The OSIRIS-REx Thermal Emission Spectrometer (OTES) Instrument

TL;DR

The OSIRIS-REx Thermal Emission Spectrometer (OTES) is a compact, highly precise instrument designed to analyze Bennu's surface mineralogy and thermophysical properties, aiding sample site selection and studying the Yarkovsky effect.

Contribution

This paper details the design, calibration, and specifications of the OTES instrument, a novel Fourier transform spectrometer for planetary surface analysis.

Findings

High radiometric precision (<= 2.2 x 10^-8 W cm^-2 sr^-1/cm^-1)

Absolute radiance error <1% for 150-380 K temperatures

Compact design with 6.27 kg mass and 10.8 W power consumption

Abstract

The OSIRIS-REx Thermal Emission Spectrometer (OTES) will provide remote measurements of mineralogy and thermophysical properties of Bennu to map its surface, help select the OSIRIS-REx sampling site, and investigate the Yarkovsky effect. OTES is a Fourier transform spectrometer covering the spectral range 5.71 - 100 {\mu}m (1750 - 100 cm-1) with a spectral sample interval of 8.66 cm-1 and a 6.5-mrad field of view. The OTES telescope is a 15.2-cm diameter Cassegrain telescope that feeds a flat-plate Michelson moving mirror mounted on a linear voice-coil motor assembly. A single uncooled deuterated L-alanine doped triglycine sulfate (DLATGS) pyroelectric detector is used to sample the interferogram every two seconds. Redundant ~0.855 {\mu}m laser diodes are used in a metrology interferometer to provide precise moving mirror control and IR sampling at 772 Hz. The beamsplitter is a 38-mm diameter, 1-mm thick chemical vapor deposited diamond with an antireflection microstructure to minimize surface reflection. An internal calibration cone blackbody target provides radiometric calibration. The radiometric precision in a single spectrum is <= 2.2 x 10-8 W cm-2 sr-1/cm-1 between 300 and 1350 cm-1. The absolute integrated radiance error is <1% for scene temperatures ranging from 150 to 380 K. The overall OTES envelope size is 37.5 x 28.9 x 52.2 cm, and the mass is 6.27 kg. The power consumption is 10.8 W average. The OTES was developed by Arizona State University with Moog Broad Reach developing the electronics. OTES was integrated, tested, and radiometrically calibrated on the Arizona State University campus in Tempe, AZ.