Apollo astronauts discovered unexpected enemy on the Moon.
Fine dust, start by their movements and attracted by static electricity coated everything.
It found its way through seals, scratched visors and clung to suits despite brushing.
Eugene Cernan described it one of most aggravating aspects of lunar operations.
Over five decades later humanity prepares to return to the Moon with sophisticated equipment solving the lunar dust problem has become critical.
Appolo
Researchers from the Beijing Institute of Technology, China Academy of Space Technology and Chinese Academy of Sciences have developed a detail theoretical model that explain how charged dust particles interact with spacecraft surfaces during low velocity collisions.
The challenge starts with Moon harsh environment.
On the dayside intense solar ultraviolet and X ray radiation strips electrons from both spacecraft and lunar surface leaving them positively charged.
This creates photoelectron sheath hovering above ground.
On the nightside spacecraft and regolith instead collect electrons from surrounding plasma becoming negative charged and forming what is called a Debye sheath.
The solar wind adds other layer of complexity continuously bathing in charged particles.
Within this electrically active environment dust particles themselves become charged and experience three distinct electrostatic forces as they approach a spacecraft.
Appolo
The electric field force acts on particle surface charge pulling it toward or pushing it away from vehicle depending on whether their charges are opposite or the same.
The dielectrophoretic forces arises because the dust particle distort the non uniform electric field around it creating attraction toward regions of stronger field regardless of particle charge.
The image force emerges when the approaching charged particle creates opposite charge in spacecraft conductive surface similar to how balloon sticks to wall creating additional attractive pull.
The researches model treats these electrostatic interactions in mathematical detail but recognizes that other forces dominate once contact starts.
When dust grain actually strikes a spacecraft coating adhesive van der Waals forces between molecules at surface become dominant for the slow velocity impacts common during lunar operations.
The collision itself unfolds in three stages. First comes adhesive elastic loading, where the particle compresses against the coating while attractive forces between surfaces grow.
Appolo
If impact is energetic enough the coating starts to deform, dissipating energy as material yields.
During unloading stage the particle either bounces away or remains stuck depending on whether the collision velocity falls within critical range.
The model announces several practical.
A dielectric coating with high thickness and low permittivity can reduce the electrostatic attraction between charged dust and spacecraft.
The particle surface charge density matter over spacecraft electrical potential in determining strength of electrostatic forces.
For particles carrying typical charge densities below o.1 milliColumbs per square meter.
The adhesive Van der Waals force overwhelms electrostatic effects during actual contact.
Most useful for mission planners the research shows that coating made from low surface energy material with rough textures can reduce dust adhesion.
Larger particles tend to have higher coefficients of restitution meaning they are more likely to bounce away rather than stick.
There exist a critical velocity range for negative charge particles where adhesion occurs. impacts slower or faster than this window permit particles to escape.
This latest mode can predict dust accumulation pattern guide selection of surface coating and help optimize dust removal systems.
Mission to moon grow more ambitious and long duration solving sticky problem of lunar dust moves from annoyance to operational necessity.
Appolo
Source
https://www.eurekalert.org/news-releases/1110112
https://www.universetoday.com/articles/the-sticky-problem-of-lunar-dust-gets-a-mathematical-solution
