Astronauts’ fingernails falling off
Victoria Jaggard
Astronauts at work |
A bionic hand |
Astronaut Heidemarie M. Stefanyshyn-Piper waves at the camera
during a spacewalk. (file photo). Photograph courtesy NASA |
If you’re headed for space, you might rethink that manicure -
Astronauts with wider hands are more likely to have their fingernails
fall off after working or training in space suit gloves, according to a
new study.
In fact, fingernail trauma and other hand injuries, no matter your
hand size, are collectively the number one nuisance for spacewalkers,
said study co-author Dava Newman, a professor of aeronautics and
astronautics at the Massachusetts Institute of Technology.
“The glove in general is just absolutely one of the main engineering
challenges,” Newman said. “After all, you have almost as many degrees of
freedom in your hand as in the rest of your whole body.”
The trouble is that the gloves, like the entire space suit, need to
simulate the pressure of Earth’s atmosphere in the chilly, airless
environment of space. The rigid, balloonlike nature of gas-pressurized
gloves makes fine motor control a challenge during extravehicular
activities (EVAs), aka spacewalks.
A previous study of astronaut injuries sustained during spacewalks
had found that about 47 percent of 352 reported symptoms between 2002
and 2004 were hand related. More than half of these hand injuries were
due to fingertips and nails making contact with the hard “thimbles”
inside the glove fingertips.
Skylab 4 commander Gerald Carr balances fellow astronaut William
Pogue, the mission’s pilot, upside down on his finger in zero
gravity. Photograph courtesy NASA |
In several cases, sustained pressure on the fingertips during EVAs
caused intense pain and led to the astronauts’ nails detaching from
their nailbeds, a condition called fingernail delamination. While this
condition doesn’t prevent astronauts from getting their work done, it
can become a nuisance if the loose nails gets snagged inside the glove.
Also, moisture inside the glove can lead to secondary bacterial or yeast
infections in the exposed nailbeds, the study authors say.
If the nail falls off completely, it will eventually grow back,
although it might be deformed. For now, the only solutions are to apply
protective dressings, keep nails trimmed short, or do some extreme
preventative maintenance.
“I have heard of a couple people who’ve removed their fingernails in
advance of an EVA,” Newman said.
In the current glove design, astronauts wear a pressurized inner
layer under a thick outer layer that offers protection from the cold and
any passing micrometeorites. On Earth, wearing such space suit gloves
might feel like donning a thick set of gardening gloves, a bit
restrictive but not too uncomfortable.
The glove Challenge
“When the glove pressurizes, that nice, flexible fabric surface
becomes stiff, like putting air into bicycle tires,” founder of
commercial space suit design company Flagsuit LLC in Maine and two-time
winner of NASA’s Astronaut Glove Challenge Peter Homer said.
“What you find is, depending on the design of the glove, there’s
pressure on the hard points the hand presses against, and that can give
you blisters or cuts,” said Homer, who was not involved in the new
study.
“Also, the materials tend to be rubberized to make the gloves
airtight, but that creates a lot of friction against the skin, and that
can again create blisters.”
During EVAs, astronauts have to work in these gloves for six to eight
hours at a stretch, Homer said: “It amazes me that astronauts push
through all that pain and get stuff done.”
To help design more comfy space suit gloves, MIT’s Newman and
colleagues initially tested whether fingernail trauma is related to the
length of astronauts’ fingers.
The team first collected data from the Injury Tracking System, a
database of astronaut medical logs at NASA’s Johnson Space Center in
Houston, Texas. Of the 232 crew members with complete injury records and
body measurements, 22 reported at least one case of fingernail
delamination.
Surprisingly, an analysis of hand measurements among injured
astronauts and a non-injured control group showed no statistical
relationship between finger length and the instances of nails falling
off, according to the study.
Instead, the team found that fingernail trauma was a bigger problem
for people with a wider hand circumference, or the size of the hand
around the metacarpophalangeal, or metacarpal, joint, where the fingers
meet the palm.
“If you take a pencil and grip it, you’re using your metacarpal
joint,” Newman said. “That’s a really difficult thing to repeat when you
have a pressurized glove on. A hard palm bar in the soft fabric glove
... helps make that crease,” but the bar also puts pressure on the
joint.
The team’s analysis, to be published in the October issue of the
journal Aviation, Space, and Environmental Medicine, showed that
astronauts with hand circumferences greater than about 9 inches (22.8
centimeters), what Newman called the “large to extra-large range”, had a
19.6 percent chance of fingernail injuries during an EVA.
By contrast, astronauts with smaller hand circumferences had just a
5.6 percent chance of losing their nails on the job.
Future space suit ideas
“What surprised me is that conventional wisdom is that fingernail
problems are caused by repetitive tapping on the fingernail ... and
you’d think that if you had longer fingers, you’d be banging on the end
of the glove more,” said Flagsuit’s Homer.
But the hand-width hypothesis “is good, too,” he said. “The bigger
the hand is, the more the glove squeezes on (the metacarpophalangeal)
joint and cuts off blood flow.”
Circulation getting repeatedly shut off then restored at the knuckle
joint would damage the tissue underneath the fingernail, leading to
delamination. It could also explain why so many astronauts have reported
that their fingertips get cold during EVAs despite their thermal gloves,
Homer said.
Overall, he added, the new paper “shines light on a whole new
direction on how to address this issue.” According to Homer, the key is
to make all parts of a glove custom fitted for each astronaut.
For anyone selected for an EVA, the airtight inner layer for the
current glove design is custom made via hand casts, laser scanning,
computer modeling, and special machining techniques. But the outer layer
is built in discrete sizes, more like a “small, medium, large”
situation, he said. “It costs around a hundred thousand dollars up front
to custom fit the airtight bladder,” Homer said.
“In my opinion that also needs to apply to the outer layer, which
really gives the glove its shape.”
Customization may not always solve the issue, though, MIT’s Newman
said: “Some may like a tighter or looser fit, there’s variability in
subjective desires. And if you have a really tight fit, you’re going to
have a lot more pressure” on the metacarpal joint.
Newman thinks another option worth looking into is robotic
amplification inside the glove.
“Say I’m grabbing on to something. I’m using muscles to act against
gas-pressurized gloves,” she said. “But what if I had little actuators
in there? My fingers can do less work, that’d be great!
“There are design trade-offs” to robotic gloves, she added. “But we
have some big dreams here: small-mass systems close to the skin that
work in concert with muscles and bones, not big clunky exoskeletons.”
Newman and colleagues have also been experimenting with entire
skintight space suits that rely on mechanical counter pressure - rather
than working in a gas-pressurized bubble, astronauts would effectively
get shrink-wrapped in a suit made of flexible material.
No matter what the approach, Newman said, “the bottom line is we want
people to be working in a space suit glove that’s working with them, not
against them.”
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