SDS (Solar Disk Sextant)

The Solar Disk Sextant (SDS) is a balloon-borne instrument whose objective is to measure the solar diameter, at different orientations, as a function of time. Results include the solar oblateness, the oscillation spectrum for use in helioseismology, and the rate of the secular variation of the solar diameter. The required instrumentation precision (a few milliarcsec) is attained by means of an objective beam splitting wedge which produces multiples solar images through consecutive reflections.

Balloon launched on: 4/18/1989 at 11:54 utc
Launch site: Scientific Flight Balloon Facility, Fort Sumner, (NM), US  
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon N40I-8/8T-11.62
Balloon serial number: R11.62-1I-109
Flight identification number: 266N
End of flight (L for landing time, W for last contact, otherwise termination time): 4/18/1989 at 21:30 utc
Landing site: 7 miles N of Onley, Texas, US

• Annual Reports of Astronomical Observatories and Departments: Yale University Bulletin of the American Astronomical Society, Vol. 22, p.724
• NASA Balloon Flights (1989-1998) in NASA Historical Data Book, Vol. VII: NASA Launch Systems, Space Transportation, Human Spaceflight, and Space Science, 1989-1998
• The solar disk sextant: Monitoring the size and shape of the sun Advances in Space Research Volume 11, Issue 4, 1991, Pages 123-132