The search for extraterrestrial bio-signatures and the origin of Earth’s water remain two of the most compelling questions in planetary science. While no direct evidence of life beyond Earth has been found, water is a key prerequisite for life, and tracing its presence throughout the solar system may provide vital clues. A leading theory suggests that Earth’s water may have originated from comets, supported by limited water isotopic measurements that match Earth’s ocean water. However, more data from a larger sample of comets is needed to validate this theory. Traditional sub-millimeter wave spectrometers, capable of such measurements, are often too large and power-intensive for small spacecraft platforms. To address this, we present WHATSUP—a next-generation, ultra-compact, low-power, room-temperature submillimeter-wave (500-600 GHz) spectrometer—designed primarily for CubeSat and SmallSat platforms, though equally well-suited for a range of other missions. WHATSUP utilizes advances in CMOS system-on-chip electronics, innovative low profile and low mass silicon lens antenna, Micro-electro mechanical system (MEMS)-based THz switching, and a novel programmable calibration load. Together, these innovations deliver a highly integrated system with a total mass of only 2 kg and power consumption under 7 W, which is a substantial improvement over previous submillimeter-wave instruments. This enables affordable, high-frequency spectral observations from multiple low-cost missions, potentially revolutionizing how isotopic studies of cometary water are conducted and opening new pathways for outer solar system exploration. WHATSUP instrument was flown on the NASA Hand Launch Payload (HLP) ballooncraft and performed atmospheric soundings across Texas, USA in July 2023.

The PRobe far-Infrared Mission for Astrophysics (PRIMA) is under study as a potential far-IR space mission, featuring actively cooled optics, and both imaging and spectroscopic instrumentation. To fully take advantage of the low background afforded by a cold telescope, spectroscopy with PRIMA requires detectors with a noise equivalent power (NEP) better than 1 × 10 ^-19 W Hz ^-12. To meet this goal, we are developing large format arrays of kinetic inductance detectors (KIDs) to work across the 25–250 μm range. Here, we present the design and characterization of a single pixel prototype detector optimized for 210 μm. The KID consists of a lens-coupled aluminum inductor-absorber connected to a niobium interdigitated capacitor to form a 2 GHz resonator. We have fabricated a small array with 28 KIDs, and we measure the performance of one of these detectors with an optical loading in the 0.01–300 aW range. At low loading, the detector achieves an NEP of 9 × 10 ^-20 W Hz ^-1/2 at a 10 Hz readout frequency. An extrapolation of these measurements suggests this detector may remain photon noise limited at up to 20 fW of loading, offering a high dynamic range for PRIMA observations of bright astronomical sources.

The PRobe far-Infrared Mission for Astrophysics (PRIMA) is an astrophysics mission concept currently under study. The instrument comprises four focal plane arrays (FPAs), each with over 1000 pixels, consisting of lens-coupled kinetic inductance detectors designed for ultra-high sensitivity spectroscopy and imaging. PRIMA covers the far-infrared band from 24 to 250 μm. We present the fundamental properties of lens-coupled absorbers, including aperture efficiency, throughput, and beam patterns. Compared with bare absorbers, lens-coupled absorbers exhibit reduced sensitivity to noise from both the instrument enclosure and the sky background. We analyze FPA sampling strategies in terms of relative observing speed, considering both detector noise–limited and background noise–limited scenarios. In the background noise–limited case, near-maximum-gain sampling is optimal only when the point spread function (PSF) in the reflector focal plane is aligned with the lens. For arbitrary PSF incidence, a near-Nyquist sampling configuration provides the best average performance. These calculations are based on a computationally efficient quasi-analytical technique and assume a hex-packed array of circular lenses, recently developed for PRIMA.

We report measurements characterizing the performance of a kinetic inductance detector array designed for a wavelength of 25 microns and very low optical background level suitable for applications such as a far-infrared instrument on a cryogenically cooled space telescope. In a pulse-counting mode of operation at low optical flux, the detectors can resolve individual 25-micron photons. In an integrating mode, the detectors remain photon noise limited over more than 6 orders of magnitude in absorbed power from 70 zW to 200 fW, with a limiting noise equivalent power of 4.6×10-20 W Hz-1 at 1 Hz. In addition, the detectors are highly stable with flat power spectra under optical load down to 1 mHz. Operational parameters of the detector are determined including the efficiency of conversion of the incident optical power into quasiparticles in the aluminum absorbing element and the quasiparticle self-recombination constant.

Future generation of astronomical imaging spectrometers are targeting the far infrared wavelengths to close the THz astronomy gap. Similar to lens antenna coupled Microwave Kinetic Inductance Detectors (MKIDs), lens absorber coupled MKIDs are a candidate for highly sensitive large format detector arrays. However, the latter is more robust to misalignment and assembly issues at THz frequencies due to its incoherent detection mechanism while requiring a less complex fabrication process. In this work, the performance of such detectors is investigated. The fabrication and sensitivity measurement of several lens absorber coupled MKID array prototypes operating at 7.8 and 12 THz central frequencies is ongoing.