AAS 205th Meeting, 9-13 January 2005
Session 67 Calibration of Post Space Missions: MSX and SNAP
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

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[67.08] Absolute Calibration Using the MSX Reference Spheres

S. D. Price (Air Force Research Laboratory), C. Paxson, T. L. Murdock (Frontier Technology, Inc.)

MSX conducted five absolute calibration experiments against emissive reference spheres between 25 August 1996 and 20 February 1997. The 2 cm diameter, T6061 Al spheres are coated with Martin Black. The thermal properties of the spheres are well known and their emissivities and reflectivities were accurately measured in the laboratory. The spheres were ejected at an elevation angle of 15 degrees above the MSX velocity vector in the orbital plane; the velocities were measured at the time of ejection. The geometric parameters of the spheres at the time of measurement were determined from orbital dynamics. The energy balance equation between the thermal input from the direct Sunlight, Sunlight reflected by the Earth and upwelling Earthshine and the total flux emitted by the sphere is solved to derive the instantaneous temperature of the sphere. The MSX in-band fluxes are then calculated from the blackbody at the temperature of the sphere predicted by the model modified by the wavelength dependent infrared emissivity at the distance of the sphere plus infrared Earthshine and Sunlight reflected by the sphere. The weighted results for the five spheres agree to within the uncertainties with the SPIRIT III responsivities determined from the absolute fluxes for infrared standard stars derived by Cohen et al. The MSX calibration against the reference spheres thus validate the absolute fluxes for the standard stars to <2%.

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