Concept Study of the Heterodyne Spectroscopy Instrument (HSI) for the proposed Far-IR Spectroscopy Space Telescope (FIRSST)
Journal article, 2026
The Heterodyne Spectroscopy Instrument (HSI) is a focal plane array receiver (FPA) for the Far-IR Spectroscopy Space Telescope (FIRSST), a proposal submitted to NASA's APEX call. Though FIRSST was not selected for further study, the receiver design allowed us to quantitatively demonstrate that small (few to few tens of pixels) heterodyne FPAs are now feasible for space missions, can be built with high TRL components, are reliable and fit within the mass/volume/power constraints of medium to large missions. The design also identified the challenges and critical design considerations, in particular that great care needs to be taken to minimize the cryogenic heat load of the cryogenic IF amplifiers and to keep the power consumption of the spectrometer backends low. The HSI was designed primarily to study the trail of water from the Interstellar Medium (ISM) to planets and to observe the important low-lying transitions of water and its isotopes between 500 and 2000 GHz undetectable from the ground due to Earth's atmosphere. HSI has a spectral resolving power of up to 107 (0.03 km/s), ideal for kinematic studies or line tomography. HSI has six 5-pixel-arrays covering 3 frequency bands and 2 linear polarizations. The concept study showed that heterodyne array receivers such as HSI can be built today even for fast missions and that they are powerful and versatile instruments, with low-risk technology capable of opening up the THz sky at very high spectral resolving power for new discoveries.
heterodyne receivers
Far-IR space instruments
THz astronomy
Heterodyne instruments
array receivers
THz detectors
Author
M.C. Wiedner
Paris Descartes University
A. M. Baryshev
University of Groningen
P. K. Grimes
Harvard-Smithsonian Center for Astrophysics
Victor Belitsky
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Vincent Desmaris
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Y. Delorme
Paris Descartes University
J. D. Gallego
Yebes Observatory
Cristina García-Miró
Yebes Observatory
U. Gorti
SETI Institute
P. Hartogh
Max Planck Society
N. Honingh
University of Cologne
Benjamin Klein
Max Planck Society
Fachhochschule Bonn-Rhein-Sieg
J. M. Krieg
Paris Descartes University
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
Sebastiano Ligori
Istituto nazionale di astrofisica (INAF)
B. K. Tan
University of Oxford
B. Thomas
RPG Radiometer Physics GmbH
European Space Agency (ESA)
V. Tolls
Harvard-Smithsonian Center for Astrophysics
J. Treuttel
Paris Descartes University
Jérôme Valentin
Paris Observatory
D. L. Clements
Imperial College London
R. Blundell
Harvard-Smithsonian Center for Astrophysics
A. Cooray
University of California
M. Macgregor
Johns Hopkins University
Ronald J. Vervack
Johns Hopkins University
IEEE Transactions on Terahertz Science and Technology
2156-342X (ISSN) 21563446 (eISSN)
Vol. In PressSubject Categories (SSIF 2025)
Other Electrical Engineering, Electronic Engineering, Information Engineering
Astronomy, Astrophysics, and Cosmology
DOI
10.1109/TTHZ.2026.3671953