• The Torso Component

    Tobias • 12/06/2024 at 05:51 • 0 comments

    In designing this suit, one of the biggest considerations was how to deal with the interface between the fabric suit body and the helmet. Joining the helmet to the suit is (relatively) simple, as we can design a ring that clamps the fabric, and includes a locking ring to mate to the helmet. But there are still two big challenges: how to comfortably support the weight of the helmet, and how to stop the helmet from flopping around.

    The torso component is a bit like a foundation for the rest of the suit, and in this project log I'm going to talk through some of the design considerations, as well as how the problems are solved in other suit designs.

    Looking at real spacesuits, there are a whole range of solutions to this problem, and some designs that avoid these problems entirely. For example, a lot of pressure suits use a conformal helmet, which is tightly fitted to the head so the weight of the helmet is born solely by the head. Some examples of this are the Soviet VKK pressure suit, the Mark IV Mercury pressure suit, and the S1034 pressure suit used in the U-2 (but not the almost identical S1035 ACES suit used in the space shuttle). I chose to avoid this kind of conformal helmet partially because I would have had to make a neck bearing to allow the helmet to turn, but also because it didn't match the look I was going for.

    Left: the non-conformal S1035 helmet used with the NASA Advanced Crew Escape Suit. Right: the conformal S1034 helmet used by in the U-2. Source: https://ttu-ir.tdl.org/server/api/core/bitstreams/882c15b9-2eb6-4dad-be37-ab709d62d9d2/content

    The NASA Advanced Crew Escape Suit (ACES), unlike the S1034, uses a non-conformal helmet, meaning the helmet cannot turn from side to side, but is large enough for the wearer to turn their head inside the helmet. But since the helmet isn’t supported by the head, we need a way to keep the helmet stable so it doesn’t flop around, and doesn't tilt too far forward or back. The ACES partially does this with the Helmet Support Assembly, essentially a yoke made of high tensile wires. The HSA also performs a much more important function - in the event of a crash or impact, a huge amount of energy could be transferred to the wearers head, neck and body, possibly doing more damage than if they simply weren't wearing a helmet. To quote a design report: "The rigid shell provides protection from impacts from dislodged objects, however as the head is free to move within the helmet, there is the risk of significant contact between the head and the rigid helmet [...] Additionally, spring support systems or other external assemblies are required to manage the helmet during landing scenarios."

    The second way the ACES suit stabilises the helmet is with a helmet tie-down strap - essentially a strap that attaches near the crotch and to the helmet (with a pulley and cable attached to the helmet neck-ring). The strap can be tightened to pull the helmet forward - essential when the suit puffs up like a balloon but you need to look down at your instruments. This kind of strap is also used in a lot of high-altitude pressure suits.

    Note the white strap, pulley, and cable attached to the neckring. (PS. click for the best image you'll see all day!)

    At the other end of the spectrum, most EVA space suits use a rigid torso. In the case of the NASA EMU suit, the torso acts like a chassis, and most components (arms, legs, the PLSS backpack,  chest mounted DCU, and helmet) are mounted to this rigid torso. Of course, in zero gravity there's no need to worry about the weight of the helmet on the shoulders, but the NASA EMU actually uses a set of internal shoulder straps. From the user manual: "A Shoulder Harness (Figure 3.3.1.2), much like a pair of suspenders [...] tends to stabilize the crewmember in the suit during 0-G pressurized conditions."

    Left: the EMU hard upper torso. Right: the EMU shoulder harness. Source: https://www.lpi.usra.edu/lunar/artemis/NASA-EMU-Data-Book-JSC-E-DAA-TN55224.pdf...

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