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The SOLar RADiation satellite program (SOLRAD) was conceived in the late 1950s as an improved means of studying the sun's effects on Earth, particularly during periods of heightened solar activity. Of prime interest were the effects of solar radiation on the ionosphere, which had critical importance to Naval communications. SOLRAD was NRL's and the nation's longest continuing series of satellite projects dedicated to a specific research program. SOLRAD I was launched in June 1960, and ten more SOLRADs were fabricated by NRL and flown through 1976.
SOLRAD I was unique in that it:
- determined that radio fade-outs were caused by solar X-ray emissions;
- was one of the two satellites launched during the world's first multiple satellite launching;
- was the world's first orbiting astronomical observatory; and
- was the first satellite to be successfully commanded to shut off.
NRL's SOLRAD series of satellites yielded important new scientific information on the sun's effects on Earth's atmosphere. The new knowledge gained by the program also yielded practical, and in some cases critical, benefits to Naval communication and the U.S. manned space program.
The Galactic Radiation and Background I (GRAB I) payload, a recently declassified co-flyer with SOLRAD I, was America's first operational intelligence satellite. In June 1960, fifty-two days after a U-2 aircraft was lost on a reconnaissance mission over Soviet territory, the GRAB I satellite soared into orbit and began transponding space-intercepted electronic intelligence signals to earthbound signals intelligence stations. The GRAB project provided proof-of-concept for satellite-collected electronic intelligence. This was accomplished by demonstrating that a platform in outer space could collect as much as all other sea-, air-, and land-based reconnaissance platforms operating within the satellite's field of view at a fraction of their cost and at no risk to personnel.