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The AOSO (Advanced Orbiting Solar Observatory) satellite, which was originally called Helios, was intended as a scaled-up extension of the OSO (Orbiting Solar Observatory) series. It was conceived as a free-flying unmanned polar-orbiting satellite system capable of continuously monitoring the sun and near solar environment using an array of detectors and electronic imaging devices covering a broad frequency band from the x-ray to the visual range. The first AOSO was to be launched in 1969 by a Thrust-augmented Thor Agena-D from Vandenberg. The AOSO program was cancelled in 1965 and a "Final" full-scale mock up was transferred to the Smithsonian in 1969. Many of the scientific instruments planned for AOSO eventually were developed for the Skylab Apollo Telescope Mount, which flew in 1973.

AOSO was intended to produce high resolution images of the solar photosphere and atmosphere in a wide range of wavelength regions. A pointing accuracy of +/-5 seconds of arc on the center of the solar disk and an overall system reliability of at least 70 percent was called for. AOSO's specifications, together with the higher spatial resolution of its larger telescopes, would allow for the detailed study of the emergence and development of individual solar flares and other localized solar photospheric and atmospheric phenomena. Budgeted at some $167 million dollars, OSSA hoped for a series of at least four AOSO flights through 1971 that would examine the sun during a peak period of the 11-year solar activity cycle.

In October 1963 Goddard Space Flight Center negotiated a $5 million dollar Phase I contract with Republic Aviation Corporation of Farmingdale, NY, for a one-year systems engineering development study as well as detailed design of the satellite). AOSO Conceptual and engineering design studies had been completed by mid-1965 and contracts for prototypes were in the process of negotiation when NASA, and OSSA in particular, suffered deep budget cuts during the 1965 budget request cycle for FY 1967 funding. AOSO was cancelled that year.

Following instruments were planned for AOSO:

  • High-Resolution X-Ray Telescope. (Goddard Space Flight Center and American Science and Engineering). Development of an x-ray spectroheliograph to examine plage regions with a spatial resolution of a few arc seconds in the 6 to 60 nm region, which covers the region where flares are active (6 - 10 nm). High and low resolution modes were contemplated, the latter to detect high speed transient events.
  • White Light Coronagraph (High Altitude Observatory). Imaging and polarizing coronagraph capable of 1 minute of arc resolution or less to provide continuous monitoring of the solar corona.
  • Ultraviolet and Hydrogen-Alpha Spectroheliographs (Naval Research Laboratory). High angular and wavelength resolution to monitor the character of the H-alpha line and its surroundings
  • UV Scanning spectroheliometer (Harvard College Observatory) - for direct studies of the solar disk and the study of fine structure in active regions in the range 300 to 1300 nm.
Nation: USA
Type / Application: Solar observatory
Operator: NASA
Contractors: Republic Aviation Corp.
Power: 8 deployable fixed solar arrays, batteries
Mass: 487 kg ?
Orbit: 482 km polar
Satellite COSPAR Date LS Launch Vehicle Remarks
AOSO A - cancelled Va Thorad-SLV2G Agena-D
AOSO B - cancelled Va Thorad-SLV2G Agena-D
AOSO C - cancelled Va Thorad-SLV2G Agena-D
AOSO D - cancelled Va Thorad-SLV2G Agena-D