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The Effects of Microgravity on Seated Height (Spinal Elongation)
ABSTRACT Many physiological factors, such as spinal elongation, fluid shifts, bone atrophy, and muscle loss, occur during an exposure to a microgravity environment. Spinal elongation is just one of the factors that can also affect the safety and performance of a crewmember while in space. Spinal elongation occurs due to the lack of gravity/compression on the spinal column. This allows for the straightening of the natural spinal curve. There is a possible fluid shift in the inter-vertebral disks that may also result in changes in height. This study aims at collecting the overall change in seated height for crewmembers exposed to a microgravity environment. During previous Programs, Apollo-Soyuz Test Project (ASTP) and Skylab, spinal elongation data was collected from a small number of subjects in a standing posture but were limited in scope. Data from these studies indicated a quick increase in stature during the first few days of weightlessness, after which stature growth reached a plateau resulting in up to a 3% increase of the original measurement [1-5]. However, this data was collected only for crewmembers in standing posture and not in a seated posture. Seated height may have a different effect than standing height due to a change in posture as well as due to a compounded effect of wearing restraints and a potential compression of the gluteal area. Seated height was deemed as a critical measurement in the design of the Constellation Program s (CxP) Crew Exploration Vehicle (CEV), called Orion which is now the point-of-departure vehicle for the Multi-Purpose Crew Vehicle (MPCV) Program; therefore a better understanding of the effects of microgravity on seated height is necessary. Potential changes in seated height that may not have impacted crew accommodation in previous Programs will have significant effects on crew accommodation due to the layout of seats in the Orion.. The current and existing configuration is such that the four crewmembers are stacked two by two with the commander and pilot seats on the top and the two remaining seats underneath, thereby limiting the amount of clearance for the crewmembers seated in the bottom seat. The inner mold line of these types of vehicles are fixed due to other design constraints; therefore, it is essential that all seats incorporate additional clearance to account for adequate spinal growth thereby ensuring that the crew can safely ingress the seat and be strapped in prior to its return to earth. If there is not enough clearance to account for spinal growth deltas between seats then there is the potential that crewmembers will not be able to comfortably and safely fit into their seats. The crewmember in the bottom stacked seat may even have negative clearance with the seat above him or her which could lead to potential ingress/egress issues or potentially injury of the crewmember during landing. These impacts are specific to these types of vehicles with stacked seat configuration. Without proper knowledge of the amount of spinal elongation, or growth, which occurs due to microgravity and space flight, the design of future vehicle(s) or suits may cause injury, discomfort, and limit crew accommodation and crew complements. The experiment primarily aimed to collect seated height data for subjects exposed to microgravity environments, and feed new information regarding the effect of elongation of the spine forward into the design of the Orion. The data collected during the experiment included, two seated height measurement and two digital pictures of seated height pre-, in-, and post-flight. In addition to seated height, crewmembers had an optional task of collecting stature , standing height. Seated height data was obtained from 29 crewmembers that included 8 ISS increment crew (2 females and 6 males) and 21 Shuttle crew (1 female, 20 males), and whose mean age was 48 years ( 4 years). This study utilized the last six Shuttle flights, STS-128 to STS-134. The results show that partipating crewmembers experienced growth up to 6% in seated height and up to 3% in stature. Based on the worst case statistical analysis of the subject data, the recommended seated height growth of 6% will be provided to the designers as the necessary seated height adjustment.
Young, K. S.↗
Development of a Methodology to Gather Seated Anthropometry in a Microgravity Environment
The Constellation Program's Crew Exploration Vehicle (CEV) is required to accommodate the full population range of crewmembers according to the anthropometry requirements stated in the Human-Systems Integration Requirement (HSIR) document (CxP70024). Seated height is one of many critical dimensions of importance to the CEV designers in determining the optimum seat configuration in the vehicle. Changes in seated height may have a large impact to the design, accommodation, and safety of the crewmembers. Seated height can change due to elongation of the spine when crewmembers are exposed to microgravity. Spinal elongation is the straightening of the natural curvature of the spine and the expansion of inter-vertebral disks. This straightening occurs due to fluid shifts in the body and the lack of compressive forces on the spinal vertebrae. Previous studies have shown that as the natural curvature of the spine straightens, an increase in overall height of 3% of stature occurs which has been the basis of the current HSIR requirements. However due to variations in the torso/leg ratio and impact of soft tissue, data is nonexistent as to how spinal elongation specifically affects the measurement of seated height. In order to obtain this data, an experiment was designed to collect spinal elongation data while in a seated posture in microgravity. The purpose of this study was to provide quantitative data that represents the amount of change that occurs in seated height due to spinal elongation in microgravity environments. Given the schedule and budget constraints of ISS and Shuttle missions and the uniqueness of the problem, a methodology had to be developed to ensure that the seated height measurements were accurately collected. Therefore, simulated microgravity evaluations were conducted to test the methodology and procedures of the experiment. This evaluation obtained seat pan pressure and seated height data to a) ensure that the lap restraint provided sufficient restraint to eliminate any gap between the subject s gluteal surface and the seat pan and b) to document any necessary design and procedural changes needed due to the microgravity environment. The methodology and setup used during the simulated microgravity evaluations was replicable to the proposed methodology and setup for in-space missions. A flight-like Shuttle seat, pressure sensors, anthropometer, and existing hardware was used to measure seated height and contact area while experiencing microgravity. The outlying buttock and thigh surface contact areas were collected to determine if the subjects were in contact with the seat pan, while a measurer recorded their seated height with an anthropometer. The Anthropometry and Biomechanics Facility (ABF) completed data collection from three microgravity flights to assess the restraint methods and techniques to be used for the in-flight procedures performed by the crewmembers in orbit. The first flight demonstrated that the restraint system on the seat, used in a nominal configuration, did not sufficiently restrain a person in the seat. The results showed the subjects were not in full contact with the seat pan, resulting in inaccurate sitting height data. Thus, a second flight was conducted to test different restraint system options. The results showed that by 1) changing the restraint system from the nominal 3-points of the 5-point harness, which is used for crewmembers when fully suited with emergency equipment, and 2) rerouting the lap straps around the joint of the backrest, where the backrest and seat pan are joined, resulted in the optimal method to restrain a subject. This rerouting method allowed for the anchor location to change and pull the subjects back into the seat instead of being anchored at the side of the subjects thighs. The results from the third flight validated the final restraint system, which resulted in a verified methodology for collecting seated anthropometry to ultimately determine the amount of spil elongation in a microgravity environment.
Rajulu, Sudhakar↗
Seating Considerations for Spaceflight: The Human to Machine Interface
Seating is one of the most critical components to be considered during design of a spacecraft. Since seats are the final interface between the occupant and the vehicle wherein all launch and landing operations are performed, significant effort must be spent to ensure proper integration of the human to the spacecraft. The importance of seating can be divided into two categories: seat layout and seat design. The layout of the seats drives the overall cabin configuration - from displays and controls, to windows, to stowage, to egress paths. Since the layout of the seats is such a critical design parameter within the crew compartment, it is one of the first design challenges that must be completed in the critical path of the spacecraft design. In consideration of seat layout in the vehicle, it is important for the designers to account for often intangible factors such as safety, operability, contingency performance, crew rescue. Seat layout will lead to definition of the quantity, shape, and posture of the seats. The seats of the craft must restrain and protect the occupant in all seated phases of flight, while allowing for nominal mission performance. In design of a spacecraft seat, the general posture of the occupant and the landing loads to be encountered are the greatest drivers of overall design. Variances, such as upright versus recumbent postures will dictate fit of the seat to the occupant and drive the total envelope of the seat around the occupant. Seat design revolves around applying sound principles of seated occupant protection coupled with the unique environments driven by the seat layout, landing loads, and operational and emergency scenarios.
Gohmert, Dustin M.↗
Crashworthy Seats Would Afford Superior Protection
Seats to prevent or limit crash injuries to astronauts aboard the crew vehicle of the Orion spacecraft are undergoing development. The design of these seats incorporates and goes beyond crash-protection concepts embodied in prior spacecraft and racing-car seats to afford superior protection against impacts. Although the seats are designed to support astronauts in a recumbent, quasi-fetal posture that would likely not be suitable for non-spacecraft applications, parts of the design could be adapted to military and some civilian aircraft seats and to racing car seats to increase levels of protection. The main problem in designing any crashworthy seat is to provide full support of the occupant against anticipated crash and emergency-landing loads so as to safely limit motion, along any axis, of any part of the occupant s body relative to (1) any other part of the occupant s body, (2) the spacecraft or other vehicle, and (3) the seat itself. In the original Orion spacecraft application and in other applications that could easily be envisioned, the problem is complicated by severe limits on space available for the seat, a requirement to enable rapid egress by the occupant after a crash, and a requirement to provide for fitting of the seat to a wide range of sizes and shapes of a human body covered by a crash suit, space suit, or other protective garment. The problem is further complicated by other Orion-application-specific requirements that must be omitted here for the sake of brevity. To accommodate the wide range of crewmember body lengths within the limits on available space in the original Orion application, the design provides for taller crewmembers to pull their legs back closer toward their chests, while shorter crewmembers can allow their legs to stretch out further. The range of hip-support seat adjustments needed to effect this accommodation, as derived from NASA s Human Systems Integration Standard, was found to define a parabolic path along which the knees must be positioned. For a given occupant, the specific position along the path depends on the distance from the heel to the back of the knee. The application of the concept of parabolic adjustment of the hip-support structure caused the seat pan to also take on a parabolic shape, yielding the unanticipated additional benefit that the seat pan fits the occupant s buttocks and thighs more nearly conformally than do seat pans of prior design. This more nearly conformal fit effectively eliminates a void between the occupant s body and the seat pan, thereby helping to prevent what, in prior seat designs, was shifting of the occupant s body into that void during an impact.
Gohmert, Dustin↗
Conical Seat Shut-Off Valve
A moveable valve for controlling flow of a pressurized working fluid was designed. This valve consists of a hollow, moveable floating piston pressed against a stationary solid seat, and can use the working fluid to seal the valve. This open/closed, novel valve is able to use metal-to-metal seats, without requiring seat sliding action; therefore there are no associated damaging effects. During use, existing standard high-pressure ball valve seats tend to become damaged during rotation of the ball. Additionally, forces acting on the ball and stem create large amounts of friction. The combination of these effects can lead to system failure. In an attempt to reduce damaging effects and seat failures, soft seats in the ball valve have been eliminated; however, the sliding action of the ball across the highly loaded seat still tends to scratch the seat, causing failure. Also, in order to operate, ball valves require the use of large actuators. Positioning the metal-to-metal seats requires more loading, which tends to increase the size of the required actuator, and can also lead to other failures in other areas such as the stem and bearing mechanisms, thus increasing cost and maintenance. This novel non-sliding seat surface valve allows metal-to-metal seats without the damaging effects that can lead to failure, and enables large seating forces without damaging the valve. Additionally, this valve design, even when used with large, high-pressure applications, does not require large conventional valve actuators and the valve stem itself is eliminated. Actuation is achieved with the use of a small, simple solenoid valve. This design also eliminates the need for many seals used with existing ball valve and globe valve designs, which commonly cause failure, too. This, coupled with the elimination of the valve stem and conventional valve actuator, improves valve reliability and seat life. Other mechanical liftoff seats have been designed; however, they have only resulted in increased cost, and incurred other reliability issues. With this novel design, the seat is lifted by simply removing the working fluid pressure that presses it against the seat and no external force is required. By eliminating variables associated with existing ball and globe configurations that can have damaging effects upon a valve, this novel design reduces downtime in rocket engine test schedules and maintenance costs.
Farner, Bruce↗
Ergonomic Evaluation of Space Shuttle Light-Weight Seat Lever Position and Operation
During a Shuttle flight in the early part of 1999, one of the crewmembers was unable to operate the backrest lever for the light-weight seat in microgravity. It is essential that the crewmembers are able to adjust this back-rest lever, which is titled forward 2 degrees from vertical during launch and then moved backwards to 10 degrees aft of vertical upon reaching orbit. This adjustment is needed to cushion the crewmembers during an inadvertent crash landing situation. The original Shuttle seats, which had seat controls located on the front left and right sides of the seat, were replaced recently with the new light-weight seats. The controls for these new, seats were moved to the night side with one control at the front and the other at the back. While it was uncertain whether the problem encountered was unique to that crewmember or not it was clear to the personnel responsible for maintaining the Shuttle seats that not knowing the cause of the problem posed a safety concern for NASA. Hence the Anthropometry and Biomechanics Facility (ABF) of the Johnson Space Center was requested to perform an evaluation of the seat controls and provide NASA with appropriate recommendations on whether the seat lever positions and operations should be modified. The ABF designed an experiment to investigate the amount of pull force exerted by subjects, wearing an unpressurized or pressurized crew launch escape suit, when controls were placed in the front and back (on the right side) of the light-weight seat. Single-axis load cells were attached to the seat levers, which measured the maximum static pull forces that were exerted by the subjects. Twelve subjects, six male and six female, participated in this study. Each subject was asked to perform the pull test at least three times for each combination of lever position and suit pressure conditions. The results from this study showed that as a whole (or in general), the subjects were able to pull on the lever at the back position with only about half the amount of force that they were able to exert on the lever at the front position. In addition, the results also showed that subjects wearing the pressurized suit were unable to reach the seat lever when it was located at the back. Furthermore, the pull forces on the front lever diminished about 50 % when subjects wore the pressurized suits. Based on these results from this study, it was recommended to NASA that the levers should not be located in the back position. In addition, further investigation is needed on whether the levers at the front of the seat could be modified or adjusted to increase the leverage for crew members wearing pressurized launch/escape suits.
Maida, J.↗
Effect of Molding and Machining on Neoflon CTFE M400H Polychlorotrifluoroethylene Rod Stock and Valve Seat Properties
Since 1997 numerous fires have been reported to the Food and Drug Administration involving cylinder valves installed on medical use oxygen cylinders sold and operated within the United States. All of the cylinder valves in question had polychlorotrifluoroethylene (PCTFE) valve seats. Subsequent failure analysis showed that the main seat was the primary source of ignition. A review of the incidents involving cylinder valve fires indicated three possible ignition mechanisms: contaminant promotion, flow friction, and resonance. However, gas purity analysis showed that uncombusted, residual oxygen was within specification. Infrared and energy dispersive spectroscopy further showed that no contaminants or organic compounds were present in the remaining, uncombusted valve seat material or on seat plug surfaces. Therefore, contaminant-promoted ignition did not appear to be responsible for the failures. Observations of extruded material along the outer edge of the coined or loaded seat area produced by cylinder overuse or poppet overload led to concerns that accelerated gas flow across a deformed seat surface could generate enough localized heating to ignite the polymeric seat. Low molecular weight or highly amorphous quick-quenched PCTFE grades might be expected to be especially prone to this type of deformation. Such a failure mechanism has been described as flow friction; however, the corresponding mechanistic parameters are poorly understood. Subsequent revelation of low-temperature dimensional instability by thermomechanical analysis (TMA) in a variety of PCTFE sheet and rod stock samples led to new concerns that PCTFE valve seats could undergo excessive expansion or contraction during service. During expansion, additional extrusion and accompanying flow friction could occur. During contraction, a gap between the seal and adjacent metal surfaces could form. Gas flowing past the gap could, in turn, lead to resonance heating and subsequent ignition as described in ASTM Guide for Evaluation Nonmetallic Materials for Oxygen Service (G 63). Attempts to uncover the origins of the observed dimensional instability were hindered by uncertainties about resin grade, process history, and post-process heat history introduced by machining, annealing, and sample preparation. An approach was therefore taken to monitor property changes before and after processing and machining using a single, well-characterized lot of Neoflon CTFE.1 M400H resin. A task group consisting of the current PCTFE resin supplier, two molders, and four valve seat manufacturers was formed, and phased testing on raw resin, intermediate rod stock, and finished valve seats initiated. The effect of processing and machining on the properties of PCTFE rod stock and oxygen gas cylinder valve seats was then determined. Testing focused on two types of extruded rod stock and one type of compression-molded rod stock. To accommodate valve seat manufacturer preferences for certain rod stock diameters, two representative diameters were used (4.8 mm (0.1875 in.) and 19.1 mm (0.75 in.)). To encompass a variety of possible sealing configurations, seven different valve seat types with unique geometries or machining histories were tested. The properties investigated were dimensional stability as determined by TMA, specific gravity, differential scanning calorimetry (DSC), compressive strength, zero strength time, and intrinsic viscosity. Findings are discussed in the context of polymer structure-process-property relationships whenever possible.
Waller, Jess M.↗
Spinal Elongation and its Effects on Seated Height in a Microgravity Environment (Spinal)
The primary objective of this project is to provide information pertaining to changes in seated height due to spinal elongation in a microgravity environment. The proposed experiment aims to collect seated height data for subjects exposed to microgravity environments, provide information relating to seated height rate of change over time, and feed new information regarding the elongation of the spine forward into the design of Constellation systems. Historical data indicates that spinal elongation occurs when crewmembers are subjected to microgravity. In as little as two days, the typical crewmember will exhibit increases in stature of up to 3 percent. However, data has been collected only for crewmembers in standing postures, and a limited pool of subjects was available. Due to the criticality of seated height in the design of the Crew Exploration Vehicle (CEV), a better understanding of the effects of microgravity on seated height is necessary. Small changes in seated height that may not have impacted crew accommodation in previous programs will have significant effects on crew accommodation due to the layout of seats in the CEV. The proposed study will directly measure changes in seated height for crewmembers in the Shuttle cockpit. An anthropometer will be used to record measurements to the top of the head of a seated subject, and an orthogonal photograph will be taken in order to measure seated height based on scaling references of known sizes as well as verify the posture and positioning remained consistent throughout the study. Data gained from this study will provide better information to CEV designers. Accurate measurements of crew seated height will be valuable for vehicle and habitation designers for future programs as well.
Rajulu, Sudhakar↗
Preliminary Results of the Effect of Microgravity on Seated Height
The new vehicle for future space travel to the International Space Station (ISS) and beyond will be highly dependent on the seat layout. A primary concern with the seat layout design of the new vehicle is the amount of seated height growth that occurs in space; this could cause a major accommodation issue. The design of the seats, seat layout, suit fit, and crew accommodation are all critically affected due to the increase in height that occurs in microgravity. The increase in height due to spinal elongation caused by the absence of gravity could lead to inadequate clearances that would have implications for the ability of crewmembers to return safely or to conduct nominal operations during the mission. This study was designed to reduce the risk of inadequate design of the vehicle, environment, tools, equipment, etc. (SHFE risk 2.3.1.1) and safely return crewmembers to earth from low-earth orbit travel, ISS, and beyond. In order to safely return the crewmembers, the design requirements must anticipate microgravity growth, elongation of the spine, bone and muscle loss, fluid shifts, etc. Thus, this study is to determine the amount of torso growth (spinal elongation) for a seated posture during Shuttle and ISS missions. Crewmembers seated heights were collected before, during, and after spaceflight to quantify the amount of growth that occurred as a result of microgravity. The changes in seated height will provide the designers with a design requirement which allows for change in spinal growth for a seated posture. Preliminary results have shown that , during flight, seated height increases by a range of approximately 2-6 percent compared to pre-launch seated height.
Rajulu, Sudhakar↗
Advanced Infant Car Seat Would Increase Highway Safety
An advanced infant car seat has been proposed to increase highway safety by reducing the incidence of crying, fussy behavior, and other child-related distractions that divert an adult driver s attention from driving. In addition to a conventional infant car seat with safety restraints, the proposed advanced infant car seat would include a number of components and subsystems that would function together as a comprehensive infant-care system that would keep its occupant safe, comfortable, and entertained, and would enable the driver to monitor the baby without having to either stop the car or turn around to face the infant during driving. The system would include a vibrator with bulb switch to operate; the switch would double as a squeeze toy that would make its own specific sound. A music subsystem would include loudspeakers built into the seat plus digital and analog circuitry that would utilize plug-in memory modules to synthesize music or a variety of other sounds. The music subsystem would include a built-in sound generator that could synthesize white noise or a human heartbeat to calm the baby to sleep. A second bulb switch could be used to control the music subsystem and would double as a squeeze toy that would make a distinct sound. An anti-noise sound-suppression system would isolate the baby from potentially disturbing ambient external noises. This subsystem would include small microphones, placed near the baby s ears, to detect ambient noise. The outputs of the microphone would be amplified and fed to the loudspeakers at appropriate amplitude and in a phase opposite that of the detected ambient noise, such that the net ambient sound arriving at the baby s ears would be almost completely cancelled. A video-camera subsystem would enable the driver to monitor the baby visually while continuing to face forward. One or more portable miniature video cameras could be embedded in the side of the infant car seat (see figure) or in a flip-down handle. The outputs of the video cameras would be transmitted by radio or infrared to a portable, miniature receiver/video monitor unit that would be attached to the dashboard of the car. The video-camera subsystem can also be used within transmission/reception range when the seat was removed from the car. The system would include a biotelemetric and tracking subsystem, which would include a Global Positioning System receiver for measuring its location. This subsystem would transmit the location of the infant car seat (even if the seat were not in a car) along with such biometric data as the baby s heart rate, perspiration rate, urinary status, temperature, and rate of breathing. Upon detecting any anomalies in the biometric data, this subsystem would send a warning to a paging device installed in the car or carried by the driver, so that the driver could pull the car off the road to attend to the baby. A motion detector in this subsystem would send a warning if the infant car seat were to be moved or otherwise disturbed unexpectedly while the infant was seated in it: this warning function, in combination with the position- tracking function, could help in finding a baby who had been kidnapped with the seat. Removable rechargeable batteries would enable uninterrupted functioning of all parts of the system while transporting the baby to and from the car. The batteries could be recharged via the cigarette-lighter outlet in the car or by use of an external AC-powered charger.
Dabney, Richard↗
A Crew Seat for Human Exploration in Multiple Gravity Environments
This work attempts to develop a single crew seating solution that is applicable across a range of gravity environments encountered by spacecraft proposed in several conceptual spacecraft architectures. All of these spacecraft will need to provide some sort of stationary accommodation for the crew for performing various activities such as work in science laboratories, maintenance and repair facilities, medical care facilities, and spacecraft operations centers, as well as for basic habitation in crew quarters, entertainment / relaxation facilities, and crew dining facilities. Depending on the spacecraft or architecture, this stationary accommodation may be experienced continuously in microgravity, such as would be the case for the Deep Space Exploration Vehicle. Alternately, it could be in continuous lunar or Martian gravity, such as the Common Habitat base camps. It could experience fractional gravity, such as a Pressurized Rover for In-Space Missions at a Near Earth Asteroid or one of the Martian moons. It could alternate between artificial gravity and microgravity, such as the Nautilus-X. It could alternate between microgravity and lunar or Martian gravity, such as the SpaceX Starship Human Landing System or the Blue Origin Blue Moon Block 2 Human Landing System. Or it could be in continuous Earth gravity, such as ground trainer systems. Prior human spaceflight systems for stationary accommodation have been focused on microgravity applications. These systems have their own limitations and cannot be used in a gravity environment. A public crowdsourcing campaign generated dozens of ideas, which ultimately generated a Gecko Mobility Aids system for crew translation and the Multi-Gravity Crew Seat (MGCS) for stationary accommodation. The MGCS functions in gravity as a traditional terrestrial seat, performing functions of load for the overall body and forearms, as well as head and neck load relief while positioning the body within range of an intended task. In microgravity, the MGCS functions as a body restraint, securing the body against inadvertent drifting by applying a restraining pressure at the front and back of the thighs, shoulders, and back. The initial MGCS concept was developed in a NASA hackathon and was refined through a review of dozens of terrestrial seating styles. Additionally, a review of anthropometry and biomechanics data related to the neutral body posture was conducted to help inform the microgravity configuration of the MGCS. A series of CAD models were iteratively developed, with subject matter expert reviews leading to design improvements. A scale model was constructed and used with a humanoid model to demonstrate MGCS accommodation of a human-like body in both gravity and microgravity modes. Work to develop a full-scale protype of the MGCS is discussed, including design and fabrication of the headrest, arm rest, seat back, seat pan, seat base, and the conversion mechanisms. A 1-g human-in-the-loop evaluation of the prototype assessed the acceptability of performing seated activities in the MGCS, collecting data on the usability, comfort, and ease of ingress/egress. Based on the evaluation results, design modifications needed for reduced gravity testing are documented and initial work is indicated for a reduced gravity test plan.
Restraints and Mobility Aids↗
Preliminary Results of the Effect of Spinal Elongation in Microgravity on Seated Height
The Constellation Program is designing a new vehicle for future space travel to the International Space Station and to the Moon and beyond. One major accommodation and design issue that needs to be addressed with the current seat layout design is spinal elongation. Spinal elongation is the spinal growth that occurs due to straightening of the spinal curve and expansion of the inter-verbal discs in microgravity. Spinal elongation is critical to the design of the seats, seat layout, suit fit, and crew accommodation because of the implications it can have on the a safe return of the crewmembers or during the mission. Inadequate clearance between crewmembers and/or between crewmember hardware interfaces may potentially result in injury during the mission or upon returning to earth. Therefore, design requirements need to be determined that will allow for the elongation of the spine. The current requirement as specified in the Human Systems Integration Requirement (HSIR) document states that a 3% increase in standing height must be accommodated. However, it cannot be assumed that the amount of standing height growth is equivalent to the amount of spinal elongation because of the variation in body proportions between the lower body and torso. Thus, the purpose of this study was to determine the amount of spinal elongation for a seated posture for 6 Shuttle and 7 ISS missions. Crewmembers seated heights were collected before, during, and after spaceflight to determine the change in seated height and the amount of spinal growth that occurs due to microgravity. The changes in seated height will provide the designers with a design requirement that will allow for change in spinal growth for a seated posture. Preliminary results have shown that increase in seated height is greater than the 3% increase currently stated in the requirement.
Rajulu, Sudhakar↗
Multiple-Use Mechanisms for Attachment to Seat Tracks
A Seat Track Attach Mechanism (SAM) is a multiple-use clamping device intended for use in mounting various objects on the standard seat tracks used on the International Space Station (ISS). The basic SAM design could also be adapted to other settings in which seat tracks are available: for example, SAM-like devices could be used as universal aircraft-seat-track mounting clamps. A SAM (see figure) is easily installed by inserting it in a seat track, then actuating a locking lever to clamp the SAM to the track. The SAM includes an over-center locking feature that prevents premature disengagement that could be caused by some inadvertent movements of persons or objects in the vicinity. A SAM can be installed in, or removed from, any position along a seat track, without regard for the locations of the circular access holes. Hence, one or more SAM(s) can be used to mount an object or objects on a track or a pair of tracks in an infinite number of preferred configurations. A SAM can be incorporated into a dual swivel device, so that two of the SAMs can be made to lock onto two side-by-side seat tracks simultaneously, as would be the case in a standard ISS rack bay where two side-by-side racks reside. The main benefit to using two SAMs in a side-by-side arrangement is to provide a coupled load. By picking up load points on two seat tracks, a coupled loading is created, improving the stability and strength since the load is spread to two seat tracks at a short distance.
Fraske, Martin↗
Design and testing of an energy-absorbing crewseat for the F/FB-111 aircraft. Volume 2: Data from seat testing
The unacceptably high injury rate during the escape sequence (including the ejection and ground impact) of the crew module for F/FB-111 aircraft is reviewed. A program to determine if the injury potential could be reduced by replacing the existing crewseats with energy absorbing crewseats is presented. An energy absorbing test seat is designed using much of the existing seat hardware. An extensive dynamic seat test series, designed to duplicate various crew module ground impact conditions is conducted at a sled test facility. Comparative tests with operational F-111 crewseats are also conducted. After successful dynamic testing of the seat, more testing is conducted with the seats mounted in an F-111 crew module. Both swing tests and vertical drop tests are conducted. The vertical drop tests are used to obtain comparative data between the energy absorbing and operational seats. Volume 1 describes the energy absorbing test seat and testing conducted, and evaluates the data from both test series. Volume 2 presents the data obtained during the seat test series, while Volume 3 presents the data from the crew module test series.
Shane, S. J.↗
Lightweight Seat Lever Operation Characteristics
In 1999, a Shuttle crew member was unable to operate the backrest lever for the lightweight seat in microgravity. It is essential that crew members can adjust this backrest lever, which is titled forward during launch and then moved backward upon reaching orbit. This adjustment is needed to cushion the crew members during an inadvertent crash landing situation. JSCs Anthropometry and Biomechanics Facility (ABF) performed an evaluation of the seat controls and provided recommendations on whether the seat lever positions and operations should be modified. The original Shuttle seats were replaced with new lightweight seats whose controls were moved, with one control at the front and the other at the back. The ABF designed a 12-person experiment to investigate the amount of pull force exerted by suited subjects, when controls were placed in the front and back of the lightweight seat. Each subject was asked to perform the pull test at least three times for each combination of lever position and suit pressure conditions. The results showed that, in general, the subjects were able to pull on the lever at the back position with only about half the amount of force that they were able to exert on the lever at the front position. In addition, the results also showed that subjects wearing the pressurized suit were unable to reach the seat lever when it was located at the back. The pull forces on the front lever diminished about 50% when subjects wore pressurized suits. Based on these results from this study, it was recommended that the levers should not be located in the back position. Further investigation is needed to determine whether the levers at the front of the seat could be modified or adjusted to increase the leverage for crew members wearing pressurized launch/escape suits.
Rajulu, Sudhakar↗
Modeling the Impact of Space Suit Components and Anthropometry on the Center of Mass of a Seated Crewmember
The Crew Impact Attenuation System (CIAS) is the energy-absorbing strut concept that dampens Orion Crew Exploration Vehicle (CEV) landing loads to levels sustainable by the crew. Significant COM variations across suited crew configurations would amplify the inertial effects of the pallet and potentially create unacceptable crew loading during launch and landing. The objective of this study was to obtain data needed for dynamic simulation models by quantifying the effects of posture, suit components, and the expected range of anthropometry on the COM of a seated individual. Several elements are required for the COM calculation of a suited human in a seated position: anthropometry, body segment mass, suit component mass, suit component location relative to the body, and joint angles defining the seated posture. Three-dimensional (3D) human body models, suit mass data, and vector calculus were utilized to compute the COM positions for 12 boundary manikins in two different seated postures. The analysis focused on two objectives: (1) quantify how much the wholebody COM varied from the smallest to largest subject and (2) quantify the effects of the suit components on the overall COM in each seat configuration. The location of the anterior-posterior COM varied across all boundary manikins by about 7 cm, and the vertical COM varied by approximately 9 to 10 cm. The mediolateral COM varied by 1.2 cm from the midline sagittal plane for both seat configurations. The suit components caused an anterior shift of the total COM by approximately 2 cm and a shift to the right along the mediolateral axis of 0.4 cm for both seat configurations. When the seat configuration was in the standard posture the suited vertical COM shifted inferiorly by as much as 1 cm, whereas in the CEV posture the vertical COM had no appreciable change. These general differences were due to the high proportion of suit mass located in the boots and lower legs and their corresponding distance from the body COM, as well as to the prevalence of suit components on the right side of the body.
Blackledge, Christopher↗
Determination of crash test pulses and their application to aircraft seat analysis
Deceleration time histories (crash pulses) from a series of twelve light aircraft crash tests conducted at NASA Langley Research Center (LaRC) were analyzed to provide data for seat and airframe design for crashworthiness. Two vertical drop tests at 12.8 m/s (42 ft/s) and 36 G peak deceleration (simulating one of the vertical light aircraft crash pulses) were made using an energy absorbing light aircraft seat prototype. Vertical pelvis acceleration measured in a 50 percentile dummy in the energy absorbing seat were found to be 45% lower than those obtained from the same dummy in a typical light aircraft seat. A hybrid mathematical seat-occupant model was developed using the DYCAST nonlinear finite element computer code and was used to analyze a vertical drop test of the energy absorbing seat. Seat and occupant accelerations predicted by the DYCAST model compared quite favorably with experimental values.
Alfaro-Bou, E.↗