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Climate and Weather - Expert Reports - Division on Earth and Life Studies

Each is about two-thirds of a meter wide and a little more than a meter long. The wings house solar cells that were designed to work well at high irradiance levels. But sufficient electrical output was not the issue—the challenge was keeping them cool. This decreases the amount of sunlight falling on the panels and puts more of the wings into the shadow or partial shadow of the centimeter-thick heat shield mounted on the sun-facing side of the spacecraft. To make this strategy work better, we designed each wing to have two distinct sections.

Most of the area of a wing, the primary section, serves as the source of power most of the time. But when the spacecraft swoops close to the sun, the wings are angled so that their primary sections are entirely in the shadow of the heat shield.

Early on, we decided to mount the secondary sections so that they would be a few degrees closer to facing the sun than the primary sections are. Our objective was to ensure that the angle of the sunlight striking the surface was never less than 10 degrees. If this angle were to become any more acute, small variations in that angle would cause large changes in power output, which could be difficult to control.

We modeled performance very carefully as we were designing this solar array. The limb is redder and dimmer than the sun as a whole. In fact, its output diminished by 50 percent, for reasons nobody could quite understand. Its highly elliptical orbit periodically takes it outside the orbit of Venus.

We resolved to figure out what had caused the anomalous degradation of the solar panels on earlier spacecraft so that we could avoid whatever the problem was. Initially, we suspected that two issues might be at play. One possibility could be outgassing from the adhesives used in the construction of these panels.

Such outgassing would, we reasoned, deposit a film of adhesive material on the top of the cells, which would then turn brown after exposure to ultraviolet light. All solar arrays outgas to some extent, but the effect is worsened by high heat and radiation. Another possibility was that the transparent adhesive used to attach the glass covers to the solar cells had turned brown, again because of exposure to ultraviolet light.

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Through extensive testing, we discovered that this process indeed accounted for most of the degradation. We soon figured out that we could reduce this darkening by driving out the more volatile components in the cover-glass adhesive.

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Doing so involved heating the array under vacuum while exposing it to intense ultraviolet light, provided by light-emitting diodes. Of course, we needed to be sure our strategy would actually work. To test the theory, we had to place the arrays in an environment that resembled what they would experience close to the sun. And such conditions are not so easy to come by. The report provides a valuable resource for industry professional Burning coal in electric utility plants produces, in addition to power, residues that contain constituents that may be harmful to the environment.

The management of large volumes of coal combustion residues CCRs is a challenge for utilities, because they must either place the CCRs in landfills, surface impoundments, or mines, or find alternative uses for the material. This study focuses on the placement of CCRs in active and abandoned coa Scientists and engineers have long relied on the power of imaging techniques to help see objects invisible to the naked eye, and thus, to advance scientific knowledge. These experts are constantly pushing the limits of technology in pursuit of chemical imaging--the ability to visualize molecular structures and chemical composition in time and space as actual events unfold--from the smallest dimension of a biological system to the widest expans The U.

Climate Change Science Program CCSP , established in to coordinate climate and global change research conducted in the United States and to support decision-making on climate-related issues, is producing twenty-one synthesis and assessment reports that address its research, observation, and decision-support needs.

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NASA asked the National Research Council NRC Committee on Toxicology to develop guidelines, similar to those developed by the NRC in for airborne substances, for examining the likelihood of adverse effects from water contaminants on the health and performance of spacecraft crews. In this report, the Subcommittee on Spacecraft Water Exposure Guidelines SWEGs examines what is known about water contaminants in spacecraft, the adequacy of current risk assessment methods, and the toxicologic issues of greatest concern.


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