Conventional EVA suits suffer from mobility and tactile sensory limitations due to their pressurization. Any articulated container which changes volume with motion will resist motion if pressurized. This is largely why EVA suits are pressurized to only about 1/3 the pressure of habited spacecraft, the lowest pressure consistent with respiration.
There are many potential advantages of constant-volume spacesuits, similar to commercial and military Atmospheric Diving Suits (ADS).
The Newtsuit (below) has been widely used since its introduction in 1987. It has an operational depth of 1000ft. It is certified for 8 hour dives with a 72 hour emergency endurance duration. The ball bearing joints seal both pressure and vacuum. The aluminum shell could be lightened since a space suit doesn’t need a 3000ft (90 atmosphere) crush depth.
The 3-finger “Prehensor” manipulators can spin a nut on a bolt. These are working suits. The operators perform activities similar to EVAs. They are just paid a lot more to do it.
Pressure-restricted mobility is particularly a problem with gloves. According to https://airandspace.si.edu/exhibitions/outside-the-spacecraft/online/walking.cfm
“Spacesuit gloves have become the limiting element of an astronaut's work performance outside a spacecraft because hand muscles become extremely fatigued during prolonged work in a pressurized glove.”
https://phys.org/news/2010-10-mit-pain-spacesuit-gloves.html The article discusses “delamination”, or loss of fingernails, after prolonged work with space gloves.
According to https://www.thespacereview.com/article/3717/1 , The Apollo Lunar astronauts
“ all felt that the gloves they had used were barely adequate and better gloves were necessary. The Apollo gloves imposed major limitations on hand mobility, finger dexterity and tactility, and resulted in serious arm fatigue. This began within minutes of the start of the EVA and continued throughout the day.”
This article https://spacecraft.ssl.umd.edu/publications/ICES01-2164.pdf gives a damning opinion of pressurized gloves. It’s along the line of: the only thing worse than gloves are the alternatives. The article says:
“Existing EVA gloves significantly reduce hand dexterity, range of motion, tactility, strength, and endurance. In addition, they are often uncomfortable to the point of pain and/or minor physical injury to the hands… Unpressurized gloves reduce dexterity by 50%, and that wearing pressurized gloves decreases dexterity by an additional 30%... Gloves increase performance time for a given task, and the addition of a pressure differential further increases performance time… Performance while wearing gloves is nearly five to six times slower than barehanded performance.”
Previous posts on SE have suggested using cosmetically appealing “Luke Skywalker hands” as a substitute for a gloved hand. These may be appropriate for prosthetic hands, but are not optimized for space work
The hand makes a great manipulator, but it is often a tool, held by the hand, that is doing the job. The field of endoscopic surgery has developed a wide variety of manipulator/tools which are manually operated from a distance. They don’t depend on telepresence or motorized actuators, but rather mechanical engineering and hand/eye coordination.
Endoscopic Widget, specialised for surgery. I’m scared to imagine what it is designed to do. Widgets for spacewalks would be equally ingenious and equally specialized.
When designing a EVA manipulator/tool, ask not if it can do all that a hand can do, but what it can do that a hand cannot. Instead of an EVA suit’s arm ending in a clumsy glove, it could end in a turret (like the objective turret on a microscope) holding multiple custom EVA tools.
ISS will be gone soon. Gateway is a clean slate. It is an opportunity to re-think EVA equipment, activities, tools, techniques. I was wondering if it time to retire conventional EVA suits for constant-volume suits with dedicated manipulators, so I'd like to ask:
Question: What are objective advantages/disadvantages of the alternatives?