LADEE analysis maps lopsided meteoric dust cloud

Artist's conception of the lunar dust exosphere surrounding the moon. The color represents the amount of material ejected from the surface, showing a peak in the apex direction. A haze of dust is shown around the moon. Gray faded circles are overlaid on the lunar surface to represent the random nature of the primary impactors. An artist's conception of the LADEE orbital inclination is also shown [UC Boulder/Daniel Morgan/Jamey Szalay].

Darryl Waller

Sharon Lozano

NASA Ames

New science results from NASA’s LADEE mission (Lunar Atmosphere and Dust Environment Explorer) indicate the Moon is regularly engulfed in a permanent, but lopsided and transitory, dust cloud increasing in density during encounters with cometary debris, like those producing the Geminids, according to a new study led by University of Colorado Boulder.

"Knowledge about the dusty environments in space has practical applications," said CU-Boulder physics Professor Mihály Horányi. "Knowing where the dust is and where it is headed in the solar system could help mitigate hazards for future human exploration, including dust particles damaging spacecraft or harming astronauts."

The cloud was discovered using data from a detector on board LADEE called the Lunar Dust Experiment (LDEX) designed and built by CU-Boulder. LDEX charted more than 140,000 impacts during the six-month survey launched in September 2013. NASA’s Ames Research Center in Moffett Field, California was responsible for spacecraft design, development, testing and mission operations.

“The LDEX team has been painstakingly analyzing their data since the LADEE mission ended on April 18, 2014,” said LADEE project scientist at Ames, Rick Elphic. “Their results answer one of the big LADEE science questions: is there a dust component to the tenuous lunar atmosphere?  And if so, why is it there?” 

According to Horányi, the cloud is primarily made up of tiny dust grains kicked up from the moon’s surface by the impact of high-speed, interplanetary dust particles. A single dust particle from a comet striking the moon’s surface lofts thousands of smaller dust specks into the airless environment, and the lunar cloud is maintained by this sometimes predictable process of regolith "gardening."

“Identifying this permanent dust cloud engulfing the moon was a nice gift from this mission,” said Horányi, the principal investigator for the LDEX instrument and lead author of the study. “We can carry these findings over to studies of other airless bodies, like the moons of other planets and the asteroids.”

Artist's composite showing LADEE spacecraft in close orbit [NASA/JAXA/LP].

A paper on the subject appears in the June 17 issue of Nature. Co-authors Jamey Szalay, Sascha Kempf, Eberhard Grun and Zoltan Sternovsky from CU-Boulder, Juergen Schmidt from the University Oulu in Finland, and Ralf Srama from the University of Stuttgart in Germany.

The first hints of a cloud of dust around the moon came in the late 1960s when cameras functioning overnight aboard the unmanned moon lander Surveyor 7 captured bright glow hours ahead of lunar sunrise. Not long after astronauts in lunar orbit described a significant glow above the lunar surface when approaching sunrise, phenomenon brighter than the sun by itself should have been able to produce over a body with only a trace, essentially non-existent, atmosphere.

Because these new findings do not square with the Apollo reports of a thicker, higher dust cloud, conditions back then may have been somewhat different. The dust on the moon -- which is dark and sticky and regularly dirtied the suits of moonwalking astronauts -- was created over several billion years as interplanetary dust particles incessantly pounded the rocky lunar surface.

Apollo 17 commander Gene Cernan's sketches and description of horizon glow and streamers observed in lunar orbit in December 1972 [NASA].

Many of the cometary dust particles impacting lunar surface are traveling at thousands of miles per hour in a retrograde, or counterclockwise orbit around the sun, the opposite orbital direction of the solar system’s planets. This causes high-speed, near head-on collisions with the dust particles and the moon’s leading surface as the Earth-moon system travel together around the sun.

Related LADEE Posts:
LADEE impact crater found (October 29, 2014)
First Science from LADEE (45th LPSC, March 18 2014)
LADEE's (star tracker) images of the Moon (February 14, 2014)
LADEE economy adds 28 days to mission (February 5, 2014)
LROC captures LADEE from 9,000 meters (January 30, 2014)
Red Moon, Blue Moon Dwayne Day, The Space Review (December 3, 2013)
LADEE begins collecting data (November 22, 2013)
LADEE transitioning out of commissioning phase (November 6, 2013)
Apollo 12 ALSEP first to measure dust accumulation (November 21, 2013)
Chang'e-3 & LADEE: The Role of Serendipity (October 31, 2013)
LADEE LLCD sets new data record (October 25, 2013)
Measuring almost nothing, looking for the almost invisible (October 16, 2013)
LADEE legacies (September 7, 2013)
LADEE Prelaunch Mission Briefing (September 6, 2013)
ESA prepares for LADEE (July 31, 2013)
LADEE arrives at Wallops Island (June 5, 2013)
LADEE ready to baseline dusty lunar exosphere (June 5, 2013)
First laser comm system ready for launch on LADEE (March 16, 2013)
LADEE project manager update (February 6, 2013)
The Mona Lisa test for LADEE communications (January 21, 2013)
Toxicity of lunar dust (July 2, 2012)
Expectations for the LADEE LDEX (March 23, 2012)
The Dust Management Project (August 9, 2010)
LADEE architecture and mission design (July 6, 2010)
DesertRatS testing electrodynamic dust shield (July 5, 2010)
Dust transport and its importance in the origin of lunar swirls (February 21, 2010)
Dust accumulation on Apollo laser reflectors may indicate a surprisingly fast and
more dynamic lunar exosphere (February 16, 2010)
NASA applies low cost lessons to LADEE (January 18, 2010)
Nanotech advances in lunar dust mitigation (August 19, 2009)
Moon dust hazard influenced by Sun's elevation (April 17, 2009)
LADEE launch by Orbital from Wallops Island (April 14, 2009)
Understanding the activation and solution properties of lunar dust
for future lunar habitation (March 2, 2009)
Respiratory toxicity of lunar highland dust (January 19, 2009)
Toxicological effects of moon dust (June 25, 2008)
Moon dust and duct tape (April 22, 2008)

LADEE economy adds 28 days to mission

NASA's LADEE, last of the unmanned Constellation precursor missions, in retrograde orbit "baselines" the dusty fallout of the Moon's tenuous exosphere ahead of lunar sunrise [NASA/ARC/JAXA/Dana Berry].

Rachel Hoover
NASA Ames Research Center

NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) has been approved for a 28-day mission extension. The spacecraft is now expected to impact the lunar surface on or around April 21, 2014, depending on the final trajectory.

The extension provides an opportunity for the satellite to gather an additional full lunar cycle worth of very low-altitude data to help scientists unravel the mysteries of the moon’s atmosphere.

"The launch vehicle performance and orbit capture burns using LADEE's onboard engines were extremely accurate, so the spacecraft had significant propellant remaining to enable extra science," said Butler Hine, LADEE project manager at NASA’s Ames Research Center in Moffett Field, California, where the mission was designed, built, tested, and its day-to-day operations are managed. "This extension represents a tremendous increase in the amount of science data returned from the mission."

The small, car-sized robotic probe launched Sept. 6, 2013, from NASA's Wallops Flight Facility on Wallops Island, Virginia, and has been orbiting the moon since October 6.

On November 10, LADEE began gathering science data and on November 20, the spacecraft entered its science orbit around the moon's equator at an altitude between 12 to 60 kilometers; a unique position that allows the spacecraft to frequently pass from lunar day to lunar night, approximately every two hours. This vantage provides data about the full scope of changes and processes occurring within the moon's tenuous atmosphere.

"The science team has already established a baseline of data for the tenuous lunar atmosphere, or exosphere, and dust impacts," said Rick Elphic LADEE project scientist at Ames. "One cool thing about this extension is that we plan to fly LADEE at only a few kilometers above the lunar surface. This will be much lower than we’ve been before."

Using a set of three instruments, scientists are able to measure the chemical composition of the atmosphere, collect and analyze samples of lunar dust particles in the atmosphere and hope to address a long-standing question: Was lunar dust, electrically charged by sunlight, responsible for the pre-sunrise glow above the lunar horizon detected during several Apollo missions?

Relative orbital positions of LRO (red), LADEE (blue) and Chang'e-3 only minutes prior to the latter's landing in Mare Imbrium, December 14 ["Post-Landing look at Chang'e trajectory," The Astrogator's League (astrogatorsleague.com)].

Specifically, the Neutral Mass Spectrometer (NSM) operates while pointing in different directions to look for atoms and molecules in the lunar atmosphere from a variety of sources, and has measured helium, neon, and argon-40; three noble gases. The Ultraviolet-Visible Spectrometer (UVS) has peered over the lunar horizon to look for the glow of atoms, molecules and dust in the lunar atmosphere and has made measurements of atmospheric sodium and potassium at lunar sunset, sunrise and noon. The Lunar Dust Experiment (LDEX) recorded dust impacts as soon as its cover opened and has measured the dust tossed up by a fairly steady "rain" of meteoroids on the lunar surface. LDEX occasionally sees an increase in dust impacts due to meteoroid showers, such as the Geminids, and "dust bursts" that may be due to LADEE flying through plumes kicked up from nearby meteoroid impacts.

Detailed information about the structure and composition of the thin lunar atmosphere and whether dust is being lofted into the lunar sky will help researchers understand other bodies in the solar system, such as large asteroids, Mercury and the moons of outer planets.

LADEE was built using an Ames-developed Modular Common Spacecraft Bus architecture, a general purpose spacecraft design that allows NASA to develop, assemble and test multiple modules at the same time. The LADEE bus structure is made of a lightweight carbon composite with an unfueled mass of 547.2 pounds.

NASA's Science Mission Directorate in Washington funds the LADEE mission. Ames manages the overall mission and serves as a base for mission operations and real-time control of the probe. NASA's Goddard Space Flight Center in Greenbelt, Maryland, catalogues and distributes data to a science team located across the country and manages the science instruments. NASA's Marshall Space Flight Center in Huntsville, Alabama manages LADEE within the Lunar Quest Program Office.

Related Recent Posts:
LROC captures LADEE from 9,000 meters (January 30, 2014)
Red Moon, Blue Moon Dwayne Day, The Space Review (December 3, 2013)
LADEE begins collecting data (November 22, 2013)
LADEE transitioning out of commissioning phase (November 6, 2013)
Apollo 12 ALSEP first to measure dust accumulation (November 21, 2013)
Chang'e-3 & LADEE: The Role of Serendipity (October 31, 2013)
LADEE LLCD sets new data record (October 25, 2013)
Measuring almost nothing, looking for the almost invisible (October 16, 2013)
LADEE legacies (September 7, 2013)

LADEE begins collecting data

NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft, in orbit above the Moon, as dust scatters light during lunar sunset [NASA/ARC/JAXA/Dana Berry].

Rachel Hoover
NASA Ames Research Center

NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) is ready to begin collecting science data about the Moon.

On November 20, the spacecraft successfully entered its planned orbit around the Moon's equator -- a unique position allowing the small probe to make frequent passes from lunar day to lunar night. This will provide a full view of the changes and processes occurring within the moon's tenuous atmosphere.

LADEE now orbits the moon about every two hours at an altitude of 12 to 60 km above the Moon's surface. For about 100 days, the spacecraft will gather detailed information about the structure and composition of the thin lunar atmosphere and determine whether dust is being lofted into the lunar sky.

Scientists will be able to study the conditions in the atmosphere during lunar sunrise and sunset, where previous crewed and robotic missions detected a glow of rays and streamers reaching high into the lunar sky.

“This is what we’ve been waiting for – we are already seeing the shape of things to come,” said Rick Elphic, LADEE project scientist at NASA's Ames Research Center in Moffett Field, California

On November 20, flight controllers in the LADEE Mission Operations Center at Ames confirmed LADEE performed a crucial burn of its orbit control system to lower the spacecraft into its optimal position to enable science collection. Mission managers will continuously monitor the spacecraft's altitude and make adjustments as necessary.

"Due to the lumpiness of the moon's gravitational field, LADEE's orbit requires significant maintenance activity with maneuvers taking place as often as every three to five days, or as infrequently as once every two weeks," said Butler Hine, LADEE project manager at Ames. "LADEE will perform regular orbital maintenance maneuvers to keep the spacecraft’s altitude within a safe range above the surface that maximizes the science return."

In addition to science instruments, the spacecraft carried the Lunar Laser Communications Demonstration, NASA's first high-data-rate laser communication system. It is designed to enable satellite communication at rates similar to those of high-speed fiber optic networks on Earth. The system was tested successfully during the commissioning phase of the mission, while LADEE was still at a higher altitude.

LADEE was launched September 6 on a US Air Force Minotaur V, an excess ballistic missile converted into a space launch vehicle and operated by Orbital Sciences Corporation of Dulles, Virginia. LADEE is the first spacecraft designed, developed, built, integrated and tested at Ames, and it is the first probe launched beyond Earth orbit from NASA's Wallops Flight Facility on the Virginia's Eastern Shore.

NASA's Science Mission Directorate in Washington funds the LADEE mission. Ames manages the overall mission and serves as a base for mission operations and real-time control of the probe. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the science instruments and technology demonstration payload, the science operations center and overall mission support. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages LADEE within the Lunar Quest Program Office.

Apollo 12 ALSEP first to measure dust accumulation

Apollo 12 ALSEP, Central Station, with DTREM (Lunar Dust Collector) marked with arrow. Alan J. Bean, EVA-1;  Oceanus Procellarum, November 19, 1969 (AS12-47-6927) [NASA/JSC/ALSJ].

A dataset thought to have been lost, from an ingenious experiment deployed on the Moon by Apollo astronauts more than four decades ago, has been rediscovered and analyzed. As a result, the Lunar Dust Collector deployed as integral to the Apollo 12 ALSEP system, has become the first instrument to record a measurable rate of dust accumulation on the lunar surface. 

The news is timely, of course, coming the beginning of the Lunar Atmosphere and Dust Environment Explorer (LADEE) science mission, and arriving on November 19, the 44th anniversary of the Apollo 12 expedition.

Keith Cowing
Moonviews.com (LOIRP)

The Lunar Dust Detector, attached to the corner of (the ALSEP Central Station, pictured above), left by the Apollo 12 astronauts, made the first measurement of lunar dust accumulation. As the matchbox-sized device's three solar panels became covered by dust, the voltage they produced dropped.

When Neil Armstrong took humanity's first otherworldly steps in 1969, he didn't know what a nuisance the lunar soil beneath his feet would prove to be. The scratchy dust clung to everything it touched, causing scientific instruments to overheat and, for Apollo 17 astronaut Harrison Schmitt, a sort of lunar dust hay fever. The annoying particles even prompted a scientific experiment to figure out how fast they collect, but NASA's data got lost.

Retrieving a surface sample behind boulders on a crater rim at Apollo 17 Science Station 5, Taurus Littrow valley; December 12, 1972 - Lunar module pilot and geologist Harrison Schmitt already carries a substantial sampling of abrasive, fine lunar dust on his moon suit. Schmitt endorsed development of 'dust mitigation' technology as a high priority for program planners prior to establishing 'extended human activity' on the Moon (Eugene Cernan - AS17-145-22157) [NASA/JSC/ALSJ].

Or, so NASA thought. Now, more than 40 years later, scientists have used the rediscovered data to make the first determination of how fast lunar dust accumulates. It builds up unbelievably slowly by the standards of any Earth-bound housekeeper, their calculations show -- just fast enough to form a layer about a millimeter (0.04 inch) thick every 1,000 years. Yet, that rate is 10 times previous estimates. It's also more than speedy enough to pose a serious problem for the solar cells that serve as critical power sources for space exploration missions.

Read the balance of Keith's excellent write up, HERE.

Related Posts:

Lunar Laser Ranging: The Millimeter Challenge (November 19, 2013)

Measuring almost nothing, looking for the almost invisible, Paul Spudis (October 18, 2013)

Toxicity of lunar dust (July 2, 2012)

Expectations for the LADEE LDEX (March 23, 2012)

The Dust Management Project (August 9, 2010)

Long term degradation of optics on the Moon (March 4, 2010)

Dust transport and lunar swirls (February 21, 2010)

Dust accumulation on Apollo reflectors and the exosphere (February 16, 2010)

Moon dust hazard influenced by solar elevation (April 17, 2009)

Understanding lunar dust and future habitation (March 2, 2009)

Respiratory toxicity of lunar highland dust (June 25, 2008)

Measuring almost nothing, looking for the almost invisible

NASA's LADEE spacecraft entered it's 250 km Commissioning phase orbit October 12 [NASA/JAXA].

Paul D. Spudis

The Once and Future Moon
Smithsonian Air & Space

Launched last month from the Wallops Island site, LADEE (for Lunar Atmosphere and Dust Environment Explorer) will spend the next few months orbiting the Moon.  This small spacecraft will attempt to characterize and measure the lunar “atmosphere,” while also looking for dust that might be electrostatically levitated above the surface or thrown into ballistic flight by impacts.

Wait a minute.  Did I say “atmosphere?”  Isn’t the Moon renowned for its lack of an atmosphere?  Indeed it is.  In fact, the 10-12 torr surface pressure of the Moon is a better vacuum than we can achieve with even the most advanced equipment in Earth laboratories.  (For comparison, sea level pressure on the Earth is about 760 torr, making the lunar surface pressure over one hundred trillion times less dense.)  A better term for the tenuous gas near the Moon is “exosphere,” meaning free flying gas molecules that may or may not be gravitationally bound to the Moon.  In such an “atmosphere,” there may be only a few thousand molecules in a cubic centimeter of space. This is very tenuous indeed.

  

After the Commissioning phase of its mission is complete, the spacecraft's current 250 km circular orbit will be reduced further down to within 50 km to begin its 100 day Science Mission [NASA/GSFC].

LADEE is designed to investigate from where these atoms and molecules come.  Presently, we think the lunar exosphere consists mostly of helium, sodium and perhaps argon atoms, each coming from a completely different source.  Helium likely comes from the Sun, as the solar wind continually “breathes” onto the surface of the Moon.  Some atoms stick to surface dust grains but many simply bounce off, randomly moving in the space above the lunar surface.  Easy to detect, lunar sodium has been observed from Earth-based telescopes.  It most likely comes from rocks vaporized by the continual rain of micrometeorites.  At least some fraction of this vaporous sodium must hang around the surface, unable to escape the Moon.  Argon might have a solar wind origin, but at least some of it comes from the natural decay of radioactive potassium in the lunar interior (potassium-40 (40K) decays to argon-40 (40Ar) with a half-life of a bit more than one billion years).  Gases like argon, venting from the interior of the Moon, were observed by subsatellites left in lunar orbit by the departing Apollo spacecraft over 40 years ago (these small spacecraft have long since crashed into the Moon).

Although helium, sodium and argon are the principal expected components of the lunar exosphere, the LADEE team will search for other species.  An interesting possibility is water (H2O) or its related species, hydroxyl (OH).  One of the most surprising results of recent lunar exploration was the discovery of adsorbed (surface) water and hydroxyl on the dust grains of the lunar surface (observed by the Moon Mineralogy Mapper (M3) aboard the Indian Chandrayaan-1 lunar orbiter in 2009).  Occurring in the form of a monolayer of molecules on dust grains in the cooler portions of the Moon, a clear water signal is best seen above latitudes of 65° and increasing in strength (i.e., increasing water abundance) toward each pole.

The surprise from M3 was not only the presence of water but observing that its abundance increases with decreasing surface temperatures.  This means that water being made or deposited on the surface is in motion, with a net movement toward the poles.  Chandrayaan-1 also carried an impact probe with a mass spectrometer.  During the probe’s half-hour descent to the South Pole, it passed through a cloud of water in space, just above the lunar surface.  The water cloud at this high latitude had a density a hundred times higher than at the equator, providing additional evidence that exospheric water is in motion, moving from lower, hotter latitudes towards higher, cooler ones.

LADEE cannot directly measure this water in a neutral state, but if some process ionizes it (e.g., if a water molecule breaks apart into a proton and a hydroxyl by UV radiation from the Sun), it will be visible to the ultraviolet spectrometer aboard the spacecraft.  If the process of water migration on the lunar surface is correct, we should be able to observe exospheric water and by measuring its density with time, track the water migration to higher latitudes.

Lunar Horizon Glow (LHC) observed for several hours following local sunset from Surveyor 7 and its landing site just north of Tycho crater. [NASA].

LADEE will also tackle another controversial issue – the amounts and mechanisms of dust movement on and around the Moon.  During the unmanned Surveyor lander missions over 40 years ago, a strange illumination or glow was observed by television for several hours after local sunset, just above the horizon.  This phenomenon was termed “horizon glow” by surprised Surveyor investigators.  At a loss to explain it, the team postulated that some mechanism was lofting dust up above the surface and this dust was scattering sunlight.  Exactly how the dust was lofted was uncertain; some thought it must be fragments in ballistic flight from distant impacts, while others thought that it might be levitated by electrostatic force, thus “hovering” above the surface.

Schematic of documented species of Lunar Horizon Glow, including mid-lunar night imagery captured by Surveyor 7 (Horanyi, et.al., The Lunar Dust Environment: Expectations for the LADEE Lunar Dust Experiment (LDEX), 43rd Lunar and Planetary Science Conference (2012), #2635.

A few years later, just before his orbiting spacecraft emerged into the daylight side of the Moon, Apollo 17 Commander Gene Cernan observed and sketched an illuminated limb and “streamers” that could be seen extending into space above where the lunar horizon would be.  At the time, this phenomenon was thought to be the same as that seen in the Surveyor pictures, although they have totally different scales (the Surveyor horizon glow must occur within a few meters of the surface, while Cernan’s horizon glow extended many kilometers above the Moon). Dust (probably of lunar provenance) is certainly involved in whatever causes this horizon glow.

Apollo 17 commander Gene Cernan's sketches and description of horizon glow and streamers observed in lunar orbit, December 1972 [NASA].

As the Moon slowly rotates once every 708 hours, the line between the sunlit and dark hemispheres (the terminator) slowly moves across the lunar surface.  The day and night hemispheres have different fluxes of electrons from the solar wind and thus, the presence of the terminator can induce an electrical charge in surface materials.  It is postulated that this charge might levitate smaller dust particles such that they would hover above the surface.  LADEE will attempt to detect and map this dust, both by searching for scattered sunlight with its ultraviolet spectrometer and via the direct detection of dust particles in flight with an instrument on the top of the orbiting spacecraft.

The issue of levitated dust is thought to be relevant to the future habitation of the Moon.  If dust is lofted above the surface by the passage of the terminator, the particles could degrade clean surfaces and create a hazard for inhabitants of the Moon.  Such a process could have major effects near the poles of the Moon, areas that are in the near-constant presence of a day-night terminator.  Although it is unlikely that levitated dust on the Moon is an environmental hazard, we currently are working in near total absence of hard data.  Thus, it makes sense to at least try to make some direct measurements of the dust environment around the Moon to assess the importance of this proposed surface process.

LADEE arrived in lunar orbit last Sunday. We wish it well on its mission to give us fresh (and welcome) data on a poorly understood aspect of lunar processes and history.

Related Posts:

LADEE, in 250 km orbit, begins commissioning phase (October 15, 2013)
LADEE Away! (September 7, 2013)
LADEE legacies (September 7, 2013)
LADEE Prelaunch Mission Briefing (September 6, 2013)
ESA prepares for LADEE (July 31, 2013)
LADEE arrives at Wallops Island (June 5, 2013)
LADEE ready to baseline dusty lunar exosphere (June 5, 2013)
First laser comm system ready for launch on LADEE (March 16, 2013)
LADEE project manager update (February 6, 2013)
The Mona Lisa test for LADEE communications (January 21, 2013)
Toxicity of lunar dust (July 2, 2012)
Expectations for the LADEE LDEX (March 23, 2012)
The Dust Management Project (August 9, 2010)
LADEE architecture and mission design (July 6, 2010)
DesertRatS testing electrodynamic dust shield (July 5, 2010)
Dust transport and its importance in the origin of lunar swirls (February 21, 2010)
Dust accumulation on Apollo laser reflectors may indicate a surprisingly fast and
   more dynamic lunar exosphere (February 16, 2010)
NASA applies low cost lessons to LADEE (January 18, 2010)
Nanotech advances in lunar dust mitigation (August 19, 2009)
Moon dust hazard influenced by Sun's elevation (April 17, 2009)
LADEE launch by Orbital from Wallops Island (April 14, 2009)
Understanding the activation and solution properties of lunar dust
for future lunar habitation (March 2, 2009)
Respiratory toxicity of lunar highland dust (January 19, 2009)
Toxicological effects of moon dust (June 25, 2008)
Moon dust and duct tape (April 22, 2008)

Originally published October 4, 2013 at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author but are better informed than average.  

LADEE, in 250 km orbit, begins commissioning phase

LADEE, last of the Constellation precursor missions, officially entered a highly eccentric orbit around the Moon on October 6, after a month gradually increasing its orbital apogee around Earth to meet up with the Moon's gravimetric Sphere of Influence. Following critical maneuvers October 9 and 12, LADEE is now inserted into a low circular lunar orbit below 250 km to begin the Commissioning phase of its mission, still shy of a much lower Nominal mission orbital altitude below 50 km. [NASA/ARC].

Related Posts:

LADEE Away! (September 7, 2013)
LADEE legacies (September 7, 2013)
LADEE Prelaunch Mission Briefing (September 6, 2013)
ESA prepares for LADEE (July 31, 2013)
LADEE arrives at Wallops Island (June 5, 2013)
LADEE ready to baseline dusty lunar exosphere (June 5, 2013)
First laser comm system ready for launch on LADEE (March 16, 2013)
LADEE project manager update (February 6, 2013)
The Mona Lisa test for LADEE communications (January 21, 2013)
Toxicity of lunar dust (July 2, 2012)
Expectations for the LADEE LDEX (March 23, 2012)
The Dust Management Project (August 9, 2010)
LADEE architecture and mission design (July 6, 2010)
DesertRatS testing electrodynamic dust shield (July 5, 2010)
Dust transport and its importance in the origin of lunar swirls (February 21, 2010)
Dust accumulation on Apollo laser reflectors may indicate a surprisingly fast and
   more dynamic lunar exosphere (February 16, 2010)
NASA applies low cost lessons to LADEE (January 18, 2010)
Nanotech advances in lunar dust mitigation (August 19, 2009)
Moon dust hazard influenced by Sun's elevation (April 17, 2009)
LADEE launch by Orbital from Wallops Island (April 14, 2009)
Understanding the activation and solution properties of lunar dust
for future lunar habitation (March 2, 2009)
Respiratory toxicity of lunar highland dust (January 19, 2009)
Toxicological effects of moon dust (June 25, 2008)
Moon dust and duct tape (April 22, 2008)

LADEE legacies

In planning since 2008, LADEE's reason-for-being emerged from mapping science goals believed essential before any permanent manned presence on the Moon's surface could begin. Fortunately, like LRO, LCROSS and GRAIL, planning and development were well underway and within budget when Congress eventually scrubbed the Constellation brand and manned Altair lander [NASA].

Like "The Blind Men and the Elephant" the most important moving part of many riding along with LADEE to the Moon very much depends on your personal perspective.

What might seem a low-priority mission, accompanied by an appropriate degree of "hype," and has modest fundamental goals under the banner of experimental modular designs and revolutionary high speed communications, - only a 100 day science mission, LADEE has been in development for more than five years. The advanced vehicle also carries with it hopes of some that go back nine times that period, covering a lot of political ground and many changes, even over the relatively short time since its framing and approval.

Gene Cernan (by Harrison Schmitt) at the close-out of the third and final EVA of Apollo 17, and the last manned visit to the Moon in December 1972. The commander's spacesuit is blackened by exceeding fine lunar dust, more than just a problem of appearances, a real hazard that might have caused hatch and spacesuit seals to fail on a longer surface mission. Constellation planners understood they needed to get a handle on mitigating the hazard posed by omnipresent dust while also gaining an better understanding of the dynamics of a primal airless Moon and its surface before humans return to stay [NASA/JSC].

Few watching the LADEE/Minotaur V launch, critical for Orbital Sciences Corporation, from Wallops Island, are likely to be reminded that the mission owes its existence to the catastrophic loss of Space Shuttle Challenger ten years ago. But it is possible to appreciate the things NASA logically wants emphasized without forgetting LADEE is the beginning of the end of the defunct Constellation program that so many wanted dead and buried in 2009.

LADEE is the last of the unmanned precursor missions once believed essential before "extended human activity" on the Moon could begin. The absolutely remarkable Lunar Reconnaissance Orbiter (LRO) will likely still be orbiting the Moon for a few years after LADEE's mission-terminating guided impact a few months from now, but none of these 21st century American unmanned lunar missions are likely to have have occurred before today without the initial political will put in motion after the report of the Challenger Accident Investigation Board (CAIB).

LRO, LCROSS, GRAIL and now LADEE each owe their reason for being to the loss of a second Space Shuttle and crew in 2003.

Very simple schematic of the lunar exosphere. The Moon's surface turned out to be a very dynamic place, after all, with water and exotic metals and volatiles trapped in permanent shadow and also hiding in plain sight [Halekas/LEAG/NASA].

If you've seen the movie footage of Neil Armstrong immediately after setting that first boot on the Moon, backing away from the ladder tethered to the spacecraft then you may have guessed there once was real fear that he might just suddenly disappear in a bog of dust.

Such concern had mostly been dispelled by July 1969, though, after none of the successful unmanned Surveyor landers had encountered anything other than a hard-packed lunar surface. And yet the Moon was correctly presumed to be a very dusty place, constantly "gardened" by micrometeorites (and some not so micro) together with energetic cosmic and solar radiation. Without direct samples, however, no one correctly guessed just how "fine" the dusty powder on the lunar surface could be.

By the time Gene Cernan climbed back into the Apollo 17 lunar module in late 1972 at the end of the program another hazard from this dust had become apparent instead. Rather than sinking into feathery banks of fluffy snowbanks astronauts had to deal instead with a film of electrostatic-charged, clinging and microscopic glassy razor blades. It smelled like gun powder and got into everything, and seemed impossible to clean.

The dark dust of the Moon's immediate surface threatened hatch seals, it scared and tore into spacesuits and, following EVA close-outs became lodged in every conceivable place on an astronaut's body, including up their noses, in their lungs and also lingering in their softest places.

Clearly, "dust mitigation," by then long acknowledged as a real mission and health hazard, came forward as a priority science goal when before new lunar surface expeditions could be carried out. It is accepted as a similar threat to manned travel to Mars, and to the asteroids.

All models of what has become known as a "dynamic" rather than "static" lunar surface include production and trapping of volatile compounds once thought essentially non-existent on the Moon. The speed of this production, it's true dynamics, badly need to be studied before we can return to the Moon with impunity.

Every time an unmanned spacecraft (or a manned lunar module) has landed or taken off from the Moon it's certain some of the dust propelled away by exhaust reaches escape velocity. A larger part of this spiny cloud is put into orbit or on a ballistic path carrying these particles all over the lunar surface. LADEE is designed to establish some natural baseline for this dust before humans start stirring things up. The impact of spacecraft is comparable to the occasional larger natural impact, but hot gas exhaust and its effects is something new.

The delicate bright dust lanes of the Reiner Gamma "swirl albedo" phenomena, stretching at least 550 km southwest from the dormant volcanic Marius domes to the western frontier of Oceanus Procellarum. Seen here in an LROC WAC mosaic from 2010 under early morning shadows. Detailed laser altimetry confirms little to no topographic component, though it does closely correlate with a well-mapped anomalous crustal magnetic field that must be older than exposure to the Sun and space weathering would allow the surface here to remain so bright. Migration of dust, alternately charged and discharged, dislodged by micro-bombardment is alternately attracted and repelled, here, by the local magnetic field lines, keeping the new dust constantly renewed and gathered no more than a meter or so deep [NASA/GSFC/Arizona State University].

Whether or not this was really a guesstimate or hard science, by the time Congress seriously committed to return to the Moon to stay investigators had acknowledged that a kind of primal state existed there that was worth scientific study for its own sake, before human engaged in any "extended activity." And herein is the compelling interest for funding the LADEE mission. It's one way of discovering the state of the lunar exosphere, its dynamics in and out of Earth's extended magnetic field, under a traveling solar incidence, and through a good sampling of lunar days and nights before things inevitably get busy.

The hyperfast laser-based communications and modular spacecraft design for LADEE will be much talked about in reports about this mission, over the next few days and months. That's "all good," as they say, but it might be worth it to also remember the mission's origins going back before Surveyor or Apollo and also offer at least some thanks to the crew of Columbia. We owe the recent renewed short burst in lunar exploration and our added knowledge of the Moon directly to the loss of that spacecraft and crew.

Another lunar mission (and one of only two American missions to the Moon between 1972 and 2009) was also justified as a test platform for new technologies. Now "lost and gone forever," Clementine (1994) spent a year in lunar orbit operated by both NASA and the U.S. Department of Defense. Here Clementine's star-tracking camera finally definitively photographed the "horizon glow" caught previously in the lunar night from the surface by Surveyor 7 and described by Apollo astronauts in lunar orbit twenty years before. This is the phenomena, believed to be back-lit lunar dust, that LADEE is designed to directly sample [NASA/DOD].

And whenever humans eventually return to the Moon for their inevitable extended stay, they will owe much of their preparation to that spacecraft and crew.

Related Posts:
LADEE Prelaunch Mission Briefing (September 6, 2013)
ESA prepares for LADEE (July 31, 2013)
LADEE arrives at Wallops Island (June 5, 2013)
LADEE ready to baseline dusty lunar exosphere (June 5, 2013)
First laser comm system ready for launch on LADEE (March 16, 2013)
LADEE project manager update (February 6, 2013)
The Mona Lisa test for LADEE communications (January 21, 2013)
Toxicity of lunar dust (July 2, 2012)
Expectations for the LADEE LDEX (March 23, 2012)
The Dust Management Project (August 9, 2010)
LADEE architecture and mission design (July 6, 2010)
DesertRatS testing electrodynamic dust shield (July 5, 2010)
Dust transport and its importance in the origin of lunar swirls (February 21, 2010)
Dust accumulation on Apollo laser reflectors may indicate a surprisingly fast and
more dynamic lunar exosphere (February 16, 2010)
NASA applies low cost lessons to LADEE (January 18, 2010)
Nanotech advances in lunar dust mitigation (August 19, 2009)
Moon dust hazard influenced by Sun's elevation (April 17, 2009)
LADEE launch by Orbital from Wallops Island (April 14, 2009)
Understanding the activation and solution properties of lunar dust
for future lunar habitation (March 2, 2009)
Respiratory toxicity of lunar highland dust (January 19, 2009)
Toxicological effects of moon dust (June 25, 2008)
Moon dust and duct tape (April 22, 2008)

Toxicity of lunar dust

Gene Cernan, soon after the completion of the third and last EVA of Apollo 17, also the final EVA of the Apollo program. His moon suit carries a heavy accumulation of lunar dust, as does his skin. Three years earlier mission planners had been worried about astronauts, along with their spacecraft, sinking into the accumulation of dust on the surface. After Apollo, and decades later, mitigating the clinging affect of dust on equipment and human life remains a problem evading easy solution [Schmitt/AS17-145-22224].

Dag Linnarsson, et al.
Karolinska Institutet, Stockholm/ESA

Abstract - The formation, composition and physical properties of lunar dust are incompletely characterized with regard to human health. While the physical and chemical determinants of dust toxicity for materials such as asbestos, quartz, volcanic ashes and urban particulate matter have been the focus of substantial research efforts, lunar dust properties, and therefore lunar dust toxicity may differ substantially. In this contribution, past and ongoing work on dust toxicity is reviewed, and major knowledge gaps that prevent an accurate assessment of lunar dust toxicity are identified. Finally, a range of studies using ground-based, low-gravity, and in situ measurements is recommended to address the identified knowledge gaps. Because none of the curated lunar samples exist in a pristine state that preserves the surface reactive chemical aspects thought to be present on the lunar surface, studies using this material carry with them considerable uncertainty in terms of fidelity. As a consequence, in situ data on lunar dust properties will be required to provide ground truth for ground-based studies quantifying the toxicity of dust exposure and the associated health risks during future manned lunar missions.

Introduction - The current renewed interest in human exploration of the Moon is driven not only by an urge to expand the human presence to other celestial bodies, but also by genuine scientific interest. Many aspects of the origin and evolution of the Earth and the other bodies in our solar system remain unclear. The Moon is thought to hold important information about the time when our own planet was formed, and humans remain capable of much more intelligent and adaptive exploration of the Moon than even the most sophisticated robotic and remote-controlled devices (e.g., Crawford et al., 2012). Identification and retrieval of representative or exotic mineral specimens, and drilling deep into the lunar subsurface are examples of tasks for which astronauts are superior to machines. The most compelling argument for human exploration is the unique ability of humans to identify and quickly assess the unexpected, enabling real time adjustment of a pre-planned exploration strategy.

Although humans have landed on and returned from the Moon during the Apollo era, it is still a formidable challenge to secure the health and safety of astronauts during Moon missions. Challenges for future missions include long-term low- or microgravity, radiation exposure, and the maintenance of a number of life support systems during a much longer period than was the case during the Apollo flights (e.g., Cain, 2010, 2011).

One of the biggest challenges may be related to the presence of dust on the lunar surface. The ubiquity of fine dust particles on the surface of the Moon plays an important and often dual role in many aspects of human lunar exploration. On the one hand, identifying the mineralogical and chemical composition of the dust fraction of lunar soils can provide in situ geological context for both robotic and human landing sites. In addition, lunar dust may be an ideal starting material for a range of future in situ resource utilization activities on the Moon (e.g., Taylor et al., 2005), and dust is an important component of the lunar exosphere (Horanyi and Stern, 2011).

On the other hand, dust can adversely affect the performance of scientific and life-support instruments on the lunar surface. Fine dust was spread over all parts of the Apollo astronauts space suits, ending up in the habitat (Figure 1a), resulting in astronaut exposure times of several days. The Apollo astronauts reported undesirable effects affecting the skin, eyes and airways that could be related to exposure to the dust that had adhered to their space suits during their extravehicular activities, and was subsequently brought into their spacecraft (Figure 1b).

Figure 2. Steps of cell and tissue interaction with nano and micron-sized particles in the lung. When attained the alveolar space the particle may react with endogenous molecules (step 1). The particle may then be cleared out of the lung either through the mucociliary escalator (step 2) or through alveolar macrophage (AM) clearance (step 3). If reactive, AM activation will follow with release of several factors and recruitment of other immune cells (AM and polymorphonucleate cells, PMN), eventual cell death and establishment of permanent cycles of ingestion (step 4). This process produces chronic inflammation (step 5). Combined with the direct action of the particle (step 6) this will cause damage to the target cells (epithelial, endothelial). If the particle is nano-sized, it may easily escape from the lung to the pleura and to systemic circulation (step 7).

Figure 3. The role of particle and cell derived free radicals and reactive oxygen species (ROS) in cell damage, oxidative stress and diseases.

Dust exposure and inhalation could have a range of toxic effects on human lunar explorers, especially if longer exposure times become the norm during future manned exploration missions. There is therefore a need to assess the risks to health. The physical and chemical determinants of dust toxicity for terrestrial materials such as asbestos, quartz, volcanic ashes and urban particulate matter have been studied in great detail, and lunar dust simulant (synthesized from terrestrial volcanic material) has been found to exhibit toxic effects (Lam et al., 2002; Latch et al., 2008; Loftus et al., 2010). Unique features of actual lunar dust (described in more detail in section 3), resulting from its formation by (micro)meteoroid impacts and its extended radiation exposure in the absence of oxygen and humidity, could lead to toxic effects significantly exceeding those of simulants made from Earth materials. At present, the formation, composition and physical properties of lunar dust remain incompletely characterized with regard to human health.

In a micro-/hypo-gravity environment the risk of inhalation of dust is increased due to reduced gravity-induced sedimentation. Inhaled particles tend to deposit more peripherally and thus may be retained in the lungs for longer periods in reduced gravity as will be the case in a future lunar habitat (Darquenne and Prisk, 2008; Peterson et al., 2008). Inhalation of particles of varying size may affect the respiratory and cardiovascular systems in deleterious ways leading to airway inflammation and increased respiratory and cardiovascular morbidity (Frampton et al., 2006; Sundblad et al., 2002).

In this contribution, we review our knowledge of the physical chemistry determinants of dust toxicity, of the composition and size of lunar dust, and all aspects related to its toxicity. We identify a number of knowledge gaps that need to be filled to constrain the required extent of mitigation activities protecting astronauts from the potentially toxic effects of lunar dust during and after a stay on the Moon. We also recommend a range of future studies using ground-based, low-gravity, and in situ measurements on the lunar surface to better constrain lunar dust toxicity.

arXiv:1206.6328 (v.1)
62 pg. (PDF)

Dusty "DAP-2012" workshop, UC Boulder, June 6-8

From 2007, a widely-circulated small scale schematic showing the interaction of the Solar Wind and the lunar surface and the Moon's dusty and dynamic exosphere [Jasper Halekas of the University of California at Berkeley].

The "Dust, Atmosphere and Plasma: Moon and Small Bodies" meeting  will take place on June 6-8, 2012, in Boulder Colorado. (Program is now available at http://lasp.colorado.edu/ccldas/ldap_2012. Attendees may register online by June 1.

The DAP-2012 workshop will be a forum to discuss current understanding of the surface environment of the Moon and asteroids, to share new results from past and ongoing missions and to describe expectations for future missions.

DAP-2012 is a follow up on the first workshop Lunar dust, atmosphere, and plasma: The next steps (LDAP-2010). Contributions to LDAP-2010 were published in the special issue of Planetary and Space Sciences, and a similar volume is planned to report the contributions to DAP-2012.

The workshop will be focused on open science questions, status of modeling and laboratory capabilities and the definitions of required measurements and instruments for future investigations from orbit or the surface.

The workshop is hosted by Alan Stern and Mihaly Horányi, and supported by the NASA Lunar Science Institute (NLSI): Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS), the Laboratory for Atmospheric and Space Physics, and the Center for Integrated Plasma Studies of the University of Colorado.

The workshop is set to take place at the LASP Space Science Building, 3665 Discovery Drive, Boulder, Colorado 80303 To register and obtain further information visit the workshop website, HERE.

Expectations for the LADEE LDEX

The 'Dust, Atmosphere, and Plasma: Moon and Small Bodies' (DAP-2012) meeting will take place in Boulder, June 6-8, 2012. Please visit our webpages http://ldap2012.colorado.edu/  to register and submit an abstract by 3/30/2012, if you plan to attend.

We are looking forward to see you in Boulder!

- Alan Stern and Mihaly Horanyi

A lasting lesson from Apollo. The lunar exosphere gets into everything, fine as talcum, abrasive as broken glass, and a significant cumulative threat to seals and any and all working parts generally, whether biological and mechanical. Beyond its demonstrated mission threat the Moon's dusty environment is a delicate, "pristine" and important  part of a 4.5 billion year history of space weather near Earth. Apollo 17 lunar module pilot and geologist Harrison H. "Jack" Schmitt moves forward with the patina of 22 hours activity on the lunar surface clinging to his suit. AS17-145-22157 [NASA/JSC/ALSJ].

The Moon's sodium tail,
Potter and Morgan (1998).

The Lunar Dust Environment:
Expectations for the LADEE
Lunar Dust Experiment (LDEX)
Mihaly Horanyi, Sternovsky & Shul
with Colette, Grün, Kempf, Srama & Mocker
43rd Lunar and Planetary Science Conference, #2635

Introduction: The lunar dust environment is expected to be dominated by submicron-sized dust particles released from the Moon due to the continual bombardment by micrometeoroids, and due to plasma-induced near-surface intense electric fields. The Lunar Dust EXperiment (LDEX) is designed to map the spatial and temporal variability of the dust size and density distributions in the lunar environment on-board the upcoming Lunar Atmosphere and Dust Environment Explorer (LADEE) mission

LDEX is an impact detector, capable of measuring the mass of submicron sized dust grains. LDEX will also measure the collective signal of dust grains below the detection threshold for single dust impacts; hence it can search for the putative population of grains with r ~ 0.1 μm lofted over the terminator regions by plasma effects.

LDEX has been developed at the Laboratory for Atmospheric and Space Physics and Colorado Center for Lunar Dust and Atmospheric Studies (LASP/CCLDAS, University of Colorado at Boulder) and has a high degree of heritage based on similar instruments on the HEOS 2, Ulysses, Galileo, and Cassini missions. The LDEX flight model will be tested and calibrated at both the (Max-Planck-Institute for Nuclear Physics, Heidelberg, Germany) and Boulder dust accelerator facilities.

At the Lunar and Planetary Science Conference, March 21, 2012, Dr. Horányi summarized expected capabilities of LDEX and made predictions for its measurements in lunar orbit, based on current theoretical models. The authors also discussed a proposed LDEXPLUS instrument being developed for a possible LADEE follow-up mission to add the instrument's design capability for in-situ chemical analysis of impacting dust particles, perhaps to verify "the existence of water ice on the lunar surface and map the density of valuable resources of commercial interest".

Figure 1. LDEX EM and FM units and the schematic drawings of the instrument.

The LDEX instrument: The two expected sources of dust in the lunar environment are ejecta production due to continual bombardment by interplanetary meteoroids and lofting due to plasma effects. LDEX is an impact ionization dust detector with a sensor area of ~0.01 m\2. LDEX is a low risk, compact instrument and uses no flight software (Figure 1). In addition to individual dust impacts of grains with radii r > 0.3 μm, LDEX can identify a large population of smaller grains (0.1 < r < 0.3 μm) by measuring their collective signal.The expected impact rates, and the signature of lofted small grains expected over the terminators are shown in Figure 2.

Figure 2. Expected impact rates on a 30x100 km orbit with its pericenter over the morning terminator.

Initial test and calibration of the LDEX FM model were done at the CCLDAS dust accelerator facility. Full calibrations are planned in early 2012 at both the Heidelberg and the Boulder facilities. Figure 3 shows the preliminary test results, indicating that LDEX will meet or exceed its measurement requirements.

Figure 3. Initial test results for the LDEX FM instrument showing the detected particle mass versus their velocity. At the expected impact speed of 1.6 km/s,

LDEX will detect particles with radii r > 0.4 μm. The ratio of detected and undetected particles matches the expected value due to the duty cycle of the electronics and the transparency of the screens that provide shielding and exclude the solar wind electrons from entering LDEX.

The LDEX-PLUS instrument extends the LDEX capabilities to also measure the chemical composition of the impacting particles with a mass resolution of M/ΔM > 30. Traditional methods to analyze surfaces of airless planetary objects from an orbiter are IR and gamma-ray spectroscopy, and neutron backscatter measurements. A complementary method is to analyze dust particles as samples of planetary objects from which they were released. The source region of each analyzed grain can be determined with accuracy at the surface that is approximately the altitude of the orbit.

This ‘dust spectrometer’ approach provides key chemical constraints for varying provinces on the lunar surfaces. LDEX-PLUS is of particular interest to verify from orbit the presence of water ice in the permanently shadowed lunar craters. LDEX-PLUS combines the impact detection capabilities of LDEX with a linear time-of-flight system, similar to the Cassini Cosmic Dust Analyzer (CDA) instrument. Figure 4 shows an example time-of-flight mass spectrum of an ice-bearing dust grain.

Figure 4. Spectrum of a water ice particle obtained at ~ 4 km/s impact speed by the Cassini CDA instrument in Saturn's E ring. The dominant peaks are mass lines of water cluster ions (H2O)nH+, generated upon impact of an ice-bearing particle.

Schematic of documented species of horizon glow, such as the famous mid-lunar night imagery captured by Surveyor 7 in 1968.

Conclusions. LDEX, on-board LADEE, is scheduled to launch in May 2013 and will be capable of mapping the density distributions of both the large ejecta particles and the collective signal of small lofted grains. LDEX-PLUS, on-board a follow-up lunar mission, can collect a large number of samples from a greater part of the entire surface for analysis.

The instrument is especially sensitive to the metallic compounds of minerals and any species which easily form ions (e.g. water). The accuracy of the trajectory back-tracing to the surface is comparable to the altitude of the satellite. This in-situ method allows compositional surface mapping of the Moon. Since the dust spectrometer is particularly sensitive to refractory compounds which are difficult to access by other methods it is also complementary to remote sensing spectroscopy and an ion or neutral mass spectrometer. A ram pointing dust spectrometer and a nadir pointing remote sensing instrument collect data from approximately the same spot on the surface of the Moon, hence the combination of these measurements greatly enhances our ability to map the chemical composition of the surface and identify water-bearing regions.

An LDEX-PLUS type instrument can also address many of the science goals of a Europa Jupiter System Mission (EJSM) regarding the surface chemistry of icy satellites. See original Conference abstract, HERE, for citations.

Lunar Horizon Glow (LHC) as televised (vidicon photography) in local night, early 1968 [NASA].