Ground Test Characterization of the SIRTF (MIPS)
Ground testing and characterization of the Multiband Imaging Photometer for SIRTF
Erick T. Young, George H. Rieke, James D. Cadien, Hervé A. Dole, et al. — Steward Observatory, University of Arizona & Ball Aerospace
Overview
This paper describes the ground testing and characterization of the Multiband Imaging Photometer for SIRTF (MIPS), a camera with three focal plane arrays covering broad spectral bands centered at 24 µm, 70 µm, and 160 µm. The observational philosophy relies heavily on the use of internal relative calibration sources and a high level of data redundancy to achieve sensitive, highly repeatable observations. The single moving mechanism — a scan mirror — was derived from a design used on the Infrared Space Observatory.
Key Highlights
Single Scan Mirror
The only cryogenic mechanism — derived from ISO design; used for source modulation, beam switching, and mapping
128×128 Si:As BIB Array
24 µm detector with 99.94% operability and 1% photometric accuracy
32×32 Ge:Ga Array
70 µm detector operating below 2 K, using CRC-696 CTIA readout
Stressed Ge:Ga Array
160 µm detector with uniaxial stress extending cutoff from 115 to 200 µm
Cryostat Testing
Tested in flight SIRTF Cryo-Telescope Assembly at 1.5 K operating temperature
Four Modes
Photometry, Scan Map, Spectral Energy Distribution, and Total Power modes
Instrument Overview
MIPS is one of three science instruments on the Space Infrared Telescope Facility (SIRTF), providing imaging, photometry, and total power measurement in broad spectral bands at 24, 70, and 160 µm and low-resolution spectroscopy from 50 to 95 µm. MIPS has a minimum number of cryogenic mechanisms and no filter wheel. The single mechanism is a scan mirror, which performs source modulation on the detectors and enables efficient mapping by freezing image motion while the telescope scans.
Flexural Pivot Role
The scan mirror mechanism (CSMM) — the only moving part in MIPS — is supported by flexural pivots that allow frictionless, wear-free rotation at cryogenic temperatures as low as 1.5 K. Flex pivots eliminate the need for lubrication in the vacuum and cryogenic environment of space, where lubricant outgassing and freezing would compromise mission lifetime.
Detector Arrays
The 24 µm array is a 128×128 Si:As BIB device with 99.94% operability and a thermal isolation mount for operation at 6 K. The 70 µm array is a 32×32 Ge:Ga photoconductor requiring temperatures below 2 K. The 160 µm array uses 2×20 stressed Ge:Ga detectors with ~500 MPa uniaxial pressure extending the photoconductive cutoff from 115 to 200 µm.
Characterization Program
Ground characterization involved test dewars for focal-plane level testing, a specialized cryostat for instrument-level testing, and tests in the flight SIRTF Cryo-Telescope Assembly. Using frequent internal calibration sources and redundant data collection, MIPS achieves rms relative photometric errors of 1% at 24 µm and under 10% for the germanium arrays.
Ground Test Characterization of the SIRTF (MIPS) — PDF
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