Infrared spectrograph for the Space Infrared Telescope Facility (SIRTF)

Abstract

The IR Spectrograph (IRS) will provide the Space IR Telescope Facility (SIRTF) with low and moderate-spectral resolution spectroscopic capabilities from 4 to 40 microns. The IRS is composed of four separate modules, with two of the modules providing R approximately 50 spectral resolution over 4 to 40 microns and two modules providing R approximately 600 spectral resolution over 10 to 37 microns. Each module has its own entrance slit in the focal plane and the IRS instrument has no moving parts. The low-resolution modules employ long slit designs that allow both spectral and 1D spatial information to be acquired simultaneously on the same detector array. Two small imaging sub-arrays in one of the low-resolution modules will also allow IR objects with poorly known positions to be accurately placed into any of the IRS modules' entrance slits. The high-resolution modules use a cross-dispersed echelle design that gives both spectral and limited spatial measurements on the same detector array. The one-sigma continuum sensitivity requirements for the IRS low-resolution modules' one-sigma line sensitivity requirements are 6.0 by 10<SUP>-23</SUP> W- cm<SUP>-2</SUP> in the same integration time. Internal calibration sources allow the IRS to perform self monitoring of detector sensitivity changes. Careful thermal design allows all four modules to be powered up simultaneously and still input less than 4 mW total power into the SIRTF liquid helium bath. The optical, mechanical, thermal, and electrical design of the IRS is discussed, as is the IRS on- orbit operational concept.