Crashworthy Seats Would Afford Superior Protection
- Friday, 01 May 2009
Adjustments enable optimization of support for different body sizes and shapes.
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 require ments 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 Inte - gration 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.
The seat includes a thigh-support structure and a lower-leg support structure that can be adjusted for various heel-to-back-of-knee lengths. The occupant’s heels are supported by a heel support pan and could be affixed to the pan by clips similar to those of mountain biking shoes and pedals or by straps over the tops of the feet. At the pivot between the thigh and lower-leg support structures there is a flat panel that provides for strength in adjustment and provides lateral support of the knees. The combination of lateral support of the knees and support and restraint the of the feet is intended to prevent flailing or other movement of the legs while the occupant is seated.
The seat includes lateral supports at the hips that serve the dual purpose of restraining the occupant from shifting laterally and providing structural support to the rest of the seat by acting as a gusset. To accommodate all hip sizes, the seat pan is designed to fit the largest hip breadth allowable. For a smaller occupant, spacer pads can be installed to fill the voids. Shoulder supports, which cover the shoulder joints and extend short distances down the arms, are also sized for occupants having shoulders of maximum breadth and to be fitted to smaller occupants by use of spacer pads. The seat supports bony protrusions of the torso at the shoulders and hips only, leaving the mid-torso area free of supports to enable the occupant to leave the seat by rolling though the clear space.
The seat includes a head support. However, head support on the prototype differs from the envisioned Orion head support: In Orion, the occupant would wear a space helmet and the head support would extend along the right and left sides of the helmet to prevent lateral motion of the head.
Another prominent design feature is a load-distributing seven-point harness similar to harnesses worn in off-road automobile racing. The seven-point harness includes straps over the tops of the shoulders that act, in effect, as wraparound extensions of the lateral shoulder supports.
This work was done by Dustin Gohmert of Johnson Space Center. MSC-24485-1
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