Hard Suits/Soft Suits: Revisiting Technologies and Applications for a New Space Era

TitleHard Suits/Soft Suits: Revisiting Technologies and Applications for a New Space Era
Publication TypeConference Paper
Year of Publication2015
AuthorsAkin DL, Davis K
Conference Name45th International Conference on Environmental Systems
Date Published07/2015

For three decades, two major types of pressure suits were developed in parallel for potential flight applications. Suits flown through Apollo were “soft suits”, where the pressure garment was exactly that: a multilayer fabric garment that provided wearer motion while retaining atmospheric pressure for life support. Never flown, “hard suits” were rigid metal suits providing body articulation via multiple sealed rotary bearings around the body. This system produced a true constant-volume suit, eliminating the primary source of joint forces driving to a “neutral” position and creating the need for continual application of torque by the wearer. Hard suits were more flexible with lower biomechanical loads on the wearer than soft suits, but had operational implications due to their mass and limited ability to stow in restricted volumes. The shuttle extravehicular mobility unit (EMU) was a “hybrid” design, adopting a rigid upper torso as a convenient mounting point for the portable life support system, helmet, and fabric limb assemblies. This paper does not rehash the competitive aspect of “hard” vs. “soft” suits, but looks at the technologies, capabil- ities, and limitations of each in the context of upcoming space operations focused on planetary exploration. Over the next decades, there are potential requirements for extravehicular activities (EVAs) in various microgravity conditions, including geostationary orbit and at microgravity bodies such as asteroids, comets, or the moons of Mars. There are also potential requirements for extensive EVA exploration tasks on the lunar surface and Mars. The paper examines the requirements for each of these locations and their associated environments, including on human protection from radiation, micrometeoroids and orbital debris, shifting structures on low-gravity bodies, and dust intrusion and fall protection on the moon and Mars. Duration is also a critical issue: missions to Mars could involve surface stay times of up to 15 months, which could translate to hundreds of EVAs per crew in a highly challenging environment. As humans move farther away from Earth for longer durations, without the feasibility of logistics resupply, the need to maintain, repair, and replace suit components will become paramount for crew productivity and safety. Given mission requirements and logistics challenges, the paper examines current and upcoming fabrication tech- nologies to assess their potential impact on EVA systems design and operations. While the access to Earth or shorter duration missions may favor the use of a fabric-based solution, the specialized equipment and high levels of required technical skills make this design difficult to maintain and repair on extended missions. One potential mitigation for this is the use of state-of-the-art fabrication techniques, such as additive manufacturing, in conjunction with wider use of hard-suit components. Recent self-funded research at the University of Maryland has demonstrated the ability to use fused deposition manufacturing to produce components of a four-roll elbow assembly, including a single-build mono- lithic construction of an elbow bearing. The paper examines potential automated fabrication technologies to produce suit replacement components on need, and compares that scenario to the challenge of providing sufficient logistics to ensure adequate spares in all potentially replaceable suit components throughout the extent of an extended-duration surface stay, or in the eventual implementation of a permanently inhabited base on the moon, Mars, or both.