Extravehicular Activity Crewmembers Research Articles

Approaches to decompression safety support of EVA for orbital and interplanetary missions

The paper is devoted to the analysis of possible methods for decompression safety support of extravehicular activity (EVA) in order to ground the perspective approaches for solution of decompression sickness (DCS) problem in space missions of the near and distant future. Current DCS risk mitigation strategies reduce operational efficiency: preoxygenation extends the time required on preparation to EVA. The crewmembers often experience general and hand fatigue during long EVA due to the lack of flexibility of space suits enclosure operated at 30–40 kPa. To create the safe and comfortable working conditions for EVA crewmembers on the Lunar and Martian surfaces the main biomedical requirements to a planetary space suit have to include low mass of EVA system, high mobility and flexibility of space suit enclosure and reliable protection against DCS with a short or zero preoxygenation period. Reviewed here are the possibilities for the use of preoxygenation, hypobaric gas atmosphere in space cabin and/or planetary habitat, idea of substitution of nitrogen in normobaric gas atmosphere to another inert gas (helium and neon) as countermeasures against DCS in EVA crewmembers. Physiological aspects of the conception for space suit with high operating pressure are considered.

The use of an extended ventilation tube as a countermeasure for EVA-associated upper extremity medical issues

Introduction: Onycholysis due to repetitive activity in the space suit glove during Neutral Buoyancy Laboratory (NBL) training and during spaceflight extravehicular activity (EVA) is a common observation. Moisture accumulates in gloves during EVA task performance and may contribute to the development of pain and damage to the fingernails experienced by many astronauts. The study evaluated the use of a long ventilation tube to determine if improved gas circulation into the hand area could reduce hand moisture and thereby decrease the associated symptoms. Methods: The current Extravehicular Mobility Unit (EMU) was configured with a ventilation tube that extended down a single arm of the crew member (E) and compared with the unventilated arm (C). Skin surface moisture was measured on both hands immediately after glove removal and a questionnaire administered to determine subjective measures. Astronauts ( n = 6 ) were examined pre- and post-run. Results: There were consistent trends in the reduction of relative hydration ratios at dorsum ( C = 3.34 , E = 2.11 ) and first ring finger joint ( C = 2.46 , E = 1.96 ) when the ventilation tube was employed. Ventilation appeared more effective on the left versus the right hand, implying an interaction with hand anthropometry and glove fit. Symptom score was lower on the hand that had the long ventilation tube relative to the control hand in 2/6 EVA crew members. Conclusions: Increased ventilation to the hand was effective in reducing the risks of hand and nail discomfort symptoms from moderate to low in one-third of the subjects. Improved design in the ventilation capability of EVA spacesuits is expected to improve efficiency of air flow distribution.

N-Nitrosodimethylamine Release from Fuel Oxidizer Reaction Product Contamined Extravehicular Activity Suits

Before extravehicular activity (EVA) on the Russian segment (RS) of the International Space Station (ISS), the docking compartment (DC1) must be depressurized, because it is used as an airlock. It is preferred to use the U.S. control moment gyros (CMGs) instead of attitude-control thruster firings to compensate for disturbances and to maintain the ISS vehicle attitude. However, when the DC1 is depressurized, the CMGs’ margin of momentum is insufficient to compensate for the disturbance and the service module (SM) attitude-control thrusters’ need to fire to desaturate the CMGs. The SM roll-control thruster firings induce fuel‐oxidizer reaction products (FORP) contamination on the adjacent SM surfaces around the thrusters. One of the components present in FORP is the potent carcinogen N-nitrosodimethylamine (NDMA). Because the EVA crewmembers often enter the area surrounding the thrusters for tasks on the aft end of the SM and when translating to other areas of the RS, the presence of FORP contamination is a concern. FORP contamination of the SM surfaces is discussed, along with the potential release of NDMA in a humid environment from crew EVA suits, whether they happen to be contaminated with FORP, the toxicological risk associated with the NDMA release, and the implementation of flight rules to mitigate the hazard.

Computational Simulation of Extravehicular Activity Dynamics During a Satellite Capture Attempt

A more quantitative approach to the analysis of astronaut extravehicular activity (EVA) tasks is needed because of their increasing complexity, particularly in preparation for the on-orbit assembly of the International Space Station. Existing useful EVA computer analyses produce either high-resolution three-dimensional computer images based on anthropometric representations or empirically derived predictions of astronaut strength based on lean body mass and the position and velocity of body joints but do not provide multibody dynamic analysis of EVA tasks. Our physics-based methodology helps fill the current gap in quantitative analysis of astronaut EVA by providing a multisegment human model and solving the equations of motion in a high-fidelity simulation of the system dynamics. The simulation work described here improves on the realism of previous efforts by including three-dimensional astronaut motion, incorporating joint stops to account for the physiological limits of range of motion, and incorporating use of constraint forces to model interaction with objects. To demonstrate the utility of this approach, the simulation is modeled on an actual EVA task, namely, the attempted capture of a spinning Intelsat VI satellite during STS-49 in May 1992. Repeated capture attempts by an EVA crewmember were unsuccessful because the capture bar could not be held in contact with the satellite long enough for the capture latches to fire and successfully retrieve the satellite.