"We could almost put all this together in a single device now, but we're not quite ready yet," said Dr. Meyer. "It's just like a Tinker Toy box. All the pieces are lying around, some of them assembled, but the complete assembly has yet to be done."
Dr. McLendon says that while "many people have done elegant synthesis and have made some lovely molecules," scientists understand the process "to about a 90 percent level.
"But that's like saying we understand engineering principles to within 90 percent of building a bridge," he said. "You wouldn't want to drive over it." Economic Question Remains
And even if all these problems are solved, years of further development will be required before any operational devices can be produced.
A major question is how much of the energy carried by photons can be converted to practical use. Theoretically, said Dr. Wrighton, 20 to 25 percent could be converted. This efficiency would rival that of conventional photovoltaic systems.
With such efficiencies, scientists believe, artificial photosynthesis might be used to produce a variety of fuels. In theory, chemists could manipulate the photochemical reaction center so as to produce methane or hydrogen in place of NADPH.
Once the technical problems are solved, the question of economic feasibility remains. But the prospect of converting the sun's energy directly into liquid fuels, and of removing unwanted carbon dioxide from the atmosphere, is too important to ignore. So scientists are pressing ahead on the basic science of the problem in the hope of an eventual payoff.
Dr. McLendon calls it "the scientific field-of-dreams approach" to technological advance: "If you build the foundation, it will come." Green Power: Inside the Plant's Energy Factory In photosynthesis, plants convert solar energy into the compounds ATP and NADPH, which play key roles in chemical reactions that create sugars out of atmospheric carbon dioxide. The sugars sustain almost all life, and the process releases oxygen to the atmosphere as a byproduct. All this takes place in tiny organs, called chloroplasts, within leaf cells. Scientists hope to open up new sources of energy by duplicating the process artificially. The Chemical Cascade of Energy Photosynthesis begins inside a complex of proteins and chorophyll, called a photochemical reaction center, when a photon, or particle of sunlight, strikes a chlorophyll molecule. The photon boosts an electron to a higher energy state, and it jumps to a special "carrier" molecule. This is the first in a sequence of such electron leaps. At the same time, protons accumulate in the lumen, or cell interior. Electrons lose energy along the way. To regain it, they jump to a second chlorophyll molecule, where a second photon reboosts the energy level, and a second cascade of electrons begins. It ends with the synthesis of NADPH. The protons that have accumulated in the lumen trigger the synthesis of ATP. Outside the photochemical reaction center, in the stroma, ATP and NADPH drive the manufacture of sugars from carbon dioxide. To restore the system to its initial state, the electron that is lost from chlorophyll at the start must be replaced. It comes from water molecules which then react to release oxygen to the air. Sources: Dr. Mark Wrighton; "Molecular Biology of the Cell"; "Molecular Cell Biology" Giant That Lost Race to Moon Soviet space officials have released details of the N1 rocket, designed to carry men to the Moon in the 1970's, a space ship whose existence was denied until a year ago. It failed because its many first-stage engines could not be mede to deliver stable, reliable thrust, the officials now say. Like the successful Unites States Saturn 5, it was about 370 feet long. The first three stages were to place the lunar module and Soyuz transport vehicle into Earth orbit. The fourth stage was to propel the vehicles toward the Moon, and the fifth stage was for insertion into lunar orbit, initial descent and return to Earth. Source: Daniel Gauthier, Aviation Week & Space Technology.
Diagrams (pgs. C1 & C10)