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.