dustAR

• Who are we?

We are a group of students committed to make a contribution to lunar exploration and science in general. Our curiosity has impulsed us to sign up to this challenge and try our best to solve the lunar dust problematic.

Our areas of interest are electronics, satellite communications, space missions, and astronomy in general.

The team is composed of five electronic engineering students and one astronomy student.

• Why is this important?

All astronauts who walked on the moon reported going through hard times with lunar dust. Because of its micrometric particles, and its electrical charge, it can stick to a wide range of materials.

1. Micrometeorites impacts cause shock-melting of lunar regolith, which results in vaporization and re-condensation.
2. Particle of lunar regolith showing sharp, jagged edges, as viewed by electron microscopy.

It can affect cameras, solar panels, mechanical parts of the rovers, and more.

Regarding space suits, which is one of the biggest concerns as it implies reducing (or not) the exploration time on the surface of the moon for astronauts, lots of problems have been described. Three of the most important points are the reduced mobility, as the dust gets into the joints of the space suits, the lowering of the external visibility, and the wear of the gloves. What is more, Apollo 17 crew members stated that is impossible to wipe the dust away, as the tiny silica particles scratch the gold visors of the helmets.

Moreover, it has been calculated that during the landing of space missions dust can travel up to 400 meters per second, as fast as a bullet, caused by the lack of atmospheric resistance. This means that in the future, craft landings near structures or delicate equipment could cause damage to them.

Studies have shown that lunar dust has not only a negative impact on equipment and spacesuits, but it also may cause neurological autoimmune diseases, due to the large amount of hydroxyl radicals suspended in the “fresh regolite”. Also, although the dust is mostly silica particles, excessive inhalation might result in a disease called silicosis which worsens the pulmonary capacity and ultimately causes death.

• What do we propose?

After thorough investigation, we have found that a unique and global solution is not possible to implement with today’s technology and information about lunar dust. That is why we decided to propose a few different solutions intended to work in particular cases.

One of the substantial constraints that we had, is the lack of precise characterization of the lunar dust’s electrical and chemical properties. Anyhow, what it is well known, is that the charge of the dust varies a lot respect to its size, so electromagnetic treatment it is not suitable for all scenarios.

Because of all the mentioned above, we propose a few solutions for different steps:

1. Self-Cleaning visor for the suit’s helmet:

This system consists of an electromagnet and pressurized gas for the visor’s cleaning when facing low visibility conditions. The main idea is that the gas will loosen the dust while the electromagnet sweeps the surface.

The advantage of this method versus others, despite its implementation costs, is that the person wearing the suit only has to press a button. Although the cleaning will not be perfect, we expect the astronaut to be able to see enough to, at least, return to the station.

Energy-wise, the system is not expected to consume more than 40 watts over 10 seconds. Providing that previous missions EMU (Extravehicular mobility unit) had 16v 25Ah batteries, we believe that the estimated consumption will not be a major issue in the future.

Implementation can vary widely in each particular case, as helmet’s technology and design is constantly changing. As a model, we took the “Apollo LEVA”, used in Apollo 13 to 17 missions. The system could be mounted on the “sunshades”, two lateral panels whose mission is to block sunlight.

It is worth noticing that using electromagnets is key, as otherwise the dust would stick to permanent magnets under any circumstances, reducing its effectiveness when needed.

Another thing to have in mind, is that research conducted in the early 90’s at Austin’s University in texas showed that the optimum angle for the gas ejection with respect to the surface is to 22,5 degrees. Besides, the investigators came to the conclusion that the most suitable gases to use were carbon dioxide and hydrogen, that due to its heavy molecules they behave similarly than on earth at the moment of the expansion. It has to be considered that when pressure changes so dramatically, gas expands in all directions and its temperature lowers rapidly.

2. Space suit cleaning chamber:

It consid sts of a closed receptacle that functions as an antechamber to the lunar module, its function is to remove the dust that has adhered to the space suit during the tasks performed on the surface at the time of starting the return to the module.

When an astronaut gets into, the chamber closes tightly, so it prevents the outside dust from entering. Then a gas is discharged out on the suit, which would cause the dust particles to detach from it. Meanwhile, the astronaut will help to the process using an electrostatically negative charged carbon fiber brush. The chamber is composed of two side panels, one on the left and one on the right, each one with an electric charge of opposite polarity, the right panel has a negative charge (-) and the left one has a positive charge (+). The dust particles detached from the suit will be repelled by the left panel and attracted by the right one, which will have a defined lateral movement. Both panels are mounted on the walls of the chamber. Parallel to the left panel, and a short distance from it, is a grid whose lower section becomes a solid section. So the dust can be deposited in the space between the panel and the grid (entering through it), and is trapped inside by the solid section when falling down by the effect of the gravitational force. Otherwise, if the dust will be deposited on the surface where the astronaut will move through the chamber, the vast majority of the dust coming from his suit would stick to the sole and sides of his boot, entering to the lunar module.

Initially, it was considered to place the panels on the ceiling and the floor of the chamber, in order to favor with this their vertical displacement towards the floor, in this case locating the grid on the lower plate to which the dust particles would be attracted. But this idea was discarded since by placing the panels on the vertical axis will cause the attractive field would disperse and weaken greatly due to the greater distance between the panels.

Calculus: Considering the average charge of a particle 1[μm³] as 300,000 times the charge of an electron, the force needed to move a particle with a force similar to earth’s gravity, requires an electric field of 0,4[V/m]. This is an approximate number that could be generated by putting the plates under 48[V].

3. Positive charged frames:

This is an extra protection for the sealing of any frame, container or door. The metallic frame is connected to a positive potential (or negative depending on the case) to avoid the dust adhering electrostatically. An automated system of brushes could be implemented in the most vulnerable parts as hinges. Nevertheless, as the dust will not be strongly attached, a vacuum cleaner or a manual brush could do the trick.

4. Capacitive centrifuge:

The presence of lunar dust in the joints of the suit is of particular interest due to the potential deterioration of the suit associated with it. Also, it is desirable that the amount of dust entering the module to be smaller as possible to prevent the damage of the equipment, and even more, ensure the health of the crew. With the aim of minimizing the remainder that could overcome the previous control stages, the idea of the mechanism arises that, through a combined effort of mechanical and electrical actions, manages to extract as much of the remaining dust in gloves, boots and helmet. The concept of the device is based on the application of centrifugal forces that, under the additional action of an electric field, manages to release the adhered dust particles.

The device consists, essentially, in a rotating drum constituted by an external cylinder perforated with an axle in the center, in which the equipment to be decontaminated is placed. The axle would also function as a positive electrode, while the negative one would be arranged around the outer cylinder . The action of centripetal forces must, in collaboration with the forces of Coulomb product of the electric field and the inherent charge of the dust, counteracts the action of the electrostatic and Van der Wals forces causing the adhesion.

According to Mitigation of lunar dust adhesion by surface modification (Adrienne Dove, 2010), the intervention of the superficial structure of the material turns out to be a key aspect, since it allows through the decrease of surface energy or conductivity, to reduce the forces that cause adhesion.

Is also possible -as with the black Kapton film - to improve the results by UV radiation, allowing the detachment with less effort. In this way, it is possible to achieve the release of up to 90% of the dust, according to experimental results.

The figure shows the rotation speeds which reached almost 50% of detachment for different samples, in both they altered version and the treated one. Likewise, figure 2 shows the contrast between the irradiated kapton and not irradiated one.

Based on this, the principle of the “Capacitive centrifuge” will be the reduction of dust adherence due to the suit’s surface alteration because of the centrifugal force product of the rotation of the tank and the electric field generated by the electrodes. The speed of rotation will depend on the material that covers the suit and its treatment, with a rotation time of about 30 seconds according to experimental results.

Lunar dust detection:

For dust detection we used x-ray fluorescence spectrometry as an analytical technique to get elemental information about lunar dust through energy-dispersion.

The EDXRF consists of an x-ray tube which acts as a source, irradiating the sample.

This kind of detector is able to measure different characteristic radiation energies of the sample in order to identify the present elements on it.

Two of the big advantages of this equipment are the real time data analysis with high precision, and the low power consumption which is one of the most important factors in aerospace development.

What is more, portable versions are available, so the region under test could be virtually anything.

• How could this investigation improve lunar explorations?

We consider that this investigation and development could have an impact on the following aspects:

• Could open new horizons regarding lunar excavation and structural experimentation.
• The enhancement of samples reliability, as sealed containers would not get damaged.
• The improvement of life quality and expectancy of astronauts who would not be as exposed ad before. Preventing any collateral illnesses.

References:

• Impact of Dust on Lunar Exploration (Stubbs T. , 2005)

• Generation and Evaluation of Lunar Dust Adhesion Mitigating Materials (Christopher J. Wohl)

• Mitigation of lunar dust adhesion by surface modification (Adrienne Dove, 2010)

• Design of equipment for lunar dust removal (Belden L,1991)

• Lunar dust levitation (Joshua Colwell, 2009)

• Electrostatic charging properties of simulated lunar dust (Mihály Horányi, 1995)

• Indicative basic issues about lunar dust in the lunar environment (Brian O’Brien, 2009)

• Lunar surface: Dust dynamics and regolith mechanics. (J. E. Colwell, 2005).

• The Chemical Reactivity of Lunar Dust Relevant to Human Exploration of the Moon. (David J. Loftus, M.D., Ph.D., 2009)

• Lunar sourcebook (Edited by Grant H. Heiken)