Part I: Breakthrough Science
The SALTUS Probe mission will provide a powerful far-infrared (far-IR) pointed space observatory to explore our cosmic origins and the possibility of life elsewhere. The observatory employs an innovative deployable 14-m aperture, with a sunshield that will radiatively cool the off-axis primary to <45K. This cooled primary reflector works in tandem with cryogenic coherent and incoherent instruments that span the 34 to 660 micron far-IR range at both high and moderate spectral resolutions.
The Single Aperture Large Telescope for Universe Studies (SALTUS) is a far-infrared space mission concept with unprecedented spatial and spectral resolution. Saltus consists of a 14-m inflatable primary, providing 16 times the sensitivity and 4 times the angular resolution of Herschel, and two cryogenic detectors spanning a wavelength range of 34-660 microns and spectral resolving power of 300 - 1e7. Spectroscopic observations in the far-infrared offer many unique windows into the processes of star and planet formation. These include observations of low energy water transitions, the H2 mass tracer HD, many CHONS constraining molecules such as NH3 and H2S, and emission lines from the phonon modes of molecular ices. Observing these species will allow us to build a statistical sample of protoplanetary disk masses, characterize the water snowline, identify Kuiper Belt like debris rings around other stars, and trace the evolution CHONS from prestellar cores, through to protoplanetary disks and debris disks. This paper details details several key star and planet formation science goals achievable with SALTUS.
This paper presents an overview of the Milky Way and nearby galaxies science case for the {Single Aperture Large Telescope for Universe Studies} (SALTUS) far-infrared NASA probe-class mission concept. SALTUS offers enormous gains in spatial resolution and spectral sensitivity over previous far-IR missions, thanks to its cold (<40~K) 14-m primary mirror. Key Milky Way and nearby galaxies science goals for SALTUS focus on understanding the role of star formation in feedback in the Local Universe. In addition to this science case, SALTUS would open a new window to to of Galactic and extragalactic communities in the 2030s, enable fundamentally new questions to be answered, and be a far-IR analog to the near- and mid-IR capabilities of JWST. This paper summarizes the Milky Way and nearby galaxies science case and plans for notional observing programs in both guaranteed and guest (open) time.
Rebecca C. Levy, Alexander Tielens, Justin Spilker, Daniel P. Marrone, Desika Narayanan, Christopher K. Walker
This paper presents an overview of the high-redshift extragalactic science case for the Single Aperture Large Telescope for Universe Studies (SALTUS) far-infrared NASA probe-class mission concept. Enabled by its 14m primary reflector, SALTUS offers enormous gains in spatial resolution and spectral sensitivity over previous far-IR missions. SALTUS would be a versatile observatory capable of responding to the scientific needs of the extragalactic community in the 2030s, and a natural follow-on to the near- and mid-IR capabilities of JWST. Key early-universe science goals for SALTUS focus on understanding the role of galactic feedback processes in regulating galaxy growth across cosmic time, and charting the rise of metals and dust from the early universe to the present. This paper summarizes these science cases and the performance metrics most relevant for high-redshift observations.
Justin Spilker, Rebecca Levy, Daniel Marrone, Stacey Alberts, Scott Chapman, Mark Dickinson, Eiichi Egami, Ryan Endsley, Desika Narayanan, George Rieke, Anthony Stark, Alexander Tielens, Christopher Walker
The high sensitivity and high spectral resolving power of the SALTUS heterodyne receivers enable both submillimeter and far-infrared observations of trace compounds comprising water and its isotopologues, hydrogen deuteride (HD), and a plethora of molecular species containing carbon, hydrogen, nitrogen, oxygen, phosphorus, or sulfur (CHNOPS), all of which are obscured by the Earth’s atmosphere. The high sensitivity and broadband spectral coverage of the SALTUS far-infrared grating spectrometer enables far-infrared observations of the lattice vibrational spectral signatures of ices and mineral grains contained within a wide variety of solar system targets, including comets, planetary atmospheres, near Enceladus’ plumes, and on the surfaces of icy moons, Jupiter trojans, centaurs, and Kuiper Belt objects. A key objective of SALTUS is to measure HDO/H2O in both Jupiter family and Oort cloud comets. Additional observations will allow us to characterize the water torus around Saturn generated by its icy moon Enceladus, determine the source of stratospheric water in the giant planets, ascertain the time evolution of water on Venus, and search for H2O plumes on Europa, Ganymede, and Callisto. SALTUS will measure HD/H2 in all four giant planets to constrain models of their origin. SALTUS can also measure the abundance of CHNOPS-containing molecules and halides in the atmosphere of Venus and in the comae of comets. We review the extensive amount of solar system science achievable with SALTUS for both the Guaranteed Time Observation and the Guest Observer APEX mission observing programs.
Carrie Anderson, Nicolas Biver, Gordon Bjoraker, Thibault Cavalié, Gordon Chin, Michael DiSanti, Paul Hartogh, Nathan Roth, Alexander Tielens, Christopher Walker
Part II: Breakthrough Technology
SALTUS will address key far-infrared science using a 14-m diameter <45 K primary reflector (M1) and will provide unprecedented levels of spectral sensitivity for planet, solar system, and galactic evolution studies, and cosmic origins. Drawing from Northrop Grumman's extensive NASA mission heritage, the observatory flight system is based on the LEOStar-3 spacecraft platform to carry the SALTUS Payload. The Payload is comprised of the inflation control system (ICS), Sunshield Module (SM), Cold Corrector Module (CCM), Warm Instrument Electronics Module, and Primary Reflector Module (PRM). SALTUS will reside in a Sun-Earth halo L2 orbit with a maximum Earth slant range of 1.8 million km thereby reducing orbit transfer delta-v. The instantaneous field of regard provides two continuous 20-deg viewing zones around the ecliptic poles resulting in full sky coverage in six months.
Leon Harding, Jonathan Arenberg, Benjamin Donovan, Dave Oberg, Ryan Goold, Bob Chang, Christopher Walker, Dana Turse, Jim Moore, Jim Pearson, John Kidd, Zach Lung, Dave Lung
The enabling element of the SALTUS program is a 14 m diameter inflatable primary mirror, M1. Due to its importance to SALTUS and potentially other space observatories, this paper focuses entirely on M1. We present a historical overview of inflatable systems, illustrating that M1 is the logical next step in the evolution of such systems. The process of design and manufacture is addressed. We examine how M1 performs in its environment in terms of operating temperature, interaction with the solar wind, and shape change due to non-penetrating particles. We investigate the longevity of the inflatant in detail and show it meets mission lifetime requirements with ample margin and discuss the development and testing to realize the flight M1.
Jonathan Arenberg, Leon Harding, Bob Chang, Steve Kuehn, Dave Oberg, Michaela Villarreal, Arthur Palisoc, Christopher Walker, Daewook Kim, Zach Lung, Dave Lung
The Single Aperture Large Telescope for Universe Studies (SALTUS) is a deployable space telescope designed to provide the astrophysics community with an extremely large far-infrared (far-IR) space observatory to explore our cosmic origins. The SALTUS observatory can observe thousands of faint astrophysical targets, including the first galaxies, protoplanetary disks in various evolutionary states, and a wide variety of solar system objects. The SALTUS design architecture utilizes radiatively cooled, 14-m diameter unobscured aperture, and cryogenic instruments to enable both high spectral and spatial resolution at unprecedented sensitivity over a wavelength range largely unavailable to any existing ground or space observatories. The unique SALTUS optical design, utilizing a large inflatable off-axis primary mirror, provides superb sensitivity, angular resolution, and imaging performance at far-IR wavelengths over a wide +/-0.02 x 0.02 degree Field of View. SALTUS design, with its highly compact form factor, allows it to be readily stowed in available launch fairings and subsequently deployed in orbit.
The High-Resolution Receiver (HiRX) is one of two instruments of the Single Aperture Large Telescope for Universe Studies (SALTUS), a mission proposed to NASA’s 2023 Astrophysics Probe Explorer. SALTUS employs a 14m aperture, leading to a 16-fold increase in collecting area and a factor of 4 increase in the angular resolution with respect to the Herschel Space Telescope. It will be radiatively cooled to <45 K and has a planned duration of >5 years. HiRX consists of four bands of cryogenic heterodyne receivers with a high sensitivity and high spectral resolution, being able to observe the gaseous components of objects across the far-IR. HiRX is going to detect water, HD and other relevant astrophysical lines while velocity resolving them. HiRX covers the following frequency ranges: Band 1 from 455 to 575 GHz, Band 2 from 1.1 to 2.1 THz, Band 3 from 2.475 to 2.875 THz, and Band 4 for both 4.744 and 5.35 THz. Bands 1 to 3 contain single, high-performance mixers. Band 4 consists of an array of seven hexagonally packed pixels, where the central pixel operates as a heterodyne mixer. Band 1 utilizes superconducting-insulator-superconducting mixers (SIS), whereas Band 2 to 4 use superconducting hot electron bolometers (HEB) mixers. The local oscillator (LO) system uses frequency-multiplier chains for Band 1 and 2, and quantum cascade lasers for band 3 and 4. Autocorrelator spectrometers are used to process the intermediate frequency (IF) signals from each science band, providing instantaneous frequency coverage of 4-8 GHz for Band 1 and 0.5-4 GHz for Band 2 to 4. SALTUS will also fly a chirp transform spectrometer system for high spectral resolution observations in Band 1.
Part III: Opportunities
The SALTUS architecture yields a telescope that is both powerful and flexible. In addition to SAFARI-Lite and HiRX, the observatory’s robust design margins allow for accommodation of a complementary, contributed 3rd instrument that benefits from a large, cooled, diffraction limited aperture.
Filamentary star formation and the role of magnetic fields on various scales with SALTUS–B-BOP
Often ignored, strong, organized magnetic fields, in rough equipartition with the turbulent and cosmic ray energy densities, have been detected in the ISM of a large number of galaxies out to z = 2 (e.g. Beck, 2015). Recent cosmological MHD simulations of structure formation in the Universe suggest that magnetic-field strengths comparable to those measured in nearby galaxies ( < 10 μG) can be quickly built up in high-redshift galaxies (in << 1 Gyr), through the dynamo amplification of initially weak seed fields (e.g. Rieder & Teyssier, 2017). Magnetic fields are therefore expected to play a dynamically important role in the formation of giant molecular clouds (GMCs) on kpc scales within galaxies (e.g. Inoue & Inutsuka, 2012) and in the formation of filamentary structures leading to individual star formation on ⇠1–10 pc scales within GMCs (e.g. Andre et al., 2014, Inutsuka et al., 2015). On dense core (< 0.1 pc) scales, the magnetic field and angular momentum of most protostellar systems are likely inherited from the processes of filament formation and fragmentation (cf. Misugi et al., 2019). On even smaller (< 0.01pc or < 2000au) scales, magnetic fields are essential to solve the angular momentum problem of star formation, generate protostellar outflows, and control the formation of protoplanetary disks (Li et al., 2014). In this context, high-dynamic- range mapping observations of linearly-polarized continuum emission from magnetically-aligned dust grains at far-infrared wavelengths with SALTUS–B-BOP can provide a unique tool for characterizing the role of magnetic fields from GMC to protostellar scales (see Andre et al., 2019, PASA, 36, e029).
Participants & Affiliations
Louis Rodriguez, CEA Paris-Saclay, Lab. AIM, France
Vincent Revéret, CEA Paris-Saclay, Lab. AIM, France
Laurent Dussopt, CEA-LETI, Univ. Grenoble Alpes, France
Albrecht Poglitsch, Max-Planck Institut für extraterrestrische Physik, Garching, Germany
Philippe André, CEA Paris-Saclay, Lab. AIM, France
Anaëlle Maury, CEA Paris-Saclay, Lab. AIM, France