Michael R. Johansen

Electrostatic precipitation of dust in the Martian atmosphere: Implications for the utilization of resources during future manned exploration missions

Future human missions to Mars will require the utilization of local resources for oxygen, fuel, and water. The In Situ Resource Utilization (ISRU) project is an active research endeavor at NASA to develop technologies that can enable cost effective ways to live off the land. The extraction of oxygen from the Martian atmosphere, composed primarily of carbon dioxide, is one of the most important goals of the Mars ISRU project. The main obstacle is the relatively large amount of dust present in the Martian atmosphere. This dust must be efficiently removed from atmospheric gas intakes for ISRU processing chambers. A common technique to achieve this removal on earth is by electrostatic precipitation, where large electrostatic fields are established in a localized region to charge, precipitate and collect dust particles. This technique is difficult to adapt to the Martian environment, with an atmospheric pressure of about one-hundredth of the terrestrial atmosphere. At these low pressures, the corona discharges required to implant an electrostatic charge to the particles to be collected is extremely difficult to sustain and the corona easily transitions to a glow/streamer discharge, which is unsuitable for particle charging. In this paper, we report on our successful efforts to establish a stable corona under Martian simulated conditions. We also present results on dust collecting efficiencies with an electrostatic precipitator prototype that could be effectively used on a future mission to the red planet.

Development of an electrostatic precipitator to remove Martian atmospheric dust from ISRU gas intakes during planetary exploration missions

Manned exploration missions to Mars will need dependable in situ resource utilization (ISRU) for oxygen production. The Martian atmosphere is composed of 95.3% CO2, other gases, and 0.13% O2 at ~ 9 mbar (1% of the Earths pressure). However, it also contains 2-10- μm dust uploaded by dust devils and high winds. Oxygen extraction requires removal of the dust with little pressure drop (Δp). An electrostatic precipitator (ESP) has lower Δp than a filter, but the low pressure causes an electrical breakdown at electric fields ( ~ 1 kV/cm) ~ 30× lower than on Earth, making implementation challenging. Molecular mean free paths (λ = 4 μm) and ion mobility values (b = 0.008 m2/V·s) are ~ 100× larger than at Earths pressure (λ = 44 nm) and (b = 8.4 ×10-5). The large λ lowers Stokes drag, particularly for smaller particles. Pauthenier field charging dominates for particles with and diffusion charging for d<;2 μm. The low E proportionally decreases both Pauthenier particle charging and the F = qE collection force. This greatly reduces the particle migration velocities (w), e.g., for d = 10 μm, w = 0.01 m/s compared with 0.4 m/s on Earth. However, for small particles (d = 1 μm), this is compensated by diffusion charging and reduced drag ( w = 0.04 m/s on Mars, 0.05 m/s on Earth). The Martian atmosphere was simulated with 95% CO2/5% humid air at 9 mbar. Paschen curves were measured, and I- V curves ( I ~ 5 - 300 μA for V ~ 1.3 - 2.3 kV) were obtained for 5-10-cm-diameter wire/rod-cylinder ESPs. Only positive polarity yielded stable uniform corona. Charging of 0.5-1.3-cm-diameter spheres agreed with the Pauthenier theory. A Martian dust simulant collection efficiency test is in progress.

History and Flight Development of the Electrodynamic Dust Shield

The surfaces of the moon, Mars, and that of some asteroids are covered with a layer of dust that may hinder robotic and human exploration missions. During the Apollo missions, for example, lunar dust caused a number of issues including vision obscuration, false instrument readings, contamination, and elevated temperatures. In fact, some equipment neared failure after only 75 hours on the lunar surface due to effects of lunar dust. NASAs Kennedy Space Center has developed an active technology to remove dust from surfaces during exploration missions. The Electrodynamic Dust Shield (EDS), which consists of a series of embedded electrodes in a high dielectric strength substrate, uses a low power, low frequency signal that produces an electric field wave that travels across the surface. This non-uniform electric field generates dielectrophoretic and electrostatic forces capable of moving dust out of these surfaces. Implementations of the EDS have been developed for solar radiators, optical systems, camera lenses, visors, windows, thermal radiators, and fabrics The EDS implementation for transparent applications (solar panels, optical systems, windows, etc.) uses transparent indium tin oxide electrodes on glass or transparent lm. Extensive testing was performed in a roughly simulated lunar environment (one-sixth gravity at 1 mPa atmospheric pressure) with lunar simulant dust. EDS panels over solar radiators showed dust removal that restored solar panel output reaching values very close to their initial output. EDS implementations for thermal radiator protection (metallic spacecraft surfaces with white thermal paint and reflective films) were also extensively tested at similar high vacuum conditions. Reflectance spectra for these types of implementations showed dust removal efficiencies in the 96% to 99% range. These tests indicate that the EDS technology is now at a Technology Readiness Level of 4 to 5. As part of EDS development, a flight version is being prepared for several flight opportunities. The flight version of the EDS will incorporate significantly smaller electronics, with an expected mass and volume of 500 g and 350 cm(exp. 3) respectively. One of the opportunities is an International Space Station (ISS) experiment: Materials for International Space Station Experiment 10 (MISSE-10). This experiment aims to verify the EDS can withstand the harsh environment of space and will look to closely replicate the solar environment experienced on the moon. A second flight opportunity exists to provide an EDS to several companies as part of NASAs Lunar CATALYST program. The current mission concept would fly the EDS on the footpad of one of the Lunar CATALYST vehicles. Dust will likely deposit on the footpad through normal surface rover activities, but also upon landing where lunar dust is expected to be uplifted. To analyze the e effectiveness of the EDS system, photographs of the footpad with one of the spacecrafts onboard cameras are anticipated. If successful in these test flights, the EDS technology will be ready to be used in the protection of actual mission equipment for future NASA and commercial missions to the moon, asteroids, and Mars.

Development of an Electrostatic Precipitator to Remove Martian Atmospheric Dust From ISRU Gas Intakes During Planetary Exploration Missions

Manned exploration missions to Mars will need dependable in situ resource utilization (ISRU) for oxygen production. The Martian atmosphere is composed of 95.3% CO2, other gases, and 0.13% O2 at ~ 9 mbar (1% of the Earths pressure). However, it also contains 2-10- μm dust uploaded by dust devils and high winds. Oxygen extraction requires removal of the dust with little pressure drop (Δp). An electrostatic precipitator (ESP) has lower Δp than a filter, but the low pressure causes an electrical breakdown at electric fields ( ~ 1 kV/cm) ~ 30× lower than on Earth, making implementation challenging. Molecular mean free paths (λ = 4 μm) and ion mobility values (b = 0.008 m2/V·s) are ~ 100× larger than at Earths pressure (λ = 44 nm) and (b = 8.4 ×10-5). The large λ lowers Stokes drag, particularly for smaller particles. Pauthenier field charging dominates for particles with and diffusion charging for d<;2 μm. The low E proportionally decreases both Pauthenier particle charging and the F = qE collection force. This greatly reduces the particle migration velocities (w), e.g., for d = 10 μm, w = 0.01 m/s compared with 0.4 m/s on Earth. However, for small particles (d = 1 μm), this is compensated by diffusion charging and reduced drag ( w = 0.04 m/s on Mars, 0.05 m/s on Earth). The Martian atmosphere was simulated with 95% CO2/5% humid air at 9 mbar. Paschen curves were measured, and I- V curves ( I ~ 5 - 300 μA for V ~ 1.3 - 2.3 kV) were obtained for 5-10-cm-diameter wire/rod-cylinder ESPs. Only positive polarity yielded stable uniform corona. Charging of 0.5-1.3-cm-diameter spheres agreed with the Pauthenier theory. A Martian dust simulant collection efficiency test is in progress.

Design of a Second Generation Electrostatic Precipitator for Martian Atmospheric Dust Mitigation of ISRU Intakes

A second generation electrostatic precipitator for use in the Martian environment has been developed by the Electrostatics and Surface Physics Laboratory (ESPL) at NASA Kennedy Space Center (KSC). This new system was designed to be modular and has three interchangeable test sections, each with a variety of replaceable high voltage electrodes, enabling optimization of the dust collection efficiency of the precipitator. It has the ability to maintain an increased atmospheric flow rate and provide more accurate dust delivery into the test section than was available in the previous prototypes. A majority of the controls for the system are provided by a software package developed to maintain a constant flow rate, low pressure, and electrode current to enable long duration performance characterization. This allows for testing of the technology in a relevant environment similar to those expected to be found in an atmospheric In-Situ Resource Utilization (ISRU) plant on Mars.