SOLRAD 1

SOLRAD 1 (from "solar radiation") is the public designation for SOLRAD/GRAB 1, a combination science and surveillance satellite launched into orbit on 22 June 1960. It was the first satellite to successfully observe solar X-rays, the first to conduct surveillance from orbit, and the first to be launched with another instrumented satellite (the unrelated navigation satellite, Transit 2A). Developed by the United States Navy's Naval Research Laboratory (NRL), the satellite was in many ways a direct successor to NRL's Project Vanguard, the first American satellite program. The satellite's scientific mission was a success, sending useful data until November 1960 that determined normal solar X-ray output and confirmed the connection between increased solar X-ray activity and radio fade-outs. The SOLRAD scientific package aboard the satellite provided cover for the Galactic Radiation and Background (GRAB) electronic surveillance package, whose mission was to map the Soviet Union's air defense radar network. The GRAB mission was also successful, operating until 22 September 1960, and revealing that the Soviet air defense radar network was more extensive than had been expected. SOLRAD/GRAB 1 was switched off in April 1961, making it the first satellite to be remotely deactivated.

Background

In 1957, the Soviet Union began deploying the S-75 Dvina surface-to-air missile, controlled by Fan Song fire control radars. This development made penetration of Soviet air space by American bombers more dangerous. The United States Air Force began a program of cataloging the rough location and individual operating frequencies of these radars, using electronic reconnaissance aircraft flying off the borders of the Soviet Union. This program provided information on radars on the periphery of the Soviet Union, but information on the sites in the interior of the country was lacking. Some experiments were carried out using radio telescopes looking for serendipitous Soviet radar reflections off the Moon, but this proved an inadequate solution to the problem. In March 1958, while the United States Naval Research Laboratory (NRL) was heavily involved in Project Vanguard, the United States Navy's effort to launch a satellite, NRL engineer Reid D. Mayo determined that a Vanguard derivative could be used to map Soviet missile sites. Mayo had previously developed a system for submarines whereby they could evade anti-submarine aircraft by picking up their radar signals. Physically small and mechanically robust, it could be adapted to fit inside the small Vanguard frame. Mayo presented the idea to Howard Lorenzen, head of the NRL's countermeasures branch. Lorenzen promoted the idea within the Department of Defense, and six months later the concept was approved under the name "Tattletale". President Eisenhower approved full development of the program on 24 August 1959. After a news leak by The New York Times, Eisenhower cancelled the project. The project was restarted under the name "Walnut" (the satellite component given the name "DYNO") after heightened security had been implemented, including greater oversight and restriction of access to "need-to-know" personnel. American space launches were not classified at the time, and a co-flying cover mission that would share space with DYNO was desired to conceal DYNO's electronic surveillance mission from its intended targets. The study of the Sun's electromagnetic spectrum provided an ideal cover opportunity. The Navy had wanted to determine the role of solar flares in radio communications disruptions and the level of hazard to satellites and astronauts posed by ultraviolet and X-ray radiation. Such a study had not previously been possible, as the Earth's atmosphere blocks the Sun's X-ray and ultraviolet output from ground observation. Moreover, solar output is unpredictable and fluctuates rapidly, making sub-orbital sounding rockets inadequate for the observation task. A satellite was required for long-term, continuous study of the complete solar spectrum.

The NRL already had a purpose-built solar observatory in the form of Vanguard 3, which had been launched in 1959. Vanguard 3 had carried X-ray and ultraviolet detectors, though they had been completely saturated by the background radiation of the lower Van Allen radiation belt. Development of the DYNO satellite from the Vanguard design was managed by NRL engineer Martin Votaw, leading a team of Project Vanguard engineers and scientists who had not migrated to NASA. The dual-purpose satellite was renamed GRAB ("Galactic Radiation And Background"), sometimes called GREB ("Galactic Radiation Experiment Background"), and referred to in its scientific capacity as SOLRAD ("SOLar RADiation"). A dummy mass simulator SOLRAD was successfully launched on 13 April 1960, attached to Transit 1B, proving the dual satellite launch technique. On 5 May 1960, just four days after the downing of Gary Powers' U-2 flight over the Soviet Union highlighted the vulnerability of aircraft-based surveillance, President Eisenhower approved the launch of an operational SOLRAD satellite.

Spacecraft

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