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SOLRAD 10 (SOLRAD X, or Explorer 44), a spin-stabilized satellite, was the third in a series of SOLar RADiation spacecraft (SOLRAD) designed to provide continuous coverage of wavelength and intensity changes in solar radiation in the UV, soft, and hard X-ray regions. It also mapped the celestial sphere using a high-sensitivity X-ray detector. Information collected was expected to contribute to a better understanding of the physical processes involved in solar flares and other solar activity, and the potential effects of this activity on short-wave communications, as well as on future human space travel.

Spacecraft and Subsystems

The spacecraft was a 12-sided cylinder that measured 76 cm in diameter and 58 cm in height with a mass of 118 kg. Four symmetrically placed 17.8-by 53.3-cm solar cell panels, hinged at the central section of the structure, served as the elements of a turnstile antenna system. Eighteen solar sensors were mounted pointing parallel to the spin axis of the satellite, which pointed directly at the solar disk. The sensors determined the angle to the Sun and automatically applied control signals to the attitude spin subsystem.

The electronic subsystems included two nonredundant telemetry transmitters operating on separate frequencies of 137.710 MHz and 136.380 MHz, three spin replenishment and four spin-axis attitude control subsystems, and a command subsystem. Three spin replenishment and four spin-axis attitude control subsystems were designed to maintain the spin rate at 60 rpm and the spin-axis within 2 degrees of the Sun line.

Fourteen experiments included the following sensors: 18 ionization chambers for solar X-ray monitor, solar electron temperature, solar Lyman Alpha bursts and monitor, solar ultraviolet monitor, solar UV continuum flash, background X-ray level, and solar hard X-ray continuum; a Cesium Iodide (Sodium) scintillating crystal and photomultiplier to monitor solar hard X-ray; Lithium Flourine photometer for solar excitation of F-layer; thermistor for skin antisolar temperature; and large-area proportional counter for X-ray variations.

Mission Profile

SOLRAD X was launched July 8, 1971, at 22:58 UT from Wallops Island, Va., into a 436 by 630 kilometer orbit. The plane of rotation shifted about 1 deg/day so that a stellar detector mounted to point radially outward from the axis scanned the celestial sphere. Data from all detectors were stored in a 54-kbs core memory and telemetered on command to the NRL tracking station at Blossom Point, MD. Data were also transmitted in real time at 137.710 MHz and were shared with the international scientific community through COSPAR. Expected lifetime was 3 years. For additional information, see Naval Res. Review, v. 25, p. 1, 1971.

Alternate Names

  • 05317
  • Explorer 44
  • PL-703A
  • SE-C
  • SOLRAD10
  • Solar Explorer-C

Facts in Brief

Launch Date: 1971-07-08
Launch Vehicle: Scout
Launch Site: Wallops Island, United States
Mass: 118 kg

Funding Agencies

  • NASA-Office of Space Science (United States)
  • Department of Defense-Department of the Navy (United States)


  • Solar Physics

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. H. Kent Hills



NameRoleOriginal AffiliationE-mail
Mr. John R. HoltzProgram ManagerNASA Headquarters
Capt Ernest W. PeterkinProject ManagerUS Naval Research Laboratory
Mr. Robert W. KreplinProject ScientistUS Naval Research
Dr. J. David BohlinProgram ScientistNASA Headquarters
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