Efforts to create a sustainable hydrogen economy are gaining momentum as governments all over the world are investing in hydrogen production, storage, distribution, and delivery technologies to develop a hydrogen infrastructure. This involves transporting hydrogen in gaseous or liquid form or using carrier gases such as methane, ammonia, or mixtures of methane and hydrogen. Hydrogen is a colorless, odorless gas and can easily leak into the atmosphere leading to economic loss and safety concerns. Therefore, deployment of robust low-cost sensors for various scenarios involving hydrogen is of paramount importance. Here, we review some recent developments in hydrogen sensors for applications such as leak detection, safety, process monitoring in production, transport and use scenarios. The status of methane and ammonia sensors is covered due to their important role in hydrogen production and transportation using existing natural gas and ammonia infrastructure. This review further provides an overview of existing commercial hydrogen sensors and also addresses the potential for hydrogen as an interferent gas for currently used sensors. This review can help developers and users make informed decisions about how to drive hydrogen sensor technology forward and to incorporate hydrogen sensors into the various hydrogen deployment projects in the coming decade.

The Importance of Venus Experimental Facilities Introduction: The planet Venus is the most Earth-like body in terms of its size, composition, and location in the solar system, and hosts some similar geologic processes, such as widespread basaltic volcanism and aeolian sand transport [1,2].At the same time, Venus offers what is likely the greatest set of technical challenges to exploration out of all terrestrial bodies [3].With an average surface temperature of ~460 ºC and pressure of ~92 bars (at mean planetary radius) [4], many types of instrumentation, including conventional electronics, are outside their standard operating conditions on Venus [5,6].On top of these factors, the Venusian atmosphere is a chemically reactive mixture of carbon and sulfur species, including SO2, CO2, H2S, and COS, in addition to other trace, but important, reactive species such as HCl and HF [4,7].This dense gas mixture will react with most structural and fabrication materials, aggressively corroding metals, and ruining electrical wiring [8,9].Nevertheless, the exploration of Venus is vital in our quest to understand the evolution of terrestrial planets, and can reveal why some sustain liquid water, plate tectonics, and a complex biosphere like Earth, while others develop hostile environments.The answers to these questions, along with numerous other vital science questions such as those presented in the VEXAG Scientific Goals, Objectives, and Investigations for Venus Exploration [10], can only be found through exploration of Venus.Crucial tools in the exploration of Venus are experimental facilities that can replicate the pressure, temperature, and chemical conditions of that world.Such facilities allow us to develop, test, and prove technologies to explore Venus, and understand how to manage the challenges caused by the Venus environment.These facilities also benefit the scientific study of Venus as they can be used as laboratories to investigate the natural processes that occur in this extreme environment.Because these facilities advance both science and technology, they contribute to all parts of the exploration cycle, including investigating environmental phenomena that missions will need to survive and measure, developing and testing of technology and mission hardware to send to Venus, and using laboratory investigations to understand past and future mission data.This capability to contribute to all parts of the Venus exploration cycle makes Venus experimental facilities critical to moving forward our understanding of this planet in the next decade.Current Capabilities: A "facility" for the purposes of this discussion consists of a chamber or reaction vessel and its accompanying heating system, gas control system, and data collection system.A list of current facilities with Venus capabilities is given in Table 1.A critical advancement in recent years is that the barriers to replication of the Venus environment have been overcome at multiple institutions; this represents a significant advancement in the development of Venus experimental facilities since the last Decadal Survey.Multiple facilities are now capable of replicating the temperature and pressure of the Venus surface.The main variations in most of these facilities are the experimental chamber volumes, and how the gas composition in the replicated environment is treated, both in terms of what species are supplied and how they are monitored.The listed facilities run the gamut ranging from supporting technology and instrumentation development, mission development, and varied science experimentation.It is important to remember that different investigations require different facility capabilities, thus diversity in capabilities is required.More complex and capable facilities are needed to provide testing for whole mission concepts, while simpler more limited systems can be used to test and develop individual subsystems or technologies, such as functionality of specific instruments or measurement techniques.Similarly, some scientific investigations may focus on select atmospheric gases, while others require a more complete replication of the atmospheric

All high-priority Venus atmosphere science is enabled or enhanced by in situ exploration elements.We describe a distributed sensing platform that allows for observation of multiple interacting regional and global phenomena over wide spatial and temporal scales and which can provide correlated, ground-truth data for remote sensing assets and modeling efforts.

More than 85% of the 23 investigations developed by VEXAG are largely accomplished via a NF mission centered on a variable-altitude balloon (aerobot) supported by a science/comm orbiter. Circling Venus >15 times over ~90 days, the aerobot repeatedly visits 52–62 km alts as it semi-continuously samples a host of environmental & surface parameters.

An exciting and novel science mission concept called Seismic and Atmospheric Exploration of Venus (SAEVe) has been developed which uses high-temperature electronics to enable a three-order magnitude increase in expected surface life (120 Earth days) over what has been achieved to date. This enables study of long-term, variable phenomena such as the seismicity of Venus and near surface weather, near surface energy balance, and atmospheric chemical composition. SAEVe also serves as a critical pathfinder for more sophisticated landers in the future. For example, first order seismic measurements by SAEVe will allow future missions to deliver better seismometers and systems to support the yet unknown frequency and magnitude of Venus events. SAEVe is focused on science that can be realized with low data volume instruments and will most benefit from temporal operations. The entire mission architecture and operations maximize science while minimizing energy usage and physical size and mass. The entire SAEVe system including its protective entry system is estimated to be around 45 kg and approximately 0.6 m diameter. These features allow SAEVe to be relatively cost effective and be easily integrated onto a Venus orbiter mission. The technologies needed to implement SAEVe are currently in development by several funded activities. Component and system level work is ongoing under NASA's Long Lived Insitu Solar System Explorer (LLISSE) project and the HOTTech program. . LLISSE, is a NASA project to develop a small Venus lander that will operate on the surface of Venus for 60 days and measure variations in meteorology, radiance, and atmospheric chemistry. LLISSE is developing a full-function engineering model of a Venus lander that contains essentially all the core capabilities of SAEVe thus greatly reducing the technology risk to SAEVe. The SAEVe long duration Venus lander promises exciting new science and is an ideal complimentary element to many future Venus orbiter missions being proposed or planned today.

Vacuum tubes were central to the early development of electronics, but were replaced, decades ago, by semiconductor transistors. Vacuum channel devices, however, offer inherently faster operation and better noise immunity due to the nature of their channel. They are also stable in harsh environments such as radiation and high temperature. However, to be a plausible alternative to solid-state electronics, nanoscale vacuum channel devices need to be fabricated on the wafer scale using established integrated circuit manufacturing techniques. Here, we show that nanoscale vacuum channel transistors can be fabricated on 150 mm silicon carbide wafers. Our devices have a vertical surround-gate configuration and we show that their drive current scales linearly with the number of emitters on the source pad. The silicon carbide vacuum devices are also compared to identically sized silicon vacuum channel transistors, which reveals that the silicon carbide devices offer superior long-term stability.

The purpose of this white paper is to provide an overview to the NRC Decadal Survey Inner Planets Sub-Panel on key technologies required for future Venus exploration missions. It covers both heritage technologies and identifies new technologies to enable future missions in all three mission classes. The technologies will focus on mission enabling and enhancing capabilities for in situ missions, because most orbiter related sub-systems are considered heritage technologies. This white paper draws heavily on the recently completed Venus Flagship Mission study that identified key technologies required to implement its Design Reference Mission and other important mission options. The highest priority technologies and capabilities for the Venus Flagship Design Reference mission consist of: surface sample acquisition and handling; mechanical implementation of a rotating pressure vessel; a rugged-terrain landing system; and a large scale environmental test chamber to test these technologies under relevant Venus-like conditions. Other longer-term Venus Flagship Mission options will require additional new capabilities, namely a Venus-specific Radioisotope Power System; active refrigeration, high temperature electronics and advanced thermal insulation. The white paper will also argue for a technology development program, since without it future Venus missions might not be achievable.