Late summer brings the hot days of summer to an often stifling crescendo, but is the perfect time to reflect on the historic efforts of the Signal Corps to capture the power of the sun for our own uses.The U.S. Army Signal Corps began experimenting with the heliograph, a method of visual signaling using reflections of sunlight bounced off of mirrors, around 1873, according to historian Rebecca Raines in her book “Getting the Message Through: A Branch History of the U.S. Army Signal Corps.”  It was a method ideally suited to the hot, sunny climate of the American Southwest, and was used extensively in the Army’s campaigns against the Apache Indians in 1886. The heliograph remained a viable means of visual signaling, and continued to be taught during Signal training through the 1920s, though it served as more of a back-up system used during periods of emergency, than as a primary system of communication.The scientists of the Signal Research and Development Laboratory began testing the application of solar cells for satellites beginning in 1955, and in 1958 the Vanguard I satellite was launched with solar cells which allowed the transmitter to operate for more than six years. Solar power quickly became standard equipment on satellites and space probes based on the success of the solar cells used on Vanguard I.  When Explorer VI was launched on August 7, 1959, the satellite carried a permanent electrical power source of 2,886 solar cells packed into two huge rings. The solar rings were designed and built by the SRDL. The establishment of the National Aeronautical and Space Agency on October 1, 1958 limited the military’s future role in space exploration, though the Signal Corps continued to work with NASA on the development of electronic and communications systems.In 1960, in celebration of the 100th Anniversary of the U.S. Army Signal Corps, the U.S. Army Signal Research and Development Laboratory achieved the first two-way, coast-to-coast radio conversation powered exclusively with solar energy. A station at Fort Monmouth, New Jersey and one in Los Angeles, California, were equipped with 20-square-foot panels of solar batteries, which were the most powerful solar arrays ever assembled for ground applications. Until this point, solar batteries had been used mainly in satellites and space vehicles.Research on solar cells continued at the SRDL throughout the 1960s, with efforts focused on determining the most efficient type of cell, the best types of materials to use for solar cells, design parameters, including the use of filters and coatings to increase performance.   One of the major discoveries made at SRDL was an “inverse” solar cell that could withstand high levels of radiation in space. In the 1970s, experiments were done with solar-reflecting and solar-absorbing paints to manage heat-load in electronic equipment under development.As increased efficiency and wide-spread use solar cells continues to be developed and the technology perfected, the summer sun is a reminder of the potential of solar energy, and the Signal Corps’ place in the ongoing story of harnessing the power of the sun.