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NASA NTRSDate not supplied

An Optimization-Based Toolchain for Parametric Mechanism Design

Design-Build-Test approaches for developing spaceflight hardware are prohibitively time and cost intensive and often lead to suboptimal mechanism designs. Approaches that couple machine learning and high-fidelity physics simulation could eliminate the need for hardware prototyping and dramatically accelerate the engineering design cycle, ultimately reducing cost. This work presents a modular NASA-developed toolchain to optimize hardware mechanisms in a virtual environment using numerical optimization and multi-body physics simulation. The toolchain enables multi-objective optimization, generates parametric CAD files that can be further post-processed by an end user, and can be expanded to optimize full systems and non-mechanical parameters such as feedback control variables. We demonstrate the toolchain through an independently verifiable design problem that optimizes wheel radius to achieve a desired linear velocity in a rigid-body physics environment when the wheel rotates at a constant angular speed, and then post-process the parametric CAD file of the optimal design generated by the tool before ultimately manufacturing it via 3D printing. We end with a discussion of how the toolchain can incorporate other analysis tools, including finite element analysis, computational fluid dynamics, and granular media simulations.

Optimization↗

NASA NTRSDate not supplied

Effect of Vacuum on Force Response of an Ultrasonic Penetrator

Introduction: The Apollo astronauts encountered higher than expected resistances when interacting with the lunar soil via the Apollo Lunar Surface Drill (ALSD) and the trenching tool. Reducing the force required to move tools or other mechanical components through regolith will impact many steps of the resource extraction process. Force reduction has been achieved in soil materials by imparting vibration to tooling interfaces such as a vibratory farming cultivator, a percussive scoop, and ultrasonically resonant penetrators. Vibration-assisted tools in granular media reduce interaction forces by fluidizing a volume around the tool, allowing the tool to progress through a dynamic (fluid) medium instead of a static (solid) medium. This work seeks to quantify ultrasonic vibration’s effect on the force response of a penetrator in lunar soil simulant in vacuum sufficient to be within the molecular flow regime of any disturbed gases. Methods: A custom vacuum chamber setup, CUBEvac, was designed and built to facilitate penetration testing in a high vacuum environment, for comparison to penetration behavior in ambient terrestrial environment. A two-stage pumping system (Agilent Triscroll 600 roughing pump, Agilent VHS-6 oil diffusion pump) reached chamber pressures of about 5x10-6 Torr with regolith simulant in place. Figure 1 is a schematic of the heart of the assembly (note the penetration drive mechanisms above the chamber feedthrough and the regolith simulant sample in the bottom are not shown). The penetration actuation stack was comprised of a stepper motor driving a lead screw to move the ultra-sonic probe vertically inside the chamber. Motion was coordinated with an Arduino Uno. GRC-3 lunar simulant was used for this set of experiments. Samples were prepared in a four-liter stain-less steel, cylindrical pot with an internal diameter of approximately 15.56 cm (6.125 in) and a depth of 19.37 cm (7 5/8 in) for testing. The soil was baked out prior to compaction preparation as a measure to reduce soil moisture which interfered with pump down capacity. The soil was not baked again if it was removed from the vacuum chamber, prepped, and immediately returned to the vacuum chamber for pump down. The soil was compacted using a 60 Hz vibration table with a surcharge of 34 kg place on top of the soil in the container. Prepared soil samples weighed approximately 6.5 kg (bulk density 1.895-1.934 g/cm3). Two probe end effectors were tested: A cone penetrometer (static only) with a nominal diameter of 12.7 mm (0.5 in) and a nominal height of 28.6 mm (1.125 in); and a vibrating cylindrical probe measuring 12.7 mm in diameter and 50.8 mm in effective length from the tip (Figure 2). The cylindrical probe vibrated resonantly at 20 kHz with an amplitude 23 μm. The cone penetration tests were conducted to assess potential soil behavior differences in vacuum. The cylinder probe tests were conducted as the primary subject of this investigation to assess force response in vacuum. For each test, a regolith simulant sample was load-ed and compacted in the chamber, which was then evacuated for roughly 18 hours to reach the lowest possible pressure (approximately 5x10-6 Torr for most tests). The probe was then moved to about 10 mm above the soil surface before being pushed to a depth of 50 mm for the cylinder probe tests and to a depth of 100 mm for the cone penetrometer tests, both at a speed of 2 mm/s. The simulant samples were prepared the same for all tests. Ideally, they would respond consistently to probe penetration under ambient and vacuum conditions. This was evaluated by measuring the resistance of representative prepared simulant beds with a standard cone penetrometer in both environments. Results and Discussion: The resistance of the simulant samples in the vacuum tests was consistently lower than in the ambient tests as determined by the cone penetration tests. Thus, the ambient and vacuum results cannot be compared directly; work is underway to de-confound and better correlate the data. Still, figures 3-6 show that probe penetration forces are lower overall in the vacuum environment. In both environments, resonant vibration of the probe provides two useful effects: It reduces the probe penetration force and smooths the force-depth curve, significantly reducing local maxima. These effects have implications for various potential applications, such as astronaut hand-tools, where benefits (reducing astronaut effort) outweigh the cost of the additional energy re-quired to generate vibration. These results demonstrate that resonantly vibrating tools can meaningfully reduce the penetration force required for excavation, probing, and drilling tools in simulated lunar regolith deposits under vacuum levels approaching those that will be experience on the Moon’s surface. Lunar-gravity, ambient environment tests are scheduled soon. The effects of realistic temperatures and temperature gradients and deeper vacuum remain to be tested.

E Rezich↗

NASA NTRS2005

Mechanical and Structural Behavior of Granular Material Packed Beds for Space Life Support System Applications

Long-term human mission to space, such as living in International Space Station (ISS), Lunar, and Martian bases, and travel to Mars, must m ake use of Advanced Life Support Systems (ALSS) to generate and recycle critical life supporting elements like oxygen and water. Oxygen Gen eration Assembly (OGA) and Water Processor Assembly (WPA), critical c omponents of ALSS, make use of series of granular material packed beds for generation and recycling of oxygen and water. Several granular m aterials can be used for generation, recycling, processing and recovery of oxygen and water. For example, they may include soft bed media, e.g. ion exchange resins for oxygen generation assembly and hard bed media such as, activated alumina, magchem (Magnesium oxide) and activa ted carbon to remove organic species like ethanol, methanol, and urea from wastewater in Water recovery/processing assembly. These beds are generally packed using a plate-spring mechanism to provide sufficien t compaction to the bed media throughout the course of operation. This paper presents results from an experimental study of a full-scale, 3 8.1 cm (15 inches) long and 3.7 cm (1.44 inches) diameter. activated alumina bed enclosed in a cylinder determining its force-displacement behavior, friction mobilizing force, and axial normal stress distribu tion under various axially applied loads and at different levels of packing. It is observed that force-displacement behavior is non-linear for low compaction level and becomes linear with increase in compaction of the bed media. Axial normal stress distribution along the length of the bed media decreased non-linearly with increase in depth from the loading end of the granular media. This paper also presents experimental results on the amount of particulates generated corresponding to various compaction levels. Particulates generated from each of the tests were measured using standard US sieves. It was found that the p articulates and the overall displacement of the bed media increased with decrease in initial compaction of the bed media. This effect could be attributed to the greater tendency for inter-particle sliding/rub bing due to smaller internal friction angles, as seen from the shear tests, at lesser initial compacted levels. Upon unloading, it was obse rved that there was no change in displacement (especially rebounding) in the bed media. This effect could be attributed to the fact that th e porous activated alumina particles fracture/break upon increase in applied load (during loading phase) and occupy void spaces in between the material grains; thereby leading to settling of the media. The lo ad-displacement curve becomes more linear with increase in initial compaction of the bed media. It is concluded that compaction considerabl y affects the load-displacement behavior of the bed media. A series of tests were also conducted on the packed bed media to determine the f orce required to mobilize the friction between the bed media and the housing cylinder. The results from these tests showed the existence of significant friction between the bed media and the encasing stainles s steel cylinder. Further, it was found that friction effects were more pronounced for media with higher initial compaction. Internal frict ion of the granular media was measured using direct shear apparatus. It was observed that the internal friction increased with increase in initial compaction of the bed media. In this study, a computational m odel (CM) is also developed using finite element software ANSYS to verify experimental results obtained for the distribution of the axial n ormal stress and axial displacement along the length of the full-scal e activated alumina bed media. In the computational model, the granular material is considered to have appropriate failure and frictional c ontact exists between the wall and the granular media. It is observed that the model predicts results closely with the experimental method. The compational results show that the axial normal stress distribution along the length of the activated alumina media decreases non-linea rly from the loading end and is negligible beyond a certain depth. Th is can be attributed to the existence of friction between the walls and the media and that the friction takes up most of the applied load.

Malla, Ramesh B.↗

NASA NTRS2016

Submicron and Nanoparticulate Matter Removal by HEPA-Rated Media Filters and Packed Beds of Granular Materials

Contaminants generated aboard crewed spacecraft by diverse sources consist of both gaseous chemical contaminants and particulate matter. Both HEPA media filters and packed beds of granular material, such as activated carbon, which are both commonly employed for cabin atmosphere purification purposes have efficacy for removing nanoparticulate contaminants from the cabin atmosphere. The phenomena associated with particulate matter removal by HEPA media filters and packed beds of granular material are reviewed relative to their efficacy for removing fine (less than 2.5 micrometers) and ultrafine (less than 0.01 micrometers) sized particulate matter. Considerations are discussed for using these methods in an appropriate configuration to provide the most effective performance for a broad range of particle sizes including nanoparticulates.

Perry, J. L.↗

NASA NTRS2003

Microgravity and Hypogravity Compatible Methods for the Destruction of Solid Wastes by Magnetically Assisted Gasification

This report summarizes a three-year collaborative effort between researchers at UMPQUA Research Company (URC) and the Chemical Engineering Department at Oregon State University (OSU). The Magnetically Assisted Gasification (MAG) concept was originally conceived as a microgravity and hypogravity compatible means for the decomposition of solid waste materials generated aboard spacecraft, lunar and planetary habitations, and for the recovery of potentially valuable resources. While a number of methods such as supercritical water oxidation (SCW0), fluidized bed incineration, pyrolysis , composting and related biological processes have been demonstrated for the decomposition of solid wastes, none of these methods are particularly well- suited for employment under microgravity or hypogravity conditions. For example, fluidized bed incineration relies upon a balance between drag forces which the flowing gas stream exerts upon the fluidization particles and the opposing force of gravity. In the absence of gravity, conventional fluidization cannot take place. Hypogravity operation can also be problematic for conventional fluidized bed reactors, because the various factors which govern fluidization phenomena do not all scale linearly with gravity. For this reason it may be difficult to design and test fluidized bed reactors in lg, which are intended to operate under different gravitational conditions. However, fluidization can be achieved in microgravity (and hypogravity) if a suitable replacement force to counteract the forces between fluid and particles can be found. Possible alternatives include: centripetal force, electric fields, or magnetic fields. Of these, magnetic forces created by the action of magnetic fields and magnetic field gradients upon ferromagnetic media offer the most practical approach. The goal of this URC-OSU collaborative effort was to develop magnetic hardware and methods to control the degree of fluidization (or conversely consolidation) of granular ferromagnetic media and to employ these innovations in sequential filtration and fluidized bed processes for the segregation and decomposition of solid waste materials, and for the concentration and collection of inorganic residue (ash). This required the development of numerous enabling technologies and tools.

Atwater, James E.↗

DOE OSTI2024

In‐operando thermal transport characterization of moving particle bed heat exchanger

The project aimed to develop modulated photothermal radiometry (MPR) for conducting in-operando measurements of thermal transport in moving particle bed heat exchangers (MPBE) located at Sandia National Laboratory (SNL). The plan was to initially conduct lab-scale measurements on a 1-meter-long particle channel at UCSD, followed by in- operando measurements at SNL on a 20 kWth MPBE prototype built for this project, and if time permitting, potential final deployment on SNL’s 1 MWth G3P3 MPBE. The first two goals were successfully achieved but due to changes with commissioning timeline of the G3P3 MPBE, in-operando measurements on the G3P3 MPBE could not be conducted. The measurement campaigns have resulted in some promising results and the MPR tool has been handed over to trained SNL personnel for future use. MPR measurements on UCSD’s 1-meter-long particle channel showed a peculiar length dependence of the particle bed thermal conductivity and near-wall thermal resistance. The bed thermal conductivity increased, and the near-wall thermal resistance decreased, with increasing distance from the channel inlet, both eventually reaching a plateau. This was found to be due to hydrostatic pressure screening by the channel walls, known as the “Janssen effect”, and is the first experimental study on its role in granular heat transfer. A 20 kWth small-scale MPBE prototype, the first of its kind with 3 mm particle channels and 2 mm sCO2 plates, was designed and manufactured by Vacuum Process Engineering (VPE) for this project. This MPBE prototype was installed in SNL’s HEX test stand and the MPR tool was integrated into the test stand for in-operando measurements. Several modifications have been made to the MPR setup for facile installation and easy operation at SNL. Measurements with Carbo HSP40/70 particles were conducted with various particle and sCO2 temperatures and flow rates. Further, apart from regular MPBE operation, fault scenarios such as plate warping, particle stagnation, and choking were also detected and MPR showed excellent sensitivity to the detection of such conditions. Through the course of this project, MPR has evolved from a sensitive laboratory technique to a rugged industrial tool with various applications in high temperature measurements and diagnostics.

14 SOLAR ENERGY↗

NASA NTRS1971

Emission characteristics of snow and ice in the microwave range

Some results are presented of a two year investigation on microwave emissions from snow. Included in the investigation were: theoretical studies; laboratory measurements of electrical properties of snow and similar materials; numerical modelling of hypothetical and real snowpacks; analysis of microwave data obtained on everflights; and quantative measurements of natural and artificial snowpacks made in the field. Results indicate that a fairly simple combination of microwave polarizations and frequencies can ultimately be used to monitor the water equivalent and free-water content as well as the distribution of snow. This understanding may also shed light on the physics of microwave emission from other wet, granular, layered media.

Meier, M. F.↗

NASA NTRS1992

STS-42 Space Shuttle mission report

The STS-42 Space Shuttle Program Mission Report contains a summary of the vehicle subsystem operations during the forty-fifth flight of the Space Shuttle Program and the fourteenth flight of the Orbiter vehicle Discovery (OV-103). In addition to the Discovery vehicle, the flight vehicle consisted of the following: an External Tank (ET) designated as ET-52 (LWT-45); three Space Shuttle main engines (SSME's), which were serial numbers 2026, 2022, and 2027 in positions 1, 2, and 3, respectively; and two Solid Rocket Boosters (SRB's) designated as BI-048. The lightweight redesigned Solid Rocket Motors (RSRM's) installed in each one of the SRB's were designated as 360L020A for the left SRM and 360Q020B for the right SRM. The primary objective of the STS-42 mission was to complete the objectives of the first International Microgravity Laboratory (IML-1). Secondary objectives were to perform all operations necessary to support the requirements of the following: Gelation of Sols: Applied Microgravity Research (GOSAMR); Student Experiment 81-09 (Convection in Zero Gravity); Student Experiment 83-02 (Capillary Rise of Liquid Through Granular Porous Media); the Investigation into Polymer Membrane Processing (IPMP); the Radiation Monitoring Equipment-3 (RME-3); and Get-Away Special (GAS) payloads carried on the GAS Beam Assembly.

Fricke, Robert W.↗

NASA NTRS2011

Antimicrobial-Coated Granules for Disinfecting Water

Methods of preparing antimicrobialcoated granules for disinfecting flowing potable water have been developed. Like the methods reported in the immediately preceding article, these methods involve chemical preparation of substrate surfaces (in this case, the surfaces of granules) to enable attachment of antimicrobial molecules to the surfaces via covalent bonds. A variety of granular materials have been coated with a variety of antimicrobial agents that include antibiotics, bacteriocins, enzymes, bactericides, and fungicides. When employed in packed beds in flowing water, these antimicrobial-coated granules have been proven effective against gram-positive bacteria, gram-negative bacteria, fungi, and viruses. Composite beds, consisting of multiple layers containing different granular antimicrobial media, have proven particularly effective against a broad spectrum of microorganisms. These media have also proven effective in enhancing or potentiating the biocidal effects of in-line iodinated resins and of very low levels of dissolved elemental iodine.

Akse, James R.↗

NASA NTRS2013

Advanced Magnetic Materials Methods and Numerical Models for Fluidization in Microgravity and Hypogravity

To support long-duration manned missions in space such as a permanent lunar base, Mars transit, or Mars Surface Mission, improved methods for the treatment of solid wastes, particularly methods that recover valuable resources, are needed. The ability to operate under microgravity and hypogravity conditions is essential to meet this objective. The utilization of magnetic forces to manipulate granular magnetic media has provided the means to treat solid wastes under variable gravity conditions by filtration using a consolidated magnetic media bed followed by thermal processing of the solid wastes in a fluidized bed reactor. Non-uniform magnetic fields will produce a magnetic field gradient in a bed of magnetically susceptible media toward the distributor plate of a fluidized bed reactor. A correctly oriented magnetic field gradient will generate a downward direct force on magnetic media that can substitute for gravitational force in microgravity, or which may augment low levels of gravity, such as on the Moon or Mars. This approach is termed Gradient Magnetically Assisted Fluidization (G-MAFB), in which the magnitude of the force on the fluidized media depends upon the intensity of the magnetic field (H), the intensity of the field gradient (dH/dz), and the magnetic susceptibility of the media. Fluidized beds based on the G-MAFB process can operate in any gravitational environment by tuning the magnetic field appropriately. Magnetic materials and methods have been developed that enable G-MAFB operation under variable gravity conditions.

Atwater, James↗

NASA NTRS2013

NASA Tech Briefs, July 2013

Dielectrophoresis-Based Particle Sensor Using Nanoelectrode Arrays; Multi-Dimensional Damage Detection for Surfaces and Structures; ULTRA: Underwater Localization for Transit and Reconnaissance Autonomy; Autonomous Cryogenic Leak Detector for Improving Launch Site Operations; Submillimeter Planetary Atmospheric Chemistry Exploration Sounder; Method for Reduction of Silver Biocide Plating on Metal Surfaces; Silicon Micromachined Microlens Array for THz Antennas; Forward-Looking IED Detector Ground Penetrating Radar; Fully Printed, Flexible, Phased Array Antenna for Lunar Surface Communication, Battery Charge Equalizer with Transformer Array; An Efficient, Highly Flexible Multi-Channel Digital Downconverter Architecture; Dimmable Electronic Ballast for a Gas Discharge Lamp; Conductive Carbon Nanotube Inks for Use with Desktop Inkjet Printing Technology; Enhanced Schapery Theory Software Development for Modeling Failure of Fiber-Reinforced Laminates; High-Performance, Low-Temperature-Operating, Long-Lifetime Aerospace Lubricants; Carbon Nanotube Microarrays Grown on Nanoflake Substrates; Differential Muon Tomography to Continuously Monitor Changes in the Composition of Subsurface Fluids; Microgravity Drill and Anchor System; 20 Granular Media-Based Tunable Passive Vibration Suppressor; 21 Miga Aero Actuator and 2D Machined Mechanical Binary Latch; Micro-XRF for In Situ Geological Exploration of Other Planets; Hydrogen-Enhanced Lunar Oxygen Extraction and Storage Using Only Solar Power; Uplift of Ionospheric Oxygen Ions During Extreme Magnetic Storms; Miniaturized, High-Speed, Modulated X-Ray Source; Hollow-Fiber Spacesuit Water Membrane Evaporator 25 High-Power Single-Mode 2.65-micrometers InGaAsSb/AlInGaAsSb Diode Lasers; Optical Device for Converting a Laser Beam Into Two Co-aligned but Oppositely Directed Beams; A Hybrid Fiber/Solid-State Regenerative Amplifier with Tunable Pulse Widths for Satellite Laser Ranging; X-Ray Diffractive Optics; SynGenics Optimization System (SynOptSys); 29 CFD Script for Rapid TPS Damage Assessment; radEq Add-On Module for CFD Solver Loci-CHEM; Science Opportunity Analyzer (SOA) Version 8; 30 Autonomous Byte Stream Randomizer; Distributed Engine Control Empirical/Analytical Verification Tools; Dynamic Server-Based KML Code Generator Method for Level-of-Detail Traversal of Geospatial Data; Automated Planning of Science Products Based on Nadir Overflights and Alerts for Onboard and Ground Processing; Linked Autonomous Interplanetary Satellite Orbit Navigation; Risk-Constrained Dynamic Programming for Optimal Mars Entry, Descent, and Landing; Scheduling Operations for Massive Heterogeneous Clusters; Deepak Condenser Model (DeCoM); Flight Software Math Library; Recirculating 1-K-Pot for Pulse-Tube Cryostats; 35 Method for Processing Lunar Regolith Using Microwaves; Wells for In Situ Extraction of Volatiles from Regolith (WIEVR); and Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft.

Source record↗

NASA NTRS2011

Granular Simulation of NEO Anchoring

NASA is interested in designing a spacecraft capable of visiting a Near Earth Object (NEO), performing experiments, and then returning safely. Certain periods of this mission will require the spacecraft to remain stationary relative to the NEO. Such situations require an anchoring mechanism that is compact, easy to deploy and upon mission completion, easily removed. The design philosophy used in the project relies on the simulation capability of a multibody dynamics physics engine. On Earth it is difficult to create low gravity conditions and testing in low gravity environments, whether artificial or in space is costly and therefore not feasible. Through simulation, gravity can be controlled with great accuracy, making it ideally suited to analyze the problem at hand. Using Chrono::Engine [1], a simulation package capable of utilizing massively parallel GPU hardware, several validation experiments will be performed. Once there is sufficient confidence, modeling of the NEO regolith interaction will begin after which the anchor tests will be performed and analyzed. The outcome of this task is a study with an analysis of several different anchor designs, along with a recommendation on which anchor is better suited to the task of anchoring. With the anchors tested against a range of parameters relating to soil, environment and anchor penetration angles/velocities on a NEO.

multibody dynamics↗

NASA NTRS2013

Dynamics and Control of a Disordered System in Space

In this paper, we present some ideas regarding the modeling, dynamics and control aspects of granular spacecraft. Granular spacecraft are complex multibody systems composed of a spatially disordered distribution of a large number of elements, for instance a cloud of N grains in orbit, with N greater than 10(exp 3). These grains can be large (Cubesat-size) or small (mm-size), and can be active, i.e., a fully equipped vehicle capable sensing their own position and attitude, and enabled with propulsion means, or entirely passive. The ultimate objective would be to study the behavior of the single grains and of large ensembles of grains in orbit and to identify ways to guide and control the shape of a cloud composed of these grains so that it can perform a useful function in space, for instance, as an element of an optical imaging system for astrophysical applications. This concept, in which the aperture does not need to be continuous and monolithic, would increase the aperture size several times compared to large NASA observatories such as ATLAST, allowing for a true Terrestrial Planet Imager that would be able to resolve exo-planet details and do meaningful spectroscopy on distant world. In the paper, we address the modeling and autonomous operation of a distributed assembly (the cloud) of large numbers of highly miniaturized space-borne elements (the grains). A multi-scale, multi-physics model is proposed of the dynamics of the cloud in orbit, as well as a control law for cloud shape maintenance, and preliminary simulation studies yield an estimate of the computational effort, indicating a scale factor of approximately N(exp 1.4) as a function of the number of grains. A granular spacecraft can be defined as a collection of a large number of space-borne elements (in the 1000s) designed and controlled such that a desirable collective behavior emerges, either from the interactions among neighboring grains, and/or between the grains and the environment. In this paper, each grain is considered to be a highly miniaturized spacecraft which has limited size and mass, hence it has limited actuation, limited propulsive capability, limited power, limited sensing, limited communication, limited computational resources, limited range of motion, limited lifetime, and may be expendable. The modeling and dynamics of clouds of vehicles is more challenging than with conventional vehicles because we are faced with a probabilistic vehicle composed of a large number of physically disconnected vehicles. First, different scales of motion occur simultaneously in a cloud: translations and rotations of the cloud as a whole (macro-dynamics), relative rotation and translation of one cloud member with respect to another (meso-dynamics), and individual cloud member dynamics (micro-dynamics). Second, the control design needs to be tolerant of the system complexity, of the system architecture (centralized vs. decentralized large scale system control) as well as robust to un-modeled dynamics and noise sources. Figure 1, top left, shows the kinematic parameters of a 1000 element cloud in orbit. The motion of the system is described with respect to a local vertical-local horizontal (LV-LH) orbiting reference frame (x,y,z)=F(sub ORF) of origin O(sub ORF) which rotates with mean motion omega and orbital semi-major axis R(sub 0). The orbital geometry at the initial time is defined in terms of its six orbital elements, and the orbital dynamics equation for point O(sub ORF) is propagated forward in time under the influence of the gravitational field of the primary and other external perturbations, described below. The origin of this frame coincides with the initial position of the center of mass of the system, and the coordinate axes are z along the local vertical, x toward the flight direction, and y in the orbit normal direction. The assumptions we used to model the dynamics are as follows: 1) The inertial frame is fixed at Earth's center. 2) The orbiting Frame ORF follows Keplerian orbit. 3) the cloud system dynamics is referred to ORF. 4) the attitude of each grain uses the principal body frame as body fixed frame. 5) the atmosphere is assumed to be rigidly rotating with the Earth. Regarding the grains forming the cloud: 1) each grain is modeled as a rigid body; 2) a simple attitude estimator provides attitude estimates, 3) a simple guidance logic commands the position and attitude of each grain, 4) a simple local feedback controller based on PD control of local states is used to stabilize the attitude of the vehicle. Regarding the cloud: 1) the cloud as a whole is modeled as an equivalent rigid body in orbit, and 2) an associated graph establishes agent connectivity and enables coupling between modes of motion at the micro and macro scales; 3) a simple guidance and estimation logic is modeled to estimate and command the attitude of this equivalent rigid body; 4) a cloud shape maintenance controller is based on the dynamics of a stable virtual truss in the orbiting frame. Regarding the environmental perturbations acting on the cloud: 1) a non-spherical gravity field including JO (Earth's spherical field) zonal component, J2 (Earth's oblateness) and J3 zonal components is implemented; 2) atmospheric drag is modeled with an exponential model; 3) solar pressure is modeled assuming the Sun is inertially fixed; and 4) the Earth's magnetic field is model using an equivalent dipole model. The equations of motion are written in a referential system with respect to the origin of the orbiting frame and the state is propagated forward in time using an incremental predictor-corrector scheme. A representative cloud with varying number of grains is simulated to identify the limitations in computation time as the number of grains grows. We derive a control law to track a desired surface in the ORF (equivalently to maintain a reference cloud shape) by defining an error from a desired surface shape, and designing a control law that is exponentially stable and reduces the tracking error to zero. Figure 1 (top right) shows a comparison of various requirements for simulation of single spacecraft vs. granular spacecraft, indicating the high degree of complexity that needs to be taken into consideration. The ORF components of control force required by one of the grains is, for this particular case, in the micro-Newton range. However, no attempt has been made yet to reconfigure (or re-orient) the cloud configuration internally, for which forces in the milli-Newton level are expected, depending on the time required to do the reconfiguration. Figure 1, bottom, shows the computation time as a function of the number of grains, indicating an order N(exp 1.43) scaling on a 8 Gb, 1067 MHz RAM MacOSX computer with a 3.06 GHz Intel Core 2 Duo processor. With this metric, the same simulation for a system of N=1000 grains would take 5.4 hours, and 146 hours (i.e., 6 days) for a system with N=10,000 grains. Therefore, efficient ways to simulate this complex system, where not only the time scales of natural system dynamics, but also the sampling times of the Guidance, Navigation, and Control are included, remain to be explored. Additional details on the cloud modeling, dynamics, and control will be described in the paper.

simulation↗

NASA NTRS2013

Multi-Scale Dynamics, Control, and Simulation of Granular Spacecraft

granular media↗

NASA NTRS2015

NIAC Phase II Orbiting Rainbows Granular Imager

In this paper, we present some ideas regarding the optics and imaging aspects of granular spacecraft. Granular spacecraft are complex systems composed of a spatially disordered distribution of a large number of elements, for instance a cloud of grains in orbit. An example of application is a spaceborne observatory for exoplanet imaging, where the primary aperture is a cloud instead of a monolithic aperture.

dynamics↗

NASA NTRS2015

Dynamics and Control of Granular Imaging Systems

optical trapping↗

NASA NTRS2021

Grand Challenges in Soft Matter Science: Prospects for Microgravity Research

At the suggestion of NASA’s Physical Science Research Program in the Space Life and Physical Science Research and Application Division, Paul Chaikin, Noel Clark, and Sidney Nagel organized a focus session and workshop for the 2020 American Physical Society (APS) March meeting under the auspices of the Division of Soft Matter. Three overarching themes emerged from the workshop and are presented with additional details: •Machines made out of machines •Scalable self-sustaining ecosystems •Active materials and metamaterials This report lays out only some of the potential directions for soft matter dynamics over the next two decades. It also lays out the role that gravity plays in the organization of the basic building blocks of matter. Not only will research on soft matter have tremendous application towards understanding its behavior in our terrestrial environment, but also potentially in other NASA programs such as planetary science, exploration, robotics, etc.

Microgravity↗

NASA NTRSDate not supplied

Demonstration of in-Situ Resource Utilization of Lunar Regolith for Plant Growing Systems Through Scaled Capillary Models

The development of reliable and bioregenerative crop growth production systems is vital for human exploration into deep space. As the National Aeronautics and Space Administration (NASA) prepares for the Artemis missions, scientists need to find a way to provide consistent and sufficient water delivery for all stages of a plant’s life cycle. NASA has been able to successfully model passive flow through felt material, to mimic the water uptake and transport through a plant, in microgravity. However, more studies need to be conducted to adapt the model for a substrate-based system and incorporate how flow will change during each stage of plant growth. For future missions, payload requirements to support crop production systems will need to be limited, leading to the use of available resources, such as lunar regolith. Although numerous lunar regolith simulants are commercially available, few have been evaluated for their suitability in agricultural applications. First, a base regolith simulant will need to be identified based on its physical and chemical properties. Then, additional amendments to improve the properties of the simulants to support plant growth will be identified. The design and composition of the substrate will be based on water transport requirements for different stages of plant growth. Scaled capillary models can be utilized to study surface-tension driven flows through various designer substrates to modify the physical properties of the selected regolith simulant. These models can accurately represent how flow will act in a reduced gravity environment, which can be used to design a full-scale facility for surface missions. This project will aid space researchers in the design of future crop production systems for surface missions by creating a refined model that can be used at all stages of plant growth and utilize in situ resources.

Fluids↗