Towards Risk Management Of Movements Of Fine Dust On Surface Of The Moon: Reality Checks From Apollo 11 To Chang'e-3 And -4
Here we summarise transport or movements of fine lunar dust on the surface of Moon. Risk management measures arising from the Workshop must necessarily be based on comprehensive quantitative and qualitative knowledge of dust movements driven by natural phenomena and by human causes, including effects of rocket exhausts. No comments are included here about possible mitigation of dust movements such as discussed by Larry Taylor or about landing sites. Focus here is on reality checks based on knowledge. From 1961 to 2013-4, the only quantitative knowledge of dust movements came from digital measurements by 270g Apollo Dust Detector Experiments (DDEs) we invented in 1966. All Apollo 11 to 17 astronauts gave qualitative descriptions of problems caused by their movements inescapably raising clouds of very fine dust that travelled ballistically. Gene Cernan, the last man on Moon after 3 years and 5 previous landings, summarised in his Debriefing: "We can overcome other physiological or physical or mechanical problems except dust”. Dust adhered ‘to everything, no matter what kind of material” with “restrictive, friction-like action". Some Apollo hardware including scientific experiments malfunctioned by overheating or friction-like effects caused by dust. One example was the Apollo 17 troubled Lunar Ejecta and Meteoroid (LEAM) experiment. Despite significant uncertainties about the causes of LEAM counts, a 30-year widely-held mindset of fine surface dust levitating to high altitudes became the major hypothetical target for the lunar orbiting LADEE spacecraft dust detector DLEX. In 2011 we published and at the 2012 Lunar Conference in Ames presented two separate and independent reasons for our doubts that such levitated fine dust existed at LADEE altitudes. Principal Investigators reported in 2015 that DLEX measurements provided no evidence of such dust. In December 2015 we published Apollo 12 Dust Detector Experiment (DDE) evidence of the cause of the Surveyor Horizon Glow, as being levitated sunrise-driven dust clouds measured at 100cm height and relevant to Landed Missions. Our measurement-driven 5-step simple model of sunrise-driven movements of lunar dust explains a range of other mysteries about lunar surface. The sunrise discovery has various far-reaching consequences applicable to Landed Missions.. A strategically important consequence was our speculation published in December 2015 that sunrise-driven dust clouds plus the friction-like effects reported by Gene Cernan might have caused immobilisation of Chang'e-3 lunar rover Yutu, in January 2014. Yutu had travelled 100m on its 6 wheels in December 2013, but was immobilised on the next lunar day, i.e. after its first sunrise. In May 2016 it was announced that the scientific priorities for Chang'e-4 lunar rover had been revised to make it the first lunar spacecraft with top priority studies of lunar surface floating dust. This represents a paradigm shift from the long-prevailing 1964 culture of dismissal of the importance of fine lunar dust, repeated in 2010 Oral History of Noel Hinners. We suggest elsewhere various unifying significant strategic explanations and measurement-based views about lunar surface dust environments. Here we include only that the 1966 invention of the DDE was a paradigm shift from traditional detectors of dust in space, Traditional dust experiments such as Apollo 17 LEAM and the LADEE DLEX are primarily plasma-impulse detectors responding to individual hypervelocity particles of dust. By contrast, the orthogonal solar cells of the Apollo 12 DDE measure cumulative movements of billions to trillions of low-energy dust particles. The DDE also measures both cause (dust) and effect (temperature change) with a bead-size thermistor (thermometer). For this briefing, we suggest for the first time that the sunrise-driven natural dust effects have made pre-flight testing of lunar landers or sub-systems of them even more difficult or impracticable. It has long been recognised that simulant dust can be credible only after increasingly sophisticated development of the physical and chemical properties of the simulant.. It has been partly recognised that simulation in laboratory experiments of the lunar dusty plasmas environment is also important and complex. But our sunrise-driven 5-step model of dust transport means than the provenance (or recent past history) of the dust environment is vitally important, and this would seem to present new challenges to reliability of simulation tests.