really the first time that the plasma contactor is going to be used as a utility, as a technology to ensure that the spacecraft can perform its function. As it turns out it's a vital component, it will be a vital component of the power system aboard space station and it's critical for space station operations. So in that context it's the first time that the technology has really been utilized and it's not a demonstration of the technology, it's there to perform a specific function. The demanding requirements for the plasma contactor system for space station freedom require us to do everything we can to push the holocaust technology that we presently have and that's a real challenge for us but we'll be able to deliver on that. One of the important space flight experiments for space station is what we call SAMPI. That's Solar Array Module Plasma Interaction Experiment. That's an experiment that's being built here at Lewis. It's going to be flown on the space shuttle in the year 1994 and it's being built right now. Hopefully when it flies we'll have confirmation that our ideas are correct. In a room much like this, Lewis will monitor the performance of the space station's electric power system once on orbit. Personal computers such as these are used daily to design systems and conduct analyses to verify characteristics of space station freedom. Soon computers will be used to run the machines that fabricate the various components. Along with SAMPI, WorkPackage 4 plans to conduct a qualification type plasma interactions test with a flight design solar array circuit to confirm the operational characteristics of the solar arrays in plasma. WorkPackage 4 also plans to take advantage of other space flight experiments such as Pass Plus and Spear 3 to gain confidence in the arrays operation before it flies. Beginning in the mid-90s with the first element launch of one photovoltaic power module and continuing with the remaining elements, space station freedom will be constructed in stages to yield a permanently manned configuration by the end of the decade. The knowledge that we gain from our research in tank 5 will enable technology that will allow us to better exploit the day star's power.