Iron Ore Mining (III)

Iron from the Sky

By IonMars

September 20, 2014

When we are suddenly caught in a thunderstorm we might exclaim: “it’s raining cars and dogs!” But three billion years ago an imaginary observer might exclaim: “it’s raining iron from the sky!” as meteors huge and meteorites small poured down on Earth and Mars.1 They are still coming down today but the downpour has slowed to a trickle.

Some of these meteorites were buried in the ground after colliding with ballistic speed. Others with less momentum merely bounced along the surface and came to a stop. On Earth the geological forces of volcanism and plate tectonics have long since buried these outer space objects2.  Any iron meteorites left on the surface have gradually rusted away due to the oxygenated atmosphere. On Mars the tectonic forces subsided long ago, the remaining atmosphere is composed of non-oxidizing carbon dioxide, and the meteorites are still lying on the surface.

Mars MeteoriteSome of these balls from outer space were composed of iron.2  They were not, however, composed of hematite, the iron-rich mineral described in the article “Iron Ore Mining I.” Nor were they composed of pure magnetite, the iron-rich mineral described in “Iron Ore Mining II.” In fact, they were not composed of any iron ore ready to be dumped into a blast furnace, but a pure iron alloy that normally exits from a steel-making furnace. If the colonists exploit the iron meteorites, they will skip two entire processes of iron and steelmaking: the blast furnace (or alternative ironmaking process) that converts iron ore to iron and an electric arc furnace where other ingredients are added to create a steel alloy. 

In two previous articles published on this website IonMars described two types of rich iron ores that may represent fabulous rich sources for ironmaking in the new Mars colony. Some people have commented that iron is just lying around on the surface, just waiting to be picked up. It would appear that iron meteorites are the premium source, the “lowest lying fruit.” This may well be the case, but certain questions have to be addressed before a definitive answer can be given. The two principal questions are: which of these sources is large enough to feed the colony’s new steel industry? Also, how much steel does the colony actually need? The question of need will be deferred to another article that will analyze the potential structures that are likely to be built. The question of quantity will be addressed here for meteoric iron. How many iron meteorites are actually lying on or near the surface and what is their size distribution?

 

Iron Meteorites on Mars

 Heat Shield RockInformation about meteorites on Mars comes to us from notable discoveries by three Mars rovers, Opportunity, Spirit and Curiosity. The first was the discovery of “Heat Shield Rock,” a basketball-sized iron-nickel meteorite found on Merdiani Planum by the rover Opportunity in January 2005. Opportunity encountered the meteorite entirely by chance, in the vicinity of its own discarded heat shield (hence the name). This was the first meteorite found on another planet4.

To analyze the meteorite, Opportunity employed a mini-Tropospheric Emissions Spectrometer (TES) and measured a spectrum that appeared unusually similar to a reflection of the sky. Then the rover employed an Alpha Particle X-ray Spectrometer (APXS) to measure its composition, which was found to be 93% Iron, 7% nickel and trace amounts of germanium (~300 ppm) and gallium (<100 ppm). Spectral readings from a Mossbauer spectrometer showed the iron to be primarily kamacite, an iron mineral alloy with 5–7% nickel. If the rock were found on Earth it would be classed as a typical IAB Allan Hillsgroup iron meteorite. The surface of the rock exhibited the characteristic regmaglypts, or pits formed by the ablation of a meteorite as it passes through the atmosphere.. As of 2011 Opportunity had traversed 26 km across the Meridiani Planum and identified six meteorites5. 

Spirit was the next NASA rover to identify likely meteorites, this time on the opposite side of the planet in Aeolis quadrangle. The panoramic camera recorded this image during the rover's 809th Martian day (April 12, 2006). The foreground rock, "Allan Hills," (named after a famous Mars meteorite found in Antarctica) and a nearby rock called "Zhong Shan," exhibited a smoother texture and lighter tone than other rocks in the area. It was similar to Heat Shield Rock identified by Opportunity6 and is likely an iron meteorite. Spirit continued its mobile explorations until April 2009, when it became stuck in a sand trap.


The rover Curiosity made headlines when it discovered a large iron meteorite along its sojourn toward Mount Sharp7. On May 25, 2014 (Curiosity’s 640th sol) the rover came across this 2-meter wide meteorite that was nicknamedLebanon Iron Meteorite “Lebanon.” This find on top of others led scientists to surmise that the majority of meteorites on Mars may be made of iron while the majority of Mars meteorites found on Earth are stony. The explanation may be that Mars meteorites were exposed to weathering that wore down any stony rocks but allowed iron to last much longer.

A Meteorite Survey

Knowing that iron can be easily found on the surface does not automatically mean that the quantity is sufficient for the first Mars steelmaking industry. If there is enough, then we can forego the shipment of ironmaking industrial equipment to the planet and go straight to steelmaking. Even if the whole industrial facility can be miniaturized into the hold of a single trip of the Mars Colonial Transporter, we are still considering the expenditure of several billion, USD. Early explorers should conduct a meteorite survey even before the first settlers arrive. This survey will require only a modicum of equipment compared to a whole industrial facility and it will be a worthwhile investment.

The first thing we must know is the method by which we can detect iron meteorites in a survey. We know that pure iron is very easily magnetized and we know that hematite is prevalent everywhere on the planet; it is a basic component of the fine-grained regolith that is dispersed everywhere8. Hematite is weakly ferromagnetic in the temperature range of 256 K (-17 degrees C) to 948 K  (675 degrees C) and a temperature above -17 degrees C will be experienced on Mars’ surface every day. The juxtaposition of iron and magnetic minerals on the surface implies that any iron on the surface will become magnetized; therefore a magnetometer can be used to detect discrete magnetic sources that are stronger than the widespread weak magnetic background of the planet.

Three LandersIn the article Iron Ore Mining II “Dune Boggle,” IonMars described the method of carrying out a magnetic survey as performed on Earth. It involved a field technician carrying a magnetometer in a backpack along a survey line that was a part of a pre-established survey plan.  The counterpart field technician on Mars would be a person in a space suit or in a Mars Utility Vehicle (MUV) with manipulators. In conducting this survey the magnetometer readings will not change slowly as the technician moves over a widespread deposit of magnetite; rather, the magnetic readings will change quickly for a much smaller object, an individual iron meteorite. In order to avoid overlooking a small object the survey path must be much more fine-grained. The parallel survey lines must be just meters apart rather than hundreds of meters.

To address the problem of conducting a fine-grained survey over a large area, a special survey vehicle will be required. It must be capable of moving quickly over any kind of terrain and close to the ground while carrying a sensitive magnetometer. It must be capable of stopping abruptly when a small anomaly is detected, then passing back and forth across the object to record its extent in 2 dimensions. It will require the capabilities of a helicopter-driven drone employed on Earth except that a helicopter will not work on Mars. Such a vehicle will be a rocket-powered Hovering Magnetometer (HovMag). It will employ much the same capability as a rocket lander on the surface of Mars, but at a micro-scale.

Some of the characteristics of the HovMag may be determined in advance. The required rocket thrust will depend on the weight of the magnetometer to be carried and the range capability (fuel capacity) that can be designed into the device. An example of the type of instrument to be carried could be the Geometrics 856 field magnetometer, which weighs in at 2.7 kg9. To save weight, no human should be brought aboard the vehicle; instead, the readings should be transmitted in real time back to a base camp, a portable field office, or a Mars satellite where the progress of the vehicle will be monitored. To avoid excessive time in communicating commands to the vehicle, many flight functions will be programmed into an onboard microprocessor. Note that such a useful device will likely find many more applications for field reconnaissance than just a meteorite survey.

 Conducting a field survey for meteorites will likely occur during a NASA exploration expedition before any colonists arrive on the planet. One must then assume that none of the Mars village vehicles will be available. The method of carrying out a field survey with a HovMag will involve employing the NASA Space Exploration Vehicle (SEV) and the Demonstration Habitat Unit (HDU) or developed equivalent as a base camp. A two-week mission will be a practical limit for this type of survey and for the SEV.  A temporary base camp for the HDU will be set up in the center of a large rectangle, the approximate center of the land area to be surveyed. (See the example of a meteorite survey plan in the figure below.)

Each day of survey will see two Astronauts/Surveyors in the SEV moving out from the base camp along a predetermined survey base line, towing the HovMag and rocket fuel in a trailer. At a predetermined point of departure the Surveyors will stop to fuel up and deploy the HovMag. The device will be sent along a survey line at a right angle to the base line. It will follow this line until it encounters a magnetic anomaly; then It will begin a crisscross pattern to locate the center of the magnetic anomaly. HocMag will hover over the object in order to take a photo of it. At this point a surveyor at the base camp may want to take over control of the hovering spectrometer to examine the object through the photographic lens.  After the examination, HovMag will transmit images of the object, location data and the magnetometry data back to the control center at the base camp data storage facility.

A series of HovMaf deployments will be conducted according to a survey plan as exemplified in the figure below. The survey process will continue until about 40 percent of the fuel has been consumed and then the vehicle will automatically reverse direction. It will set a course along a line parallel to the outgoing survey line and back to the survey base line near the point of deployment. It will continue recording anomalies on the return trip. Note that the length of the outgoing flight and return flight will vary, depending the number of objects that are encountered. This is because crisscrossing and hovering will require additional fuel and the fuel limit will be reached earlier when more objects are found. Note that the distance between outgoing and incoming survey lines will be determined by the capability of the magnetometer in this terrain on Mars. The midway point between survey lines should lie near the detection limit of the instrument.

Meteorite Survey Plan

Once the data has been collected from a meteorite survey, how should we analyze it? How will we determine whether there is enough iron lying on the ground to justify skipping the ironmaking process and proceeding directly to steelmaking?

 

One way to classify the meteorite data is according to the “three bears” principle. By this we mean:

  1. Too small to merit the effort to collect it; or
  2. Too large so that its sheer mass would overwhelm the collection system; or
  3. Just right. The mass is within the capability of the collection system.

In order to determine the correct division of meteorite masses we need to assess the probable collection method to be employed. We envision that the proposed vehicle should be capable of moving across rough terrain like the NASA SEV. It also should have a substantial carrying capacity like a heavy-duty dump truck. It should be equipped with a manipulator arm for picking up meteorites and placing them into the vehicle truck box. Finally, it would be desirable to identify a collection device that already exists and that meets these criteria. As it happens, an Earth analogue for such a vehicle exists and it is a garbage truck. Truck with Manipulator Arm

One example of a garbage truck with a manipulator arm is the Starr System built by Heil Corporation of Chattanooga, Tennessee. (See photo above.) The company describes their system as an automated semi-trailer rapid-rail side loader.9  The lift arm has a capacity of 1600 pounds Earthside, which converts to 4200 pounds (1400 kg) when used on Mars. The estimated total weight of the system including lift arm is 17,750 pounds (8051 kg) at liftoff from planet Earth, a substantial portion of one freight load of the Mars Colonial Transporter. 

To convert an Earth analogue into a Mars capable vehicle the steps delineated in the article “Mars Village Vehicles” will be adopted10 as follows:

  1. The cab must become completely airtight.
  2. The cabin must be rebuilt to install an EVA hatch.
  3. The engine must be converted to use methane fuel and 100 percent O2 from pressurized tanks.
  4. Equipment for Environmental Control and Life Support System (ECLSS) must be installed.
  5. Extra protection to guard against Galactic Cosmic Rays (GCR) and micrometeorites must be installed.

In addition to these generic rules of conversion, additional requirements will apply to this particular type of system, as follows:

  1. The end effector for the lifting arm must be changed out to enable picking up meteorites rather than round garbage containers. This will entail installing a grabber that can operate from the top of an object rather than from the side and flexible finger joints that can adapt to an irregular shaped object.
  2. An additional arm will be required to pick up smaller meteorites as compared to the first arm. This could be mounted on the opposite side of the truck.
  3. An Earthside garbage truck is designed to compress garbage en route so that a large number of containers can be serviced. This feature is not needed for meteorite collecting so the entire system should be dismantled and removed. This step will reduce the overall weight considerably.

Once the specifications for the collection system are determined then the correct range of meteorite masses to be collected will be known. In the example system the upper mass limit is 1400 kg Mars weight. The lower mass limit will be determined by the capability of the end effector of the smaller of the two arms, and may depend on size and shape of the meteorites as much as mass. In any case it will be feasible to add up the estimated masses of the meteorites that were found on the survey(s) and compare the total with the needs of the steel industry of the Mars village. 

One major exception to the size range analysis will be the chance discovery of a truly massive meteorite. This could be a mass that lies partly above ground and partly below ground. It would be large enough to serve the entire industrial requirement for five or more years. In this special case the collecting of meteorites will be set aside and all the industrial processing equipment for steelmaking will be transported out to the meteorite and set up beside it.

  

References

 

  1. National Geographic News (July 35, 2002) “First Evidence for Early Meteorite Bombardment of Earth,” Retrieved 8-11-2013 from http://news.nationalgeographic.com/news/2002/07/0725_020725_meteor.html
  2. J. Erickson (2001) “Plate Tectonics: unveiling the mysteries of the universe,” Retrieved 8-11-2014 from http://books.google.com/books?id=g0SY7j3iGHsC&pg=PA233&lpg=PA233&dq=tectonics+submerge+meteorites&source=bl&ots=itz_9oN43q&sig=LLyiujjr_OZUUNjs3k0eMOkw1qc&hl=en&sa=X&ei=gL_oU_m6IMv_yQT38YHQCw&ved=0CCcQ6AEwAQ#v=onepage&q=tectonics%20submerge%20meteorites&f=false
  3. NASA (2014) “Curiosity finds iron meteorite on Mars,” Retrieved 9-19-2014 from http://www.nasa.gov/jpl/msl/pia18387/#.VBvmCUtTKGk
  4.  “Heat Shield Rock,” Wikipedia (undated) Retrieved 9-15-2014 from http://en.wikipedia.org/wiki/Heat_Shield_Rock
  5. Fairen, Alberto G., et.al. (2011) “Meteorites at Meridiani Planum provide evidence for significant amounts of surface and near-surface water on early Mars,” Meteoritics & Planetary Science, Volume 46, Issue 12, pp. 1832-1841.
  6. NASA (2006) “Possible meteorite in ‘Columbia Hills’ on Mars,” Retrieved 9-18-2014 from http://mars.jpl.nasa.gov/msl/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1399  
  7. Stewart Clark (July 16, 2014) “NASA’s Curiosity rover finds large iron meteorite on Mars,” The Guardian, Retrieved 9-16-2014 from http://www.theguardian.com/science/across-the-universe/2014/jul/16/nasa-curiosity-rover-iron-meteorite-mars
  8. NASA (2012) NASA Mars rover fully analyzes first soil samples,” Retrieved 9-18-2014 from http://mars.jpl.nasa.gov/msl/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1399
  9. “Automated semi-trailer rapid-rail side loader product specifications” (undated) Retrieved 9-16-2014 from http://www.heil.com/sites/default/files/pdf/Heil_STARRSystem_ASL_brch_1212.pdf
  10. Paul, R. (2014), “Mars Village Vehicles,” The Mars Pioneer (website), Retrieved 9-16-2014 from http://themarspioneer.com/MarsVehicles.html