Instruments Partially Developed
Science instruments canceled before completion
Airborne Infra-Red Echelle Spectrometer: AIRES was to be a Long-slit Spectrograph covering 17 - 210 micron wavelengths, with spectral resolving power R = 10 4 at 100 microns. The Principal Investigator was Edwin F. Erickson (NASA/Ames). A report includes some of the technical details and scientific potential of AIRES.
Submillimeter And Far InfraRed Experiment: SAFIRE was to be a versatile imaging Fabry-Perot spectrograph covering the spectral region from 145 to 655 µm with spectral resolving powers ranging from 5 to 104. The instrument design had two 8 x 32 arrays of bolometers to provide background limited performance. A chain of fixed and tunable fabry-perot filters were to provide a wide choice of order selection and fixed spectral resolution. The principal investigator was S. H. Moseley (NASA/Goddard).
CAltech Submillimeter Interstellar Medium Investigations Receiver: CASIMIR was a planned high-resolution heterodyne spectrometer to have operated in five bands between 500 and 1500 GHz. The receiver was to use sensitive superconducting mixers, including both tunnel junction (SIS) and hot electron bolometers (HEB), with double-sideband receiver noise temperatures are projected to be 4-10 times the quantum limit. The Principal Investigator was Jonas Zmuidzinas (Caltech). The NASA SOFIA Program made a programmatic decision to cease the science instrument development of CASIMIR by the end of 2010.
High Resolution Mid-infrared Spectrometer: HIRMES was to provide high-resolution (resolving power 100,000) far-infrared spectroscopy from 25 to 122 micron wavelengths. In April 2020, the development of HIRMES was terminated by the Director of the NASA Astrophysics Division.
The SOFIA telescope, which was provided by the German Aerospace Agency (DLR), consisted of a parabolic 2.7m (2.5m illuminated diameter) primary mirror and a hyperbolic secondary mirror in a bent Cassegrain configuration with two Nasmyth foci: the nominal IR focus and an additional visible light focus for guiding. The secondary mirror was attached to a chopping mechanism providing chop amplitudes of up to ± 5 arcmin at chop frequencies between 0 and 20 Hz. A flat tertiary mirror reflected the IR beam into the infrared Nasmyth focus, 300mm behind the instrument flange.
In addition to the infrared science instruments, which were mounted at Nasmyth focus and took light form the infrared port reflected from the dichroic tertiary mirror, SOFIA had other sensitive sensors. The guide cameras included two ring-mounted CCD cameras and the Focal Plane Imager that took the light transmitted through dichroic tertiary mirror.
A port on the upper deck of the aircraft allowed operation of a Water Vapor Monitor (WVM), which was developed by Thomas Roellig (NASA/ARC). The WVM determined water vapor overburden by comparing radiometric measurements of the center and wings of the 183.3 GHz rotational line of water observed in the atmosphere to atmospheric models. The Radiometer Head contained an antenna that viewed the sky, two calibrated reference targets (one heated and one ambient temperature microwave blackbody), an RF switch, a mixer, a local oscillator, an IF amplifier, and an inclinometer. These components were mounted together on a baseplate attached to the inner surface of the aircraft fuselage, so that the antenna could observe the sky through a microwave-transparent window.
Instrument Development Roadmap
To create a plan and timeline for SOFIA’s instrument development during 2020-2025 period, the SOFIA project held community workshops and delivered a Roadmap document. While the timeline was superceded by the cancellation of the SOFIA mission, we include the proceedings here as potentially valuable information for future far-infrared development.