Concept study of the heterodyne spectroscopy instrument (HSI) for the proposed Far-IR Spectroscopy Space Telescope (FIRSST)
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
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 astrophysics probe explorer 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, that they can be built with high technology readiness level 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 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 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.
Date Issued
2026-04-01
Date Acceptance
2026-02-24
Citation
IEEE Transactions on Terahertz Science and Technology, 2026, 16 (4), pp.487-495
ISSN
2156-342X
Publisher
Institute of Electrical and Electronics Engineers
Start Page
487
End Page
495
Journal / Book Title
IEEE Transactions on Terahertz Science and Technology
Volume
16
Issue
4
Copyright Statement
© 2026 IEEE. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Publication Status
Published
Date Publish Online
2026-03-09