Crashing Into The Moon

LRO-LCROSS project. Image source: Northrop Grumman.

The ability to either easily recover the moon’s existing water, or to convert its seemingly plentiful hydrogen and oxygen concentrations into air, water and fuel, will have a huge impact on the future direction of NASA’s Space Program.. Past missions have informed us that there are large concentrations of hydrogen on the north and south poles of the Moon. Soon, NASA’s LCROSS/ LRO (Lunar Reconnaissance Orbiter) robotic missions will perform a crucial experiment to get a closer look at what’s causing the large hydrogen signatures at the Moon’s south pole. It should also help settle the current debate over the form of that hydrogen.

A cache of hydrogen located in the Moon’s dark craters has a number of important implications. For humans to live for any extended period of time in space, we will need to have a water source. Bringing water from home currently costs around $100,000 a kilogram. Lunar exploration would be greatly facilitated if we were able to generate water resources right there on the moon.

“There are a number of different ways that we’ll be able to create water from whatever form of lunar hydrogen we find,” explains Brian Day, Education and Public Outreach Lead for the LCROSS mission. “Oxygen has been also confirmed to exist naturally in the mineral lattices of the Moon’s rocks, in various oxides (aluminum, silicon, calcium, magnesium, iron, and titanium) and the Sun is constantly delivering a stream of hydrogen to the Moon with its solar wind.”

LRO-LCROSS Launch Configuration. Image approved for Public Release by Dirk Schreier, LMCO, 1-29-08.

In 1994, the Clementine Mission gave NASA its first piece of evidence of the possible existence of water, when a radar beam it bounced off the surface of the Moon came back polarized in a way that is consistent with having gone through crystals of water ice. In 1998, Lunar Prospector detected hydrogen at the poles using its neutron spectrometer, which looks at the flux of epithermal neutrons emanating off the surface of the Moon. But neither mission was able to identify exactly what chemical form the hydrogen was in, so the data remained inconclusive on the water issue.

LRO-LCROSS project. Image source: Northrop Grumman.On June 18th, 2009 LRO (Lunar Reconnaissance Orbiter) and LCROSS probes were launched together aboard an Atlas V-Centaur rocket out of Cape Kennedy. The LRO is going to map the Moon in very fine photographic detail (better than sub-meter resolution), scan the topography with a laser altimeter, and characterize its radiation and thermal environments. LRO’s LAMP uses Lyman-Alpha ultraviolet light, which is invisible to us, but illuminates the dark polar craters — allowing appropriate cameras to see the shadowed topography.

NASA’s LCROSS mission hopes to raise some of the material from the bottom of a permanently shadowed crater of the Moon’s south pole into the sunlight where it can be analyzed. After LCROSS helps to confirm whether or not it’s water ice that is giving off the hydrogen signature, the LRO mapping results can be used to show the most likely areas of high hydrogen concentration, and thus the likelihood of water. NASA will consider the LCROSS and LRO missions a success if they are able to resolve the water question.

“Bombing” The Moon?
To get to the bottom of things, NASA is dropping a completely empty upper stage of the Centaur rocket smack into one of these southern polar craters. Contrary to some inaccurate reports in the popular media, there will be no explosives or military weapons involved. The upper stage is from the LCROSS and LRO’s launch back in June, which was retained for this experiment.

“It weighs roughly 2,200 kilograms, and will be moving at about 2.5 kilometers per second (5,600 miles per hour),” explains Day. “It will be coming in very steep, at about 80 degrees, and will make a large enough impact to loft approximately 200 metric tons of material about 10 kilometers into the lunar sky, where it will remain long enough for the LRO and ground-based assets to obtain their data.”

NASA is making sure that it comes in at a sharp enough angle this time to cause a recognizable plume or other reaction from the surface. The angle wasn’t steep enough when they crashed the Lunar Prospector into the crater in 1999, with no discernable results.

LRO-LCROSS Mission Trajectory. Image approved for Public Release by Dirk Schreier, LMCO, 1-29-08.

Dropping the upper stage into the large polar crater will create a small crater approximately 20 meters across — many times smaller than craters created by meteoroids impacting the Moon on the average of four times a month. “If you look at the Moon through a small telescope, you can see that it’s covered with large craters,” explains Day. “Most of these are measuring tens to hundreds of kilometers across, so you see it’s a very different scale.”

Many experts are already pretty confident about what’s at the Moon’s poles, although they still agree with NASA that water on the Moon has not been definitively proven. “We know whatever we see in cometary tails is likely to also be in the polar craters,” explains Ed McCullough, an independent consultant and former Principal Scientist at Boeing.

LRO-LCROSS project. Image source: Northrop Grumman.Why are Ed, and others, so confident about water being there? Because the building blocks of water, hydrogen and oxygen, are already everywhere — all over the Moon. We know that water is created naturally from meteors striking the surface and flash-heating the regolith, which causes iron oxide to be gradually reduced by the hydrogen implanted by the solar wind. The hydrogen in the regolith reacts with the oxygen in the iron oxide to create water. This water, generated on or deposited onto the Moon, is either lost to space or migrates to higher latitudes. The southern polar region, with its permanently shadowed craters, is thought to retain water and other volatiles more efficiently than any other region. We also know that water is deposited into the poles directly via cometary tails that periodically envelope the entire Moon.

Does that mean we can just use the water that’s already there? Well, most experts agree there are two main sides to that issue. “Water is water. If you can find it naturally, that’s better than having to resort to a chemical combination of hydrogen and oxygen, which requires energy to activate the process,” explains Donald Sadoway, a Professor of Materials Chemistry at MIT who has developed a “molten oxide electrolysis” technique for extracting oxygen out of Moon regolith. “However, if the water is to be potable, then purity is an issue. So in any given situation, you need to assess whether it is more costly to purify existing water or to synthesize water from hydrogen and oxygen.”

NASA is dropping a completely empty upper stage of the Centaur rocket smack into one of these southern polar craters.

What’s The Moon Made Of?
If you look up at the Moon at night, you’ll notice dark material and lighter material. The dark matter is quite similar to the lava coming out of some Earth volcanoes (in Hawaii, for instance), which cools to form basalt (lava rocks). This is made up of oxides of iron, aluminum, calcium, magnesium, silicon, and titanium. The white matter is made up of the oxides of calcium, aluminum and silicon. The whole backside of the Moon is also believed to be made of anorthosite, a whitish mineral. (Although there is no “dark side” of the Moon, as almost the entire Moon’s surface gets some sunlight at some time, to us here on Earth, there is a “back side.” This is because the same face of the Moon always faces Earth, revolving once on its axis as it rotates once around the Earth.)

“The poles, as well as the rest of the Moon, will contain ‘agglutinates,’ which are created from the continuous impact of meteors and micro-meteoroids over time,” explains McCullough. “If you picture a sort of glassy substance holding together smashed pieces of glass and various minerals, the resulting substance is a heterogeneous agglomerate of glass bonded particulate material (breccias), or a fluffy ‘agglutination,’ with an iron oxide-containing surface area that will react with hydrogen if it is in an elemental form.” This is a special form of iron that has only been detected on the Moon, so far.

“One big difference between the Moon and the Earth is in the iron content. The Moon, with its vacuum-like atmosphere, is so highly reducing that the only form of iron we find in compounds is Fe2+,” explains Sadoway. “In addition, there is a strange form of elemental iron ‘agglutinates,’ which are fine particles, typically with nanocrystalline microstructure. There is nothing like this stuff to be found on Earth, so when people try to simulate the mechanical properties of regolith, they fail on account of the lack of agglutinates like these in the Earth’s crust.”

LRO-LCROSS project. Image source: Northrop Grumman.Whether it’s water ice or “dry” hydrogen trapped in mineral oxides, we’ll still have to go to these extremely cold places to recover it. There is also the issue of how we would deal with all the material handling issues.

Is it possible to mine too much of the Moon, and somehow upset a delicate balance between it and our own fragile planet? Experts seem to agree that such a scenario is highly unlikely, mainly because the Moon is just too big. In addition, the hydrogen and mineral oxides that we’re talking about removing are being constantly replenished.

“If you dig down within one meter of the lunar surface, there will be enough implanted hydrogen to make 30 billion tons of water. Dig down another meter and you get another 30 billion tons of potential water. These are minimum values. The actual resource can be three to five times higher,” explains Ed McCullough. “Plus the reservoir is always being constantly refilled by the solar wind and cometary activity.”

“The more we know about the Moon, the better prepared we’ll be for putting people back on its surface,” says Sadoway. “Right now, I know how to get oxygen, iron, and silicon (a semiconductor that can be used in photovoltaic devices), and in my lab at MIT I have made iron, nickel, chromium, and titanium by molten oxide electrolysis. But there’s got to be more there.”

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