New satellite constellations to provide high-resolution atmospheric observations from microwave (MW) sounders operating in low-Earth orbit are now coming online and are providing operationally useful data. The first of these missions, the NASA Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) Earth Venture (EVI-3) mission, was successfully launched into orbit on May 7 and 25, 2023 (Eastern Daylight Time, two CubeSats in each of the two launches). TROPICS is now providing nearly all-weather observations of 3-D temperature and humidity, as well as cloud ice and precipitation horizontal structure, at high temporal resolution to conduct high-value science investigations of tropical cyclones (TCs). TROPICS is providing rapid-refresh MW measurements (median refresh rate of better than 60 min early in the mission with four functional CubeSats, and now approximately 70–90 min with three functional CubeSats) over the tropics that can be used to observe the thermodynamics of the troposphere and precipitation structure for storm systems at the mesoscale and synoptic scale over the entire storm lifecycle. Hundreds of high-resolution images of TCs have been captured thus far by the TROPICS mission, revealing the detailed structure of the eyewall and surrounding rain bands. The new 205-GHz channel in particular (together with a traditional channel near 92 GHz) is providing new information on the inner storm structure, and, coupled with the relatively frequent revisit and low downlink latency, is already informing TC analysis at operational centers. Here, we present an overview of the TROPICS mission after two years of successful science operations with a focus on the suite of geophysical (Level 2) products (atmospheric vertical temperature and moisture profiles, instantaneous surface rain rate, and TC intensity) and the science investigations that have been enabled by these new measurements.

Highly scaled indium phosphide (InP) heterojunction bipolar transistor (HBT) technologies have been demonstrated with maximum frequencies of oscillation ( f max) of >1 THz and circuit operation has been extended into the lower end of the terahertz (THz) frequency band. InP HBTs offer high radio-frequency (RF) output power density, millivolt (mV) threshold uniformity, and high levels of integration. Integration with multilevel thin-film wiring permits the realization of compact and complex THz monolithic integrated circuits (TMICs). Circuit results reported from InP HBT technologies include: 200-mW power amplifiers at 210 GHz, 670-GHz amplifiers and fundamental oscillators, and fully integrated 600-GHz transmitter circuits. We review the state of the art in THz-capable InP HBT devices and integrated circuit (IC) technologies. Challenges in extending transistor bandwidth and in circuit design at THz frequencies will also be addressed.