In 1968, astronauts on NASA’s Apollo 8 mission
saw something that should have been impossible. In the last moments before the lunar sunrise
and sunset every day, they noticed a haze developing on the horizon, and then in the
final few seconds before the sun had risen or fallen, they saw bright bands of light
radiating out from the surface, sharply ascending out into the darkness [1]. On Earth, we enjoy these dazzling rays twice
a day as a result of our atmosphere scattering sunlight But the moon doesn’t have an atmosphere. There are tiny amounts of some noble gases
like helium and argon in the lunar exosphere, but for all purposes, the space above the
surface of the moon is a vacuum. So, where did these bands of light come from? The answer doesn’t lie with atmospheric
gasses, but, instead, dust. The phenomenon observed by Apollo astronauts
was caused by light passing through and being scattered by layers of microscopic lunar dust
that had been kicked off the surface of the moon. For the astronauts of the Apollo missions,
this would have been a beautiful thing to witness, but lunar dust has a dark side. After the end of the final Apollo mission,
Gene Cernan - who was also the last person to set foot on the moon - said the following:
“I think dust is probably one of our greatest inhibitors to a nominal operation on the Moon. I think we can overcome other physiological
or physical or mechanical problems except dust.” [2]
From reports taken from the seventeen Apollo missions as well as analysis of spacesuits,
machinery and equipment after they had returned to Earth, we now have a very clear picture
of just how damaging lunar dust can be. It significantly obscured the vision of astronauts
during lunar landings; it caused damage to pre-existing machinery and objects on the
lunar surface when blown around by the blast from landing spacecraft; it found its way
into the lunar and command modules, not only causing eye, nose and lung irritation for
the astronauts, but also covering screens, damaging electronic equipment and corroding
mechanical switches; it affected and sometimes complete broke watches, cameras, rovers and
experimental equipment used on the surface of the moon and found its way into every crevice
in the astronauts spacesuits. Hose locks and zippers became difficult to
use, the mobility of the suit was reduced, life-support system displays were difficult
to see, visors were scratched, electronics overheated, and leaks in the suits became
more prevalent, leading to pressure losses. And even when they tried to remove the dust
with vacuums and brushes in the lunar module, they were never able to completely get rid
of it, causing the spacesuits to become gradually worse over time [3]. The astronauts of Apollo 17 spent the longest
amount of time outside of the lunar module, but only managed 22 hours of Surface EVAs,
during which almost irreparable damage was done to the spacesuits - had they conducted
more work on the lunar surface, the suits would eventually have been rendered useless.. But 22 hours is only a fraction of what would
be required for any future mission to the moon. In 2015, NASA laid out its Space Technology
Roadmaps which identified one key and hugely ambitious goal [4]. They wanted their spacesuits to be able to
survive for 100 EVAs - a total of 800 hours spent on the Lunar surface, almost 37 times
the duration the Apollo 17 astronauts spent outside. More than any other problem facing NASA or
any other space agency, this could be the making or breaking of a long-term outpost
on the surface of our moon. But how do you begin to extend the life of
a spacesuit by this much? To get to an answer, we first need to understand
how lunar dust is formed and why it sticks to anything it comes in contact with. Unlike the surface of the Earth, the surface
of the moon is under almost constant bombardment from small and large meteorites, some of them
only micrometers in diameter. This rain of debris causes parts of lunar
rocks to break off, creating a layer of fine dust on the lunar surface. Occasionally, these micrometeorite impacts
hit with such force that they melt the minerals contained in the soil, turning them into glass. Lunar dust is a mixture of super-fine particles
and razor-sharp glass that’s also incredibly dry - there’s no water in the soil or air
to clump the particles together and no natural erosion through wind to blunt the sharp edges
[5]. So, this obviously does not mix well with
the intricate mechanisms of the lunar spacesuits. The dust is small enough to get into almost
any gap, and, thanks to the shards of glass in the dust, it can easily scratch glass or
metallic surfaces. But this is only the beginning of the problem. Thanks to the lack of atmosphere or magnetic
field on the moon, lunar dust is exposed to every fraction of radiation that’s fired
at it. On the side of the moon exposed to the sun,
particles in the dust are hit with X-ray and ultraviolet radiation, causing electrons to
be knocked off, creating positive charges on the surface of the dust particles. Then, on the side shielded from the sun, the
opposite happens. The particles pick up electrons from solar
winds, causing them to become negatively charged. These positive and negative charges on the
particles create electrostatic potentials on the surface of the moon, reaching up to
20 V on the day side, and an astonishing -3800 V on the night side. When the Apollo 8 astronauts saw the beautiful
bands of light at sunset and sunrise, they weren’t seeing the scattering of radiation
through atmospheric gasses, but instead light passing through a column of fine dust fired
up from the surface of the moon by electrostatic levitation - dust particles of like charges
repel each other, and are repelled by the lunar surface, creating a fountain of sharp
microdust that rises above the horizon. This is the same dust that Apollo astronauts
walked through and kicked up as they worked outside the lunar module, sticking to their
suits in the same way a statically-charged balloon sticks to your clothes. Charge is one of the main reasons the dust
is so annoying, but it could also be the way we get rid of it. In 2021, as part of NASA’s Breakthrough,
Innovative & Game-changing Idea Challenge, they tasked university students from across
the world to come up with novel ways of dealing with the lunar dust problem [6]. Some of the winning solutions included conductive
fibers inspired by chinchilla hair, an electrically charged brush that could be powered by UV
radiation, and a fabric for spacesuits that mimicked the way certain insects use hair-like
structures to collect and deposit pollen. All these ideas use different ways to solve
the same problem, but they share a common approach - using charge to either passively
or actively remove dust from spacesuits. At its simplest, the problem comes down to
this - how do you make the outer layer of the spacesuit repel the charged dust instead
of attracting it? NASA came up with an elegant solution.Instead
of trying to completely redesign the outer layer of the suit, they decided to create
a system that could be easily integrated into the pre-existing layers of fabric and material
found in the current generation of spacesuits. Their idea was to create a suit that could
make its own electrical current which would actively eject dust, acting like some sort
of energy shield. And the first challenge was choosing the conductive
material that the electrodes would be made from. This method of dust-ejection wasn’t new. It was inspired by the Electrodynamic Dust
Shield systems th at had been used by NASA since the late 1960s, on things like solar
panels, cameras and thermal radiators [7]. But in almost all of these cases, the electrodes
- which were made out of silver, copper or a compound of indium and tin - were placed
on rigid, fixed bodies. A spacesuit is designed to move - the outer
layer is made up of segments of overlapping fabric that roll over each other at the joints
when the astronaut moves their arms or legs. So, while the silver and copper electrodes
used in the pre-existing EDS systems might be excellent electrical conductors, with their
low elasticity, they wouldn’t survive the fatigue caused by the constant flexing of
the joints. So, a new conductor was needed, one that had
a high electrical conductivity, but that was flexible enough to withstand the significant
forces exerted on it during extravehicular activities. And the answer was carbon nanotubes. These are cylindrical tubes of carbon atoms
stretching only a nanometer across, with walls one atom thick - like a long, thin layer of
graphene that’s been rolled into a tube. Carbon nanotubes are incredibly strong, with
a considerably higher tensile strength than copper, silver or gold and they have a very
high electrical conductivity. \
Animation 9 continued… CNTs are also very light. If you compare the mass of different conductors
required to create an Electrodynamic Dust Shield on the knees, elbows and boot areas
of a lunar spacesuit, around 101 g of copper wire would be needed, but if you replace the
copper with carbon nanotubes, you only need about 16g: Carbon nanotubes are an excellent choice,
as they could provide high conductivity with low mass, while also being able to withstand
the 800 hours of EVAs required for future lunar missions. So, after settling on CNTs, it was then a
matter of finding a way of integrating these nanotubes into the outer layer of the spacesuit. Lunar spacesuits are made up of up to 21 layers
of material, with an outer orthofabric layer composed of a mixture of fibers like GORE-TEX
and Kevlar. The carbon nanotube electrodes were made into
yarns and then woven into this outer layer in a longitudinal direction to limit the tensile
force applied to the electrodes, and they were also spaced out from each other to prevent
electrical arcing. The orthofabric in this outer layer acts as
a natural insulator, but there is a chance it could be broken down by high voltages. Through testing, it was found that the orthofabric
could withstand up to 1200 V, so the dust removal system was capped at around 1000 V
to prevent dielectric breakdown of the insulating material. So, how does the dust removal system actually
work? The carbon nanotube electrodes are first connected
in parallel, and then activated by a multi-phase alternating current at voltages between 600
and 1000 V and very low currents, at around 3 mA. This sets up repeating waves of electrical
fields which move across the outer surface of the spacesuit. As they interact with the charged dust particles,
they add an additional repulsive force to the particles based on coulomb interactions
- repulsion due to the interaction of two charged objects. This repulsive force is, overall, greater
than the gravitational and adhesive forces which stick the particles to the suit, causing
the particle to be ejected from the orthofabric. But this also works for uncharged particles
that are stuck to the suit. When interacting with a non-uniform electric
field, like in this system, uncharged dust can be repelled through something called a
dielectrophoretic force.. Overall, the electrical energy of the system
is transformed into mechanical energy as the dust is kicked off the suit. To test the system, NASA constructed a prototype
knee joint with carbon nanotubes woven into an outer orthofabric layer, and used it to
measure how much of a lunar dust simulant was removed in different scenarios. [8]. And what they found was remarkable. Through analysis of high resolution images
taken of the fabric before and after activation of the electrodes, they saw, that up to 96%
of the lunar dust simulant was removed by the system (see here for video)
This has enormous potential for use as part of future moon missions. The dust removal system could be on continuously
during EVAs, preventing any dust from binding, or it could be manually activated when an
astronaut noticed a large build up of dust. This dust prevention technology may seem trivial,
but this razor sharp lunar dust is a life limiting threat to any future moon colony. This kind of simple environment effect, that
requires a breakthrough material to overcome, is the core of what makes engineering exciting
for me. A relatively simple solution that any new
engineering graduate could have helped develop, and go on to see their work land on the moon. Seeing your work go from the lab, to the factory
floor, to the real world is one of the most satisfying creative processes in the world. Engineering is a job for creatives, with a
penchant for science and math, and many talented people are scared off from engineering by
the scary looking physics, but Brilliant is here to help. Brilliant has curated learning paths that
will be perfect for preparing you for an education in engineering, or if you are simply an experienced
engineer that wants to brush up on your math skills. From courses on the fundamentals of maths,
to a curated course called College Maths. Brilliant is the perfect place to hone your
skills, with easy to follow interactive courses that will take you from knowing nothing to
having a well rounded understanding of the building blocks of an engineering career. Brilliant’s thought-provoking courses help
you see STEM in a new way. They’ll guide you from curiosity to mastery
through storytelling, interactive challenges, and problems to solve. You’ll start by having fun with their interactive
puzzles and visuals, but with a little bit of persistence and effort, you’ll be amazed
at what you can accomplish. If you are naturally curious, want to build
your problem-solving skills, want to develop confidence in your analytical abilities, or
like me find fulfillment in continual lifelong learning. then get Brilliant Premium to learn something
new every day. If you are looking for something else to watch
right now, why not watch my previous video about Air Crash Investigation of the Concorde,
or watch Real Sciences latest video about the world's most deadly venom.
Space dust is a real issue
Imagine being a multi-doctorate, best of the best astronaut and you finally get to live on a moon base, but you find that your whole job is "Lunar Environment Protection for Infrastructure and Systems Safety" which is just a nice way of saying 'Duster'.
Talk to a Kirby salesmen.
Just came across this couple of days ago. It was an interesting video.
I did an innovation project proposal on this, it got shot down lol
Mars dust is pretty serious as well.
Someone should get the guys from Martian Realty and Sewer Bong 3000 together. Seems like they could solve this problem in a jiffy.
In space everyone can hear you clean.