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Thursday, 16 June 2011

Unexpected facts have been discovered that change long-accepted interpretations of two of three lunar dust experiments carried out during the Apollo moon missions.

Sticky lunar dust was the top environmental problem for every one of the 12 Apollo astronauts who walked on the surface of the Moon.

A recent review by an original Apollo Principal Investigator, Adjunct Professor Brian J O'Brien, of The University of Western Australia's School of Physics, indicates results from the Apollo 17 experiment, designed to measure cosmic dust but thought for the past 33 years to have measured levitated lunar dust particles, were based on electrical interference instead of dust measurements.

Professor J O'Brien has analysed about a thousand raw data from the Lunar Ejecta and Meteoroids (LEAM) experiment and has presented a chain of evidence that the data were not caused by lunar dust as commonly assumed, but by noise bits generated by electrical interference in the circuits of LEAM on the moon - interference which was noted in LEAM systems tests on earth prior to the lunar missions.

Professor O'Brien was put on the track of the new findings when he became the first person to recognise that the LEAM raw data occurred in short bursts of  ‘events' with long intervals before the next burst, reminding him of electromagnetic interference from switching of heavy currents in a space payload.

He then found two Bendix Aerospace Corporation reports of acceptance testing in 1972 of the Apollo 17 scientific observatory before launch where on three occasions, LEAM was the only one of five major experiments to produce noise bits caused by such effects.  One reviewer of Professor O'Brien's manuscript confirmed that LEAM "carried some of the most sensitive amplifiers existing at that time".

Professor O'Brien suggests that the peaks in number of LEAM events around sunrise and sunset on the moon which so excited theories that dust was energised by hypothetical electrical fields at those special times, were most probably caused by electromagnetic interference when big currents were switched on and off in about a dozen large heaters, needed to protect the deployed equipment during 350 hours of each lunar night when temperatures reach minus 170 degrees centigrade.

After LEAM was deployed on the moon in December 1972, it was quickly agreed that most data were not caused by rare impacts of cosmic dust for which it was designed.  Theoretical analyses of the circuits and laboratory tests of a spare showed the data were consistent with being caused by energised and highly charged dust particles, so that over the past 33 years this interpretation has stimulated theories of transport and levitation of lunar dust high above the lunar surface, and added significant motivation to return to the moon for further detailed studies including the  Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft  planned to orbit the Moon in mid-2013.

Professor O'Brien says his report cannot prove that LEAM did not measure any lunar dust, but simply assembles four independent pieces of evidence favouring noise bits as the cause of LEAM data.  Consistent with this view are seven more pieces of evidence, such as the daily number of events and the five-times higher rates at lunar sunrise than sunset, which advocates of lunar dust interpretations have never explained.

Particularly persuasive were measurements during lunar eclipses.  "No increased rates were observed during lunar eclipses (which are) surrogate tests where partial sunrise and sunset conditions should excite increased LEAM counts if the ‘lunar dust' hypothesis applies.  Because eclipses were of such short duration that switching of well-insulated heaters were not necessary, no increased noise bits should be produced, consistent with the facts."

His report uses raw data, documents and studies published between 1973 and 1977.  "My hands-on experiences with Apollo payloads and testing, and with building several complete successful satellites with small teams, perhaps also helped a bit", he said.

Knowledge of lunar dust is important not only to scientists but to astronauts and designers of robotic moon buggies, planned by China, the European Union, India, Japan, Russia and the USA.  Apollo 17's scientist-astronaut Dr Harrison-Schmitt has said that "dust is the Number 1 problem on the moon".  Professor O'Brien reports that "Scores of times during and after each expedition each Apollo astronaut commented on effects of clinging dust.  All Apollo astronauts emphasise the importance of inescapable dust."

"Yet the voices of Apollo lunar explorers were and still are largely neglected.  Apollo put only two minimalist experiments on the moon to assist astronaut and robotic activities on the lunar surface and to research lunar dust"

O'Brien was the inventor and Principal Investigator of the first such experiments, matchbox-sized Dust Detector Experiments (DDEs) put on the Moon by Apollo 11, 12, 14 and 15 astronauts, which made about 30 million measurements between 21 July 1969 and 30 September 1977 when all Apollo scientific systems were switched off.

His review also updates his first suite of seven discoveries in the journal Geophysical Research Letters on 6 May 2009, made after he revisited the data in 2007 after hearing that NASA had misplaced all copies of the computer tapes before they were archived.  The results were acclaimed globally and he has subsequently given invited lectures to European and USA space scientists in three overseas trips.

Professor O'Brien noted that modern lunar scientists were previously unaware of his 1970 published discoveries with the Apollo 11 DDE, or of important discoveries made by Professor Tommy Gold and NASA and published by Gold in 1972, about dust behaviour on the plates of samples of 12 different surfaces, such as Teflon and various white paints and metals, in the Thermal Degradation Samples (TDS) experiment performed by astronaut Alan Shepard in 1971.

NASA engineers needed to find surfaces which would minimise coverage by sticky lunar dust, causing overheating. Shepard sprinkled dust on the plates, brushed one and tapped the other, and took 3D photographs.  Professor O'Brien praises the experiment as a "simple, very low-cost experiment", little known until he discussed it at a NASA conference in Boulder Colorado last year.

"To our knowledge, this is the only example where it may be possible to analyse fine-scale cohesive forces between particles/ensembles of lunar dust."  The plates of the experiment were returned to Earth and put in quarantine at NASA Manned Spacecraft Center in Houston, then lost.  But 7 photographs remain for analyses."

Professor O'Brien also knew that on Apollo 12, the Cold Cathode Gage experiment was saturated by contaminating gases from out-gassing of a spacesuit by Alan Bean at distances of several metres.  Consequently, he has placed the first caveat on any lunar experiment, the TDS, that it was carried out completely within the contaminating gaseous aura, more than 10,000 times higher pressure than the lunar atmosphere, surrounding the astronaut-experimenter.  "Alan Shepard's comment after the TDS experiment that Apollo 14 dust was unexpectedly easily brushed off must be assessed with that caveat," he reports.

Professor O'Brien, the only Apollo Principal Investigator in two different disciplines of experiments - radiation and dust - deployed by astronauts on the moon, was invited to write the first review of the three Apollo dust experiments for a Special issue of Planetary and Space Sciences devoted to "Lunar Dust, Atmosphere and Plasmas: The Next Steps".

Speaking of Professor O'Brien's latest work, Dr James Gaier, Senior Research Scientist at the NASA Glenn Research Centre said: "The O'Brien review is the definitive work on what Apollo can teach us about dust in the lunar environment.  It is not just a collection of the experimental results, but a fundamental re-interpretation of them.  This review should trigger a cascade of new studies on the basic properties of lunar dust in the lunar environment ... It may also call for the re-interpretation of the results from other experiments carried out on the lunar surface during the Apollo program."

Professor O'Brien will present his report at the 4 th Lunar Science Forum on 19-21 July at the NASA Lunar Science Institute in Ames, California, and at Rice University, Houston on 25 July.

Media references

Professor Brian O'Brien (+61 8)  9387 3827 / 8003
Aleta Johnston (UWA Public Affairs)  (+61 8)  6488 7797  /  (+61 4) 31 514 677

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