Calibration System Design and Determination of Filter Calibration Requirements for SNAP

Abstract

The SuperNova/Acceleration Probe (SNAP) is a proposed space-based, wide-field telescope designed to measure the properties of dark energy in our universe. SNAP will measure ~2000 type Ia supernovae, and the reduction of systematic errors in the relative spectrophotometric measurements will be critical to the mission science. A stringent systematic error requirement of 2% in color photometry is driving the SNAP calibration methodology and system design into new areas of space-based, radiometric calibration for astronomical missions.

At the forefront of these new calibration techniques is the use of narrowband light and photodiodes to measure the precise irradiance incident on SNAP filters and detectors. Using these techniques, I have built the Monochromatic Illumination and Cryogenic Calibration System (MICCS) to address the SNAP calibration hardware requirements. With this system, I can transfer the NIST irradiance calibration of an InGaAs photodiode to transfer photodiodes operated at 140K as well as measure the transmission of interference filters at incident angles and temperature similar to that used on the SNAP focal plane.

Due to size and light efficiency constraints, I also investigated the use of light emitting diodes (LEDs) as calibrating light sources onboard SNAP. When coupled with calibrated photodiodes, a selection of LEDs could fly onboard SNAP and be used to track changes in the SNAP interference filters during the lifetime of the experiment. The error from this LED calibration technique will be propagated to the dark energy parameters to determine what design constraints are required of the onboard illumination system.