{"paper_id":"09d7f746-8ea1-4318-bef6-7eda52fed8ce","body_text":"Vibration-Assisted Granular Flow Under Simulated Lunar Conditions: Parabolic Flight Validation of Lunar Regolith Feed System | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Vibration-Assisted Granular Flow Under Simulated Lunar Conditions: Parabolic Flight Validation of Lunar Regolith Feed System Anastasia Stepanova, Christopher Dreyer, Ryan Garvey This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9034538/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 11 You are reading this latest preprint version Abstract Reliable transport of granular materials through hoppers presents significant challenges in reduced-gravity environments due to diminished driving forces and increased susceptibility to flow blockages. This study reports results from parabolic flight experiments evaluating whether vertical vibration can maintain continuous regolith flow under simulated lunar gravity and vacuum conditions. Eight parallel feed assemblies were tested inside vacuum chambers, spanning four outlet geometries ranging in diameter from 11 to 45 mm and hopper angles from 46.5° to 90°. Vibration was applied at frequencies of between 43 and 65 Hz with displacement amplitudes from 0.2 to 0.8 mm. Across 60 reduced-gravity parabolas comprising 480 individual experiments, continuous material discharge was observed whenever vibration was active, regardless of outlet geometry. When vibration was disabled, all configurations exhibited flow termination within seconds. Reactivating vibration promptly restored flow without manual intervention. A rotary pocket feeder at each hopper outlet provided proportional flow rate control, yielding mass flow rates of 0.3 to 1.0 g/s with a lunar highlands regolith geotechnical simulant. These results demonstrate that vertical vibration effectively prevents flow blockages in reduced gravity, establishing validated design parameters for regolith handling systems intended for lunar surface operations. lunar regolith in-situ resource utilization reduced gravity vertical vibration granular flow hopper design Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction In-situ resource utilization (ISRU) on the Moon requires reliable handling and transport of lunar regolith for applications including construction, resource processing, and scientific sampling (Abbud-Madrid 2021). A central challenge for ISRU system design is ensuring that regolith can be consistently delivered through hoppers and feed systems without clogging or flow interruption. Recognizing the importance of understanding regolith behavior under non-terrestrial conditions, recent efforts have focused on developing laboratory methods to measure mechanical properties of granular materials in simulated lunar and planetary gravity environments (Duffey et al. 2024). The lunar environment presents unique difficulties for granular material handling. At one-sixth terrestrial gravity, the driving forces for gravity-fed systems are substantially reduced. Previous parabolic flight experiments by Reiss et al. (2014) demonstrated that flow rate through hoppers varies linearly with gravitational acceleration, and that reduced gravity leads to lower sample compaction but increased susceptibility to random arching and flow restrictions. Their work showed that the cohesive character of lunar simulants becomes particularly problematic at lunar gravity levels, with material flow occasionally stopping abruptly or failing to initiate. According to established hopper design principles, the minimum outlet size to prevent cohesive arching scales inversely with gravity; under lunar conditions, outlet diameters approximately six times larger than terrestrial requirements would theoretically be needed (Reiss et al.2014, Walton 2012). Walton (2012) reviewed the challenges of transporting and handling regolith in the lunar environment, noting that fine lunar dust particles exhibit increased cohesion due to both surface-energy-related (van der Waals) adhesion forces and electrostatic effects. The absence of atmosphere allows fine particles to remain in the regolith at higher concentrations than typical terrestrial deposits, increasing the overall cohesive behavior. These factors promote the formation of stable arches across hopper outlets, where frictional and cohesive forces at particle contacts can exceed the gravitational body forces attempting to displace material downward. Recent work by Madden et al. (2025) using drop tower experiments demonstrated that JSC-1A lunar simulant, while flowing smoothly through hoppers under Earth gravity, exhibits jamming and clogging under simulated lunar gravity. Their study employed the granular Bond number (Bo g ), which compares cohesive interparticle forces to gravitational forces, to characterize this gravity-dependent behavior. Discrete element method (DEM) simulations confirmed that granular flow behavior is extremely sensitive to the interplay between gravitational conditions and attractive/cohesive forces among particles, with a clear transition between flowing and clogged states in the gravity-cohesion parameter space. These findings highlight that extrapolating hopper design results obtained on Earth will not hold true under lunar gravity conditions without active flow enhancement mechanisms. This study addresses the regolith flow problem through systematic flight testing of vibration-assisted feed systems under representative lunar gravity and vacuum conditions. Vertical vibration is a well-established technique in terrestrial powder handling for disrupting arch formation and promoting continuous flow. Wassgren et al. (2002) demonstrated that vertical vibration applied to hoppers significantly increases mass flow rates and prevents clogging by periodically breaking the contact networks between particles that would otherwise form stable blocking structures. Their work showed that vibration effectiveness depends on both frequency and amplitude, with optimal parameters varying based on material properties and hopper geometry. The present work evaluates whether this approach remains effective when gravitational driving forces are reduced to lunar levels and in vacuum. It also establishes quantitative parameters for vibration frequency, amplitude, and outlet geometry that enable reliable regolith handling for ISRU applications. 2. Materials and Methods 2.1 Experimental apparatus A smaller ground test platform shown in Fig. 1 was developed that enabled operation of one or two regolith feed systems rather than the eight systems of the full flight payload. This reduced-scale platform was implemented in early stage ground testing to allow faster iteration of the experimental design, accelerate selection of sensors and electronic hardware, and perform initial characterization of regolith flowability. Extensive parametric analyses were conducted at 1g using this platform, including sensitivity studies on design and process parameters, repeatability assessments between tests for given conditions, and identification of potential issues prior to full assembly of the flight payload. The small test platform was also used to identify geometries and process parameters that produced optimal results, helping to establish the complete test matrix for the parabolic flights. The geometric parameters tested included the minimum hopper draw angle (30 degrees), the minimum hopper outlet diameter (16 mm), the pocket feeder geometry (such as depth, spacing, and number of pockets), the minimum regolith feed tube diameter (11 mm), and the minimum allowable slope angle of the feed tube, shown in Fig. 2 . Key process parameters tested include the minimum frequency (43 Hz) and amplitude of the hopper vibratory motor, the rotational speed of the pocket feeder drum relative to the regolith mass flow rate, and the need for a secondary vibratory motor on the regolith feed tube, which proved unnecessary, as testing showed that the primary vibration was sufficient to maintain reliable flow without it.. A test matrix developed for ground testing to determine the maximum vacuum chamber pressure at which flowability remains consistent with further pressure reductions. The final experimental payload comprised eight independent feed assemblies integrated with vacuum chamber, shown in Fig. 3 . Each assembly used a common hopper geometry conforming to KF-50 vacuum flange dimensions, with different conical reducer sections to create four distinct outlet configurations. Reducers sized to KF-16, KF-25, KF-40, and KF-50 standards produced outlet apertures of 11, 17.5, 30 and 45 mm diameter with corresponding hopper angles of 46.5°, 55°, 72°, and 90° respectively (Table 1 ). Duplicate assemblies for each geometry permitted comparison of replicate measurements. The KF-16 configuration represented the most challenging geometry due to its large area reduction, low draw angle, and small outlet diameter. Table 1 Geometric parameters of each configuration in ground and flight tests. Configuration Combination Hopper outlet diameter (mm) Hopper angle Cross tee outer diameter (mm) Regolith feed tube inner diameter (mm) 1,5 KF-50 to KF-16 50 46.5 16 11 2,6 KF-50 to KF-25 50 55 25 17.5 3,7 KF-50 to KF-40 50 72 40 30 4,8 KF-50 to KF-50 50 90 50 45 Below each conical reducer was a rotary pocket feeder to control material discharge. This mechanism consisted of a rotor with pockets machined along its circumference, sized to capture discrete volumes of regolith as the rotor turned. An external stepper motor drove rotation through a magnetically-coupled vacuum feedthrough, permitting speed adjustment to vary mass flow rate proportional to rotational RPM. Discharged material collected in transparent acrylic boxes mounted on load cells within the vacuum chamber to obtain mass measurements and to calculate the mass flow rate for a given operating condition. Mechanical vibration was provided by vibration motor secured to each hopper. The mounting arrangement used vibration isolators to minimize transmission to surrounding structure while allowing vertical oscillation of the hopper assembly. Between two and four elastomeric isolator pads supported each feed unit, with the quantity adjusted between flights to modify vibration amplitude. 2.2 Vacuum system The modular vacuum chamber had internal dimensions of 600 × 600 × 300 mm and included glass windows to allow visual observation. Twin dry scroll pumps maintained internal pressure below 200 mTorr (27 Pa) during the first flight and 450 mTorr (60 Pa) during the second flight. Although 450 mTorr represents a higher pressure, hundreds of ground tests demonstrated that regolith simulant flow behavior and trapped gas dynamics remain consistent across the pressure range from 70 to 500 mTorr, with no observable difference. Pressure was monitored using a Pirani gauge and was recorded throughout each test. Ground tests achieved pressures as low as 40 mTorr. Preliminary ground testing established that approximately two hours of pump-down was required to achieve target pressure while allowing trapped interparticle gases to escape from the regolith simulant. A sight glass located at the top of the hopper on one KF-16 configuration provided visual indication of regolith height and presence of ratholing. 2.3 Instrumentation Each collection box rested on a strain-gauge load cell for measuring mass accumulation during parabolas (sampling rate: 5 Hz, range: 0–5 kg, accuracy: ± 0.05% F.S. Accelerometers sampling at 500 Hz recorded vibration waveforms on each oscillating hopper assembly and on the aircraft mounting plate to measure gravitational acceleration. Eight GoPro cameras documented material behavior through the chamber windows at 1920×1080 pixel resolution and 30 frames per second, enabling post-flight classification of flow conditions. All sensor data was recorded using Arduino-based data acquisition systems. 2.4 Regolith simulant Various lunar regolith simulants were evaluated for use in the parabolic flight tests and associated ground tests, including CSM-LHT-1, ICN-LHT-1, JSC-1A-VF (very fine), and LHA-1 (agglutinates). ICN-LHT-1 was ultimately selected as the primary simulant due to its representation of a lunar highlands type regolith suitable for general geotechnical analysis. JSC-1A-VF was excluded from consideration due to the extreme respirable health hazards presented by its sub-20-micron particle size, though this simulant may be evaluated in future ground testing within more confined environments. LHA-1 agglutinate particles, which are manufactured by partial melting of lunar regolith simulant grains to bond unmelted grains into a lacy, highly irregular grain structure, were excluded because these particles fragment during handling and flowability analyses. Such fragmentation causes changes to soil mechanics properties that are difficult to track, introducing additional uncertainty in the experiments. Supplementary ground tests incorporating 40 weight percent agglutinate additions (0.4–1.2 mm diameter) to the ICN-LHT-1 baseline showed no increased clogging susceptibility despite the irregular particle shapes, though throughput decreased slightly, presumably reflecting reduced packing efficiency within the pocket feeder (see Fig. 4 ). While initial ground testing with the LHA-1 showed no impact on clogging and flowability, future flowability studies on the inclusion of agglutinates and irregular grain shapes are warranted to identify if physical interlocking of grains and increased electrostatic forces has some impact on regolith soil mechanics properties in reduced gravity conditions. CSM-LHT-1 was excluded due to limited supply availability for the parabolic and ground test campaigns. ICON Technology, Inc.’s ICN-LHT-1 is designed as a “general-purpose” regolith simulant material with a focus on the “Average Lunar Highlands” with a composition of minerals mimicking the anorthositic (plagioclase-rich) nature of highlands regolith.. The ICN-LHT-1 simulant has uncompressed bulk density of 1.32 g/cm³ when first introduced into the hoppers. 2.5 Parabolic flight operations Two dedicated flights were conducted on May 16–17, 2025 from Fort Lauderdale, Florida aboard a Zero Gravity Corporation modified Boeing 727. Each flight executed 30 lunar-gravity parabolas yielding approximately 18–25 seconds of 0.16g conditions per maneuver, interspersed with hypergravity pullout phases near 1.6g and level-flight intervals at 1g. The payload was secured to the aircraft cabin floor via a machined aluminum baseplate engineered for 9g loading in all directions with a minimum safety factor of 2.0. Test parameters were varied systematically across parabolas. The vibration system was operated at its minimum and maximum frequency settings. Different vibration amplitudes were achieved between flights by adjusting the number of vibration isolators. Pocket feeder rotation rates spanned the operational range for each outlet size. Several parabolas deliberately omitted vibration to verify blockage occurrence under reduced gravity without mechanical agitation. 2.6 Data analysis Video recordings were taken for each of the eight experimental configurations across all parabolas. Video data were reviewed to categorize each test as exhibiting flow, no flow, reduced flow, or intermittent flow conditions. Load cell data was processed using an automated routine that averaged force measurements before and after each parabola, divided by the concurrent gravitational acceleration, to determine the change in deposited mass. Accelerometer records were analyzed to extract dominant frequency and peak-to-peak displacement amplitude for correlation with flow outcomes. 3. Theory Gravitational flow through hopper outlets requires that particle weight exceed the resistive capacity of frictional and cohesive interparticle contacts. Reducing gravitational acceleration proportionally diminishes available driving force while leaving resistance mechanisms largely unchanged, shifting the balance toward blockage through arch formation. This behavior can be interpreted in terms of the granular Bond number (Ɓ). The granular Ɓ provides a framework for understanding flow behavior across gravitational environments. At the particle scale, Madden et al. (2025) define Ɓ as the ratio of interparticle cohesive forces to individual particle weight, demonstrating that for fine particles (~ 50 µm) under lunar gravity, cohesive forces can exceed particle weight by orders of magnitude. At the bulk scale, Gaida et al. (2025) define Ɓ using experimentally measured granular tensile strength from fluidization tests. They report that Ɓ increases by approximately one order of magnitude when shifting from Earth to lunar gravity. For LHS-2E, a lunar highlands simulant with d₅₀ = 54.5 µm, they measured Ɓ ≈ 0.89 under Earth gravity and Ɓ ≈ 5.4 under lunar gravity, consistent with the theoretical scaling Ɓ ∝ 1/g (Gaida et al. 2025). Given that ICN-LHT-1 is also a lunar highlands-type simulant with comparable particle size distribution (mean = 50 µm) and similar mineralogical composition, equivalent Bond number values are expected. Both approaches predict that lunar gravity shifts granular materials into a cohesion-dominated regime (Ɓ > 1), consistent with our observation that ICN-LHT-1 flow ceased within seconds when vibration was disabled during lunar-gravity parabolas. Vertical vibration counteracts this effect by periodically adding inertial forces that overcome cohesion-driven blockage, effectively reducing Bond number temporarily during each oscillation cycle. The experiments employed two distinct vibration frequencies, with representative acceleration waveforms from Flight 1 and Flight 2 shown in Fig. 5 . A commonly used criterion for effective flow initiation is when the dimensionless peak vibrational acceleration, defined as the ratio of peak vibrational acceleration to local gravitational acceleration and denoted Γ, exceeds unity (Clement et al. 2000). However, for cohesive granular materials, higher values of Γ are typically required to sustain continuous flow, with thresholds depending on particle properties and system geometry. For applied sinusoidal vibration, Γ may be calculated as where a is half of the peak-to-peak amplitude, f is the applied frequency in Hz, and g is the gravitational acceleration. On the lunar surface, where gravity is 1.62 m/s², this means the vibration must generate peak accelerations greater than this value to momentarily overcome gravitational confinement and allow particles to detach from arch structures and flow. In practice, higher values of Γ are often required for cohesive materials such as lunar regolith simulants, with the exact threshold influenced by particle size distribution, surface roughness, electrostatic charging, and hopper geometry. The vibration parameters selected for this investigation (43–65 Hz, 0.2–0.8 mm peak-to-peak amplitude) produced Γ values in lunar gravity ranging from 4.5 to 41, well above these thresholds, ensuring repeated disruption of arch formation before stable blockages could develop. 4. Results 4.1 Flow behavior A total of 480 experiments were conducted over the two parabolic flights, each consisting of 30 lunar parabolas testing all eight configurations. The low and high settings for each variable are defined in Table 2 . Table 2 Experimental parameter levels Input parameter Low High Frequency (Hz) 43 65 Amplitude peak-to-peak (mm) 0.2 0.8 Flow rate (g/min) 34.70 52.32 Six test conditions were evaluated by varying parameters at high/low/off levels with corresponding dimensionless peak vibrational acceleration (Γ) values shown in Table 3 for Flight 1 and Table 4 for Flight 2. Table 3 Flight 1 test conditions. Condition Frequency Flow Rate Amplitude Γ 1 High High Low 10.28 2 Low High Low 4.50 3 High Low Low 10.28 4 Low Low Low 4.50 5 Off Low Low 0 6 Off High Low 0 Table 4 Flight 2 test conditions. Condition Frequency Flow Rate Amplitude Γ 1 High High High 41.14 2 Low High High 18.00 3 High Low High 41.14 4 Low Low High 18.00 5 Off Low High 0 6 Off High High 0 When both vibration and pocket feeder rotation were active, continuous regolith flow was observed for all geometric configurations across all parabolas. Video documentation through the chamber window (e.g., Fig. 6 ) was used to qualitatively verify that no clogging events occurred during lunar gravity conditions when vibrations were applied, including the most restrictive KF-16 geometry with its 11 mm outlet and 46.5° draw angle. When vibration was disabled while maintaining pocket feeder rotation, all experimental setups exhibited flow cessation within a few seconds. This occurred for all four geometric configurations, including the least restrictive KF-50 geometry with its 45 mm outlet and 90° (vertical) wall angle. The stark contrast between vibration-on and vibration-off conditions demonstrated the critical role of mechanical agitation for maintaining regolith flow at 0.16g. When blockages occurred during vibration-off periods, subsequent reactivation of the vibration motor promptly restored flow without manual intervention. The primary vertical vibration alone was sufficient to clear blockages in reduced gravity. 3.3 Mass flow rates Mass flow rates derived from load cell measurements ranged from 0.3 to 1.0 g/s across operating conditions with active vibration. The pocket feeder provided proportional control of mass flow rate based on rotational RPM and vibration parameters. Comparison between reduced-gravity and terrestrial ground test measurements revealed minimal differences in deposited mass between 1/6g and 1g conditions, indicating that the vibration-assisted design effectively mitigated gravity-dependent flow variations. An average mass flow rate of regolith is between 0.3 g/s and 1.0 g/s across all conditions and configurations with vibration applied, and no flow or 0 g/s for when no vibration was applied. The load cell data were then analyzed by dividing the load cell measurement by the gravitational acceleration recorded by the baseplate accelerometer. The highest 20% of resultant mass measurements for the 30 seconds prior to the start of each parabola were then averaged and the resultant mass measurements for the 45 seconds following each parabola were then averaged. The top 20% of values were isolated because of increased measurement precision by the load cell for higher loads. A mass deposition rate was then found by dividing the total deposited mass by the duration of deposition (25 seconds in Flight 1, 18 seconds in Flight 2). This automated calculation method is shown graphically in Fig. 7 . The results of the load cell data following this process are shown across all conditions for Flight 1 in Table 5 and for Flight 2 in Table 6 . Although observations at conditions 5 and 6 (with vibration turned off) showed some initial regolith discharge, this did not represent continuous flow. The material observed falling during the first seconds consisted of residual regolith left in the pocket feeder drum from the previous run (when vibration was active). Once this residual amount emptied, flow ceased entirely because vibration was absent, preventing any further mobilization or discharge of the bulk regolith in the hopper. Table 5 Mean mass discharged from hoppers across 4 geometric configurations for 6 conditions in Flight 1. Condition Mean Mass Flow Rate (g/s) 1 0.83 2 0.49 3 0.73 4 0.39 5 0.16 6 0.12 Table 6 Mean mass discharged from hoppers across 4 geometric configurations for 6 conditions in Flight 2. Condition Mean Mass Flow Rate (g/s) 1 0.67 2 0.55 3 0.52 4 0.54 5 0.47 6 0.27 3.4 Geometric effects All four hopper geometries successfully maintained continuous flow when vibration was applied, spanning regolith feed tube diameters from KF-16 to KF-50 and draw angles from 46.5° to 90°. The most restrictive configurations 1 and 5 with minimum feed tube diameter of KF-16 had previously been identified in ground testing as a worst-case scenario for flowability due to its large area reduction and small outlet. Its successful operation under lunar gravity with vibration demonstrates that compact hopper geometries are viable for space applications when appropriate vibration is applied. 3.5 Vibration characteristics Accelerometer measurements indicated operating frequencies between 40 and 50 Hz across all configurations during both flights, compared to the broader range of 43–65 Hz operating frequencies observed during ground tests. Peak-to-peak displacement amplitudes ranged from 0.2 to 0.8 mm depending on isolator configuration. Frequencies and amplitudes measured during reduced-gravity parabolas were consistently lower than corresponding terrestrial values despite identical motor excitation, attributed to altered system dynamics when the gravitational preload was diminished. These lower frequencies and amplitudes remained sufficient for maintaining continuous flow across all test conditions. 5. Discussion These results demonstrate that vertical vibration effectively overcomes the flow cessation problem that has challenged regolith handling systems in reduced gravity. Previous work by Reiss et al. (2014) showed that lunar regolith simulants exhibit random arching and flow restrictions at lunar gravity, with flow occasionally stopping abruptly or failing to initiate. Walton (2012) noted that hopper outlet diameters would need to be approximately six times larger under lunar gravity to prevent cohesive arching. More recently, Madden et al. (2025) demonstrated using drop tower experiments that JSC-1A lunar simulant clogs under simulated lunar gravity even when it flows freely under Earth gravity, confirming that cohesive interparticle forces become dominant as gravitational driving forces decrease. The present study shows that applying vibration with Γ >> 1 eliminates this gravity-dependent clogging, allowing compact geometries with outlets as small as 11 mm in diameter to function reliably at 0.16g. The physical mechanism can be understood through the granular Bond number framework described by Madden et al. (2025), which compares cohesive interparticle forces to gravitational forces. When gravity decreases, the Bond number increases and particles become more likely to form stable arches through cohesive and frictional contacts. Applying periodic vertical accelerations that exceed gravitational magnitude repeatedly disrupts these contact networks before stable configurations can consolidate, effectively reducing the Bond number and permitting continuous material discharge. This explains why vibration-assisted systems maintain flow under lunar gravity conditions where passive hoppers fail. The vibration-assisted hopper system demonstrated here provides an approach for controlled regolith dispensing at lower flow rates (0.3–1.0 g/s) suitable for additive manufacturing, additive construction, reactor feeds, and precision sampling applications. The pocket feeder mechanism proved essential for precise flow control. Mass flow rates varied proportionally with rotational RPM independent of gravity level, enabling repeatable material delivery for applications requiring controlled deposition. Preliminary space system analysis indicates that a complete feed assembly with mass of approximately 1.0 kg would be capable of depositing regolith through a minimum outlet diameter of 11 mm at rates up to 0.8 g/s. The system could dispense approximately 3.3 kg of regolith (assuming bulk density of 1.5 g/cm³) before refilling. Several limitations should be acknowledged. Parabolic trajectories provide reduced gravity for only 18–25 seconds per maneuver, precluding assessment of long-duration thermal or wear effects. The simulant employed, while geotechnically representative, does not capture all properties of actual lunar regolith, particularly electrostatic effects from prolonged vacuum exposure. Additionally, while irregular particle shapes were investigated through inclusion of a regolith agglutinate simulant in ground testing, examining the role that lunar agglutinates may play on flowability in a reduced gravity environment should be pursued via future testing. 6. Conclusions This study demonstrates that vertical vibration enables reliable regolith flow under simulated lunar gravity and vacuum conditions (see Fig. 9 ). The principal findings are: When vibration was applied, continuous regolith flow occurred for all tested geometries across all 60 lunar-gravity parabolas, with no clogging events observed. When vibration was disabled, all configurations exhibited flow cessation within seconds, including the largest outlet geometry (45 mm diameter, 90° wall angle). Blockages that formed during vibration-off periods were immediately cleared by reactivating vibration, demonstrating an inherent resilience to the design of the system. The pocket feeder provided proportional mass flow rate control based on rotational speed, independent of gravity level. These results establish vibration-assisted hopper discharge as a validated approach for lunar regolith handling, with quantitative design parameters directly applicable to ISRU system development. 7. Future Work Several development pathways are recommended to advance this technology toward operational deployment. Parabolic flights provide only 18–25 seconds of reduced gravity per maneuver. Testing on orbital platforms or extended suborbital flights would enable characterization of steady-state behavior, and mechanism longevity over operationally relevant durations. Definitive validation requires testing on the lunar surface under actual 1/6g gravity, hard vacuum, and lunar thermal cycling. A lunar surface mission through NASA's Commercial Lunar Payload Services program (NASA 2025) or Artemis campaign (Smith et al. 2020) would provide the environment necessary to demonstrate system performance in an operational lunar environment. Key parameters to evaluate include long-term performance with actual lunar regolith and electrostatic charging effects absent from simulant testing. The ICN-LHT-1 used in this study provides representative particle size distribution and mineralogy, but actual lunar regolith possesses unique properties from billions of years of space weathering, including extreme particle angularity. Testing with Apollo return samples or future Artemis collection material would further help to validate simulant-based predictions. Finally, integration of the regolith feed system with downstream ISRU processes including additive construction, oxygen extraction reactors, and sample handling requires interface development and end-to-end demonstration. The successful demonstration reported here positions the vibration-assisted regolith feed system for near-term lunar surface validation as part of the Artemis program and commercial lunar infrastructure development. Declarations Competing Interests R.Garvey is employed by Blueshift, LLC doing business as Outward Technologies, developer of the tested hardware. The remaining authors declare no competing interests. Author Contribution Anastasia Stepanova built the test apparatus, conducted all testing and analysis, wrote the main manuscript text, and organized the co-authors. Ryan Garey supervised all activities of the work, assisted in conducting all testing, assisted in writing portions of the main manuscript text, and reviewed the manuscript text. Christopher Dreyer reviewed and edited the manuscript text. Acknowledgements The authors acknowledge the support of the Colorado School of Mines Space Resources Program, Blueshift, LLC doing business as Outward Technologies, and NASA Flight Opportunities Program under Contract 80NSSC24CA208. Data Availability Experimental data including load cell records, accelerometer measurements, and video documentation are available from the corresponding author upon reasonable request. References Abbud-Madrid, A. (2021, June 28). Space resource utilization. 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Retrieved January 13, 2026, from https://www.nasa.gov/commercial-lunar-payload-services/ Olson, A., Buhler, C., Toth, J., Acosta, K., Phillips, J., & Wang, J. (2022). Suborbital lunar gravity experiment of an electrodynamic regolith conveyor. In 2022 Joint Conference on Electrostatics. NASA Technical Reports Server. https://ntrs.nasa.gov/citations/20220009246 Reiss, P., Hager, P., Hoehn, A., Rott, M., & Walter, U. (2014). Flowability of lunar regolith simulants under reduced gravity and vacuum in hopper-based conveying devices. Journal of Terramechanics, 55, 61–72. https://doi.org/10.1016/j.jterra.2014.04.005 Smith, M., Craig, D., Herrmann, N., Mahoney, E., Krezel, J., McIntyre, N., & Goodliff, K. (2020). The Artemis program: An overview of NASA's activities to return humans to the Moon. IEEE Aerospace Conference Proceedings, 1–10. https://doi.org/10.1109/AERO47225.2020.9172323 Walton, O. R. (2012). Challenges in transporting, handling and processing regolith in the lunar environment. In V. Badescu (Ed.), Moon: Prospective energy and material resources (pp. 267–308). Springer. https://doi.org/10.1007/978-3-642-27969-0_11 Wassgren, C. R., Hunt, M. L., Freese, P. J., Paber, J., & Brennen, C. E. (2002). Effects of vertical vibration on hopper flows of granular material. Physics of Fluids, 14(10), 3439–3448. https://doi.org/10.1063/1.1503354 Additional Declarations Competing interest reported. R.Garvey is employed by Blueshift, LLC doing business as Outward Technologies, developer of the tested hardware. The remaining authors declare no competing interests. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 12 May, 2026 Reviews received at journal 12 Apr, 2026 Reviews received at journal 31 Mar, 2026 Reviews received at journal 25 Mar, 2026 Reviewers agreed at journal 18 Mar, 2026 Reviewers agreed at journal 17 Mar, 2026 Reviewers agreed at journal 11 Mar, 2026 Reviewers invited by journal 11 Mar, 2026 Editor assigned by journal 05 Mar, 2026 Submission checks completed at journal 05 Mar, 2026 First submitted to journal 04 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-9034538\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":605006272,\"identity\":\"aae7c3ae-3e6c-44e0-84f2-54a097ee4ed4\",\"order_by\":0,\"name\":\"Anastasia Stepanova\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4klEQVRIiWNgGAWjYHAD5gMMCRCWASGVMAZbAslaeOAq8Wvh7z9/8HFBzR05g+Nnvm54uMPGnoG9eZsEPi0SN5KZjWcce2ZscCZ3243EM2mJDTzHyvBqYbjBzCbNw3Y4cWYDSEvb4QQGiRwzvFrkzx9m/83zD6il/80zoJb/9gzyb/BrMTiQzMbM23Y4sV8ihw2o5QBjgwQPfi2GN5KNpWf2HTbml3hmBtSSnNjGk1ZsgU+L3PmDDz8XfDssx8af/OzmzzY7e372wxtv4NMCAswoPDZCyjG1jIJRMApGwShABwBdykrthuHSxQAAAABJRU5ErkJggg==\",\"orcid\":\"\",\"institution\":\"Colorado School of Mines\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Anastasia\",\"middleName\":\"\",\"lastName\":\"Stepanova\",\"suffix\":\"\"},{\"id\":605006273,\"identity\":\"914a3f44-1dc8-4996-af57-f6c4eaffd4f7\",\"order_by\":1,\"name\":\"Christopher Dreyer\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Colorado School of Mines\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Christopher\",\"middleName\":\"\",\"lastName\":\"Dreyer\",\"suffix\":\"\"},{\"id\":605006275,\"identity\":\"7ede29c7-5228-4c1c-9dc8-90c5e486d157\",\"order_by\":2,\"name\":\"Ryan Garvey\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Blueshift, LLC (DBA Outward Technologies)\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Ryan\",\"middleName\":\"\",\"lastName\":\"Garvey\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2026-03-05 01:08:28\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-9034538/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-9034538/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":104693252,\"identity\":\"a5e3f2b4-7408-4bd3-b398-b2e49040ad09\",\"added_by\":\"auto\",\"created_at\":\"2026-03-16 06:45:58\",\"extension\":\"jpg\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":98816,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSmaller ground test platform\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"1.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/5f0a2d5075efa2bb97934c7b.jpg\"},{\"id\":104693250,\"identity\":\"3963b060-6932-4c24-a120-87438d64fc43\",\"added_by\":\"auto\",\"created_at\":\"2026-03-16 06:45:58\",\"extension\":\"jpg\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":51909,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eGeometric and process parameters in the design of experiments. Configuration for KF-16.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"2.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/00b7b879923df43b07a90cf2.jpg\"},{\"id\":104693253,\"identity\":\"da430ab1-924d-47bc-a92f-bc7085ff1b40\",\"added_by\":\"auto\",\"created_at\":\"2026-03-16 06:45:58\",\"extension\":\"jpg\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":100128,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eIsometric view of combined payload assembly showing baseplate, vacuum chamber, framing components, motor supports, and vibration assembly mounting plates.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"3.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/0b8840ca9da666742c80a6c5.jpg\"},{\"id\":104693255,\"identity\":\"c5dc6d34-0e25-4832-920b-00d8433c9c02\",\"added_by\":\"auto\",\"created_at\":\"2026-03-16 06:45:58\",\"extension\":\"jpg\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":97451,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eAlternative simulant used for ground testing which was composed of ICN-LHT-1 with irregular LHA-1 agglutinate inclusions manufactured by Outward Technologies.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"4.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/be9139374cf5f3498f869391.jpg\"},{\"id\":104693256,\"identity\":\"f6b0b6d1-8d3b-4981-80bb-a76e2f23cbd5\",\"added_by\":\"auto\",\"created_at\":\"2026-03-16 06:45:58\",\"extension\":\"jpg\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":140293,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eMeasured acceleration waveforms for low-frequency and high-frequency vibration configurations during Flight 1 and Flight 2.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"5.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/00c7618332645d4711d74ffb.jpg\"},{\"id\":104693251,\"identity\":\"f0465335-526e-47b9-a627-52d39dba5626\",\"added_by\":\"auto\",\"created_at\":\"2026-03-16 06:45:58\",\"extension\":\"jpg\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":76653,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eView of regolith deposited by KF-16 geometry during the first lunar parabola of Flight 1.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"6.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/13e46d902446573905a73715.jpg\"},{\"id\":104782560,\"identity\":\"d93ed2aa-7c60-4799-9826-909d60c1b0e8\",\"added_by\":\"auto\",\"created_at\":\"2026-03-17 07:57:31\",\"extension\":\"jpg\",\"order_by\":7,\"title\":\"Figure 7\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":87529,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eExample of automated calculation of deposited regolith and mass deposition rate during a lunar parabola.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"7.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/9adfd6b44fb56ce1ce01af30.jpg\"},{\"id\":104783070,\"identity\":\"da733755-4fcd-432b-98ef-b3171cb2c007\",\"added_by\":\"auto\",\"created_at\":\"2026-03-17 07:58:10\",\"extension\":\"jpg\",\"order_by\":8,\"title\":\"Figure 8\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":220469,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eFigure 9: View of flight crew conducting tests with the payload during lunar gravity conditions\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"8.jpg\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/e0f1f4d41237ada26819cc5a.jpg\"},{\"id\":104784834,\"identity\":\"8cde0287-ce54-45ff-9708-35f89bdb1ea8\",\"added_by\":\"auto\",\"created_at\":\"2026-03-17 08:09:00\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":1584900,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9034538/v1/360a095c-f716-4f2b-9629-319af6d43dad.pdf\"}],\"financialInterests\":\"Competing interest reported. R.Garvey is employed by Blueshift, LLC doing business as Outward Technologies, developer of the tested hardware. The remaining authors declare no competing interests.\",\"formattedTitle\":\"Vibration-Assisted Granular Flow Under Simulated Lunar Conditions: Parabolic Flight Validation of Lunar Regolith Feed System\",\"fulltext\":[{\"header\":\"1. Introduction\",\"content\":\"\\u003cp\\u003eIn-situ resource utilization (ISRU) on the Moon requires reliable handling and transport of lunar regolith for applications including construction, resource processing, and scientific sampling (Abbud-Madrid 2021). A central challenge for ISRU system design is ensuring that regolith can be consistently delivered through hoppers and feed systems without clogging or flow interruption. Recognizing the importance of understanding regolith behavior under non-terrestrial conditions, recent efforts have focused on developing laboratory methods to measure mechanical properties of granular materials in simulated lunar and planetary gravity environments (Duffey et al. 2024).\\u003c/p\\u003e \\u003cp\\u003eThe lunar environment presents unique difficulties for granular material handling. At one-sixth terrestrial gravity, the driving forces for gravity-fed systems are substantially reduced. Previous parabolic flight experiments by Reiss et al. (2014) demonstrated that flow rate through hoppers varies linearly with gravitational acceleration, and that reduced gravity leads to lower sample compaction but increased susceptibility to random arching and flow restrictions. Their work showed that the cohesive character of lunar simulants becomes particularly problematic at lunar gravity levels, with material flow occasionally stopping abruptly or failing to initiate. According to established hopper design principles, the minimum outlet size to prevent cohesive arching scales inversely with gravity; under lunar conditions, outlet diameters approximately six times larger than terrestrial requirements would theoretically be needed (Reiss et al.2014, Walton 2012).\\u003c/p\\u003e \\u003cp\\u003eWalton (2012) reviewed the challenges of transporting and handling regolith in the lunar environment, noting that fine lunar dust particles exhibit increased cohesion due to both surface-energy-related (van der Waals) adhesion forces and electrostatic effects. The absence of atmosphere allows fine particles to remain in the regolith at higher concentrations than typical terrestrial deposits, increasing the overall cohesive behavior. These factors promote the formation of stable arches across hopper outlets, where frictional and cohesive forces at particle contacts can exceed the gravitational body forces attempting to displace material downward.\\u003c/p\\u003e \\u003cp\\u003eRecent work by Madden et al. (2025) using drop tower experiments demonstrated that JSC-1A lunar simulant, while flowing smoothly through hoppers under Earth gravity, exhibits jamming and clogging under simulated lunar gravity. Their study employed the granular Bond number (Bo\\u003csub\\u003eg\\u003c/sub\\u003e), which compares cohesive interparticle forces to gravitational forces, to characterize this gravity-dependent behavior. Discrete element method (DEM) simulations confirmed that granular flow behavior is extremely sensitive to the interplay between gravitational conditions and attractive/cohesive forces among particles, with a clear transition between flowing and clogged states in the gravity-cohesion parameter space. These findings highlight that extrapolating hopper design results obtained on Earth will not hold true under lunar gravity conditions without active flow enhancement mechanisms.\\u003c/p\\u003e \\u003cp\\u003eThis study addresses the regolith flow problem through systematic flight testing of vibration-assisted feed systems under representative lunar gravity and vacuum conditions. Vertical vibration is a well-established technique in terrestrial powder handling for disrupting arch formation and promoting continuous flow. Wassgren et al. (2002) demonstrated that vertical vibration applied to hoppers significantly increases mass flow rates and prevents clogging by periodically breaking the contact networks between particles that would otherwise form stable blocking structures. Their work showed that vibration effectiveness depends on both frequency and amplitude, with optimal parameters varying based on material properties and hopper geometry. The present work evaluates whether this approach remains effective when gravitational driving forces are reduced to lunar levels and in vacuum. It also establishes quantitative parameters for vibration frequency, amplitude, and outlet geometry that enable reliable regolith handling for ISRU applications.\\u003c/p\\u003e\"},{\"header\":\"2. Materials and Methods\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.1 Experimental apparatus\\u003c/h2\\u003e \\u003cp\\u003eA smaller ground test platform shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e was developed that enabled operation of one or two regolith feed systems rather than the eight systems of the full flight payload. This reduced-scale platform was implemented in early stage ground testing to allow faster iteration of the experimental design, accelerate selection of sensors and electronic hardware, and perform initial characterization of regolith flowability. Extensive parametric analyses were conducted at 1g using this platform, including sensitivity studies on design and process parameters, repeatability assessments between tests for given conditions, and identification of potential issues prior to full assembly of the flight payload. The small test platform was also used to identify geometries and process parameters that produced optimal results, helping to establish the complete test matrix for the parabolic flights.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe geometric parameters tested included the minimum hopper draw angle (30 degrees), the minimum hopper outlet diameter (16 mm), the pocket feeder geometry (such as depth, spacing, and number of pockets), the minimum regolith feed tube diameter (11 mm), and the minimum allowable slope angle of the feed tube, shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e. Key process parameters tested include the minimum frequency (43 Hz) and amplitude of the hopper vibratory motor, the rotational speed of the pocket feeder drum relative to the regolith mass flow rate, and the need for a secondary vibratory motor on the regolith feed tube, which proved unnecessary, as testing showed that the primary vibration was sufficient to maintain reliable flow without it.. A test matrix developed for ground testing to determine the maximum vacuum chamber pressure at which flowability remains consistent with further pressure reductions.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe final experimental payload comprised eight independent feed assemblies integrated with vacuum chamber, shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e. Each assembly used a common hopper geometry conforming to KF-50 vacuum flange dimensions, with different conical reducer sections to create four distinct outlet configurations. Reducers sized to KF-16, KF-25, KF-40, and KF-50 standards produced outlet apertures of 11, 17.5, 30 and 45 mm diameter with corresponding hopper angles of 46.5\\u0026deg;, 55\\u0026deg;, 72\\u0026deg;, and 90\\u0026deg; respectively (Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e). Duplicate assemblies for each geometry permitted comparison of replicate measurements. The KF-16 configuration represented the most challenging geometry due to its large area reduction, low draw angle, and small outlet diameter.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab1\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 1\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eGeometric parameters of each configuration in ground and flight tests.\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"6\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c4\\\" colnum=\\\"4\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c5\\\" colnum=\\\"5\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c6\\\" colnum=\\\"6\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eConfiguration\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eCombination\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHopper outlet diameter (mm)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eHopper angle\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eCross tee outer diameter (mm)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003eRegolith feed tube inner diameter (mm)\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e1,5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eKF-50 to KF-16\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e50\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e16\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e11\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e2,6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eKF-50 to KF-25\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e50\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e55\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e25\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e17.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e3,7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eKF-50 to KF-40\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e50\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e72\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e40\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e30\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4,8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eKF-50 to KF-50\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e50\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e90\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e50\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e45\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eBelow each conical reducer was a rotary pocket feeder to control material discharge. This mechanism consisted of a rotor with pockets machined along its circumference, sized to capture discrete volumes of regolith as the rotor turned. An external stepper motor drove rotation through a magnetically-coupled vacuum feedthrough, permitting speed adjustment to vary mass flow rate proportional to rotational RPM. Discharged material collected in transparent acrylic boxes mounted on load cells within the vacuum chamber to obtain mass measurements and to calculate the mass flow rate for a given operating condition.\\u003c/p\\u003e \\u003cp\\u003eMechanical vibration was provided by vibration motor secured to each hopper. The mounting arrangement used vibration isolators to minimize transmission to surrounding structure while allowing vertical oscillation of the hopper assembly. Between two and four elastomeric isolator pads supported each feed unit, with the quantity adjusted between flights to modify vibration amplitude.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec4\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.2 Vacuum system\\u003c/h2\\u003e \\u003cp\\u003eThe modular vacuum chamber had internal dimensions of 600 \\u0026times; 600 \\u0026times; 300 mm and included glass windows to allow visual observation. Twin dry scroll pumps maintained internal pressure below 200 mTorr (27 Pa) during the first flight and 450 mTorr (60 Pa) during the second flight. Although 450 mTorr represents a higher pressure, hundreds of ground tests demonstrated that regolith simulant flow behavior and trapped gas dynamics remain consistent across the pressure range from 70 to 500 mTorr, with no observable difference. Pressure was monitored using a Pirani gauge and was recorded throughout each test. Ground tests achieved pressures as low as 40 mTorr. Preliminary ground testing established that approximately two hours of pump-down was required to achieve target pressure while allowing trapped interparticle gases to escape from the regolith simulant. A sight glass located at the top of the hopper on one KF-16 configuration provided visual indication of regolith height and presence of ratholing.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec5\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.3 Instrumentation\\u003c/h2\\u003e \\u003cp\\u003eEach collection box rested on a strain-gauge load cell for measuring mass accumulation during parabolas (sampling rate: 5 Hz, range: 0\\u0026ndash;5 kg, accuracy: \\u0026plusmn; 0.05% F.S. Accelerometers sampling at 500 Hz recorded vibration waveforms on each oscillating hopper assembly and on the aircraft mounting plate to measure gravitational acceleration. Eight GoPro cameras documented material behavior through the chamber windows at 1920\\u0026times;1080 pixel resolution and 30 frames per second, enabling post-flight classification of flow conditions. All sensor data was recorded using Arduino-based data acquisition systems.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec6\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.4 Regolith simulant\\u003c/h2\\u003e \\u003cp\\u003eVarious lunar regolith simulants were evaluated for use in the parabolic flight tests and associated ground tests, including CSM-LHT-1, ICN-LHT-1, JSC-1A-VF (very fine), and LHA-1 (agglutinates). ICN-LHT-1 was ultimately selected as the primary simulant due to its representation of a lunar highlands type regolith suitable for general geotechnical analysis. JSC-1A-VF was excluded from consideration due to the extreme respirable health hazards presented by its sub-20-micron particle size, though this simulant may be evaluated in future ground testing within more confined environments. LHA-1 agglutinate particles, which are manufactured by partial melting of lunar regolith simulant grains to bond unmelted grains into a lacy, highly irregular grain structure, were excluded because these particles fragment during handling and flowability analyses. Such fragmentation causes changes to soil mechanics properties that are difficult to track, introducing additional uncertainty in the experiments. Supplementary ground tests incorporating 40 weight percent agglutinate additions (0.4\\u0026ndash;1.2 mm diameter) to the ICN-LHT-1 baseline showed no increased clogging susceptibility despite the irregular particle shapes, though throughput decreased slightly, presumably reflecting reduced packing efficiency within the pocket feeder (see Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e). While initial ground testing with the LHA-1 showed no impact on clogging and flowability, future flowability studies on the inclusion of agglutinates and irregular grain shapes are warranted to identify if physical interlocking of grains and increased electrostatic forces has some impact on regolith soil mechanics properties in reduced gravity conditions. CSM-LHT-1 was excluded due to limited supply availability for the parabolic and ground test campaigns. ICON Technology, Inc.\\u0026rsquo;s ICN-LHT-1 is designed as a \\u0026ldquo;general-purpose\\u0026rdquo; regolith simulant material with a focus on the \\u0026ldquo;Average Lunar Highlands\\u0026rdquo; with a composition of minerals mimicking the anorthositic (plagioclase-rich) nature of highlands regolith.. The ICN-LHT-1 simulant has uncompressed bulk density of 1.32 g/cm\\u0026sup3; when first introduced into the hoppers.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec7\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.5 Parabolic flight operations\\u003c/h2\\u003e \\u003cp\\u003eTwo dedicated flights were conducted on May 16\\u0026ndash;17, 2025 from Fort Lauderdale, Florida aboard a Zero Gravity Corporation modified Boeing 727. Each flight executed 30 lunar-gravity parabolas yielding approximately 18\\u0026ndash;25 seconds of 0.16g conditions per maneuver, interspersed with hypergravity pullout phases near 1.6g and level-flight intervals at 1g. The payload was secured to the aircraft cabin floor via a machined aluminum baseplate engineered for 9g loading in all directions with a minimum safety factor of 2.0.\\u003c/p\\u003e \\u003cp\\u003eTest parameters were varied systematically across parabolas. The vibration system was operated at its minimum and maximum frequency settings. Different vibration amplitudes were achieved between flights by adjusting the number of vibration isolators. Pocket feeder rotation rates spanned the operational range for each outlet size. Several parabolas deliberately omitted vibration to verify blockage occurrence under reduced gravity without mechanical agitation.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec8\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.6 Data analysis\\u003c/h2\\u003e \\u003cp\\u003eVideo recordings were taken for each of the eight experimental configurations across all parabolas. Video data were reviewed to categorize each test as exhibiting flow, no flow, reduced flow, or intermittent flow conditions. Load cell data was processed using an automated routine that averaged force measurements before and after each parabola, divided by the concurrent gravitational acceleration, to determine the change in deposited mass. Accelerometer records were analyzed to extract dominant frequency and peak-to-peak displacement amplitude for correlation with flow outcomes.\\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"3. Theory\",\"content\":\"\\u003cp\\u003eGravitational flow through hopper outlets requires that particle weight exceed the resistive capacity of frictional and cohesive interparticle contacts. Reducing gravitational acceleration proportionally diminishes available driving force while leaving resistance mechanisms largely unchanged, shifting the balance toward blockage through arch formation. This behavior can be interpreted in terms of the granular Bond number (Ɓ). The granular Ɓ provides a framework for understanding flow behavior across gravitational environments. At the particle scale, Madden et al. (2025) define Ɓ as the ratio of interparticle cohesive forces to individual particle weight, demonstrating that for fine particles (~\\u0026thinsp;50 \\u0026micro;m) under lunar gravity, cohesive forces can exceed particle weight by orders of magnitude. At the bulk scale, Gaida et al. (2025) define Ɓ using experimentally measured granular tensile strength from fluidization tests. They report that Ɓ increases by approximately one order of magnitude when shifting from Earth to lunar gravity. For LHS-2E, a lunar highlands simulant with d₅₀ = 54.5 \\u0026micro;m, they measured Ɓ \\u0026asymp; 0.89 under Earth gravity and Ɓ \\u0026asymp; 5.4 under lunar gravity, consistent with the theoretical scaling Ɓ \\u0026prop; 1/g (Gaida et al. 2025). Given that ICN-LHT-1 is also a lunar highlands-type simulant with comparable particle size distribution (mean\\u0026thinsp;=\\u0026thinsp;50 \\u0026micro;m) and similar mineralogical composition, equivalent Bond number values are expected. Both approaches predict that lunar gravity shifts granular materials into a cohesion-dominated regime (Ɓ \\u0026gt; 1), consistent with our observation that ICN-LHT-1 flow ceased within seconds when vibration was disabled during lunar-gravity parabolas.\\u003c/p\\u003e \\u003cp\\u003eVertical vibration counteracts this effect by periodically adding inertial forces that overcome cohesion-driven blockage, effectively reducing Bond number temporarily during each oscillation cycle. The experiments employed two distinct vibration frequencies, with representative acceleration waveforms from Flight 1 and Flight 2 shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e. A commonly used criterion for effective flow initiation is when the dimensionless peak vibrational acceleration, defined as the ratio of peak vibrational acceleration to local gravitational acceleration and denoted Γ, exceeds unity (Clement et al. 2000). However, for cohesive granular materials, higher values of Γ are typically required to sustain continuous flow, with thresholds depending on particle properties and system geometry. For applied sinusoidal vibration, Γ may be calculated as \\u003cimg src=\\\"data:image/png;base64,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\\\" width=\\\"102\\\" height=\\\"52\\\"\\u003e where \\u003cem\\u003ea\\u003c/em\\u003e is half of the peak-to-peak amplitude, \\u003cem\\u003ef\\u003c/em\\u003e is the applied frequency in Hz, and \\u003cem\\u003eg\\u003c/em\\u003e is the gravitational acceleration. On the lunar surface, where gravity is 1.62 m/s\\u0026sup2;, this means the vibration must generate peak accelerations greater than this value to momentarily overcome gravitational confinement and allow particles to detach from arch structures and flow. In practice, higher values of Γ are often required for cohesive materials such as lunar regolith simulants, with the exact threshold influenced by particle size distribution, surface roughness, electrostatic charging, and hopper geometry. The vibration parameters selected for this investigation (43\\u0026ndash;65 Hz, 0.2\\u0026ndash;0.8 mm peak-to-peak amplitude) produced Γ values in lunar gravity ranging from 4.5 to 41, well above these thresholds, ensuring repeated disruption of arch formation before stable blockages could develop.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e\"},{\"header\":\"4. Results\",\"content\":\"\\u003cdiv id=\\\"Sec11\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e4.1 Flow behavior\\u003c/h2\\u003e \\u003cp\\u003eA total of 480 experiments were conducted over the two parabolic flights, each consisting of 30 lunar parabolas testing all eight configurations. The low and high settings for each variable are defined in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab2\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 2\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eExperimental parameter levels\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"3\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eInput parameter\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eFrequency (Hz)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e43\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e65\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eAmplitude peak-to-peak (mm)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e0.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eFlow rate (g/min)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e34.70\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e52.32\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eSix test conditions were evaluated by varying parameters at high/low/off levels with corresponding dimensionless peak vibrational acceleration (Γ) values shown in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e for Flight 1 and Table\\u0026nbsp;\\u003cspan refid=\\\"Tab4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e for Flight 2.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab3\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 3\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eFlight 1 test conditions.\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"5\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c4\\\" colnum=\\\"4\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c5\\\" colnum=\\\"5\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCondition\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eFrequency\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eFlow Rate\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eAmplitude\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eΓ\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e10.28\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e4.50\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e10.28\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e4.50\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eOff\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eOff\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab4\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 4\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eFlight 2 test conditions.\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"5\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c4\\\" colnum=\\\"4\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c5\\\" colnum=\\\"5\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCondition\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eFrequency\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eFlow Rate\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eAmplitude\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eΓ\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e41.14\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e18.00\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e41.14\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e18.00\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eOff\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eLow\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eOff\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eHigh\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eWhen both vibration and pocket feeder rotation were active, continuous regolith flow was observed for all geometric configurations across all parabolas. Video documentation through the chamber window (e.g., Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e) was used to qualitatively verify that no clogging events occurred during lunar gravity conditions when vibrations were applied, including the most restrictive KF-16 geometry with its 11 mm outlet and 46.5\\u0026deg; draw angle.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eWhen vibration was disabled while maintaining pocket feeder rotation, all experimental setups exhibited flow cessation within a few seconds. This occurred for all four geometric configurations, including the least restrictive KF-50 geometry with its 45 mm outlet and 90\\u0026deg; (vertical) wall angle. The stark contrast between vibration-on and vibration-off conditions demonstrated the critical role of mechanical agitation for maintaining regolith flow at 0.16g.\\u003c/p\\u003e \\u003cp\\u003eWhen blockages occurred during vibration-off periods, subsequent reactivation of the vibration motor promptly restored flow without manual intervention. The primary vertical vibration alone was sufficient to clear blockages in reduced gravity.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec12\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.3 Mass flow rates\\u003c/h2\\u003e \\u003cp\\u003eMass flow rates derived from load cell measurements ranged from 0.3 to 1.0 g/s across operating conditions with active vibration. The pocket feeder provided proportional control of mass flow rate based on rotational RPM and vibration parameters. Comparison between reduced-gravity and terrestrial ground test measurements revealed minimal differences in deposited mass between 1/6g and 1g conditions, indicating that the vibration-assisted design effectively mitigated gravity-dependent flow variations. An average mass flow rate of regolith is between 0.3 g/s and 1.0 g/s across all conditions and configurations with vibration applied, and no flow or 0 g/s for when no vibration was applied.\\u003c/p\\u003e \\u003cp\\u003eThe load cell data were then analyzed by dividing the load cell measurement by the gravitational acceleration recorded by the baseplate accelerometer. The highest 20% of resultant mass measurements for the 30 seconds prior to the start of each parabola were then averaged and the resultant mass measurements for the 45 seconds following each parabola were then averaged. The top 20% of values were isolated because of increased measurement precision by the load cell for higher loads. A mass deposition rate was then found by dividing the total deposited mass by the duration of deposition (25 seconds in Flight 1, 18 seconds in Flight 2). This automated calculation method is shown graphically in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe results of the load cell data following this process are shown across all conditions for Flight 1 in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e and for Flight 2 in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e. Although observations at conditions 5 and 6 (with vibration turned off) showed some initial regolith discharge, this did not represent continuous flow. The material observed falling during the first seconds consisted of residual regolith left in the pocket feeder drum from the previous run (when vibration was active). Once this residual amount emptied, flow ceased entirely because vibration was absent, preventing any further mobilization or discharge of the bulk regolith in the hopper.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab5\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 5\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eMean mass discharged from hoppers across 4 geometric configurations for 6 conditions in Flight 1.\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"2\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCondition\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMean Mass Flow Rate (g/s)\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.83\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.49\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.73\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.39\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.16\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.12\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab6\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 6\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eMean mass discharged from hoppers across 4 geometric configurations for 6 conditions in Flight 2.\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"2\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCondition\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMean Mass Flow Rate (g/s)\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.67\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.55\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.52\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.54\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.47\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.27\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec13\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.4 Geometric effects\\u003c/h2\\u003e \\u003cp\\u003eAll four hopper geometries successfully maintained continuous flow when vibration was applied, spanning regolith feed tube diameters from KF-16 to KF-50 and draw angles from 46.5\\u0026deg; to 90\\u0026deg;. The most restrictive configurations 1 and 5 with minimum feed tube diameter of KF-16 had previously been identified in ground testing as a worst-case scenario for flowability due to its large area reduction and small outlet. Its successful operation under lunar gravity with vibration demonstrates that compact hopper geometries are viable for space applications when appropriate vibration is applied.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec14\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.5 Vibration characteristics\\u003c/h2\\u003e \\u003cp\\u003eAccelerometer measurements indicated operating frequencies between 40 and 50 Hz across all configurations during both flights, compared to the broader range of 43\\u0026ndash;65 Hz operating frequencies observed during ground tests. Peak-to-peak displacement amplitudes ranged from 0.2 to 0.8 mm depending on isolator configuration. Frequencies and amplitudes measured during reduced-gravity parabolas were consistently lower than corresponding terrestrial values despite identical motor excitation, attributed to altered system dynamics when the gravitational preload was diminished. These lower frequencies and amplitudes remained sufficient for maintaining continuous flow across all test conditions.\\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"5. Discussion\",\"content\":\"\\u003cp\\u003eThese results demonstrate that vertical vibration effectively overcomes the flow cessation problem that has challenged regolith handling systems in reduced gravity. Previous work by Reiss et al. (2014) showed that lunar regolith simulants exhibit random arching and flow restrictions at lunar gravity, with flow occasionally stopping abruptly or failing to initiate. Walton (2012) noted that hopper outlet diameters would need to be approximately six times larger under lunar gravity to prevent cohesive arching. More recently, Madden et al. (2025) demonstrated using drop tower experiments that JSC-1A lunar simulant clogs under simulated lunar gravity even when it flows freely under Earth gravity, confirming that cohesive interparticle forces become dominant as gravitational driving forces decrease. The present study shows that applying vibration with Γ \\u0026gt;\\u0026gt; 1 eliminates this gravity-dependent clogging, allowing compact geometries with outlets as small as 11 mm in diameter to function reliably at 0.16g.\\u003c/p\\u003e \\u003cp\\u003eThe physical mechanism can be understood through the granular Bond number framework described by Madden et al. (2025), which compares cohesive interparticle forces to gravitational forces. When gravity decreases, the Bond number increases and particles become more likely to form stable arches through cohesive and frictional contacts. Applying periodic vertical accelerations that exceed gravitational magnitude repeatedly disrupts these contact networks before stable configurations can consolidate, effectively reducing the Bond number and permitting continuous material discharge. This explains why vibration-assisted systems maintain flow under lunar gravity conditions where passive hoppers fail.\\u003c/p\\u003e \\u003cp\\u003eThe vibration-assisted hopper system demonstrated here provides an approach for controlled regolith dispensing at lower flow rates (0.3\\u0026ndash;1.0 g/s) suitable for additive manufacturing, additive construction, reactor feeds, and precision sampling applications.\\u003c/p\\u003e \\u003cp\\u003eThe pocket feeder mechanism proved essential for precise flow control. Mass flow rates varied proportionally with rotational RPM independent of gravity level, enabling repeatable material delivery for applications requiring controlled deposition.\\u003c/p\\u003e \\u003cp\\u003ePreliminary space system analysis indicates that a complete feed assembly with mass of approximately 1.0 kg would be capable of depositing regolith through a minimum outlet diameter of 11 mm at rates up to 0.8 g/s. The system could dispense approximately 3.3 kg of regolith (assuming bulk density of 1.5 g/cm\\u0026sup3;) before refilling.\\u003c/p\\u003e \\u003cp\\u003eSeveral limitations should be acknowledged. Parabolic trajectories provide reduced gravity for only 18\\u0026ndash;25 seconds per maneuver, precluding assessment of long-duration thermal or wear effects. The simulant employed, while geotechnically representative, does not capture all properties of actual lunar regolith, particularly electrostatic effects from prolonged vacuum exposure. Additionally, while irregular particle shapes were investigated through inclusion of a regolith agglutinate simulant in ground testing, examining the role that lunar agglutinates may play on flowability in a reduced gravity environment should be pursued via future testing.\\u003c/p\\u003e\"},{\"header\":\"6. Conclusions\",\"content\":\"\\u003cp\\u003eThis study demonstrates that vertical vibration enables reliable regolith flow under simulated lunar gravity and vacuum conditions (see Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig8\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe principal findings are:\\u003c/p\\u003e \\u003cp\\u003e \\u003col\\u003e \\u003cspan\\u003e \\u003cli\\u003e \\u003cp\\u003eWhen vibration was applied, continuous regolith flow occurred for all tested geometries across all 60 lunar-gravity parabolas, with no clogging events observed.\\u003c/p\\u003e \\u003c/li\\u003e \\u003c/span\\u003e \\u003cspan\\u003e \\u003cli\\u003e \\u003cp\\u003eWhen vibration was disabled, all configurations exhibited flow cessation within seconds, including the largest outlet geometry (45 mm diameter, 90\\u0026deg; wall angle).\\u003c/p\\u003e \\u003c/li\\u003e \\u003c/span\\u003e \\u003cspan\\u003e \\u003cli\\u003e \\u003cp\\u003eBlockages that formed during vibration-off periods were immediately cleared by reactivating vibration, demonstrating an inherent resilience to the design of the system.\\u003c/p\\u003e \\u003c/li\\u003e \\u003c/span\\u003e \\u003cspan\\u003e \\u003cli\\u003e \\u003cp\\u003eThe pocket feeder provided proportional mass flow rate control based on rotational speed, independent of gravity level.\\u003c/p\\u003e \\u003c/li\\u003e \\u003c/span\\u003e \\u003c/ol\\u003e \\u003c/p\\u003e \\u003cp\\u003eThese results establish vibration-assisted hopper discharge as a validated approach for lunar regolith handling, with quantitative design parameters directly applicable to ISRU system development.\\u003c/p\\u003e\"},{\"header\":\"7. Future Work\",\"content\":\"\\u003cp\\u003eSeveral development pathways are recommended to advance this technology toward operational deployment. Parabolic flights provide only 18\\u0026ndash;25 seconds of reduced gravity per maneuver. Testing on orbital platforms or extended suborbital flights would enable characterization of steady-state behavior, and mechanism longevity over operationally relevant durations.\\u003c/p\\u003e \\u003cp\\u003eDefinitive validation requires testing on the lunar surface under actual 1/6g gravity, hard vacuum, and lunar thermal cycling. A lunar surface mission through NASA's Commercial Lunar Payload Services program (NASA 2025) or Artemis campaign (Smith et al. 2020) would provide the environment necessary to demonstrate system performance in an operational lunar environment. Key parameters to evaluate include long-term performance with actual lunar regolith and electrostatic charging effects absent from simulant testing.\\u003c/p\\u003e \\u003cp\\u003eThe ICN-LHT-1 used in this study provides representative particle size distribution and mineralogy, but actual lunar regolith possesses unique properties from billions of years of space weathering, including extreme particle angularity. Testing with Apollo return samples or future Artemis collection material would further help to validate simulant-based predictions.\\u003c/p\\u003e \\u003cp\\u003eFinally, integration of the regolith feed system with downstream ISRU processes including additive construction, oxygen extraction reactors, and sample handling requires interface development and end-to-end demonstration. The successful demonstration reported here positions the vibration-assisted regolith feed system for near-term lunar surface validation as part of the Artemis program and commercial lunar infrastructure development.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003ch2\\u003eCompeting Interests\\u003c/h2\\u003e\\u003cp\\u003eR.Garvey is employed by Blueshift, LLC doing business as Outward Technologies, developer of the tested hardware. The remaining authors declare no competing interests.\\u003c/p\\u003e\\u003c/p\\u003e\\u003ch2\\u003eAuthor Contribution\\u003c/h2\\u003e\\u003cp\\u003eAnastasia Stepanova built the test apparatus, conducted all testing and analysis, wrote the main manuscript text, and organized the co-authors. Ryan Garey supervised all activities of the work, assisted in conducting all testing, assisted in writing portions of the main manuscript text, and reviewed the manuscript text. Christopher Dreyer reviewed and edited the manuscript text.\\u003c/p\\u003e\\u003ch2\\u003eAcknowledgements\\u003c/h2\\u003e \\u003cp\\u003eThe authors acknowledge the support of the Colorado School of Mines Space Resources Program, Blueshift, LLC doing business as Outward Technologies, and NASA Flight Opportunities Program under Contract 80NSSC24CA208.\\u003c/p\\u003e\\u003ch2\\u003eData Availability\\u003c/h2\\u003e\\u003cp\\u003eExperimental data including load cell records, accelerometer measurements, and video documentation are available from the corresponding author upon reasonable request.\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\u003cli\\u003e\\u003cspan\\u003eAbbud-Madrid, A. (2021, June 28). Space resource utilization. Oxford Research Encyclopedia of Planetary Science. https://doi.org/10.1093/acrefore/9780190647926.013.13\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eCl\\u0026eacute;ment, E., \\u0026amp; Labous, L. (2000). Pattern formation in a vibrated granular layer: The pattern selection issue. Physical Review E, 62(6), 8314\\u0026ndash;8323. https://doi.org/10.1103/PhysRevE.62.8314\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eDuffey, C., Lea, M., \\u0026amp; Brisset, J. (2024). Measuring regolith strength in reduced gravity environments in the laboratory. arXiv. https://arxiv.org/abs/2411.11571\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eGaida, O., D'Angelo, O., \\u0026amp; Kollmer, J. E. (2025). To flow or not to flow? The granular Bond number to predict clogging in low gravity. arXiv preprint. https://doi.org/10.48550/arXiv.2506.18771\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eMadden, I. P., Muruganandam, S., Missaoui, A., Gries, O., Kollmer, J., D'Angelo, O., \\u0026amp; Sinha-Ray, S. (2025). Behaviors of lunar regolith simulants under varying gravitational conditions. npj Microgravity, 11, 69. https://doi.org/10.1038/s41526-025-00501-z\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eNASA. (2025). Commercial Lunar Payload Services. Retrieved January 13, 2026, from https://www.nasa.gov/commercial-lunar-payload-services/\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eOlson, A., Buhler, C., Toth, J., Acosta, K., Phillips, J., \\u0026amp; Wang, J. (2022). Suborbital lunar gravity experiment of an electrodynamic regolith conveyor. In 2022 Joint Conference on Electrostatics. NASA Technical Reports Server. https://ntrs.nasa.gov/citations/20220009246\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eReiss, P., Hager, P., Hoehn, A., Rott, M., \\u0026amp; Walter, U. (2014). Flowability of lunar regolith simulants under reduced gravity and vacuum in hopper-based conveying devices. Journal of Terramechanics, 55, 61\\u0026ndash;72. https://doi.org/10.1016/j.jterra.2014.04.005\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eSmith, M., Craig, D., Herrmann, N., Mahoney, E., Krezel, J., McIntyre, N., \\u0026amp; Goodliff, K. (2020). The Artemis program: An overview of NASA's activities to return humans to the Moon. IEEE Aerospace Conference Proceedings, 1\\u0026ndash;10. https://doi.org/10.1109/AERO47225.2020.9172323\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eWalton, O. R. (2012). Challenges in transporting, handling and processing regolith in the lunar environment. In V. Badescu (Ed.), Moon: Prospective energy and material resources (pp. 267\\u0026ndash;308). Springer. https://doi.org/10.1007/978-3-642-27969-0_11\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eWassgren, C. R., Hunt, M. L., Freese, P. J., Paber, J., \\u0026amp; Brennen, C. E. (2002). Effects of vertical vibration on hopper flows of granular material. Physics of Fluids, 14(10), 3439\\u0026ndash;3448. https://doi.org/10.1063/1.1503354\\u003c/span\\u003e\\u003c/li\\u003e\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":false,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"space-and-planetary-resources\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"\",\"sideBox\":\"Learn more about [Space and Planetary Resources](https://link.springer.com/journal/44461)\",\"snPcode\":\"44461\",\"submissionUrl\":\"https://submission.springernature.com/new-submission/44461/3\",\"title\":\"Space and Planetary Resources\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"stoa\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false},\"keywords\":\"lunar regolith, in-situ resource utilization, reduced gravity, vertical vibration, granular flow, hopper design\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-9034538/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-9034538/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eReliable transport of granular materials through hoppers presents significant challenges in reduced-gravity environments due to diminished driving forces and increased susceptibility to flow blockages. This study reports results from parabolic flight experiments evaluating whether vertical vibration can maintain continuous regolith flow under simulated lunar gravity and vacuum conditions. Eight parallel feed assemblies were tested inside vacuum chambers, spanning four outlet geometries ranging in diameter from 11 to 45 mm and hopper angles from 46.5\\u0026deg; to 90\\u0026deg;. Vibration was applied at frequencies of between 43 and 65 Hz with displacement amplitudes from 0.2 to 0.8 mm. Across 60 reduced-gravity parabolas comprising 480 individual experiments, continuous material discharge was observed whenever vibration was active, regardless of outlet geometry. When vibration was disabled, all configurations exhibited flow termination within seconds. Reactivating vibration promptly restored flow without manual intervention. A rotary pocket feeder at each hopper outlet provided proportional flow rate control, yielding mass flow rates of 0.3 to 1.0 g/s with a lunar highlands regolith geotechnical simulant. These results demonstrate that vertical vibration effectively prevents flow blockages in reduced gravity, establishing validated design parameters for regolith handling systems intended for lunar surface operations.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Vibration-Assisted Granular Flow Under Simulated Lunar Conditions: Parabolic Flight Validation of Lunar Regolith Feed System\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2026-03-16 06:45:48\",\"doi\":\"10.21203/rs.3.rs-9034538/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0},{\"type\":\"decision\",\"content\":\"Revision requested\",\"date\":\"2026-05-12T20:26:51+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2026-04-12T17:40:51+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2026-04-01T01:05:22+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2026-03-25T22:15:37+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"205504396082572492049441357188258008996\",\"date\":\"2026-03-18T07:04:51+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"45549883917906621966244176709895538022\",\"date\":\"2026-03-17T14:58:03+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"175024317741643490773105405463936192677\",\"date\":\"2026-03-11T13:11:58+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewersInvited\",\"content\":\"\",\"date\":\"2026-03-11T13:04:07+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorAssigned\",\"content\":\"\",\"date\":\"2026-03-05T11:50:51+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"checksComplete\",\"content\":\"\",\"date\":\"2026-03-05T11:49:33+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"submitted\",\"content\":\"Space and Planetary Resources\",\"date\":\"2026-03-05T00:59:57+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"space-and-planetary-resources\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"\",\"sideBox\":\"Learn more about [Space and Planetary Resources](https://link.springer.com/journal/44461)\",\"snPcode\":\"44461\",\"submissionUrl\":\"https://submission.springernature.com/new-submission/44461/3\",\"title\":\"Space and Planetary Resources\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"stoa\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false}}],\"origin\":\"\",\"ownerIdentity\":\"170dc27f-93a8-4127-90b3-112202c29a0a\",\"owner\":[],\"postedDate\":\"March 16th, 2026\",\"published\":true,\"recentEditorialEvents\":[{\"type\":\"decision\",\"content\":\"Revision requested\",\"date\":\"2026-05-12T20:26:51+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"in-revision\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2026-05-12T20:39:20+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2026-03-16 06:45:48\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-9034538\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-9034538\",\"identity\":\"rs-9034538\",\"version\":[\"v1\"]},\"buildId\":\"XKTyCvWXoU3ODBz1xrDgd\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}