UV/Visible Observations of C/2012 K1 PanSTARRS and C/2013 A1 Siding Spring from a Stratospheric Telescope
Abstract:The UV-VIS (Ultra-Violet/Visible) instrument on the BOPPS mission (Balloon Observation Platform for Planetary Science) has two main goals: to demonstrate pointing stability at the 0.1” level, commensurate with the near-space PSF (Point Spread Function) expected from the 80 cm aperture telescope, and to observe targets in wavelengths where the telluric transmission is low. Two potential targets of a BOPPS flight in September 2014 are comets C/2012 K1 PanSTARRS and C/2013 A1 Siding Spring. The UV-VIS science camera has been outfitted with four filters from the NASA’s Hale-Bopp filter set: an OH filter at 308 nm, a CN filter at 385 nm and continuum filters at 345 and 445 nm. UV-VIS can potentially measure OH emission from the cometary targets if the BOPPS flight extends past sunset; the sky background due to Rayleigh scattering at 310 nm is too high for daytime observations, even from float altitudes near 35 km.
The BOPPS telescope is stabilized at the few arcsecond level by inertial-guidance gyroscopes that control coarse elevation and azimuth reaction wheels. The UV-VIS bench includes a fast guide camera and an FSM (fine steering mirror) – both COTS items – to bridge the pointing gap from a few arcseconds to a tenth of an arcsecond. In two separate hang tests, the guide camera was able to provide a 50 Hz pointing error signal on a star, and the resulting FSM-corrected images were reduced in areal size by 50% (e.g., linear PSF widths reduced from 2.4” to 1.6”). The FSM performance is expected to achieve the 0.1” stability goal in the stratosphere, where the image degradation is caused by motion of the optical system instead of atmospheric turbulence.