This picture shows the Solar Disk Sextant (SDS) intrument just prior to the September 26, 1994 flight from Ft. Sumner, New Mexico. Below the payload are the various NSBF antennas and the ballast hopper. The large brown squares are the crush pads that cushion the payload when it lands. Also visable is the WAOD (Wide Area Ozone Detector) instrument that flies with the SDS. The WAOD normally takes data during the ascent and descent phase of the mission.The Solar Disk Sextant is an experiment which until now has been flown on stratospheric balloons, although we eventually hope to fly it in space. It consists of a 7" telescope, a 1/50 wave, optically bonded wedge assembly, and 7 linear CCD detectors. These components are mounted in a low thermal expansion INVAR tube that is mounted in an altitude-azimuth yoke arrangement. The prime guidance sensor is a LISS (Lockheed Intermediate Sun Sensor) coupled together with the output from the actual CCD information. Despite the motions introduced by the balloon environment this system is capable of guiding to a few arc-seconds absolute pointing, with a drift rate below 3 arc-seconds/sec. The 6-8 Gigabytes of data obtained per flight are stored in a special on-board VCR system. Some data are also transmitted to the ground via an 82 Kbit/sec line-of-sight radio link. This allows us to monitor the health of the instrument, and uplink any commands that might be needed. These flights take place from the NSBF Ft. Sumner, New Mexico facility. Typical flights take place in late September, and last for about 10 hours. Termination of the flight normally occurs in Texas or Oklahoma, although the 1994 flight landed less than 40 miles from Ft. Sumner.
This Figure shows the most recent solar oblateness function found by fitting the 1992 and 1994 SDS data. Defining the oblateness as (Re - Rp)/Rp, where Re and Rp stand for the solar equatorial and polar diameter, yields a new value of for the oblateness of 9 x 10**-6.
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Author: Larry Twigg
Last Updated: 27 October 1998
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