Abstract Low frequency sound can travel great distances in planetary atmospheres. When these waves reflect off the air/ground interface, energy may be absorbed or transferred to mechanical waves in the subsurface. This study describes the direct and reflected acoustic wave generated by the re‐entry of the OSIRIS‐REx Sample Return Capsule captured on a pair of balloon‐borne recorders. Reflection attenuation at high incidence angles on alluvium deposits are minimal below 10 Hz. Frequency‐dependent ground absorption between 10 and 50 Hz was evident on a low‐floating platform, but masked by atmospheric attenuation and nonlinear wave propagation at higher altitudes. These results bridge the gap between near‐lossless reflection assumed by infrasound studies and frequency‐dependent losses noted in the low audio range.

Aerial robotic platforms (aerobots) can perform landmark investigations in geophysics (seismology, magnetism) and atmospheric science (dynamics, chemistry, astrobiology) while operating in the middle atmosphere of Venus (similar to 55 km); however, without the ability to replenish buoyant gases, aerobot lifetime is constrained due to helium loss from the balloon envelope. While dropping ballast can improve aerobot lifetime, ballast drops are a consumable solution that is not scalable to long-duration missions. Exploring Venus with Electrolysis (EVE) is a mission concept currently under development that has investigated technology gaps to increase the nominal mission lifespan of a Venus aerobot by leveraging in-situ resource utilization (ISRU) to replace the lost helium from a balloon with the products of Solid Oxide Electrolysis (SOE). SOE, as demonstrated by the Mars Oxygen ISRU Experiment (MOXIE), can electrolyze the 97% carbon dioxide atmosphere of Venus into carbon monoxide and oxygen to be used as buoyant lifting gases. This work introduces the proposed aerobot mission and outlines the technology gaps investigated by the EVE project. A detailed system model of a Venus ISRU-equipped aerobot is presented, and a hyperparameter grid search simulation compares traditional aerobot designs with ISRU-equipped designs to identify competitive architectures. In all cases, aerobots that leverage ISRU outperform their non-ISRU counterparts.

One of NASA's priorities is to investigate the internal structure of Venus by measuring the signatures of seismic activity. Seismic activity has never been measured at Venus because the high surface temperature and pressure severely limit the lifetime of current state-of-the-art electronic components and conventional approaches to monitoring seismic activity. However, seismic activity generates low-frequency pressure waves known as infrasound. Given the high atmospheric density on Venus, ground motion couples with the atmosphere 60 times better than on Earth. These waves may be detected directly from balloons floating in the Earth-like temperature and pressure at similar to 50-60 km altitude on Venus. Infrasound originating from seismic events has been successfully detected using barometers deployed on high-altitude balloons on Earth. This paper will focus on our development of a miniaturized infrasound sensor assembly that can be arrayed for operation on a balloon or multi-balloon platforms. The primary capability that we are seeking is the accurate sensing of the infrasonic pressure levels. However, we are also looking to determine directional dependencies via sound localization techniques with vector infrasound or time of arrival differences on a large array baseline. The developed infrasonic sensors array will have a detection limit approaching 0.005 Pa over a bandwidth of 0.05 to 10 Hz. This sensitivity will allow detecting quakes having a magnitude similar to 5 at a distance of 1000 km. In order to enable and enhance this technology for planetary exploration, we are basing our design on a lightweight low power flex circuit that allows for data acquisition and control of a variety of infrasonic sensors including piezoresistive pressure sensors, resonance pressure sensors. Also, the instrument assembly includes a rigidly fixed and flex circuit tethered lightweight BNO055 Inertial Measurement Units (IMU) for differential acceleration corrections and vector infrasonic sensing. The current design is controlled via an ESP32-PICO microcontroller with an external Analog to Digital Converter ADC and has a serial CP2102 (USB to UART bridge) for programming the microcontroller and data access. In our final application we will program directly via contact pads and transmit data via a serial bus or a wireless adaptor. For a multi-balloon measurement scenario, we are investigating the use of LoRa or other extended range low power communications options. This paper will focus on our flex board designs and novel resonance, vector infrasound sensor designs, and the initial testing of these array elements. These tests will be done in an infrasonic testbed that we developed at JPL to quantify and compare our system with state-of-the-art infrasonic sensors developed for Earth applications. Although primarily designed for Venus applications these sensor arrays have the potential for exploration on other planetary bodies with atmospheres for monitoring fluctuations in atmospheric pressure caused by other physical processes that move atmospheric gas including volcanoes, thunder, ocean waves, wind and bolide entry.

This paper details a significant milestone toward maturing a buoyant aerial robotic platform, or aerobot, for flight in the Venus clouds. We describe two flights of our subscale altitude-controlled aerobot, fabricated from the materials necessary to survive Venus conditions. During these flights over the Nevada Black Rock Desert, the prototype flew at the identical atmospheric densities as 54-55 km cloud layer altitudes on Venus. We further describe a first-principle aerobot dynamics model, which we validate against the Nevada flight data and subsequently employ to predict the performance of future aerobots on Venus. The aerobot discussed in this paper is under JPL and Aerostar development for an in-situ mission flying multiple circumnavigations of Venus, sampling the chemical and physical properties of the planet's atmosphere and also remotely sensing surface properties.

Sample return capsules (SRCs) entering Earth’s atmosphere at hypervelocity from interplanetary space are a valuable resource for studying meteor phenomena. The 2023 September 24 arrival of the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer SRC provided an unprecedented chance for geophysical observations of a well-characterized source with known parameters, including timing and trajectory. A collaborative effort involving researchers from 16 institutions executed a carefully planned geophysical observational campaign at strategically chosen locations, deploying over 400 ground-based sensors encompassing infrasound, seismic, distributed acoustic sensing, and Global Positioning System technologies. Additionally, balloons equipped with infrasound sensors were launched to capture signals at higher altitudes. This campaign (the largest of its kind so far) yielded a wealth of invaluable data anticipated to fuel scientific inquiry for years to come. The success of the observational campaign is evidenced by the near-universal detection of signals across instruments, both proximal and distal. This paper presents a comprehensive overview of the collective scientific effort, field deployment, and preliminary findings. The early findings have the potential to inform future space missions and terrestrial campaigns, contributing to our understanding of meteoroid interactions with planetary atmospheres. Furthermore, the data set collected during this campaign will improve entry and propagation models and augment the study of atmospheric dynamics and shock phenomena generated by meteoroids and similar sources.

We use a customized radiative transfer model to show that sharp (∼10 m resolution) images of the Venus surface can be achieved at night in spectral windows free of CO2 absorption found between 1.0 and 1.2μm using a camera at 47 km altitude, just below the planet’s optically thick clouds. This is in spite of the Rayleigh scattering by the dense but still semi-transparent lower atmosphere, and the potential for underlying hazes beneath the clouds. The thermal radiation transmitted directly to the camera forms images of spatially varying surface emissivity and/or temperature at the native sensor resolution, platform stability permitting and under reasonable seeing conditions. Near-isotropic Rayleigh scattering dominates in the 1.0μm window. Combined with near-Lambertian reflections off the base of the cloud layer, the diffuse light field builds up a background radiance from surface emission averaged spatially out to several 10s of km, i.e., beyond the camera’s field-of-view. At the longer wavelengths (1.1 and 1.18μm windows), the sub-cloud atmosphere itself partially absorbs (hence less direct light), and therefore weakly emits (hence more background light), but the rapidly decreasing Rayleigh scattering compensates and contrast is maintained. In all cases, we demonstrate that the directly-transmitted surface-leaving radiance from the native sensor resolution element (∼10 m) is a significant fraction of the total radiance, and thus can be detected above the background light. Extending down to the 0.85 and 0.90μm spectral windows, there is less direct and more background due to the enhanced Rayleigh scattering, but the resulting reduction in contrast can be mitigated by co-adding the ∼10 m pixels. This technological advance will open a new era in Venusian geology by enabling discrimination between different surface materials at fine scales. Moreover, potentially active volcanism on our sister planet may be revealed by surface spots that are much hotter than their surroundings.

The atmospheric radio occultation (RO) technique was developed six decades ago for planetary missions and has since resulted in numerous scientific discoveries throughout the Solar System. The traditional experimental configuration utililizes spacecraft communication links with phase-stable radio signals transmitted from a spacecraft orbiting or flying past a planet and received at a ground station after propagating through the atmosphere. Alterations in the phase and amplitude are used to infer properties of that atmosphere. A reverse configuration with a ground-to-spacecraft one-way link has been used with the appropriately instrumented mission to Pluto to overcome severe signal-to-noise ratio limitations. A more recently investigated spacecraft-to-spacecraft occultation technique utilizes UHF communication links between Mars landers and orbiters to measure ionospheric properties.In 1995, the Earth science community demonstrated a variation of this technique that enabled remote sensing of Earth’s atmosphere and ionosphere. By tracking spacecraft-to-spacecraft crosslinks utilizing the global navigation satellite constellations as the transmitting terminals and specially instrumented satellites as the receiving terminals, high resolution vertical profiles are routinely retrieved with valuable utility in numerical weather prediction and atmospheric dynamics. Applying crosslinks more generally to planetary missions would allow large increases in spatial and temporal coverage of atmospheric structures and composition; however, this has been prohibitively costly until recent technological advances and breakthroughs.The advances of the required technologies for crosslink RO experiments currently enable realistic planning of their use in future planetary missions. These crosslinks could use orbiting small spacecraft for one or multiple links, and possibly probes, aerobots (e.g., balloons), and landers equipped for relay communications. These technologies and techniques include:1.Small software-defined radios2.Multi-frequency communication links3.Smaller ultra-stable oscillators4.Advancedsignal processing and holographic methods5.Interplanetary flight, orbit insertion, and formation-flyingThis paper presents the state of the art of these technologies and introduces lower cost mission concepts to Venus, the giant planets, and other planetary targets in the context of recent Decadal Surveys. These multi-spacecraft missions provide natural opportunities for international collaboration. Design requirements, recent simulations, radio-holographic analysis methods, and lessons from an opportunistic UHF crosslink demonstration at Mars will be discussed.

Balloon-based seismology through the study of low-frequency seismo-acoustic signals (infrasound) has gained acceptance as a viable way to study seismic activity on Venus. Balloon-based barometers have the potential to detect and characterize atmospheric waves launched by venusquakes and volcanic eruptions while offering substantially longer instrument lifetimes in the Venus middle atmosphere, where temperature and pressure are significantly more benign (0–100°C, ∼1 atm) as compared to the surface (>460 °C, ∼90 atm). One of the major challenges in performing balloon-based seismology on Venus is the absence of ground-truth data for event identification and discrimination. To address this challenge, our activities are aimed at building a catalog of terrestrial balloon-recorded infrasound signals of geophysical provenance, using which signal predictions can be extended to Venus and the detectability of events can be analyzed. We will highlight our recently concluded Balloon-based Acoustic Seismology Study (BASS) flight campaign, which served as Earth-analog experiments for Venus balloon-based seismology. Data collected were used to validate seismo-acoustic simulation tools, which are being expanded to include the Venus atmosphere. These tools will used to generate predictions of infrasound signals from geophysical events on Venus. We will also provide perspective on directions for future instrument development for Venus balloon flights.

Does radiometry (e.g., signal-to-noise ratio) limit the performance of near-IR subcloud imaging of our sister planet's surface at night? It does not. We compute subcloud radiometry using above-cloud observations, an assumed ground temperature, sub-cloud absorption and emission modeling, and Rayleigh scattering simulations. We thus confirm both archival and recent studies that deployment of a modest subcloud camera does enable high-resolution surface imaging.

Venus is essential to our understanding of the evolution and habitability of Earth-size planets throughout the galaxy. The selection of the VERITAS, EnVision, and DAVINCI missions by NASA and ESA in June 2021 is an important step in advancing the science. However, addressing many of the most challenging questions will require in situ platforms that can operate in the Venus environment for extended periods in order to capture the full complexity of our sister planet. Aerobots are aerial vehicles that exploit buoyancy to achieve long-duration operation in the Venus cloud layer where environmental conditions are comparatively benign. Buoyancy control, explained in more detail in a companion paper at this conference, allows aerobots to change altitude with little energy expenditure enabling new scientific measurement opportunities. These include atmospheric chemistry, dynamics, geophysical measurements of the crust and interior and geological investigations enabled by high resolution surface imaging. One aspect to our approach to defining missions that fit within the resource constraints of competitive missions is keeping the scale small. Today's science-driven appetite for sophisticated measurements and large volumes of data is driving size upwards but advances in technology can enable aerobots that can be delivered to Venus at manageable costs. The other aspect is supporting the aerobot at Venus with orbiters providing data relay, localization and synergistic science. The recently selected orbiters, equipped with low-cost proximity relay systems routinely used at Mars may obviate the need for dedicated orbiters thereby enabling Discovery mission candidates. Four aerobot mission concepts have been defined which fit comfortably within the current New Frontiers (NF) cost cap ($900M in $FY22). One of these concepts would also be a candidate for a Discovery mission if that cost cap ($500M in $FY19) were raised. Raising the NF cost cap would enable more capable aerobot missions combining both altitude control with synergistic orbital observations. Investigations of surface geology at high resolution with subcloud NIR nightside imaging and dropsondes on the dayside of Venus could also benefit from collaborations with foreign contributions.

In-situ exploration of Venus is challenging due to its severe environment, which is benign (-25 ???C and 1 bar) at an altitude of 55 km, but rapidly becomes hostile at lower altitudes. The temperature increases to -465 ???C, and pressure reaches 90 bars at the surface. These conditions have limited in-situ missions to high altitude balloons at 55 km that survived only 48 h. High-altitude balloon missions are stymied by the opaqueness of the Venusian clouds and constant altitude. Long-duration, extended range variable-altitude balloons covering below the clouds could enhance the science capabilities of the missions by measuring chemical species, isotopes and atmospheric flow patterns in and underneath the clouds. A new energy storage system tolerant to the high temperatures at low altitudes is needed to support such a balloon. A novel variable altitude balloon architecture with an extended range of 55???20 km (VAB-X) was developed under the NASA Innovative and Advanced Concepts (NIAC) program and is described here. The architecture comprises a high-temperature tolerant balloon and photovoltaic array for providing spacecraft power, a reversible solid oxide fuel (SOFC) for low-altitude power and fuel regeneration, and reversible metal hydride (MH) for hydrogen storage. Hydrogen is used for the buoyancy and altitude control of the zero-pressure balloon and as fuel for SOFC. Water brought from Earth can replenish the hydrogen lost to leaks during the mission. Preliminary analyses reveal the efficacy of the architecture for long-term Venus exploration over 55-20 km altitude, with a high proportion (-20%) of the total suspended mass (>20 kg) available for science payload.

A quantitative and comparative assessment of the feasibility and mass benefit of using aerocapture at all atmosphere-bearing solar system destinations is presented, considering both lift and drag modulation control techniques. Aerocapture is shown to be feasible at Mars, Titan, and Venus with existing entry vehicles and flight-proven thermal protection system (TPS) materials, and requires no significant technology developments before use on a science mission. Aerocapture at Uranus and Neptune is viable with blunt-body aeroshells (L/D of 0.30-0.40) and Heatshield for Extreme Entry Environment Technology TPS for certain high arrival V & INFIN; interplanetary trajectories. The mass benefit offered by aerocapture is compared to alternative orbit insertion techniques such as purely propulsive insertion and aerobraking. Aerobraking outperforms aerocapture for missions to Mars and Venus with arrival V & INFIN; less than 6 km/s. For outer planet missions, aerocapture offers substantial mass benefit depending on the arrival V & INFIN;, Titan (300-1700% more mass), Uranus (100-600%), and Neptune (80-400%), in addition to significant reduction in flight time. The study recommends a low-cost drag modulation aerocapture demonstration mission at Earth to establish flight heritage for aerocapture and lower the risk for future science missions.

The history of in-situ Venus exploration has been limited to a few opportunities with different probes that were capable to operate, for short periods of time, under the extreme atmospheric conditions of the planet. Among these missions, the VeGa balloons deployed in the Venus atmosphere in the mid-eighties of previous century revealed the advantages of using this concept for investigating the atmosphere of Venus. In this regard, the recent studies for the 2023-2030 Planetary Decadal Survey [1-3] have pointed the potential of using balloon platforms for planetary science exploration, considering that the different technologies required for these missions are currently mature enough to develop long-lived and possibly even altitude-varying probes or more specifically, aerobots. In this work, we present an early concept of a lightweight radiometer for future balloon missions to Venus. Its primary scientific objectives are: i) to measure solar and ii)thermal infrared fluxes and their deposition in the cloud layer, iii) to characterize the variability of the cloud structure and its constituents, and iv) to detect and characterize atmospheric lightning events. Those investigations will allow us to understand the role of each objective in determining the atmospheric structure and the driving circulation of the planet. Due to the limitations on resources for this kind of platforms, the key characteristics of the proposed instrument are its high scientific performance and the scarce resources needs: low accommodation volume, size, and mass; low power and data volume consumption. The radiometer combines different spectral bandpass channels (from UVA to IR) with particular orientations and field of view (FoV) selected to meet the scientific objectives. The instrument also incorporates a visible camera to provide context images for cloud investigations. The Spanish National Institute of Aerospace Technology (INTA) has established a long-term strategy in the last decade with the program InMARS [4] that is devoted to developing high-performance, low-power, miniature sensors designed for in-situ planetary missions [5-10]. Within this program, we have developed an intensive selection, qualification, and screening activity in our particular technological roadmap called CERES (Compact Electronic Resources for the Exploration of Space), which allowed INTA to acquire critical technologies, components (including mixed ASICs [11-12]), materials and procedures for such instrumentation developments. [1] K.H. Baines et al, 2020. White Pape. [2] Martha S. Gilmore et al, 2020. Venus Flagship Mission Decadal Study Final Report [3] Joseph O’Rourke, ADVENTS misión concept study. [4] I.Arruego et al. IPPW 2018. Boulder. Colorado. USA. [5] H. Guerrero et al. EGU 2010. Geophysical Research Abstracts Vol. 12, EGU2010-13330, 2010. [6] I. Arruego et al. DREAMS-SIS. ASR 2017. 60 (1): 103-120. [7] V. Apéstigue et al. Sensors.2022. [8] D. Rodionov et al. Sixth International Workshop on the Mars Atmosphere: Modelling and Observations. 2017. Granada. Spain. [9] D. Scaccabarozzi et al. IEEE MetroAeroSpace proccedings. 2019. Torino.Italy. [10] A. Russu et al. Proc. SPIE 11129. [11] S. Sordo-Ibáñez et al. IEEE Transactions on Nuclear Science, vol. 63, pp. 2379-2389, 2016. [12] S. Sordo-Ibáñez et al. IEEE Transactions on Magnetics, vol. 51, pp. 1-4, 2015

Venus aerobots, balloon-based platforms capable of floating an order-100kg spacecraft payload, are under active technology development at JPL for variable-altitude flights in the Venus cloudlayer. In this paper, we describe a roughly 1:3 subscale prototype aerobot manufactured in collaboration with Near Space Corporation. The prototype is made of the requisite materials for surviving the Venus environment from 52km to 62km altitude, including protection from sulfuric acid aerosols and the strong solar & infrared fluxes. In preparation for outdoor flights of this prototype at the relevant densities here on Earth, we present initial results from our indoor hangar calibration flights. These flights provide insight into the dynamics of these aerobots, and provide a basis for comparing our first-principle simulation models to the flight data.

We present a case for the exploration of Venus as an astrobiology target-(1) investigations focused on the likelihood that liquid water existed on the surface in the past, leading to the potential for the origin and evolution of life, (2) investigations into the potential for habitable zones within Venus' present-day clouds and Venus-like exo atmospheres, (3) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus' clouds and Venus-like atmospheres, and (4) application of these investigative approaches toward better understanding the atmospheric dynamics and habitability of exoplanets. The proximity of Venus to Earth, guidance for exoplanet habitability investigations, and access to the potential cloud habitable layer and surface for prolonged in situ extended measurements together make the planet a very attractive target for near term astrobiological exploration.

Introduction: Events on planetary surfaces and atmospheres can generate low frequency sound waves capable of traveling across regional to global scales. These waves carry information not only on the phenomenon that generated them but also the medium through which they passed. Sensitive microbarometers are used to capture these signals on Earth (e. g. the globe-spanning International Monitoring System) and Mars (the InSight lander). However, temperature and pressure conditions on the surface of Venus are inimical to long term sensor deployment, and oceans cover large regions of the Earth. In the last half decade, microbarometers on free flying balloons have emerged as an alternative to surfacebased deployments[1]. This has led to the possibility of monitoring seismic activity on Venus using acoustic waves induced by ground motion captured on balloons floating in the relatively clement cloud deck[2]. However, microbarometers deployed on a single balloon cannot determine signal direction-of-arrival; in particular, there is no practical way to ascertain the azimuth without multiple stations. We are developing the aeroseismometer, a sensor that measures the balloon acceleration induced by impinging sound waves, as an answer to this problem.