Long-duration Experiment Research Articles

Data-worth analysis for the design of the HotBENT monitoring system

The safety of a geologic repository for heat-generating nuclear waste relies in part on the long-term performance of the clay-based buffer material that surrounds the waste canisters. The sealing and waste-isolation properties of the bentonite may degrade as temperatures rise to high values. To improve the understanding of the evolution of the repository's near field and in particular the effects of increased temperatures on the bentonite buffer, a full-scale, long-duration experiment named HotBENT is underway at the Grimsel Test Site, Switzerland. The HotBENT monitoring system was designed with the support of a modelling-based data-worth analysis in which the contribution of individual sensors to the reduction in estimation or prediction uncertainties is formally evaluated. Two examples are described; the first demonstrates optimization of the monitoring system for the estimation of parameters of a clay-swelling model, whereas the second example shows how to select monitoring data that help improve the quality of model predictions needed for decision support. A data-worth analysis was considered a useful approach to identify the information content of actual and planned monitoring data for the specific objectives of the experiment. The HotBENT monitoring system was eventually designed in part based on the results presented in this paper. Thematic collection: This article is part of the Sustainable geological disposal and containment of radioactive waste collection available at: https://www.lyellcollection.org/topic/collections/radioactive

Hexagonal boron nitride nanosheets as metal-free electrochemical catalysts for oxygen reduction reactions

A high-performance ball milling technique was developed for synthesizing hexagonal boron nitride (h-BN) carbon paper (CP) electrodes as metal-free catalyst for the oxygen reduction reaction (ORR) and hydrogen storage (electrochemically) in acidic media. The h-BN nanosheets were functionalized with glycine to enhance the number of active sites and to boost the catalytic activity. The ball-milled h-BN catalytic electrodes demonstrated ultra-high catalytic activity toward electrochemical hydrogen adsorption/desorption (∼3.5 times higher than pristine electrodes) as well as ORR in acidic electrolytes. Furthermore, in-situ durability analysis of the h-BN electrodes was performed via conducting a long-duration cycling experiment (>200 cycles). A mechanistic reaction pathway (sequential) including chemisorption and charge transfer reactions (four-electron and two-electron pathways) was also proposed for the ORR. Considering superior catalytic activity of as-prepared h-BN/CP electrodes, this class of metal-free nanostructured materials can be employed as inexpensive catalysts for the electrochemical H-storage and ORR within various energy storage/conversion devices (e.g., batteries, electrolyzers, and fuel cells).

The Payload for Ultrahigh Energy Observations (PUEO): a white paper

The Payload for Ultrahigh Energy Observations (PUEO) long-duration balloon experiment is designed to have world-leading sensitivity to ultrahigh-energy neutrinos at energies above 1 EeV. Probing this energy region is essential for understanding the extreme-energy universe at all distance scales. PUEO leverages experience from and supersedes the successful Antarctic Impulsive Transient Antenna (ANITA) program, with an improved design that drastically improves sensitivity by more than an order of magnitude at energies below 30 EeV. PUEO will either make the first significant detection of or set the best limits on ultrahigh-energy neutrino fluxes.

Separation of fine waste catalyst particles from methanol-to-olefin quench water via swirl regenerating micro-channel separation (SRMS): A pilot-scale study

From the perspective of resource reserves, the development of coal-based methanol-to-olefins (MTO) technology is regarded as an important direction for the sustainable development of the chemical processing industry in China. However, the wastewater generated in the process of industrial operation has a significant impact on the stability of the process. To remove the fine waste catalyst particles from MTO quench water, a swirl regenerating micro-channel separation (SRMS) technology was developed. A 25 m3/h pilot-scale study was conducted to examine the separation and regeneration effects under different operating parameters and verify the feasibility of this technology through a long-duration experiment. Results showed that for filtration velocities ranging from 11 to 15 m/h, the total separation efficiency was 95–99 %, the removal efficiency of 0.2 μm particles was 83–90 %, and the regeneration cycle was 24–40 h while the waste catalyst particle concentration in quench water was 300–600 mg/L. The optimum regeneration water and gas speeds were determined to be 11–15 m/h and 56.6 m/h, respectively. Moreover, the performance of the pilot plant over 600 h continuous operation effect of was tested, and an average separation efficiency > 95 % with excellent regeneration was obtained.

A search for ultrahigh-energy neutrinos associated with astrophysical sources using the third flight of ANITA

The ANtarctic Impulsive Transient Antenna (ANITA) long-duration balloon experiment is sensitive to interactions of ultrahigh-energy (E>1018 eV) neutrinos in the Antarctic ice sheet. The third flight of ANITA, lasting 22 days, began in December 2014. We develop a methodology to search for energetic neutrinos spatially and temporally coincident with potential source classes in ANITA data. This methodology is applied to several source classes: the potential IceCube-identified neutrino sources TXS 0506+056 and NGC 1068, flaring high-energy blazars reported by the Fermi All-Sky Variability Analysis, gamma-ray bursts, and supernovae. Among searches within the five source classes, one candidate was identified as associated with SN 2015D, although not at a statistically significant level. We proceed to place upper limits on the source classes. We further comment on potential application of this methodology to more sensitive future instruments.

Automated Adaptation and Stabilization of a Tunable WDM Polarization-Independent Receiver on Active Silicon Photonic Platform

We demonstrate automated adaptation, and stabilization of a silicon photonic wavelength-division multiplexing (WDM), polarization-independent receiver. A two-channel, tunable WDM polarization-independent receiver is designed, and used to demonstrate automated WDM polarization control. Using a control algorithm based on Barzilai, and Borwein's two-point step size gradient descent method, we realize automated polarization adaptation, and wavelength stabilization for two arbitrarily polarized input data streams. 10 Gb/s on-off keying, and 20 Gb/s pulse-amplitude modulation 4-level formats are generated as the high-speed input data streams. In addition, we implement a long-duration experiment, in which we measure the bit-error-ratio for continuously varying polarization states, and changing chip temperatures. The experimental results show that, with the automated control, the WDM polarization-independent receiver can adapt, stabilize, and track the arbitrary input polarization states from a standard optical fiber into the transverse electric mode of a silicon waveguide, and simultaneously stabilize the transmitted wavelength channels at various chip temperatures. We also show how the presented WDM polarization-independent receiver scales with N channels, and propose an improved design for large-scale WDM applications.

Mesospheric Bore Evolution and Instability Dynamics Observed in PMC Turbo Imaging and Rayleigh Lidar Profiling Over Northeastern Canada on 13 July 2018.

Two successive mesospheric bores were observed over northeastern Canada on 13 July 2018 in high‐resolution imaging and Rayleigh lidar profiling of polar mesospheric clouds (PMCs) performed aboard the PMC Turbo long‐duration balloon experiment. Four wide field‐of‐view cameras spanning an area of ~75 × 150 km at PMC altitudes captured the two evolutions occurring over ~2 hr and resolved bore and associated instability features as small as ~100 m. The Rayleigh lidar provided PMC backscatter profiling that revealed vertical displacements, evolving brightness distributions, evidence of instability character and depths, and insights into bore formation, ducting, and dissipation. Both bores exhibited variable structure along their phases, suggesting variable gravity wave (GW) source and bore propagation conditions. Both bores also exhibited small‐scale instability dynamics at their leading and trailing edges. Those at the leading edges comprised apparent Kelvin‐Helmholtz instabilities that were advected downward and rearward beneath the bore descending phases extending into an apparently intensified shear layer. Instabilities at the trailing edges exhibited alignments approximately orthogonal to the bore phases that resembled those seen to accompany GW breaking or intrusions arising in high‐resolution modeling of GW instability dynamics. Collectively, PMC Turbo bore imaging and lidar profiling enabled enhanced definition of bore dynamics relative to what has been possible by previous ground‐based observations, and a potential to guide new, three‐dimensional modeling of bore dynamics. The observed bore evolutions suggest potentially important roles for bores in the deposition of energy and momentum transported into the mesosphere and to higher altitudes by high‐frequency GWs achieving large amplitudes.

AC electrowetting promoted droplet shedding on hydrophobic surfaces

Condensation is significantly enhanced by condensing vapor as droplets (instead of a film), which rapidly shed-off. Electrowetting (EW)-induced coalescence and shedding of droplets have been recently shown to accelerate condensation. This work studies the influence of AC electrowetting fields on short-duration droplet shedding on hydrophobic surfaces. Experiments involve tracking the shedding of an ensemble of water droplets under the influence of EW fields, with three parameters being varied (voltage, AC frequency, and device geometry). Significant physical insights into EW-induced droplet shedding are obtained. First, EW enables almost complete removal of water (dry area fraction ∼98%) in very short time durations (∼ 1 s). Second, while the dry area fraction does depend on the applied voltage, significant water shedding can be achieved without needing to apply voltages significantly higher than the threshold voltage. Third, the frequency of the AC waveform does not influence the dry area fraction (for voltages above the threshold voltage); however the time constant associated with droplet shedding strongly depends on the AC frequency. Fourth, the orientation of the device influences water removal due to electrostatic pinning of droplets. Importantly, the measured water removal fluxes immediately after the application of an EW field are two orders of magnitude higher than those measured over a long-duration condensation experiment; this highlights the benefits of intermittent EW fields as opposed to continuous EW fields. Overall, these results suggest that EW on hydrophobic surfaces offers benefits comparable to those offered by superhydrophobic surfaces.

Automated control algorithms for silicon photonic polarization receiver.

We demonstrate greedy linear descent-based, basic gradient descent-based, two-point step size gradient descent-based, and two-stage optimization method-based automated control algorithms and examine their performance for use with a silicon photonic polarization receiver. With an active feedback loop control process, time-varying arbitrary polarization states from an optical fiber can be automatically adapted and stabilized to the transverse-electric (TE) mode of a single-mode silicon waveguide. Using the proposed control algorithms, we successfully realize automated adaptations for a 10 Gb/s on-off keying signal in the polarization receiver. Based on the large-signal measurement results, the control algorithms are examined and compared with regard to the iteration number and the output response. In addition, we implemented a long-duration experiment to track, adapt, and stabilize arbitrary input polarization states using the two-point step size gradient descent-based and two-stage optimization method-based control algorithms. The experimental results show that these control algorithms enable the polarization receiver to achieve real-time and continuous polarization management.

Nanosatellites for Biology in Space: In Situ Measurement of Bacillus subtilis Spore Germination and Growth after 6 Months in Low Earth Orbit on the O/OREOS Mission.

We report here complete 6-month results from the orbiting Space Environment Survivability of Living Organisms (SESLO) experiment. The world’s first and only long-duration live-biology cubesat experiment, SESLO was executed by one of two 10-cm cube-format payloads aboard the 5.5-kg O/OREOS (Organism/Organic Exposure to Orbital Stresses) free-flying nanosatellite, which launched to a 72°-inclination, 650-km Earth orbit in 2010. The SESLO experiment measured the long-term survival, germination, metabolic, and growth responses of Bacillus subtilis spores exposed to microgravity and ionizing radiation including heavy-ion bombardment. A pair of radiation dosimeters (RadFETs, i.e., radiation-sensitive field-effect transistors) within the SESLO payload provided an in-situ dose rate estimate of 6–7.6 mGy/day throughout the mission. Microwells containing samples of dried spores of a wild-type B. subtilis strain and a radiation-sensitive mutant deficient in Non-Homologoous End Joining (NHEJ) were rehydrated after 14, 91, and 181 days in space with nutrient medium containing with the redox dye alamarBlue (aB), which changes color upon reaction with cellular metabolites. Three-color transmitted light intensity measurements of all microwells were telemetered to Earth within days of each 24-hour growth experiment. At 14 and 91 days, spaceflight samples germinated, grew, and metabolized significantly more slowly than matching ground-control samples, as measured both by aB reduction and optical density changes; these rate differences notwithstanding, the final optical density attained was the same in both flight and ground samples. After 181 days in space, spore germination and growth appeared hindered and abnormal. We attribute the differences not to an effect of the space environment per se, as both spaceflight and ground-control samples exhibited the same behavior, but to a pair of ~15-day thermal excursions, after the 91-day measurement and before the 181-day experiment, that peaked above 46 °C in the SESLO payload. Because the payload hardware operated nominally at 181 days, the growth issues point to heat damage, most likely to component(s) of the growth medium (RPMI 1640 containing aB) or to biocompatibility issues caused by heat-accelerated outgassing or leaching of harmful compounds from components of the SESLO hardware and electronics.

Analysis of temporal and spatial variability of atmospheric CO<sub>2</sub> concentration within Paris from the GreenLITE™ laser imaging experiment

Abstract. In 2015, the Greenhouse gas Laser Imaging Tomography Experiment (GreenLITE™) measurement system was deployed for a long-duration experiment in the center of Paris, France. The system measures near-surface atmospheric CO2 concentrations integrated along 30 horizontal chords ranging in length from 2.3 to 5.2 km and covering an area of 25 km2 over the complex urban environment. In this study, we use this observing system together with six conventional in situ point measurements and the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) and two urban canopy schemes (Urban Canopy Model – UCM; Building Effect Parameterization – BEP) at a horizontal resolution of 1 km to analyze the temporal and spatial variations in CO2 concentrations within the city of Paris and its vicinity for the 1-year period spanning December 2015 to November 2016. Such an analysis aims at supporting the development of CO2 atmospheric inversion systems at the city scale. Results show that both urban canopy schemes in the WRF-Chem model are capable of reproducing the seasonal cycle and most of the synoptic variations in the atmospheric CO2 point measurements over the suburban areas as well as the general corresponding spatial differences in CO2 concentration that span the urban area. However, within the city, there are larger discrepancies between the observations and the model results with very distinct features during winter and summer. During winter, the GreenLITE™ measurements clearly demonstrate that one urban canopy scheme (BEP) provides a much better description of temporal variations and horizontal differences in CO2 concentrations than the other (UCM) does. During summer, much larger CO2 horizontal differences are indicated by the GreenLITE™ system than both the in situ measurements and the model results, with systematic east–west variations.

Performance studies of textured race ball bearing

PurposeThe purpose of this paper is to develop an energy-efficient and dynamically improved thrust ball bearing using textured race. A texture has been used on the stationary race of the test bearing to conduct the long-duration experiment for exploring its tribological and vibrational behaviours under starved lubricating condition using micro size MoS2 blended grease. The performance behaviours of the textured race bearing have been compared with conventional bearing (i.e. having both races without textures) under the identical operating conditions for demonstrating the advantages of textured race.Design/methodology/approachTexture was created on stationary race of the test ball bearing (51308) using nano-second pulsed Nd: YAG laser. Performance parameters (frictional torque, temperature rise and vibrations) of textured ball bearings were measured under severe starved lubricating conditions for understanding the critical role of texture in the long duration of the test. S-type load cell and miniature accelerometer were used for measuring the frictional torque and vibration, respectively. Bulk temperature at stationary races (at the back side) of test bearings was measured in operating conditions using a non-contact infrared thermometer.FindingsSignificant reduction in frictional torque and decrease in amplitude of vibration with textured ball bearing were found even under the severe starved lubricating condition in comparison to conventional bearing.Originality/valueThere is dearth of research pertaining to the performance behaviours of ball bearings using textures on the races. Therefore, an attempt has been made in this study to explore the tribo-dynamic performance behaviours of a thrust ball bearing using a texture on its stationary race under severe starved lubricating condition for the longer duration of the test.

Producing Renewable Methane – Demonstration of CCU from Biomass

Producing renewable methane can contribute in several ways to the mitigation of greenhouse gas emissions. When produced from biomass – either by anaerobic digestion of green waste, sewage sludge etc. or by gasification of lignocellulosic biomass and subsequent gas cleaning and methanation – a significant amount of CO2 is produced in addition to the methane, due to the oxygen content in the biomass. This biogenic CO2 is then available almost without additional cost or efficiency losses for further synthesis of chemicals (CCU), replacing in this way equivalent amounts of fossil CO2. Renewable methane is one of the potential synthesis products derived from this CO2. It can be used as a green energy carrier, as long as the additional hydrogen needed for the synthesis is produced by electrolysis in Power-to-Gas applications from renewable energy resources like wind, hydropower or photovoltaics. A techno-economic assessment of several concepts for CCU within Power-to-Gas applications was conducted, considering direct methanation of biogas, i.e. “in situ” (without CO2 separation) synthesis of methane from biogenic CO2. Various catalytic methanation processes were analyzed with respect to how the residual hydrogen (after the synthesis step) can be minimized (either separated or converted further). On the basis of this study, the concept for fluidized-bed methanation with a downstream hydrogen membrane was chosen for the presented work, as this concept is most flexible in the operation of a commercial plant. A 20 kWCH4 pilot plant (COSYMA) was built and commissioned at the Energy System Integration (ESI) Platform of the Paul Scherrer Institut (PSI) in Switzerland to prove the validity of the proposed concept. In a subproject, promising sorbent materials were tested in the laboratory and integrated into the COSYMA pilot plant to protect the nickel-based methanation catalyst from being poisoned by sulfur compounds present in biogas. Then, the COSYMA was installed close to an existing biogas production plant and connected to the gas grid. A 1ˈ100 hour long-duration experiment was successfully conducted with a single catalyst charge. The predicted gas quality of the methanation was reached and the gas was injected into the natural gas grid. These experimental results of fluidized bed methanation and gas cleaning can now be scaled up from the COSYMA scale to that of an industrial plant.

Demonstrating direct methanation of real biogas in a fluidised bed reactor

The catalytic direct methanation of biogas to produce biomethane was conducted in a pilot plant with real biogas from a biogas plant in Zurich. Stable operation of the methanation system including a bubbling fluidised bed could be demonstrated for over 1100 h of regular operation with subsequent injection into the gas grid. An average methane yield of 96% was reached. During the long-duration experiment, the slow deactivation process was monitored and found to be only moderate. Organic sulphur compounds could be identified as the main source of deactivation. However, deactivation from coking could not be fully excluded. With appropriate measures in the gas cleaning unit, so that no sulphur compounds were measured subsequently (limit of detection: <0.05 ppm of relevant components), the yield reduction went close to zero. Additionally, experimental results were compared to simulation results from a rate-based model presented elsewhere. Model predictions and experimental results are in accordance. The kinetics used in the rate-based model allowed a correct prediction of the optimum reaction temperature found by experimental results.

The EBEX Balloon-borne Experiment—Detectors and Readout

Abstract EBEX was a long-duration balloon-borne experiment to measure the polarization of the cosmic microwave background. The experiment had three frequency bands centered at 150, 250, and 410 GHz and was the first to use a kilopixel array of transition edge sensor bolometers aboard a balloon platform. We describe the design and characterization of the array and the readout system. From the lowest to highest frequency, the median measured detectors’ average thermal conductances were 39, 53, and 63 pW/K, the medians of transition temperatures were 0.45, 0.48, and 0.47 K, and the medians of normal resistances were 1.9, 1.5, and 1.4 Ω; we also give the measured distributions. With the exception of the thermal conductance at 150 GHz, all measured values are within 30% of their design. We measure median low-loop-gain time constants τ 0 = 88, 46, and 57 ms. Two measurements of bolometer absorption efficiency gave results consistent within 10% and showing high (∼0.9) efficiency at 150 GHz and medium (∼0.35 and ∼0.25) efficiency at the two higher bands. We measure a median total optical power absorbed of 3.6, 5.3, and 5.0 pW. EBEX pioneered the use of the digital version of the frequency domain multiplexing system. We multiplexed the bias and readout of 16 bolometers onto two wires. The median per-detector noise-equivalent temperatures are 400, 920, and 14,500 . We compare these values to our preflight predictions and to a previous balloon payload. We discuss the sources of excess noise and the path for a future payload to make full use of the balloon environment.

Establishing cycling processes in an experimental model of a closed ecosystem

The purpose of this study was to investigate mass exchange processes in the experimental model of a closed ecological system intended for an estimated portion of a human in the long-duration (several-month) experiment. The diversity of the vegetable crop community in the system was increased, human wastes were involved in mass exchange processes, and human respiration was periodically connected to the system. The system has been designed to test different prospective technologies for future closed life support systems intended for prolonged autonomous operation in space and terrestrial applications. Three methods of plant cultivation in the conveyer mode have been used: hydroponics on expanded clay aggregate, growing plants on the soil-like substrate, and plant cultivation in aquaculture. The technology of more effective oxidation of organic wastes in a physicochemical processing reactor has been developed. A human exhaled the air into the system and consumed the air from the system. O2 concentration did not drop below 20.8% and did not rise above 22.6%. CO2 concentration varied between 800 ppm and 2500 ppm. Plants growing under this CO2 range at a preset light irradiance showed optimal photosynthetic activity. The closure coefficients for Ca, Mg, S, N, K and P were above 90%. However, compared with the inflow, only 55% Ca, about 80% Mg, and 75% Na and P were removed from the system. The technological processes developed in this study will need to be modified and improved before they can be used in a full-scale closed biotechnical life support system intended for prolonged operation.

Analysis of the gas exchange and water balance in a closed experimental model of the artificial ecosystem intended for an estimated portion of a human

This study was performed to investigate water and gas exchange in the experimental model of a closed ecological system (CES) intended for an estimated portion of a human in the long-duration (several-month) experiment. The diversity of the vegetable conveyor in the system was increased. Human wastes were involved in mass exchange processes, and human respiratory function was periodically connected to the experimental model of a CES. The experimental model of a CES was used to quantify regeneration of the gaseous atmosphere with oxygen and carbon dioxide loops by linking the photosynthesizing compartment with the heterotrophic compartment (soil-like substrate) and by the periodic connection of the human respiratory function. Under the preset light and temperature conditions, atmospheric CO2 concentration in the CES model intended for a portion of a human was maintained at a level that neither limited photosynthetic processes nor was harmful to humans (800–2000 ppm) during the 154-day experiment. At the same time, O2 concentration did not either drop below 20.8% or rise above 22.6%. The amount of the evapotranspiration water collected in the system could satisfy 50% of the daily water requirement of a human (with all the water used and excreted by the human being processed and used to irrigate plants). The evapotranspiration water did not need to be additionally purified before being used by humans. Thus, in the experimental model of the closed ecological system, human oxygen and food requirements (per 0.05 portion of a human) were matched to the function of the heterotrophic compartment and the photosynthesizing activity of the multispecies uneven-aged higher plant community.

Dynamic tunable notch filters for the Antarctic Impulsive Transient Antenna (ANITA)

The Antarctic Impulsive Transient Antenna (ANITA) is a NASA long-duration balloon experiment with the primary goal of detecting ultra-high-energy (>1018eV) neutrinos via the Askaryan Effect. The fourth ANITA mission, ANITA-IV, recently flew from Dec 2 to Dec 29, 2016. For the first time, the Tunable Universal Filter Frontend (TUFF) boards were deployed for mitigation of narrow-band, anthropogenic noise with tunable, switchable notch filters. The TUFF boards also performed second-stage amplification by approximately 45 dB to boost the ∼μV-level radio frequency (RF) signals to ∼ mV-level for digitization, and supplied power via bias tees to the first-stage, antenna-mounted amplifiers. The other major change in signal processing in ANITA-IV is the resurrection of the 90° hybrids deployed previously in ANITA-I, in the trigger system, although in this paper we focus on the TUFF boards. During the ANITA-IV mission, the TUFF boards were successfully operated throughout the flight. They contributed to a factor of 2.8 higher total instrument livetime on average in ANITA-IV compared to ANITA-III due to reduction of narrow-band, anthropogenic noise before a trigger decision is made.

In-situ fast and long observation system for friction surfaces during scuffing of steel

The objective of this study is to better understand the scuffing phenomenon using a specially designed in-situ observation system. The developed in-situ observation system comprises four sets of a digital CCD camera and a xenon flashing lamp. The independent operation of the capture devices could capture four successive images over short time intervals during a long-duration experiment. Scuffing behaviour that occurs in a friction surface between a rotating sapphire disc and a stationary martensitic steel pin in dry conditions was observed by the developed in-situ observation system. The results showed the behaviour of plastic flow that occurred in the frictional contact area. Plastic flow was observed to occur immediately after the transfer layer passed through the contact area. Each instance of plastic flow was a few milliseconds long. The speed of plastic flow was much less than the sliding speed. At the end of the fast plastic flow process, the brightness of the area of the plastic flow increased, which could be attributed to the oxidation of the steel surface.

A high-altitude balloon experiment to probe stratospheric electric fields from low latitudes

Abstract. The Earth's electrical environment hosts a giant electrical circuit, often referred to as the global electric circuit (GEC), linking the various sources of electrical generators located in the lower atmosphere, the ionosphere and the magnetosphere. The middle atmosphere (stratosphere and mesosphere) has been traditionally believed to be passively transmitting electric fields generated elsewhere. Some observations have reported anomalously large electric fields at these altitudes, and the scientific community has had to revisit the earlier hypothesis time and again. At stratospheric altitudes and especially at low latitudes, horizontal electric fields are believed to be of ionospheric origin. Though measurements of these fields from a balloon platform are challenging because of their small magnitudes (around a few mV m−1), a suitably designed long-duration balloon experiment capable of detecting such small fields can provide useful information on the time evolution of ionospheric electric fields, which is otherwise possible only using radar or satellite in situ measurements. We present herein details of one such experiment, BEENS (Balloon Experiment on the Electrodynamics of Near Space), carried out from a low-latitude site in India. The instrument package for this experiment is comprised of four deployable booms for measurements of horizontal electric fields and one inclined boom for vertical electric field measurements, all equipped with conducting spheres at the tip. The experiment was conducted from Hyderabad (17.5° N, 78.6° E) during the post-midnight hours on 14 December 2013. In spite of a few shortcomings we report herein, a noticeable feature of the observations has been the detection of horizontal electric fields of ∼ 5 mV m−1 at the stratospheric altitudes of ∼ 35 km.