Dust collector

A highly speculative image of an array of dust collectors feeding atmospheric compressors on Mars. Sized for 50 m3/s of martian air, or about 1 kg/s.

A dust collector is a device used to separate dust from air in an atmospheric processing system. In some cases clean air is the desired result, in others, the dust is the object of interest.

Most dust collectors operate below atmospheric pressure with the fan on the clean side, after the dust separation system. In the thin martian atmosphere, the available pressure is very low, much lower than the standard operating pressure of dust collectors. So the fan will probably be installed on the dusty side, before the filters.

Dust collectors are filtration systems. For effective filtration of small particles they will often operate in cascade fashion, with a pre-filter and secondary filters.

Prior to the first stage the air can be routed through a torturous path with baffles. The incoming air hits the baffle and larger particles are removed from the air stream. Multiple stages of centrifugal air separation tubes cleans the air that much better.

In the traditional first stage, cyclonic separation, a type of inertial separation, can remove a large fraction of the heavier particles. To observe how a cyclone separator works, put some dirt into a glass of water and swirl it. The dirt collects in the center of the bottom of the glass. A cyclone separator puts high speed air into a vertical tube and spins the air around the edge of the tube. The particles fall down, clean air rises out.

HEPA grade filters can filter down to 5 microns, removing bacteria. However they have no effect on gases, only dust and particulate matter. Filters can clog over time. Mechanical shakers or pneumatic jets can be used to clear filters and knock the accumulated dust into a bin for disposal (or further use).

Dust collectors might be used in a number of cases:

• Extraction of in situ resources from the martian atmosphere.
• Cabin filtration in vehicles.
• Airlock pump down systems.
• Interior air filtration of a settlement.
• Interior air filtration of settlement production facilities.

The background (average) dust loading of Mars is estimated at 1,8e-7 kg/m3. A dust collector treating 1 kg/s of martian atmosphere, about 50 m3/s, would need to remove 283 kg of dust per year. This would be sufficient to produce the propellant for 40 Starship type vehicles. So for a single vehicle about 7 kg of dust per year would need to be removed from an airflow of about 1,1 m3/s (2400 cfm).

Dust collection		average background
Volume flow rate	m3/s	50
dust loading	kg/m3	1.80E-07
dust capture	kg/s	9.00E-06
per day	s	86400
	kg/day	7.78E-01
per year	kg/year	283.82

These figures would go up during dust storms. For a solar powered settlement, cutting back on propellant production during storms would means that the dust collectors would be idle anyway.

The MEDUSA instrument, part of ESA EXO Mars 2020 mission, is designed to measure in situ the dust conditions of the Martian atmosphere.

Electrostatic dust collectors

An alternative to cartridges and bag filters is the use of electrostatic separators, that do not require air pressure differences to operate.

Electrostatic precipitators might be effective in removing the fine particulates in the martian atmosphere, and are part of most process proposals. Electrically charge the air particles and drive them to a plate of the opposite charge. Plates can be periodically clean the plate by vibrating them. This works best with a slow air flow so that the particles have time to be charged and attracted to the plates.