Gotta love that “turd” instead of “third” Irish accent.
Transcript (YouTube will generate one if you ask nicely):
0:48
In 1968, astronauts on NASA’s Apollo 8 mission saw something that should have been impossible.
0:54
In the last moments before the lunar sunrise and sunset every day, they noticed a haze
1:00
developing on the horizon, and then in the final few seconds before the sun had risen
1:05
or fallen, they saw bright bands of light radiating out from the surface, sharply ascending
1:11
out into the darkness [1].
1:13
On Earth, we enjoy these dazzling rays twice a day as a result of our atmosphere scattering
1:18
sunlight
1:19
But the moon doesn’t have an atmosphere.
1:22
There are tiny amounts of some noble gases like helium and argon in the lunar exosphere,
1:28
but for all purposes, the space above the surface of the moon is a vacuum.
1:34
So, where did these bands of light come from?
1:38
The answer doesn’t lie with atmospheric gasses, but, instead, dust.
1:44
The phenomenon observed by Apollo astronauts was caused by light passing through and being
1:49
scattered by layers of microscopic lunar dust that had been kicked off the surface of the
1:54
moon.
1:55
For the astronauts of the Apollo missions, this would have been a beautiful thing to
1:59
witness, but lunar dust has a dark side.
2:03
After the end of the final Apollo mission, Gene Cernan - who was also the last person
2:08
to set foot on the moon - said the following: “I think dust is probably one of our greatest
2:13
inhibitors to a nominal operation on the Moon.
2:15
I think we can overcome other physiological or physical or mechanical problems except
2:21
dust.”
2:22
[2] From reports taken from the seventeen Apollo
2:24
missions as well as analysis of spacesuits, machinery and equipment after they had returned
2:29
to Earth, we now have a very clear picture of just how damaging lunar dust can be.
2:36
It significantly obscured the vision of astronauts during lunar landings; it caused damage to
2:41
pre-existing machinery and objects on the lunar surface when blown around by the blast
2:46
from landing spacecraft; it found its way into the lunar and command modules, not only
2:52
causing eye, nose and lung irritation for the astronauts, but also covering screens,
2:58
damaging electronic equipment and corroding mechanical switches; it affected and sometimes
3:03
complete broke watches, cameras, rovers and experimental equipment used on the surface
3:08
of the moon and found its way into every crevice in the astronauts spacesuits.
3:13
Hose locks and zippers became difficult to use, the mobility of the suit was reduced,
3:18
life-support system displays were difficult to see, visors were scratched, electronics
3:23
overheated, and leaks in the suits became more prevalent, leading to pressure losses.
3:27
And even when they tried to remove the dust with vacuums and brushes in the lunar module,
3:32
they were never able to completely get rid of it, causing the spacesuits to become gradually
3:36
worse over time [3].
3:38
The astronauts of Apollo 17 spent the longest amount of time outside of the lunar module,
3:43
but only managed 22 hours of Surface EVAs, during which almost irreparable damage was
3:49
done to the spacesuits - had they conducted more work on the lunar surface, the suits
3:54
would eventually have been rendered useless..
3:57
But 22 hours is only a fraction of what would be required for any future mission to the
4:03
moon.
4:04
In 2015, NASA laid out its Space Technology Roadmaps which identified one key and hugely
4:10
ambitious goal [4].
4:11
They wanted their spacesuits to be able to survive for 100 EVAs - a total of 800 hours
4:17
spent on the Lunar surface, almost 37 times the duration the Apollo 17 astronauts spent
4:23
outside.
4:24
More than any other problem facing NASA or any other space agency, this could be the
4:29
making or breaking of a long-term outpost on the surface of our moon.
4:34
But how do you begin to extend the life of a spacesuit by this much?
4:39
To get to an answer, we first need to understand how lunar dust is formed and why it sticks
4:43
to anything it comes in contact with.
4:46
Unlike the surface of the Earth, the surface of the moon is under almost constant bombardment
4:52
from small and large meteorites, some of them only micrometers in diameter.
4:57
This rain of debris causes parts of lunar rocks to break off, creating a layer of fine
5:02
dust on the lunar surface.
5:04
Occasionally, these micrometeorite impacts hit with such force that they melt the minerals
5:10
contained in the soil, turning them into glass.
5:13
Lunar dust is a mixture of super-fine particles and razor-sharp glass that’s also incredibly
5:19
dry - there’s no water in the soil or air to clump the particles together and no natural
5:25
erosion through wind to blunt the sharp edges [5].
5:28
So, this obviously does not mix well with the intricate mechanisms of the lunar spacesuits.
5:33
The dust is small enough to get into almost any gap, and, thanks to the shards of glass
5:38
in the dust, it can easily scratch glass or metallic surfaces.
5:42
But this is only the beginning of the problem.
5:45
Thanks to the lack of atmosphere or magnetic field on the moon, lunar dust is exposed to
5:50
every fraction of radiation that’s fired at it.
5:53
On the side of the moon exposed to the sun, particles in the dust are hit with X-ray and
5:58
ultraviolet radiation, causing electrons to be knocked off, creating positive charges
6:03
on the surface of the dust particles.
6:06
Then, on the side shielded from the sun, the opposite happens.
6:10
The particles pick up electrons from solar winds, causing them to become negatively charged.
6:16
These positive and negative charges on the particles create electrostatic potentials
6:21
on the surface of the moon, reaching up to 20 V on the day side, and an astonishing -3800
6:28
V on the night side.
6:30
When the Apollo 8 astronauts saw the beautiful bands of light at sunset and sunrise, they
6:36
weren’t seeing the scattering of radiation through atmospheric gasses, but instead light
6:41
passing through a column of fine dust fired up from the surface of the moon by electrostatic
6:46
levitation - dust particles of like charges repel each other, and are repelled by the
6:51
lunar surface, creating a fountain of sharp microdust that rises above the horizon.
6:57
This is the same dust that Apollo astronauts walked through and kicked up as they worked
7:02
outside the lunar module, sticking to their suits in the same way a statically-charged
7:07
balloon sticks to your clothes.
7:09
Charge is one of the main reasons the dust is so annoying, but it could also be the way
7:13
we get rid of it.
7:15
In 2021, as part of NASA’s Breakthrough, Innovative & Game-changing Idea Challenge,
7:20
they tasked university students from across the world to come up with novel ways of dealing
7:25
with the lunar dust problem [6].
7:27
Some of the winning solutions included conductive fibers inspired by chinchilla hair, an electrically
7:32
charged brush that could be powered by UV radiation, and a fabric for spacesuits that
7:37
mimicked the way certain insects use hair-like structures to collect and deposit pollen.
7:42
All these ideas use different ways to solve the same problem, but they share a common
7:47
approach - using charge to either passively or actively remove dust from spacesuits.
7:53
At its simplest, the problem comes down to this - how do you make the outer layer of
7:57
the spacesuit repel the charged dust instead of attracting it?
8:01
NASA came up with an elegant solution.Instead of trying to completely redesign the outer
8:05
layer of the suit, they decided to create a system that could be easily integrated into
8:11
the pre-existing layers of fabric and material found in the current generation of spacesuits.
8:17
Their idea was to create a suit that could make its own electrical current which would
8:22
actively eject dust, acting like some sort of energy shield.
8:26
And the first challenge was choosing the conductive material that the electrodes would be made
8:30
from.
8:31
This method of dust-ejection wasn’t new.
8:33
It was inspired by the Electrodynamic Dust Shield systems th at had been used by NASA
8:38
since the late 1960s, on things like solar panels, cameras and thermal radiators [7].
8:44
But in almost all of these cases, the electrodes - which were made out of silver, copper or
8:49
a compound of indium and tin - were placed on rigid, fixed bodies.
8:54
A spacesuit is designed to move - the outer layer is made up of segments of overlapping
9:00
fabric that roll over each other at the joints when the astronaut moves their arms or legs.
9:05
So, while the silver and copper electrodes used in the pre-existing EDS systems might
9:10
be excellent electrical conductors, with their low elasticity, they wouldn’t survive the
9:15
fatigue caused by the constant flexing of the joints.
9:18
So, a new conductor was needed, one that had a high electrical conductivity, but that was
9:24
flexible enough to withstand the significant forces exerted on it during extravehicular
9:29
activities.
9:30
And the answer was carbon nanotubes.
9:33
These are cylindrical tubes of carbon atoms stretching only a nanometer across, with walls
9:39
one atom thick - like a long, thin layer of graphene that’s been rolled into a tube.
9:44
Carbon nanotubes are incredibly strong, with a considerably higher tensile strength than
9:49
copper, silver or gold and they have a very high electrical conductivity.
9:53
\ Animation 9 continued…
9:54
CNTs are also very light.
9:56
If you compare the mass of different conductors required to create an Electrodynamic Dust
10:01
Shield on the knees, elbows and boot areas of a lunar spacesuit, around 101 g of copper
10:08
wire would be needed, but if you replace the copper with carbon nanotubes, you only need
10:13
about 16g:
10:15
Carbon nanotubes are an excellent choice, as they could provide high conductivity with
10:19
low mass, while also being able to withstand the 800 hours of EVAs required for future
10:25
lunar missions.
10:26
So, after settling on CNTs, it was then a matter of finding a way of integrating these
10:31
nanotubes into the outer layer of the spacesuit.
10:35
Lunar spacesuits are made up of up to 21 layers of material, with an outer orthofabric layer
10:40
composed of a mixture of fibers like GORE-TEX and Kevlar.
10:44
The carbon nanotube electrodes were made into yarns and then woven into this outer layer
10:50
in a longitudinal direction to limit the tensile force applied to the electrodes, and they
10:56
were also spaced out from each other to prevent electrical arcing.
11:00
The orthofabric in this outer layer acts as a natural insulator, but there is a chance
11:05
it could be broken down by high voltages.
11:08
Through testing, it was found that the orthofabric could withstand up to 1200 V, so the dust
11:14
removal system was capped at around 1000 V to prevent dielectric breakdown of the insulating
11:19
material.
11:20
So, how does the dust removal system actually work?
11:24
The carbon nanotube electrodes are first connected in parallel, and then activated by a multi-phase
11:29
alternating current at voltages between 600 and 1000 V and very low currents, at around
11:35
3 mA.
11:36
This sets up repeating waves of electrical fields which move across the outer surface
11:41
of the spacesuit.
11:42
As they interact with the charged dust particles, they add an additional repulsive force to
11:48
the particles based on coulomb interactions - repulsion due to the interaction of two
11:53
charged objects.
11:54
This repulsive force is, overall, greater than the gravitational and adhesive forces
11:59
which stick the particles to the suit, causing the particle to be ejected from the orthofabric.
12:05
But this also works for uncharged particles that are stuck to the suit.
12:09
When interacting with a non-uniform electric field, like in this system, uncharged dust
12:14
can be repelled through something called a dielectrophoretic force..
12:18
Overall, the electrical energy of the system is transformed into mechanical energy as the
12:24
dust is kicked off the suit.
12:26
To test the system, NASA constructed a prototype knee joint with carbon nanotubes woven into
12:32
an outer orthofabric layer, and used it to measure how much of a lunar dust simulant
12:37
was removed in different scenarios.
12:39
[8].
12:40
And what they found was remarkable.
12:42
Through analysis of high resolution images taken of the fabric before and after activation
12:47
of the electrodes, they saw, that up to 96% of the lunar dust simulant was removed by
12:53
the system (see here for video) This has enormous potential for use as part
12:57
of future moon missions.
12:58
The dust removal system could be on continuously during EVAs, preventing any dust from binding,
13:04
or it could be manually activated when an astronaut noticed a large build up of dust.
13:09
This dust prevention technology may seem trivial, but this razor sharp lunar dust is a life
13:14
limiting threat to any future moon colony.
13:17
This kind of simple environment effect, that requires a breakthrough material to overcome,
13:22
is the core of what makes engineering exciting for me.
13:25
A relatively simple solution that any new engineering graduate could have helped develop,
13:30
and go on to see their work land on the moon.
13:33
Seeing your work go from the lab, to the factory floor, to the real world is one of the most
13:37
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13:41
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If you are looking for something else to watch right now, why not watch my previous video
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Did you do that transcription manually? Very helpful. Thank you.
S.C. Great notes! Thanks for providing. (I think we can dispense with that idea of a German dark side moon base once and for all! :)
Just ask the biomeds in Wuhan.
Overly dramatic video title - its lunar dust short answer.
Very interesting information. Had heard about the ‘rays’ the astronauts saw, but this explains it.
Just a note. Used a regular expression in geany:
^(0?[0-9]|1?[0-9]:[0-5][0-9])$
to strip out the time stamps, and then ran that output through a spreadsheet filter to get rid of the blank (empty) lines. Cleans up real well.