Exoskeleton energetics: Implications for planetary extravehicular activity

Humans first visited another world nearly 50 years ago and are poised to return to the Moon and visit Mars in the coming decade(s). Developing a space suit that supports safe, efficient, and effective exploration despite the extremes of temperature, pressure, radiation, and environmental hazards like dust and topography remains a critical challenge. Space suits impose restrictions on movement that increase metabolic rate and limit the intensity and duration of extravehicular activity. In this study, a lower body exoskeleton was used to test a simple model that predicts the energy cost of locomotion across gait and gravity. Energetic cost and other variables were measured during treadmill locomotion, with and without a lower body exoskeleton, in simulated reduced gravity and in Earth gravity. Six subjects walked and ran at constant Froude numbers, non-dimensional parameters used to characterize gait. The springlike energy recovery of the exoskeleton legs was estimated using energetics data in combination with the model. Model predictions agreed with the observed results (no statistical difference). High spring-like energy recovery of the exoskeleton legs lowered measures of the energetic cost of locomotion. For planetary extravehicular activity, our work reveals potential approaches to optimizing space suits for efficient locomotion, for example, tuning the stiffness and spring-like energy recovery of space suit legs

A Compact Anomaly Detection Solution for Science Instruments

Small low-cost instruments enable new and exciting mission opportunities yet their constrained volume and limited budgets make them especially susceptible to suffering anomalies during flight. Radiation effects as well as sensor or actuator failure can all pose a serious threat to the continued collection of scientific data as well as cause the partial or complete loss of a mission science payload. Onboard anomaly detection could allow instruments to recover from such events but its ad hoc development typically falls outside the mission timeline or monetary constraints. Here we describe a compact solution for the implementation of onboard anomaly detection meant for space science missions. The device is designed to be interoperable with a broad range of instruments utilizing easily accessible power and logic signals to monitor the state of peripherals and actuators without disrupting their functionality. By leveraging a commercially available microcontroller with a radiation hardened alternative package the device can be inexpensively sourced and assembled with minimal work enabling instrument characterization on an expedited timeline. The system can then be exchanged for a radiation hardened version ensuring the replicability of observed anomalies in a laboratory environment during instrument operations. We also present currently implemented anomaly detection algorithms which enable the system to detect anomalies in instruments with varying failure modes and allow mission designers to choose which detection approach best fits the specific needs of their instrument. Finally, we showcase an example application of this system in the detection of anomalies during the operation of a lysis motor designed for use in biological space instruments.Comment: 7 pages, 10 figure

Biochemical and High Throughput Microscopic Assessment of Fat Mass in Caenorhabditis Elegans

The nematode C. elegans has emerged as an important model for the study of conserved genetic pathways regulating fat metabolism as it relates to human obesity and its associated pathologies. Several previous methodologies developed for the visualization of C. elegans triglyceride-rich fat stores have proven to be erroneous, highlighting cellular compartments other than lipid droplets. Other methods require specialized equipment, are time-consuming, or yield inconsistent results. We introduce a rapid, reproducible, fixative-based Nile red staining method for the accurate and rapid detection of neutral lipid droplets in C. elegans. A short fixation step in 40% isopropanol makes animals completely permeable to Nile red, which is then used to stain animals. Spectral properties of this lipophilic dye allow it to strongly and selectively fluoresce in the yellow-green spectrum only when in a lipid-rich environment, but not in more polar environments. Thus, lipid droplets can be visualized on a fluorescent microscope equipped with simple GFP imaging capability after only a brief Nile red staining step in isopropanol. The speed, affordability, and reproducibility of this protocol make it ideally suited for high throughput screens. We also demonstrate a paired method for the biochemical determination of triglycerides and phospholipids using gas chromatography mass-spectrometry. This more rigorous protocol should be used as confirmation of results obtained from the Nile red microscopic lipid determination. We anticipate that these techniques will become new standards in the field of C. elegans metabolic research

Acceleration Profiles and Processing Methods for Parabolic Flight

Parabolic flights provide cost-effective, time-limited access to "weightless" or reduced gravity conditions experienced in space or on planetary surfaces, e.g. the Moon or Mars. These flights facilitate fundamental research - from materials science to space biology - and testing/validation activities that support and complement infrequent and costly access to space. While parabolic flights have been conducted for decades, reference acceleration profiles and processing methods are not widely available - yet are critical for assessing the results of these activities. Here we present a method for collecting, analyzing, and classifying the altered gravity environments experienced during a parabolic flight. We validated this method using a commercially available accelerometer during a Boeing 727-200F flight with $20$ parabolas. All data and analysis code are freely available. Our solution can be easily integrated with a variety of experimental designs, does not depend upon accelerometer orientation, and allows for unsupervised and repeatable classification of all phases of flight, providing a consistent and open-source approach to quantifying gravito-intertial accelerations (GIA), or $g$ levels. As academic, governmental, and commercial use of space increases, data availability and validated processing methods will enable better planning, execution, and analysis of parabolic flight experiments, and thus, facilitate future space activities.Comment: Correspondence to C.E. Carr ([email protected]). 15 pages, 4 figures, 3 supplemental figures. Code: https://github.com/CarrCE/zerog, Dataset: https://osf.io/nk2w4

The bioenergetics of walking and running in space suits

Thesis (Sc. D.)--Harvard-MIT Division of Health Sciences and Technology, 2005.Includes bibliographical references (p. 185-195).Space-suited activity is critical for human spaceflight, and is synonymous with human planetary exploration. Space suits impose kinematic and kinetic boundary conditions that affect movement and locomotion, and in doing so modify the metabolic cost of physical activity. Metabolic requirements, found to be significantly elevated in space-suited activity, are a major driver of the allowable duration and intensity of extravehicular activity. To investigate how space suited locomotion impacts the energetics of walking and running, I developed a framework for analyzing energetics data, derived from basic thermodynamics, that clearly differentiates between muscle efficiency and energy recovery. The framework, when applied to unsuited locomotion, revealed that the human run-walk transition in Earth gravity occurs when energy recovery for walking and running are approximately equal. The dependence of muscle efficiency on gravity -during locomotion and under a particular set of assumptions- was derived as part of the framework. Next, I collected and transformed data from prior studies of suited and unsuited locomotion into a common format, and performed regression analysis. This analysis revealed that in reduced gravity environments, running in space suits is likely to be more efficient, per unit mass and per unit distance, than walking in space suits. Second, the results suggested that space suits may behave like springs during running. To investigate the spring-like nature of space suit legs, I built a lower-body exoskeleton to simulate aspects of the current NASA spacesuit, the Extravehicular Mobility Unit (EMU).(cont.) Evaluation of the exoskeleton legs revealed that they produce knee torques similar to the EMU in both form and magnitude. Therefore, space suit joints such as the EMU knee joint behave like non-linear springs, with the effect of these springs most pronounced when locomotion requires large changes in knee flexion such as during running. To characterize the impact of space suit legs on the energetics of walking and running, I measured the energetic cost of locomotion with and without the lower-body exoskeleton in a variety of simulated gravitational environments at specific and self- selected Froude numbers, non-dimensional parameters used to characterize the run-walk transition. Exoskeleton locomotion increased energy recovery and significantly improved the efficiency of locomotion, per unit mass and per unit distance, in reduced gravity but not in Earth gravity. The framework was used to predict, based on Earth gravity data, the metabolic cost of unsuited locomotion in reduced gravity; there were no statistical differences between the predictions and the observed values. The results suggest that the optimal space-suit knee-joint torque may be non-zero: it may be possible to build a 'tuned space suit' that minimizes the energy cost of locomotion. Furthermore, the observed lowering of the self-selected run-walk transition Froude number during exoskeleton locomotion is consistent with the hypothesis that the run-walk transition is mediated by energy recovery. The major contributions of the dissertation include: 1. A model that predicts metabolic cost in non-dimensional form for unsuited locomotion across running and walking and across gravity levels, 2.(cont.) An assessment of historical data that reveals the effect of pressure suits on work output and the metabolic cost of locomotion, 3. A method of simulating a space suit using a lower-body exoskeleton, and methods for designing and characterizing the exoskeleton, 4. An explanation for the differences in the energetic costs of walking and running in space suits, 5. Evidence that there is an optimal space suit leg stiffness, perhaps an optimal space suit leg stiffness for a given gravity environment, 6. Evidence, mostly indirect, that energy recovery plays a role in gait switching.by Christopher Edward Carr.Sc.D

Distributed architectures for Mars surface exploration

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001.Includes bibliographical references (p. [361]-370).by Christopher E. Carr.S.M

Driving self-restriction and age: A study of emergency department patients

BACKGROUND: Driving self-restriction is well-documented among older drivers but might also occur among younger drivers. Little is known about the driving patterns of emergency department (ED) patients, who may be a high-risk population for motor vehicle crashes (MVCs). We sought to compare the driving patterns and MVCs of younger and older adult ED patients in order to inform development of injury prevention interventions in EDs. METHODS: We surveyed English-speaking younger adult (age 25–64) and older adult (age ≥65) ED patients, excluding non-drivers and those who were cognitively-impaired or too sick to participate. We compared drivers by age group and used logistic regression with adjustment for driving frequency to examine factors associated with driving self-restriction. RESULTS: Of those eligible, 82% (n = 178) of younger adult and 91% (n = 134) of older adult patients participated; approximately half were women. Similar proportions of younger and older adult patients reported driving everyday/almost everyday (80%) but also self-restricting driving in inclimate weather (48%), heavy traffic (27%), in unfamiliar places (21%), when travelling with passengers (1.6%) or when alone (1.3%). Fewer younger adult than older adult patients avoided driving at night (22% versus 49%) or on highways (6.7% versus 26%). In multivariable logistic regression, factors significantly associated self-imposed driving restriction in ≥1 driving situation were female gender (Odds Ratio [OR] 2.40; 95% CI 1.42-4.05) and ever feeling “confused, nervous or uncomfortable” while driving (OR 1.87; 95% CI 1.03-3.39). There was a non-significant trend for differences in proportions between younger adult (11%) and older adult (6.8%) drivers reporting ≥1 MVC as a driver in the past 12 months. CONCLUSIONS: Similar proportions of younger and older adult ED patients self-restrict driving, albeit in different situations, which has implications for behavioral interventions for injury prevention and for education of patients and medical providers. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s40621-014-0018-z) contains supplementary material, which is available to authorized users

Constant Size Molecular Descriptors For Use With Machine Learning

A set of molecular descriptors whose length is independent of molecular size is developed for machine learning models that target thermodynamic and electronic properties of molecules. These features are evaluated by monitoring performance of kernel ridge regression models on well-studied data sets of small organic molecules. The features include connectivity counts, which require only the bonding pattern of the molecule, and encoded distances, which summarize distances between both bonded and non-bonded atoms and so require the full molecular geometry. In addition to having constant size, these features summarize information regarding the local environment of atoms and bonds, such that models can take advantage of similarities resulting from the presence of similar chemical fragments across molecules. Combining these two types of features leads to models whose performance is comparable to or better than the current state of the art. The features introduced here have the advantage of leading to models that may be trained on smaller molecules and then used successfully on larger molecules.Comment: 18 pages, 5 figure

Crystallization and preliminary X-ray diffraction analysis of two N-terminal fragments of the DNA-cleavage domain of topoisomerase IV from Staphylococcus aureus. Corrigendum

A corrigendum to the paper by Carr et al. (2006), Acta Cryst. F62, 1164–1167