|Energy Supply Problem|
From Fiction to Reality
During the 1960s, the United States was competing with Russia in a great space race. The race spurred on both scientific invention and the scientific imagination. One of the most imaginative writers of that day was Gene Roddenberry, a former war pilot and policeman-turned-television scriptwriter. He was the man who envisioned Star Trek and the starship Enterprise. In this wonderful story, a multinational crew lives and works together, exploring the far reaches of the universe. In some ways, with the building of the International Space Station, the Enterprise has turned into reality. As the station orbits the earth with its international crew, it provides a platform to explore the frontier of space.
A fictional substance called dilithium (dye-li-thee-um) crystals powered the Enterprise between galaxies. With these crystals, Roddenberry provided one of the most important resources needed to sustain life in space: an endless supply of energy. According to the science behind the fiction, dilithium crystals created electricity from a reaction between matter and antimatter.
The space stations dilithium crystal is the sun. As the station orbits from sunlight to shadow, from darkness back to light, the sun's rays generate the electrical power needed to sustain life on board the space station. While in the earth's shadow, nickel-hydrogen batteries provide power to the station.
Just like Roddenberry's Enterprise, the space station requires an uninterrupted flow of electricity for its life support systems, computers, telecommunications equipment, and experiments. Electricity is the station's lifeblood. Without electricity, the space station would be uninhabitable.
Solving the Energy Supply Problem in
Turning Sunlight Directly into Electricity
No progress was made with the photoelectric effect until several ideas came together between 1897 and 1905. In 1897, physicist J.J. Thompson provided the first evidence for the existence of electrons. Soon thereafter, a group of scientists were exploring the relationships between light, radioactivity, magnetism, and electricity. Max Planck, a German physicist, suggested that light behaves not only as waves, but also as small "packets" of energy called photons. In 1905, Einstein connected all of the earlier discoveries together. He said that the photons energy is transferred to an electron when it collides with an atom. In turn the electron releases a photon of energy in the form of light. This process is what Becquerel had witnessed years before.
In the 1950s, scientists at Bell Laboratories made a huge discovery. They found that the electrons in silicon atoms responded to the light from the sun in much the same way as the atoms in Becquerel's metal strips had responded. The space race motivated Bell Labs' scientists to find new ways to modify silicon crystals that would transform solar energy into the electrical energy needed to provide endless power for communications satellites.
Below is a diagram of how an earth-bound PV array
The boron atoms buried in the "p-type layer", which can be seen in the illustration above, keep the electrons flowing toward the n-type layer. As the electrons accumulate, they create an electromotive force. This force drives the electricity out along the copper wires leading to the space station and back to the PV array's positive terminal. This primary circuit on the space station is the power grid.
Football Fields of Solar Cells
In order to create a photovoltaic array, engineers first connect 200 PV cells together into a panel. Multiple panels are then joined, forming the array. The more panels used, the more electrical energy you can generate.
At completion, the station will have eight solar arrays arranged in several flexible wings that can be closed or opened from within the space station. Each of the arrays will measure about 107 feet (32 m) in length and 38 feet (11.5 m) wide. They will be connected to a center truss 310 feet (94 m) long. Each array will consist of many panels that are attached so they open and close like an accordion. When fully extended, the eight arrays will cover an area of 32,000 square feet, or about two-thirds the length of a football field. They are the largest deployable structures ever to be sent into space.