Post-Apollo Lunar Exploration Part-2 - Remote Sensing Application - Completely Remote Sensing, GPS, and GPS Tutorial
Post-Apollo Lunar Exploration Part-2

NASA has mounted two missions in 2009, namely LCROSS (Lunar Crater Observing and Sensing Satellite), which will try to validate the evidence for water ice at the poles ultimately by crashing a probe onto the surface, and LRO, the Lunar Reconnaissance Orbiter.

The two satellites were successfully launched together by an Atlas 5 rocket on June 18, 2009 and entered orbit with perilune at 35 and 50 km respectively. The LRO spacecraft is pictured below. These are its onboard instruments:

The Lunar Reconnaissance Orbiter with instrument locations.

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) will characterize the lunar radiation environment and determine its potential biological impacts. CRaTER will also test models of radiation effects and shielding, which may enable the development of protective technologies.

The Diviner Lunar Radiometer (DLRE) will provide orbital thermal mapping measurements, giving detailed information about surface and subsurface temperatures (identifying cold traps and potential ice deposits), as well as landing hazards such as rough terrain or rocks.

The Lyman Alpha Mapping Project (LAMP) will map the entire lunar surface in the far ultraviolet. LAMP will search for surface ice and frost in the polar regions and provide images of permanently shadowed regions illuminated only by starlight.

The Lunar Exploration Neutron Detector (LEND) will create high resolution hydrogen distribution maps and provide information about the lunar radiation environment. LEND can be used to search for evidence of water ice on the Moon's surface, and will provide space radiation environment measurements useful for future human exploration.

The Lunar Orbiter Laser Altimeter (LOLA) will measure landing site slopes, lunar surface roughness, and generate a high resolution 3D map of the Moon. LOLA will also identify the Moon's permanently illuminated and permanently shadowed areas by analyzing Lunar surface elevations.

The Lunar Reconnaissance Orbiter Camera (LROC) will retrieve high resolution black and white images of the lunar surface, capturing images of the lunar poles with resolutions down to 1m, and will image the lunar surface in color and ultraviolet. These images will provide knowledge of polar illumination conditions, identify potential resources & hazards, and enable safe landing site selection.

The Mini-RF technology demonstration's primary goal will be to search for subsurface water ice deposits. In addition, Mini-RF will take high-resolution imagery of permanently-shadowed regions.

The first LRO image was released on July 2, 2009. It shows a scene 1800 meters across in cratered terrain within Mare Nubium:

Cratered terrain in Mare Nubium.

This image shows part of the crater Hahn; below it is a series of secondary craters formed from ejecta from a distant large impact crater:

LRO view of a string of secondary craters.

The montage below shows five of the Apollo landing sites; arrows point to the base equipment from which the LMs were launched.:

LRO images of five Apollo landing sites.

So, how good is the image resolution obtained by LRO? In this next image, again of the Apollo 14 landing site, some of the tracks made by the walking astronauts are visible as dark streaks:

Look for the several dark streaks in this LRO image; one is near the Antares Lunar Module; another is near the center, as marked by 4 white arrows.

LRO carries Mini-RF, a SAR-type radar instrument whose main task is to search for ice, especially in the polar regions. Here is a radar strip of terrain near the South Pole.

A SAR image of terrain in the South Polar region.

LCROSS can be treated as a separate mission. After establishing orbit, sensors (visible and spectrographic) on LCROSS were programmed to examine craters in the polar regions seeking more detailed evidence that any of these contain water. The final event, at 4:35 AM PDT on October 9, 2009 was a one-time-only "shoot the moon", in which the Centaur rocket upper stage was made to crash onto the south polar surface at a small crater that looks promising as containing ice. The LCROSS remained nearby in orbit to observe the collision and the ejecta spray or plume produced by the first impact Following that, this shepherding spacecraft was deliberately crashed onto the same Cabeus A. Here is an artist's sketch of LCROSS as the impacting projectile is released:

The LCROSS operational schematic, with a Centaur rocket being sent to the lunar surface.

The target for LCROSS was the Cabeus crater, shown below. Note the nearby 'Short' crater. Regretably, it was not named to refer to the present writer of this Tutorial. Instead, it honors James Short, an 18th century British mathematician who built several innovative telescopes.

Cabeus and Short craters.

Expectations were high that the collision and resulting plume would be "spectacular". Professional and amateur observatories on Earth were trained on the polar region. No one in fact saw much of anything. LCROSS itself picked up a brief flash but no obvious plume. (The writer explains this as a consequence of the dark material in any such plume lacking notable contrast against the dark surface of the crater itself.) The spectrograph did pick up a strong signal but this will take awhile to be analyzed.

In the next three images, we show first the target crater, then a sequence of four images made by LCROSS just after Centaur impact, and finally an image which shows the Centaur impact as a bright flash:

Cabeus, the target crater.
Four images of the crash site, made by lCROSS.
The impact flash made by the Centaur collision.

Some two weeks after launch, an image of the faint plume was processed and released to the public. To make it visible, the scene had to be strongly contrast-stretched, making the lighter tones almost white. Here it is:

The post-impact plume from the Centaur hitting the Cabeus surface.

Another processing, which narrowed the contrast range, shows how little difference there actually was in the tone level of the plume compared with its shadow background:

A lesser contrast version of the LCROSS impact image.

The resulting crater has been imaged. It is at least 20 meters wide, with a surrounding ejecta blanket between 100 and 200 meters in width:

The new impact craters

On November 13, 2009 at a press conference held at Ames Research Center in California, the LCROSS Science team announced (with great enthusiasm) that instruments on board LCROSS had detected even more water (greater amounts than in some terrestrial deserts) than anticipated. The preliminary analysis pins the amount to be at least 24 gallons. The water appears to be present as discrete ice particles scattered within the surface soil of the shadowed part of the Cabeus crater. This is the spectrum for the thermal Infrared instrument, with the yellow bands representing the bands related to the water.

Thermal IR spectrum plot showing the water peak signals.

Although not as pronounced and definitive, the UV spectrum also shows water peaks.

The water peaks in the UV, for the LCROSS impact.

The bottom line: THERE IS DISCRETE WATER ON THE MOON. Whether it is confined to ice in the polar regions, or is more generally distributed over lower latitudes of the lunar surface, is yet to be determined. But the implications for water being available at future lunar bases is distinctly positive.

The lunar probes shown above are all providing new data that will help in planning for eventual manned Moon missions. The question now being asked: Is such a resumption of exploration by humans affordable in the current world economy?

Humans Return to the Moon: The (now mothballed) Master Plan

As mentioned earlier in this Section, in the mid-2000s NASA and other space agencies started planning a manned return to the Moon under the mandate given by Pres. George W. Bush (which, unfortunately, has now been canceled by Pres. Barack Obama). Despite this reorientation of the space program, it is instructive to review below the master plan for America' return to the Moon, since someday it might be reactivated:

A new, more versatile Space Transportation System will be needed. The first landings would probably be more like the Apollo ones but in time it is hoped to establish a permanent (or at least long term) lunar base where astronauts can subsist and explore for extended stays. Four things are essential in making a safe, flexible base: 1) a means of replenishing oxygen; 2) water; 3) source(s) of power; and 4) suitable shielding from extralunar radiation.

Oxygen, in principle, is extractable from the lunar silicate minerals but a reliable, practical means of obtaining this is yet to be worked out (in May 2005, NASA issued a Call for Proposals for innovative solutions). Water can, in part, be recycled from sources (such as astronaut urine) brought with the explorers. But, if substantial water is found near the polar regions, extraction should not be too difficult - thus the base would likely be located at high latitudes. Power requirements can be met with nuclear generators and/or with efficient solar arrays. Shielding may prove difficult since the base units (presumably separate from the landing craft) need to be of light materials. Still, growing experience should aid in selecting radiation-absorbing outer components of the base.

There is another strong argument for selecting polar regions for the base besides the water potential. Placing astronomical observatories at either or both poles would allow almost ideal observing conditions (for some applications better than the present Hubble Space Telescope since systems and components would be state-of-the-art). Nearly all of both celestial hemispheres would be accessible, whereas locating an observatory at lower latitudes would have some light interference from earthshine. But exploration would be curtailed somewhat by dependence on a polar station.

A recent National Academy of Sciences report offers another cogent argument for resumption of Moon visits: The observatory that would eventually be built would be of immense value in astronomical studies and in continual monitoring of the Sun. But, even more valuable to earth-dwellers, 21st Century technology operating through telescopes would produce copious data on the Earth itself. While geostationary satellites can do some of that, the fact that any part of the non-polar Earth is bathed in sunlight every 24 hours makes "observation on demand" feasible. The value of the Moon as a platform was demonstrated during Apollo 16 when astronaut John Young pointed a geocoronagraph towards Earth, getting this image that shows a shroud of low density excited hydrogen around much of the planet:

The envelope of hydrogen ions above the Earth, as imaged from the Apollo 16 site.

Establishment of a Moon base would be a giant step in mankind's renewal of outer space exploration. Among its benefits, it could serve as the launching site for a trip to Mars. On September 18, 2005 NASA made its first public announcement of how its approach to the Moon landings (and probably Mars later) will be made. There is a striking similarity to the Apollo approach in that landing craft will be on a large multistage rocket, with the main thrust section falling back to Earth after putting the manned vehicle on its journey. This vehicle and a companion for sending material to build a lunar base shown here, with other existing vehicles side by side for comparison:

Saturn V and Space Shuttle on left; second from the right is the new concept for a rocket to carry astronauts in a Crew Exploration Vehicle (CEV) to the Moon; farthest right is a large rocket (aided by auxiliary rockets like the Shuttle) which would be separately launched unmanned with a cargo (Cargo Launch Vehicle; CLV) that could eventually include lunar base components but normally contains the Lander assembly.

A closer look at the rocket that would carry a crew of into lunar orbit is pictured here. At its tip is the Crew Exploration Vehicle (CEV).

Artist's drawing of the rocket that would propel astronauts to the Moon.

This panel diagram shows the sequence of events or stages now envisioned in the current plan for renewed lunar exploration:

Launch, touchdown, exploration, and return of astronauts to the Moon.

As the lunar trip gets underway, the Departure Vehicle (jettisoned after burn) and Lander group have mated with the Crew Exploration Vehicle (CEV) capsule, as shown here:

The Departure, Lander, and Crew capsule, beginning the journey to the Moon.

The Service module remains unmanned during the days spent on the lunar surface. The lunar landing craft, housing all 4 astronauts (but, eventually, able to support 6 astronauts), as envisioned on the Moon's surface, is displayed here:

The Lunar Vehicle landing craft (capsule) attached to an orbiting Service module; artist's conception.

The landing units descend to the surface, much like during the Apollo program, with the larger unit consisting of a braking rocket and fuel. After the lunar stay is ended, the upper crew unit fires its rocket to put it into orbit and eventual docking with the service unit.

The spherical crew unit departs the landing unit, to dock with the service capsule.

The schedule calls for the CEV system, without the Lander units, to be ready to fly sometime after 2010. It could replace the phased-out Space Shuttle program and will be NASA's means of servicing the International Space Station. This will provide extended experience in CEV use up to the first Moon landings.

The CEV docking with the ISS

In the master plan (now in 'limbo') a crew of 4 would descend on the CEV and stay for (at least) a week. Over time, the stay will be longer as the astronauts build a lunar base capable of sustaining the mission for weeks to months. This will provide the needed experience for prolonged missions that would take place on Mars at a later time. When the crew returns to Earth in the detached capsule, it will have the capability of landing either on land or at sea. If no serious damage occurs, the CEV can be used up to 10 flights.

The crew capsule touching down on land; it is attached to 3 large parachutes.

NASA, and even its critics, together recognize that a Moon exploration resumption followed by Mars exploration (which would gain from the lunar experiences) may be vital to keeping the American space program healthy enough to press forward, rather than wither and diminish by loss of dedicated personnel.

Imaginative futurists being a common breed today, one could predict that no sooner did NASA announce plans for a Moon Base, the Internet would start accruing many "artist's conceptions" of the layout of such an endeavor. Here are two:

NASA's first released sketch of a future Moon Base.
A more elaborate lunar base.

Two active websites offer more discussion of such a base: 1) Colonization of the Moon, and 2) Solar Voyager.

Source: http://rst.gsfc.nasa.gov