Superpressure Balloons Research Articles

Computational Fluid Dynamics Study of Balloon System Tethered to a Stratosail

In this paper, we present a numerical study of a stratospheric balloon system tethered to a passive device, known as the Stratosail, for station-keeping operation. For scientific applications, stratospheric balloons that operate at altitudes between 15 and 20 km will need to maintain station over a fixed point above the earth for a prescribed period of time. This is a challenging problem due to the limitation of payloads and lack of an energy source. The present study uses computational fluid dynamics (CFD) simulations to analyze the drift velocity of such a balloon-Stratosail system under typical wind conditions in the stratosphere. The Stratosail is attached below the super-pressure helium balloon via a long and thin tether about 10 to 15 km below the balloon, providing a drag force to alter the flight path of the balloon. Its operation depends on the natural differences in the wind speed and wind direction at different altitudes in the atmosphere that act on the balloon and the Stratosail (spaced far apart by 10km to 15 km). In this study, we calculated the drag forces on the balloon and Stratosail for typical wind speeds at various altitudes in the stratosphere. The tether was also modelled as a cable joining the balloon and sail. With this model, the drift velocity of the system was calculated for various altitudes and the angle of attack of the sail.

Observation of Gravity Waves at the Tropical Tropopause Using Superpressure Balloons

AbstractTropical gravity wave activity is investigated using measurements of momentum fluxes gathered during Strateole‐2 superpressure balloon flights. The data set consists of eight balloon flights performed in the deep tropics from November 2019 to February 2020. The flights lasted for 2–3 months each, and in‐situ meteorological data were collected every 30 s. The relation between gravity waves and deep convection is investigated using geostationary satellite data from the NOAA/NCEP GPM_MERGIR satellite data product, at 1 h resolution. The amplitude of gravity wave momentum fluxes shows a clear dependence on the distance to the nearest convective system, with a strong decay as distance to convection increases. The largest momentum‐flux values (>mPa) are only found less than 200 km away from deep convection. The sensitivity of the wave flux to distance from convection is stronger for high frequency gravity waves (periods shorter than 60 min). Lower frequency waves tend to a non‐zero, background value away from convection, supporting some background value in gravity‐wave drag parameterizations. On the other hand, the wide range of momentum flux values observed close to the convection emphasizes the intermittent nature of the gravity‐wave source. The large scale variation of gravity‐wave intermittency within the equatorial belt is also studied. The results highlight spatial variations of gravity wave activity, with the highest momentum flux recorded over land.

Influence of polyethylene terephthalate/ polyamide (PET/PA) bilayer structure on physical and strength-related properties of superpressure angioplasty balloons.

Percutaneous transluminal coronary angioplasty (PTCA), including balloon angioplasty, is a standard clinical invasive treatment for coronary artery disease. The coronary lesion with calcification is difficult to dilate and the prevention of balloon failure is especially important. A novel superpressure balloon was fabricated with bilayered structure of polyethylene terephthalate (PET) and PA12 (polyamide). The structures of bilayer balloon were adjusted to achieve overall excellent performance. Physicochemical, thermal and mechanical properties of bilayer balloons were characterized by X-ray diffraction, differential scanning calorimeter, hydraulic tester and theoretical simulation. Compared with pure PA12 and PET balloons, PA12 outer layer: PET inner layer balloon with layer ratio of 3:7 shows the highest burst stress and relatively low compliance due to an increase in crystallinity and orientation. The produced bilayer balloon proved to possess a small folding dimension thanks to its ultrathin bilayer structure, which is good for crossing cramped vessels. We believe these optimally fabricated bilayer balloons are proved to provide attractive opportunities for preparation, performance enhancement, and practical applications of super-pressure balloon catheters and cryoablation balloons, that will significantly promote the development of percutaneous transluminal coronary angioplasty for clinical applications.

Observational Validation of Parameterized Gravity Waves From Tropical Convection in the Whole Atmosphere Community Climate Model

AbstractTropical gravity waves that are generated by convection are generally too small in scale and too high in frequency to be resolved in global climate models, yet their drag forces drive the important global‐scale quasi‐biennial oscillation (QBO) in the lower stratosphere, and models rely on parameterizations of gravity wave drag to simulate the QBO. We compare detailed properties of tropical parameterized gravity waves in the Whole Atmosphere Community Climate Model version 6 (WACCM6) with gravity waves observed by long‐duration superpressure balloons and also compare properties of parameterized convective latent heating with satellite data. Similarities and differences suggest that the WACCM6 parameterizations are excellent tools for representing tropical gravity waves, but the results also suggest detailed changes to the gravity wave parameterization tuning parameter assumptions that would bring the parameterized waves into much better agreement with observations. While WACCM6 currently includes only nonstationary gravity waves from convection, adding gravity waves generated by the steady component of the heating that are stationary relative to moving convective rain cells is likely to improve the simulation of the QBO in the model. The suggested changes have the potential to alleviate common biases in simulated QBO circulations in models.

Toward Transient Subgrid-Scale Gravity Wave Representation in Atmospheric Models. Part I: Propagation Model Including Nondissipative Wave–Mean-Flow Interactions

AbstractCurrent gravity wave (GW) parameterization (GWP) schemes are using the steady-state assumption, in which an instantaneous balance between GWs and mean flow is postulated, thereby neglecting transient, nondissipative interactions between the GW field and the resolved flow. These schemes rely exclusively on wave dissipation, by GW breaking or near critical layers, as a mechanism leading to forcing of the mean flow. In a transient GWP, without the steady-state assumption, nondissipative wave–mean-flow interactions are enabled as an additional mechanism. Idealized studies have shown that this is potentially important, and therefore the transient GWP Multiscale Gravity Wave Model (MS-GWaM) has been implemented into a state-of-the-art weather and climate model. In this implementation, MS-GWaM leads to a zonal-mean circulation that agrees well with observations and increases GW momentum-flux intermittency as compared with steady-state GWPs, bringing it into better agreement with superpressure balloon observations. Transient effects taken into account by MS-GWaM are shown to make a difference even on monthly time scales: in comparison with steady-state GWPs momentum fluxes in the lower stratosphere are increased and the amount of missing drag at Southern Hemispheric high latitudes is decreased to a modest but nonnegligible extent. An analysis of the contribution of different wavelengths to the GW signal in MS-GWaM suggests that small-scale GWs play an important role down to horizontal and vertical wavelengths of 50 km (or even smaller) and 200 m, respectively.

Recent Developments on the Super-Pressure Balloon with a Diamond Shaped Net — Ground Inflation Tests of Two 2,000 m<sup>3</sup> Balloons —

Recent Developments on the Super-Pressure Balloon with a Diamond Shaped Net — Ground Inflation Tests of Two 2,000 m<sup>3</sup> Balloons —

Autonomous navigation of stratospheric balloons using reinforcement learning.

Efficiently navigating a superpressure balloon in the stratosphere1 requires the integration of a multitude of cues, such as wind speed and solar elevation, and the process is complicated by forecast errors and sparse wind measurements. Coupled with the need to make decisions in real time, these factors rule out the use of conventional control techniques2,3. Here we describe the use of reinforcement learning4,5 to create a high-performing flight controller. Our algorithm uses data augmentation6,7 and a self-correcting design to overcome the key technical challenge of reinforcement learning from imperfect data, which has proved to be a major obstacle to its application to physical systems8. We deployed our controller to station Loon superpressure balloons at multiple locations across the globe, including a 39-day controlled experiment over the Pacific Ocean. Analyses show that the controller outperforms Loon's previous algorithm and is robust to the natural diversity in stratospheric winds. These results demonstrate that reinforcement learning is an effective solution to real-world autonomous control problems in which neither conventional methods nor human intervention suffice, offering clues about what may be needed to create artificially intelligent agents that continuously interact with real, dynamic environments.

Balloon‐Borne Observations of Short Vertical Wavelength Gravity Waves and Interaction With QBO Winds

AbstractThe quasi‐biennial oscillation (QBO), a ubiquitous feature of the zonal mean zonal winds in the equatorial lower stratosphere, is forced by selective dissipation of atmospheric waves that range in periods from days to hours. However, QBO circulations in numerical models tend to be weak compared with observations, probably because of limited vertical resolution that cannot adequately resolve gravity waves and the height range over which they dissipate. Observations are required to help quantify wave effects. The passage of a superpressure balloon (SPB) near a radiosonde launch site in the equatorial Western Pacific during the transition from the eastward to westward phase of the QBO at 20 km permits a coordinated study of the intrinsic frequencies and vertical structures of two inertia‐gravity wave packets with periods near 1 day and 3 days, respectively. Both waves have large horizontal wavelengths of about 970 and 5,500 km. The complementary nature of the observations provided information on their momentum fluxes and the evolution of the waves in the vertical. The near 1 day westward propagating wave has a critical level near 20 km, while the eastward propagating 3‐day wave is able to propagate through to heights near 30 km before dissipation. Estimates of the forcing provided by the momentum flux convergence, taking into account the duration and scale of the forcing, suggests zonal force of about 0.3–0.4 m s−1 day−1 for the 1‐day wave and about 0.4–0.6 m s−1 day−1 for the 3‐day wave, which acts for several days.

Project of high altitude balloon launched micro glider: Aircraft design, control and flight test

This paper presents the design details and flight tests validation of printed circuit board fabricated micro gliders. The purpose of the micro glider is to be launched from a super pressure balloon at high altitude, glide to the target position to collect data and upload data to the staying balloon. The mission demand requires the micro glider to finish precise landing with small size and low fabrication cost. To complete this concept, we designed a PCB fabricated aircraft with limited sensors including GPS and IMU. The first part of the article describes the aerodynamic design methods. The second part introduced the control and guidance system design by controlling the roll angle and flight path angle to complete the precise landing. In the simulation results presented in the third part, launch with no wind condition shows desirable precise landing ability. As a contrast, wind direction and magnitude have significant effects on the guidance ability and accuracy. In the last part, two real flight tests conducted in Inner Mongolia of China are described to compare the flight performance with the current aerodynamics and control system design. Returned data indicated the micro gliders could successfully fly at high altitude. The control algorithm can compute the command roll angle only with GPS and IMU, but some design details still need to be improved to achieve precise landing ability.

Simultaneous uniaxial creep testing of time-dependent membrane materials with optical devices

Membrane materials have been widely used in the fields of building structures, super-pressure balloons, stratosphere airships and space deployable antennas. Among the material properties, long-term creep of membranes is a very essential factor in influencing the structural safety. This paper thus presents the simultaneous uniaxial creep testing of a typical time-dependent membrane material with optical devices. To achieve this goal, a low-cost testing method integrated with a main frame, some special clamps and loading weights was firstly developed together with the optical devices for measuring deformations. Then, in order to validate this method, 7-day uniaxial creep tests were carried out on ethylene tetrafluoroethylene (ETFE) foils with simultaneously considering eight groups of loading stresses. Additionally, 24-hour creep tests of ETFE foils were also carried out with the same eight loading stresses with an electronic universal machine. The 24-hour strain-time curves of ETFE foils agree well between two methods with the 4.59% maximum error, resulting in validating the effectiveness of the 7-day curves. These findings confirm the high efficiency for the presented simultaneous uniaxial creep testing method of time-dependent membrane materials with optical devices.

Computational method for in-situ finite element modeling of inflatable membrane structures based on geometrical shape measurement using photogrammetry

Inflatable membrane structures with the advantages of light weight, large span, long duration and aesthetical appearance have gained considerable attentions from buildings, super-pressure balloons, airships and deployable antennas. This paper presents a novel computational method for in-situ finite element modeling of inflatable membrane structures based on geometrical shape measurement using photogrammetry for further structural analysis. Firstly, kinematic equations of membrane link structure simplified from the measured inflatable membrane structure are established on force equilibrium between membrane internal and external forces to calculate the tensile forces. Then, computational method for solving zero-stress state is proposed through unloading internal pressure based on equilibrium matrix theory. Finally, true finite element model is established through numerical simulation of reloading internal pressure with considering the zero-stress state as initial model. For verifying purpose, inflated forming and normal working tests of an ethylene-tetrafluoroethylene (ETFE) air-inflated cushion structure were carried out. By comparing geometrical shapes and stress distributions of ETFE cushion between numerical and experimental results, good agreements with 0.72% and 4.76% maximum errors are acquired. These findings strongly confirm the need of in-situ finite element modeling of inflatable membrane structures undergoing long-term service and provide an effective computational method for further structural analysis.

Benchmarking simulations of the Compton Spectrometer and Imager with calibrations

The Compton Spectrometer and Imager (COSI) is a balloon-borne gamma-ray (0.2-5 MeV) telescope designed to study astrophysical sources. COSI employs a compact Compton telescope design utilizing 12 high-purity germanium double-sided strip detectors and is inherently sensitive to polarization. In 2016, COSI was launched from Wanaka, New Zealand and completed a successful 46-day flight on NASA's new Super Pressure Balloon. In order to perform imaging, spectral, and polarization analysis of the sources observed during the 2016 flight, we compute the detector response from well-benchmarked simulations. As required for accurate simulations of the instrument, we have built a comprehensive mass model of the instrument and developed a detailed detector effects engine which applies the intrinsic detector performance to Monte Carlo simulations. The simulated detector effects include energy, position, and timing resolution, thresholds, dead strips, charge sharing, charge loss, crosstalk, dead time, and detector trigger conditions. After including these effects, the simulations closely resemble the measurements, the standard analysis pipeline used for measurements can also be applied to the simulations, and the responses computed from the simulations are accurate. We have computed the systematic error that we must apply to measured fluxes at certain energies, which is 6.3% on average. Here we describe the detector effects engine and the benchmarking tests performed with calibrations.

Using Project Loon Superpressure Balloon Observations to Investigate the Inertial Peak in the Intrinsic Wind Spectrum in the Midlatitude Stratosphere

AbstractLocation information from superpressure balloons flown by Project Loon provide an unprecedented opportunity to analyze wind fields in the midlatitude stratosphere. Horizontal velocity spectra from the balloons' quasi‐intrinsic frame of reference show clear evidence of a persistent peak in the intrinsic wind spectrum around the inertial frequency. In the Southern Hemisphere midlatitudes, peak‐to‐peak amplitudes of horizontal velocity perturbations (on the order of 20 m/s) are larger than those seen in previous superpressure balloon campaigns in polar regions and similar to those observed in vertical soundings in the midlatitudes. A rotary spectral analysis shows that near‐circular anticyclonic rotation of horizontal wind perturbations around the inertial frequency dominate at most times and locations. The strongest anticyclonic rotation is more common in balloon flight segments with weak zonal winds and during the austral summer. Flight segments with strong eastward zonal velocities during austral winter and spring are more likely to have mixed cyclonic and anticyclonic power around the inertial frequency. These results confirm previous model and radiosonde observations of the peak in horizontal kinetic energy at the inertial frequency and demonstrate they are associated with increased anticyclonic wave power indicative of near‐inertial oscillations or inertia‐gravity waves. Flight segments with mixed cyclonic and anticyclonic power around the inertial frequency display a continuum of wave power from planetary to gravity wave scales. These results help explain the divergence of actual and modeled balloon trajectories in previous studies and provide a baseline against which reanalysis or meteorological model realizations of the intrinsic velocity field can be assessed.

The EUSO-SPB2 mission

EUSO-SPB2 is a second generation Extreme Universe Space Observatory (EUSO) on a Super-Pressure Balloon (SPB). The mission broadens the scientific objectives of the JEM-EUSO program and constitutes the first step toward the study of neutrino signals from the high atmosphere and space.The EUSO-SPB2 science payload will be equipped with two detectors designed for a long duration mission. One is a fluorescence telescope developed to detect Ultra High Energy Cosmic Rays via the UV fluorescence emission of the particle showers generated in the atmosphere. The other telescope will measure Cherenkov light emission from showers of lower energy cosmic rays to study and measure the background contribution for detecting cosmogenic neutrinos. These specific techniques and detection methods are performed in light of the realization of the Probe of Extreme Multi Messenger Astronomy (POEMMA), a space mission, currently under NASA-funded conceptual design studies. The EUSO-SPB2 mission has been approved by NASA and foreseen to be launched in 2022.In this paper we will give a description of the payload, including details on the detection techniques and the telescopes design.

Global Assimilation of Loon Stratospheric Balloon Observations

AbstractAccurate analyses of stratospheric winds are important for determining realistic constituent transport and providing improved diagnostic studies and forecasts of the stratosphere. This study examines impacts on global meteorological analyses resulting from using winds derived from Loon superpressure balloons in the lower stratosphere (hereafter Loon winds) as additional input observations to the Goddard Earth Observing System (GEOS) data assimilation system. To fully investigate the impacts of assimilating the Loon winds, two steps are taken: (1) comparison of the GEOS analysis winds with Loon winds (Control experiment) and (2) examination of the impacts of assimilating the Loon winds into the GEOS data assimilation system (Loon experiment). The time period selected is June–August 2014 when over 150 Loon balloons were launched, mainly in the Southern Hemisphere. In the middle latitudes, the Loon winds and Control winds agree well (Loon balloon zonal wind observation minus forecast, O − F, root‐mean‐square (RMS) values of ~2.75 m/s) and assimilating the Loon winds has a small impact (O − F RMS values unchanged). In the tropics, the Loon observations and Control analysis winds differ more than in middle latitudes (zonal wind O − F RMS ~3.75 m/s) and assimilating the Loon winds improves the zonal wind O − F RMS by ~1 m/s. In selected cases where the Loon observations and Control analysis differ greatly (O − F RMS values greater than 10 m/s), assimilating Loon winds significantly decreases the zonal wind O − F RMS by 5 m/s. These decreases in O − F RMS values show that the 6‐hr forecasts are improved at the Loon balloon observation locations.

Accuracy of Balloon Trajectory Forecasts in the Lower Stratosphere

This paper investigates the accuracy of simulated long-duration super-pressure balloon trajectories in the lower stratosphere. The observed trajectories were made during the (tropical) Pre-Concordiasi and (polar) Concordiasi campaigns in 2010, while the simulated trajectories are computed using analyses and forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System model. In contrast with the polar stratosphere situation, modelling accurate winds in the tropical lower stratosphere remains challenging for numerical weather prediction systems. The accuracy of the simulated tropical trajectories are quantified with the operational products of 2010 and 2016 in order to understand the impact of model physics and vertical resolution improvements. The median errors in these trajectories are large (typically ≳ 250 km after 24 h), with a significant negative bias in longitude, for both model versions. In contrast, using analyses in which the balloon-borne winds have been assimilated reduces the median error in the balloon position after 24 h to ∼60 km. For future campaigns, we describe operational strategies that take advantage of the geographic distribution and the episodic nature of large error events to anticipate the amplitude of error in trajectory forecasts. We finally stress the importance of a high vertical resolution in the model, given the intense shears encountered in the tropical lower stratosphere.

Results of the missions within JEM-EUSO program

The JEM-EUSO program includes several missions employing fluorescence detectors to make a proof-of-principle of the UHECR observation from space and to raise the technological level of the instrumentation to be employed in a space mission like K-EUSO and POEMMA. EUSO-TA, installed at the Telescope Array (TA) site in Utah in 2013, has already detected 9 UHECRs in coincidence with TA Fluorescence Detector. EUSO-Balloon flew on board a stratospheric balloon in 2014. It measured the UV intensity on forests, lakes and the city of Timmins as well as proved the observation of UHECR-like events by shooting laser tracks. EUSO-SPB was launched on board a Super Pressure Balloon (SPB) in 2017. It proved the functionality of all the subsystems of the telescope on a long term; observed the UV emission on oceans and had a self-trigger system to detect UHECRs. A more ambitious mission (EUSOSPB2) is planned. TUS, on board the Lomonosov satellite in orbit since 2016, has detected a few interesting signals in the UHECR trigger-mode. Mini-EUSO is in a final phase of integration and will be installed inside the International Space Station (ISS) in 2019. The main results obtained so far by these experiments are summarized.

Flight performance simulation and station-keeping endurance analysis for stratospheric super-pressure balloon in real wind field

For the absence of the propeller system to resist wind load, the balloon will float everywhere with unstable position. In order to fix the balloon within a specific district and extend the station-keeping endurance, an effective approach that utilizes the wind from different directions by altering the float altitude was proposed. A program was developed to simulate the flight performance and the station-keeping endurance of the stratospheric super-pressure balloon in the real wind field. The influences of the initial Helium volume ratio and the float altitude on the traveled horizontal distance of the balloon were analyzed. The results indicate that the altitude of the balloon fluctuates with the change of the volume of the balloon during the day-night cycle, providing the possibility to catch the wind from different directions. By choosing the appropriate Helium volume ratio and float altitude, the traveled horizontal distance of the balloon can be shortened greatly. Our study can provide guidance for investigation on active control algorithm for station-keeping of the balloon that can fix the balloon within the desired district for months and years.

Cloud distribution evaluated by the WRF model during the EUSO-SPB1 flight

EUSO-SPB1 was a balloon-borne mission of the JEM-EUSO (Joint Experiment Missions for Extreme Universe Space Observatory) Program aiming at the ultra-high energy cosmic ray (UHECR) observations from space. We operated the EUSO-SPB1 telescope consisting of 1 m2 Fresnel refractive optics and multi-anode photomultiplier tubes. With a total of 2304 channels, each performed the photon counting every 2.5 µs, allowing for spatiotemporal imaging of the air shower events in an ~ 11°× 11° field of view. EUSO-SPB1 was the first balloon-borne fluorescence detector with a potential to detect air shower events initiated by the EeV energy cosmic rays. On 24 April 2017 UTC, EUSO-SPB1 was launched on the NASA’s Super Pressure Balloon that flew at ~16 – 33 km flight height for ~12 days. Before the flight was terminated, ~27 hours of data acquired in the air shower detection mode were transmitted to the ground. In the present work, we aim at evaluating the role of the clouds during the operation of EUSO-SPB1. We employ the WRF (Weather Research and Forecasting) model to numerically simulate the cloud distribution below EUSO-SPB1. We discuss the key results of the WRF model and the impact of the clouds on the air shower measurement and the efficiency of the cosmic ray observation. The present work is a part of the collaborative effort to estimate the exposure for air shower detections.

Results from the first missions of the JEM-EUSO program

The origin and nature of Ultra-High Energy Cosmic Rays (UHECRs) remain unsolved in contemporary astroparticle physics. To give an answer to these questions is rather challenging because of the extremely low flux of a few per km2 per century at extreme energies such as E > 5 × 1019 eV. The objective of the JEM-EUSO program, Extreme Universe Space Observatory, is the realization of a space mission devoted to scientific research of cosmic rays of highest energies. Its super-wide-field telescope will look down from space onto the night sky to detect UV photons emitted from air showers generated by UHECRs in the atmosphere. The JEM-EUSO program includes different missions using fluorescence detectors to make a proof-of-principle of the UHECR observation from space and to raise the technological level of the instrumentation to be employed in a space mission. EUSO-TA, installed at the Telescope Array site in Utah in 2013, is in operation. It has already detected 9 UHECRs in coincidence with Telescope Array fluorescence detector at Black Rock Mesa. EUSO-Balloon flew on board a stratospheric balloon in August 2014. It measured the UV intensity on forests, lakesandthecityofTimminsaswellasprovedtheobservationofUHECR-likeeventsbyshootinglasertracks. EUSO-SPB was launched on board a super pressure balloon on April 25th and flew for 12 days. It proved the functionality of all the subsystems of the telescope on a typical duration of a balloon flight; observed the UV emission on oceans and has a self-trigger system to observe UHECRs with energy E > 3×1018 eV. TUS, the Russian mission on board the Lomonosov satellite in orbit since April 28th 2016, is now included in the JEMEUSO program and has detected so far in the UHECR trigger-mode a few interesting signals. Mini-EUSO is in its final phase of integration in Italy, where several performance tests are being held. Mini-EUSO will be installed inside the International Space Station (ISS) in 2019. The main results obtained so far by such missions are summarized and put in prospect of future space detectors such as K-EUSO and POEMMA.