page_title: SOLRAD 2
section_title: Spacecraft
hierarchical_section_title: SOLRAD 2 / Spacecraft
caption_attribution_description: English: NRL solar radiation (SOLRAD) I satellite schematic
context_page_description: SOLRAD 2 was the public designation for a combination surveillance and solar X-Ray and ultraviolet scientific satellite, the second in the SOLRAD program developed by the United States Navy's Naval Research Laboratory. The SOLRAD scientific package aboard the satellite provided cover for the GRAB electronic surveillance package, the mission of which was to map the Soviet Union's air defense radar network.
  SOLRAD 2 was launched along with Transit 3A atop a Thor DM-21 Ablestar rocket on November 30, 1960, but both satellites failed to reach orbit when the booster flew off course and was destroyed, raining debris over Cuba, which prompted official protests from the Cuban government. As a result, future SOLRAD flights were programmed to avoid a Cuban flyover during launch.
context_section_description: SOLRAD 2 was roughly a duplicate of its predecessor, SOLRAD/GRAB 1, spherical and 51 centimeters (20 in) in diameter, slightly lighter than SOLRAD/GRAB 1 despite carrying the same scientific experiments (18 kilograms (40 lb) versus 19.05 kilograms (42 lb)), and powered by six circular patches of solar cells. The solar cells powered nine D cell batteries in series (12 volts total) providing 6 watts of power.
  The satellite's SOLRAD scientific package included two Lyman-alpha photometers (nitric oxide ion chambers) for the study of ultraviolet light in the 1,050–1,350 Å wavelength range and one X-ray photometer (an argon ion chamber) in the 2–8 Å wavelength range, all mounted around the equator of the satellite. As with SOLRAD 1, permanent magnets were installed to deflect charged particles from the detector windows to address the saturation issue that had impacted the Vanguard 3 mission.
  The satellite's GRAB surveillance equipment was designed to detect Soviet air defense radars broadcasting on the S band (1,550–3,900 MHz), over a circular area 6,500 kilometers (4,000 mi) in diameter beneath it. A receiver in the satellite was tuned to the approximate frequency of the radars, and its output was used to trigger a separate VHF transmitter in the spacecraft.  As it traveled over the Soviet Union, the satellite would detect the pulses from the missile radars and immediately re-broadcast them to American ground stations within range, which would record the signals and send them to the NRL for analysis. Although GRAB's receiver was omnidirectional, by looking for the same signals on multiple passes and comparing that to the known location of the satellite, the rough location of the radars could be determined, along with their exact pulse repetition frequency.
  Telemetry was sent via four whip-style 63.5-centimeter (25.0 in) long antennas mounted on SOLRAD's equator.  Scientific telemetry was sent on 108 MHz, the International Geophysical Year standard frequency used by Vanguard. Commands from the ground and electronic surveillance were collected via smaller antennas on 139 MHz. Data received on the ground was recorded on magnetic tape and couriered back to the NRL, where it was evaluated, duplicated, and forwarded to the National Security Agency (NSA) at Army Fort Meade, Maryland, and the Strategic Air Command at Offut Air Force Base Omaha, Nebraska, for analysis and processing.
  Like most early automatic spacecraft, SOLRAD 2, though spin stabilized, lacked active attitude control systems and thus scanned the whole sky without focusing on a particular source.  So that scientists could properly interpret the source of the X-rays detected by SOLRAD 2, the spacecraft carried a vacuum photocell to determine when the Sun was striking its photometers and the angle at which sunlight hit them.
caption: SOLRAD 1, its principal external features labeled.