Background

Lunar dust has been described to be fine like flour (one micron) and coarse like sandpaper [1]. When disturbed, dust particles will travel unimpeded in the microgravity setting of the lunar surface. The problem of dust is presented when astronauts traverse the moon terrain only to arrive back to the landing site covered in the particulate matter. The dust is prone to cling to the fabric of the space suits, find its way into space suit joints, obstruct the airlock seal of the hatch, and remain in the capsule when the astronauts are ready to return home.

The problem has been broken into five possible scenarios:

1. Dust clings to spacesuit
2. Dust is present in the air before entering the spacecraft hatch
3. Dust is in the airlock/ascent vehicle at nominal temperature and pressure
4. Dust is in the ascent vehicle before take off during pressurized
5. Dust is in the ascent vehicle during weightlessness

Solutions

Electromagnetic Armour (EmA)

To prevent dust from clinging to the spacesuit fabric, Boeing has developed a system (SPIcDER) by which an electric current travels through parallel carbon nanotubes in the fabric of the spacesuit creating a varying electric field [2]. Since lunar dust particles are ionized through the bombardment of charged UV particles from the sun, the electric field levitates and transports the dust particles away from the fabric [1]. The electromagnetic armour is a proposed system that uses the dust removal method by Boeing to mitigate dust clinging to the spacesuit fabric. In addition, to prevent dust from entering the bearings at each joint of the spacesuit (wrist, shoulder, waist, ankles), a Carbon Nanotube (CNT) fabric piece covers the bearing joints and is fastened in a way similar to fashionable overalls.

Assumptions

1. The air bladder that contains the air within the suit can withstand the voltage being supplied to the CNTs in proximity.
2. There is no interference between differently oriented CNTs.
3. Next generation space suits have not already incorporated SPIcDER.

Dust Removal & Attraction Wand (DRAW)

DRAW was presented as a dust mitigation tactic which removes and collects lunar dust from the seal of the hatch to the lunar module. DRAW is a handheld tool which attracts lunar dust using an electric charge. On the door of the hatch is a knife edge seal, under the assumption that the seal design is similar to that of Apollo 11 [3]. With the press of a button, we can pass the wand over the thermal seal on the ship, and knife edge on the door, and collect lunar dust along the wand. To release this dust back onto the moon, the button is released with the wand facing away from the lander, and the charge is dropped.

To do this, the design of DRAW was made to be a trident which run a positive charge along one rod, and a negative charge along the other two rods. With the assumption that astronauts will only venture out during the day, and due to the photoelectric effect on the soil, much of the dust will be positively charged, which is why the wand has two negatively charged rods. This rod would be powered by the onboard system.

Assumptions

1. The hatch has a knife-edge seal, like on Apollo 11.
2. The material of the hatch door and module are an Aluminum-Silicon composite called NASA 398-T5.
3. There are only mechanical or hydraulic parts on the door and seal.

UV Dust Detection (UV DuDe)

Lunar dust contains small amounts of Titanium dioxide and Magnesium oxide that absorb UV light [4]. This information was discovered by an analysis conducted by NASA on the lunar rock and dust samples collected during the Apollo missions [4]. Assuming that the spacesuit is designed to reflect UV light, lunar dust may then be detected on the spacesuit by means of a UV flash and a camera. In this way, the dust can be mapped on the spacesuit with an image capturing the locations of the absorbed UV light where the dust exists. The astronauts will immediately receive an image revealing the lunar dust on their space suit. This system is also used to detect lunar dust on the hatch of the ascent vehicle.

Assumptions

1. The spacesuit is designed to reflect UV.
2. The airlock is separate from the ascent vehicle cabin, there is room for the astronaut to stand in the spacesuit for UV dust detection.

Challenges Faced

The availability of information regarding the technology for the next generation spacesuits was limited during the research of spacesuit dust mitigation methods. The assumption was made that CNT technology has not yet been implemented for next generation xEMU spacesuits. Trace amounts of lunar dust at the microscopic level are likely to remain in the fabric of the spacesuit even after the SPIcDER method is used. Tests conducted using the SPIcDER removal method revealed that 80% of dust was repelled [2]. The decision to use overall-style buckles to fasten the fabric bearing covers was based on the assumption that the CNT mitigation would prevent dust from entering underneath the cover; it would be beneficial to pursue a more sophisticated solution to offer a better seal.

The design of a dust removal method for the hatch was proven difficult as information regarding the design of current capsule hatch doors was not readily available. The design for the hatch door removal method was based on the presumption that the Apollo era hatch door knife seal would be used.

The team underwent numerous feasibility studies to determine viable solutions for dust detection and mitigation. An initial idea was to use a thin polymer applied to the surface of the space suit that could be removed after completion of extravehicular activities. This polymer would attract lunar dust and could disposed of after use; though it was undecided what would become of the spent polymer. For dust detection in the hinge seal, a calculation was conducted to determine if a magnet could be used to detect the presence of lunar dust. The calculation revealed that the magnetic properties of the dust was far too weak and would require a very large magnetic field. In addition, LiDAR was also considered for detection of lunar dust in the seal. For dust removal, the use of an air pressure differential was considered as an option to blow dust particles out of the seal.

Next Steps

Moving forward with the mitigation and detection systems proposed; extensive testing for the mentioned systems is required to quantify the success of said systems under a variety of test environments. Ensuring the validity of each solution would require the establishment of test environments resemblant of microgravity and lunar dust sized particulate matter.

Testing the SPIcDER system would yield success rates of repelled dust while also providing opportunities to increase the efficiency of dust removal beyond 80%. Ensuring that the voltage does not affect the air bladder is also necessary. Testing alternative styles of fastening methods for the bearing covers would be beneficial to identify an option with minimal dust entrapment.

Dust detection through UV flash imaging must be tested to yield the accuracy of dust mapping on the hatch as well as the spacesuit. There may also be additional image processing necessary to display the data in an appropriate way to the astronaut.

Resources

[1] Soil Science Society of America. "NASA’s Dirty Secret: Moon Dust." ScienceDaily. ScienceDaily, 29 September 2008. <www.sciencedaily.com/releases/2008/09/080924191552.htm>.

[2] J. P. Feng, J. Wang, W. T. Hwang, and Y. M. Jo, “Characterization of filter media prepared from aligned nanofibers for fine dust screen,” J Appl Polym Sci, vol. 136, no. 44, p. 48166, June 2019.

[3] J. R. Finkbeiner, P. H. Dunlap, B. M. Steinetz, “Apollo Seals: A Basis for the Crew Exploration Vehicle Seals,” NASA Glenn Research Center, Oct. 2019.

[4] David J. Loftus et al. NASA Ames Research Center.

[5] Fozia Z. Haque b, Ruchi Nandanwar a, Purnima Singh, 2016, Evaluating photodegradation properties of anatase and rutile TiO2 nanoparticles for organic compounds

[6] Y. Lu, J. Jiang, X. Yan, and L. Wang, “A new photovoltaic lunar dust removal technique based on the coplanar bipolar electrodes,” Smart Mater. Struct., vol. 28, no. 8, p. 085010, Aug. 2019.

[7] H. Kawamoto and N. Hara, “Electrostatic Cleaning System for Removing Lunar Dust Adhering to Space Suits,” J. Aerosp. Eng., vol. 24, no. 4, pp. 442–444, Oct. 2011.

[8] K. K. Manyapu, L. Peltz, and P. De Leon, “Self-cleaning spacesuits for future planetary missions using carbon nanotube technology,” Acta Astronautica, vol. 157, pp. 134–144, Apr. 2019.