Martian In-Situ Resource Utilization (ISRU)
Global Justice Alliance

Results 1 to 8 of 8

Thread: Martian In-Situ Resource Utilization (ISRU)

  1. #1
    Registered User Exalted Member Fireand'chutes77's Avatar
    Join Date
    Jan 2005
    Location
    The Old Dominion
    Posts
    2,946

    Martian In-Situ Resource Utilization (ISRU)

    I've been given my final project task for the VASTS program I'm in:

    --------------------------

    Dear scholars,

    At the Summer Academy, you will be working within your team and collaboratively
    with other teams to construct a manned-mission design to Mars and return to
    Earth...... You are applying the knowledge you learned during the online course and from reading the final
    projects to solving the real-life problem of designing a complex and important
    mission.

    Your final online project will provide the necessary content to all scholars to
    make decisions to facilitate the completion of the mission design during the
    week you are at NASA Langley. A week seems like a long time, but you will be
    amazed how fast your time will fly when you are working during the Summer
    Academy.

    Mission Background:

    Data from the surface of Mars was collected by robots and rovers. Serious
    chemical and visual signs of existing life were discovered. While robots can
    identify possible life signs, humans need to be sent to collect, test, and
    verify rock samples that have the highest probability of confirming the
    existence of life.

    Mission Parameters:

    • 2035 to 2050 time frame (different levels of technology determine mission
    date)
    • Total mission duration = 2 years
    • Minimum surface time of 30 days
    • Crew of 2 or more
    • 50% must return alive
    • Total mission success of 7/10 (70%)
    • Affordable
    • Minimum technology platform of Ares I & V used
    • In situ resource utilization (ISRU) permissible
    • Staging from Martian moons permissible


    ****Identify (3) system concepts that meet guidelines and requirements for your
    designated focus areas in your team. These system concepts should span various
    levels of technology utilization and system configurations to meet the
    functional needs as defined by your mission team. Describe the differences in
    capabilities afforded by the differing systems concepts in meeting mission
    requirements. Compare and contrast required levels of technology, system mass,
    volume, energy requirements, etc. Identify the system concept that you feel is
    best for meeting your mission goals understanding that cost, technology, risk,
    and system mass must all be minimized to the maximum extent to assure
    viability. (Resources will be posted to provide assistance and examples. You
    are not limited to just these resources for use in your report)****

    Suggested outline:

    Mission focus area (page 1)
    • Team responsibility description
    • Focus area description
    • Focus area mission requirements

    System Concept One, Two, Three (pages 2, 3, 4)
    • Graphic
    • Mass and system properties (metric units)
    • Enabling technologies
    • Performance capabilities
    • How requirements are satisfied


    System Concept recommendations (page 5)
    • Comparison of system concepts (system properties, technology assumptions,
    objective satisfaction)
    • Recommendation and justification

    Citations (page 6)


    --------------------

    My area of focus will be "Living There" > "ISRU." ISRU is the process of using existing materials on the Martian/Lunar surface to make
    materials for space crews - fuel, oxygen, water, building material, glass, etc - so we don't have to transport all that stuff on the original rocket,
    which, obviously, would make it outrageously heavy and expensive.

    As the scientists and teachers have stressed, "don't reinvent the wheel!" They want us to research existing/developing technologies, find three viable ones, see how they apply to our mission,
    and pick the one I/we think will work best for our sitch.


    Is there anyone on the board that has knowledge of ISRU or information that could help me out?

    Maybe I could ask JAKT on FF.net. He's a rocket scientist, right?




    --------------------

    You know, it's kinda funny how my moniker has made a round-trip to relevance. I chose it way-back-when in the TV Tome days while I was working in a rocketry-related school science project, and now, what with the program I'm in, it has a lot of meaning again.

    Carpe Navi: Because you never know when you'll get to go boating at government expense again.

  2. #2
    Registered User Exalted Member lunchmeat's Avatar
    Join Date
    Apr 2005
    Location
    The Tick Capitol Of The Known Universe
    Posts
    4,025
    Well, what sort of data have they provided you for materials?

    If we're using current data, it appears there is at least some water. That makes for a great start, since that is one of the heaviest fundamental supplies we need for survivial and industry. There is lots of things that are possible when water is available.

    It can be dissaciated to provide oxygen. The hydrogen componant can be plowed back into fuel cells or methane for either electrical power and fuel. This also dictates your primary landing sites: the polar areas where water is known to exist.

    The character of the geology will be a big controlling factor. If it is largely carbonate rock, it can be sintered (cooked, probably with solar furnaces) to make slaked lime, which with water, can be rendered into concrete and mortar. This gives you a source of building materials. My own choice would be to establish long term quarters and facilities entirely or at least partially underground to provide a refuge from radiation. Depending on the composition of the soil you may be able to use it as substrate for growing food. If the soil is wrong, then it'll have to be hydroponics, but again there appears to be water available to perform that task (seeds, rootings and cuttings are light, so they won't take up much of your allowable mass on the spacecraft). The next critical things are nitrates and phosphates for fertilizer, it will take some variant on the haber process http://en.wikipedia.org/wiki/Haber_processto provide basal elements for nitrate fertilzers (this also useful for lots of other industrial chemicals) you are essentially going from the late 1400s to the 1890s in one sharp jump, industrially (you'll need these, too, to have a basis for most industries: http://en.wikipedia.org/wiki/Ostwald_process http://en.wikipedia.org/wiki/Leblanc_process http://en.wikipedia.org/wiki/Contact_process.

    I look forward to seeing what you and your classmates come up with, this is the next defining event in humanity's journey (asuming we don't do something stupid and throw Ares away in fit of political pandering).
    Admiral Isoroku Yamamoto - “You cannot invade the mainland United States. There would be a rifle behind each blade of grass.”

  3. #3
    Registered User Exalted Member Fireand'chutes77's Avatar
    Join Date
    Jan 2005
    Location
    The Old Dominion
    Posts
    2,946
    Quote Originally Posted by lunchmeat View Post
    Well, what sort of data have they provided you for materials?

    If we're using current data, it appears there is at least some water. That makes for a great start, since that is one of the heaviest fundamental supplies we need for survival and industry. There is lots of things that are possible when water is available.

    It can be dissected to provide oxygen. The hydrogen component can be plowed back into fuel cells or methane for either electrical power and fuel. This also dictates your primary landing sites: the polar areas where water is known to exist.

    The character of the geology will be a big controlling factor. If it is largely carbonate rock, it can be sintered (cooked, probably with solar furnaces) to make slaked lime, which with water, can be rendered into concrete and mortar. This gives you a source of building materials. My own choice would be to establish long term quarters and facilities entirely or at least partially underground to provide a refuge from radiation. Depending on the composition of the soil you may be able to use it as substrate for growing food. If the soil is wrong, then it'll have to be hydroponics, but again there appears to be water available to perform that task (seeds, rootings and cuttings are light, so they won't take up much of your allowable mass on the spacecraft). The next critical things are nitrates and phosphates for fertilizer, it will take some variant on the haber process

    http://en.wikipedia.org/wiki/Haber_process

    to provide basal elements for nitrate fertilzers (this also useful for lots of other industrial chemicals) you are essentially going from the late 1400s to the 1890s in one sharp jump, industrially (you'll need these, too, to have a basis for most industries:

    http://en.wikipedia.org/wiki/Ostwald_process

    http://en.wikipedia.org/wiki/Leblanc_process

    http://en.wikipedia.org/wiki/Contact_process.

    I look forward to seeing what you and your classmates come up with, this is the next defining event in humanity's journey....
    Wow, thanks!

    Here're the resources I've got so far (with my own notes on what's in each):

    Sabatier - http://www.clas.ufl.edu/jur/200109/p...er_canton.html

    Reverse gas-water shift: http://spot.colorado.edu/~meyertr/rwgs/rwgs.html

    http://ston.jsc.nasa.gov/collections...001-209371.pdf
    general overview

    *isdc2.xisp.net/~kmiller/isdc_archive/fileDownload.php/?link=fileSelect&file_id=19 –
    pics, flowcharts, different processes (Sab, r-g-w, solid oxide) mass, volumes

    http://science.nasa.gov/newhome/head...pdf/insitu.pdf
    - Using alloys and melting metals on Mars + Moon; weights of different materials

    http://marsjournal.org/contents/2006...rsDuke2005.pdf
    Very, very good – benefits, mass reduction, risks, flow-charts, dates of deployment, mass (table near bottom)

    http://nssdc.gsfc.nasa.gov/planetary/mars/marssurf.html
    Mostly about fuel production (Sab, CO2 use); equations; some about life-support

    *http://science.nasa.gov/newhome/head.../materials.pdf
    - Materials and resources found in Martian/Lunar soils that can be used to make stuff

    Map of landing sites: http://marsoweb.nas.nasa.gov/landing...ous/sites.html

    * http://ares.jsc.nasa.gov/marsref/contents.html
    ***http://ares.jsc.nasa.gov/marsref/Mars3txt.pdf --- Mass, tables, pictures, processes


    ******WATER IS HUGE CONCERN – CAN WE FIND IT???********





    ISRU Moon:

    https://secure.spacegrant.org/vasts/...iew.php?id=128

    pics, ways to do it – *http://www.nasa.gov/pdf/203084main_I...11-07%20V3.pdf





    Habitat:
    http://www.hq.nasa.gov/office/pao/Hi...3/contents.htm



    --------------------



    I think they're giving us some of the Powerpoints and PDFs that NASA is actually using.

    Here's a download link for a .html file I made from the sources page they gave us:

    http://www.mediafire.com/?boetemjvc6x

    If that doesn't work, I just took a screenshot of the sources and made it into a .jpg.

    http://img529.imageshack.us/img529/6308/sourcesgp4.jpg



    So now what I've got to do, I guess, is research *where* the water is located on the planet, how hard it is to get to, and how deep we have to go to get it. From my reading, most of the ice water (the stuff Phoenix just found!) is near the poles, and they're trying to stay away from those because the climate up there is so extreme.



    I've also got to find out what the Martian soil is actually made out of. (Both might be in my notes somewhere! )


    My own choice would be to establish long term quarters and facilities entirely or at least partially underground to provide a refuge from radiation.
    That's been my line of thought too. For both Mars and Lunar habs, I've proposed to hammer the base site, swords-to-plowshares-style, with kinetic-energy penetrators and/or GPS-guided cluster bombs to soften up the soil for easy excavation. Send bulldozers in before the humans, then once the people arrive, they can easily dig out trenches in the loosened soil, plunk the modules in place, and cover them back up again with backfill. Natural light could be filtered into the underground living spaces through fiber-optic cables.


    If it is largely carbonate rock, it can be sintered (cooked, probably with solar furnaces)
    The sunlight received on the surface of Mars is about 43% of Earth's. Would that be strong enough to support solar furnaces?



    (assuming we don't do something stupid and throw Ares away in fit of political pandering).
    I wouldn't put it past them....

    Carpe Navi: Because you never know when you'll get to go boating at government expense again.

  4. #4
    Moderator Venerated Elder TransWarpDrive's Avatar
    Join Date
    Jul 2007
    Location
    The suburbs of Go City
    Posts
    10,019
    Quote:
    (assuming we don't do something stupid and throw Ares away in fit of political pandering).
    I wouldn't put it past them....
    There's a way to make sure they don't do that - write your Congressman. Write your Senators. Urge them to support NASA's Moon and Mars missions wholeheartedly, and ask them not to allow the space budget to be cut for any reason. You might also want to send the same message to both Presidential candidates, so no matter who wins the White House this fall, they'll at least be aware of your stance on space exploration and less likely to cut NASA's budget. And, of course, get out and VOTE for any and all pro-space candidates in the running.
    That's what I've done. I don't know how many letters I've sent to the White House, my congressman and senators supporting the space program over the years; I know I've sent out quite a few. But the important thing is, I did write, and made my voice heard on this and other issues that matter to me.
    That's what it means to participate in a democracy.

    I'll get down off my soapbox now. Thanks for listening.

  5. #5
    Registered User Exalted Member Fireand'chutes77's Avatar
    Join Date
    Jan 2005
    Location
    The Old Dominion
    Posts
    2,946
    Quote Originally Posted by lunchmeat View Post
    Depending on the composition of the soil you may be able to use it as substrate for growing food.... The next critical things are nitrates and phosphates for fertilizer, it will take some variant on the haber process http://en.wikipedia.org/wiki/Haber_processto provide basal elements for nitrate fertilzers....
    Just read an MSN report - there's another one down! Boooyaaahhhhh!

    http://www.msnbc.msn.com/id/25396378


    ....Phoenix discovered that a sample of Martian dirt contained several soluble minerals, including potassium, magnesium and chloride. Though the data is preliminary, the results are very exciting, scientists said.

    "We basically have found what appears to be the requirements for nutrients to support life," said Phoenix's wet chemistry lab lead, Sam Kounaves of Tufts University. "This is the type of soil you'd probably have in your backyard. You might be able to grow asparagus pretty well, but probably not strawberries."
    Carpe Navi: Because you never know when you'll get to go boating at government expense again.

  6. #6
    Registered User Exalted Member Fireand'chutes77's Avatar
    Join Date
    Jan 2005
    Location
    The Old Dominion
    Posts
    2,946
    Here's my close-to-final draft of my ISRU report. I'm tight on time, but I've still got room (9 hours) to edit - the final draft deadline is 11:55 tonight.

    Mission Background:

    Final Online Project – due 11:55 PM EST, July 4th, 2008

    Identify (3) system concepts that meet guidelines and requirements for your designated focus areas in your team. These system concepts should span various levels of technology utilization and system configurations to meet the functional needs as defined by your mission team.
    Describe the differences in capabilities afforded by the differing systems concepts in meeting mission requirements.
    Compare and contrast required levels of technology, system mass, volume, energy requirements, etc.
    Identify the system concept that you feel is best for meeting your mission goals understanding that cost, technology, risk, and system mass must all be minimized to the maximum extent to assure viability.


    Suggested outline:


    Mission
    focus area (page 1)
    • Team responsibility description
    • Focus area description

    • Focus area mission requirements


    System Concept One, Two, Three (pages 2, 3, 4)

    • Graphic

    • Mass and system properties (metric units)

    • Enabling technologies

    • Performance capabilities

    • How requirements are satisfied


    System Concept recommendations (page 5)


    • Comparison of system concepts (system properties, technology assumptions,
    objective satisfaction)
    • Recommendation and justification


    Citations (page 6)

    --------------------------------------------------------------------------

    Mission Focus

    The responsibility of the “Living There” team, at its core, is to design shelter, life-support, and manufacturing systems that will keep the astronauts on Mars alive in relative comfort for the specified time, allow them to perform experiments and fulfill mission requirements, and return home safely. It is also the team’s responsibility that the structures and components have extensive redundancy, survivability, failure tolerance, and field-serviceability to withstand threats beyond ideal parameters.

    My area of focus area within the “Living There” team is in-situ resource utilization (“ISRU”). The point of ISRU is to allow astronauts to use indigenous Martian resources to produce fuel, oxygen, water, building materials, and other necessities of life. This will reduce the size, mass, and complexity of materials that will need to be launched from Earth. In fact, a single kilogram of mass made through ISRU processes on the surface of Mars eliminates five kilograms of mass that would need to be propelled from Low-Earth-Orbit, and 85 kilograms launched from the Earth itself! To remain mission-viable, ISRU technologies and processes must reduce cost, minimize weight, maximize output and efficiency, increase durability, and remain small in stowage. In addition, ISRU design must be simple and provide the mission-critical resources the astronauts need without fail.

    The ISRU design itself must work autonomously long before the arrival of humans. In fact, the system’s ability to start up and remain running for an extended period of time – 600 days or more – is mission-critical. Above all, fuel – liquid oxygen (“LOX”) and another liquid propellant (methane, ethylene, etc) – must be produced for the return vehicle and constitutes a human mission go/no-go. If the Mars Ascent Vehicle (MAV) tanks are not full before the astronauts arrive, they cannot return home in the event of an abort-to-surface or later surface emergency, and the mission is doomed before it even starts.

    In addition to making fuel, water and breathable oxygen must be cached (both by-products of the fuel-making reactions) to serve as a backup should primary life-support resources fail. The system must survive unforeseen threats, meet mission goals, and recycle/reuse the greatest amount of resultant products as possible, maintaining a renewable, semi-sustaining closed-loop system – waste and squander is not an option. After mission completion, the system must be able to remain in a dormant state to be restarted should another team ever return.

    Further down the totem pole of ISRU criticality, fertilizer for plants could be produced from the soil with relatively simple reactions if nitrogen and phosphates are present, plants could be grown in the soil itself if the substrate supports it, and useful materials could be made if the geological composition of the Martian soil is suitable.

    In my paper, I will focus on three ISRU systems for making MAV fuel. They are: the Sabatier reaction, the “Reverse Water-Gas Shift” (RWGS) reaction piggy-backing with the Sabatier reaction, and RWGS alone coupled with an ethylene-producing reaction. I will also discuss, in brief, cached oxygen, water, and other useful byproducts produced by the various reactions.

    Systems

    To begin, the Sabatier reaction. This reaction appears most often in Mars ISRU literature, and is one of the most mature options technology-wise. The basic reaction is:

    CO2 (carbon dioxide) + 4H2 (hydrogen) = CH4 (methane) + 2H2O (water)



    CO2 is gathered from the atmosphere; Mars’s atmosphere is 95% carbon dioxide. Hydrogen is introduced from imported stores from Earth, or if we’re very lucky, electrolyzed Martian water. Martian water is not a given, and hydrogen will most likely be imported. Thankfully, it is the lightest element known, so weight is not a problem. However, storage is, and more research will need to be devoted to keeping the hydrogen physically in the tank during transport and use. (Not only must it be kept cryogenic, the element is so small it seeps out of most containers through the “cracks” between molecules.) To extract the CO2, the atmosphere must be collected, filtered of dust, and pressurized to one atmosphere to be of use in the reaction. “Scrubbers” must clean out traces of hydrogen, nitrogen, and argon to purify the CO2. Thankfully, these “contaminants” are all useful – hydrogen in the reaction itself, and nitrogen and argon as buffer gases.

    The reaction vessel is surprisingly simple, a lightweight metal tube stuffed with nickel, ruthenium, or alumina catalyst (The latter two are more efficient, but more expensive). Once the reactants are introduced, the vessel is heated via electric heaters to 300-400° C and the reaction begins. However, once started, the reaction is exothermic (energy producing) and will sustain itself at 300-400° C. Products of the reaction are methane (CH4) and water. The methane is put into cryogenic storage, while the water is run through an electrolysis machine to break it into oxygen and hydrogen. The oxygen is also put in cryogenic storage, while the hydrogen is sloughed back into the reaction in a continuous loop.

    To quote the “Ares” pdf:

    “For each MAV mission, a plant is required to produce 20 metric tons (mt) of oxygen and methane propellants at a 3.5 to 1 ratio: Each plant must produce 5.8 mt of methane and 20.2 mt of oxygen. Further, the system is required to produce 23.2 mt of water, 4.5 mt of breathing oxygen, and 3.9 mt of nitrogen/argon buffers….”

    In the Sabetier process, for each metric ton (mt) of imported hydrogen that is reacted, 2 mt of methane and 4.5 mt of water will be produced. Electrolysis of the water gives you 4 mt of oxygen and 0.5 mt of hydrogen; by recycling the hydrogen to the reaction, the net amount that must be imported is cut in half (that is, only a net .5 mt must be added for each cycle).

    As stated above, the MAV requires an oxygen:methane ratio of about 4:1. Unfortunately, the Sabatier reaction produces an oxygen:methane ratio of only 2:1. To prevent production of needless methane (the extra oxygen would simply be cached), a second source of oxygen is needed.

    Thankfully, just as water can be electrolyzed into O2 and H2, so can carbon dioxide electrolysis convert CO2 into CO and O2 (2CO2 = 2CO + O2). The O2 would be harvested, and the CO could be vented as waste, used as fuel, or incorporated into manufacturing (see below). The process is still under development, unlike the centuries-old processes of Sabatier and water electrolysis, and uses zirconia-based cells heated to 900°C. This system has several significant disadvantages. First, the high operating temperature requires ceramics, since metal catalysts would clog quickly. Secondly, the ceramic catalysts must be very thin to work efficiently. Together, this produces a system that is uniquely vulnerable to thermal/physical shock, and any crack in the zirconia cells results in unacceptable contamination of the O2 product with CO2 or CO (carbon monoxide!). A better alternative is molten carbonate electrolytes. Their operating temperature (500 - 700 ºC) is lower, which significantly reduces power demand. Furthermore, the process is very similar to molten carbonate fuel cells, a mature technology widely used in high-volume systems.

    Operating over a 15-month period, the system would produce all the LOX and methane needed for the MAV, and then divert excess water and O2 into storage. Excess O2 produced by CO2 electrolysis would also be put in storage.



    Total proposed mass of the system of the system, as shown below, would be 4,802 kg.



    Total power is unknown, due to what I believe to be an error with the water electrolysis power requirement. I was able to find that the process needs 57 kilocalories per 18 grams of water (3.16 kcal/gram), but I could not figure out how to convert that into kWe.

    -------------------------

    A second, more elegant, option consists of an RWGS reaction piggy-backed with the Sabatier reaction. Before going into depth on that, however, the RWGS reaction itself must be defined. The RWGS process was discovered in the mid-1800’s. It is written as:

    CO2 + H2 = CO + H2O



    This reaction is mildly endothermic (Delta H= +9 kcal/mole), meaning it needs continuous energy to continue running, and will occur rapidly in the presence of an iron-chrome catalyst at temperatures of 400° C or greater. By itself, the reaction is only of moderate use to ISRU. Electrolyzing the water will recycle the hydrogen back into the reaction in a closed loop while releasing O2 as product and CO as waste; this makes it a viable alternative to CO2 electrolysis with zirconia cells.

    However, something amazing occurs when the reaction is piggy-backed with Sabatier. RWGS is endothermic, while Sabatier is exothermic. Since both run at about the same temperature, if a Sabatier reaction vessel is wrapped around a RWGS reaction cylinder, the heat produced by the Sabatier reaction will drive the RWGS reaction in a self-sustaining cycle that requires no input power beyond the initial activation energy. Furthermore, if the
    RWGS and Sabatier reactions operate at a 2:1 speed ratio (2CO2 + 2H2 = 2CO + 2H2O : CO2 + 4H2 = CH4 + 2H2O), the net result of reactants and products is:

    3CO2 + 6H2 = CH4 + 4H2O + 2CO.
    Delta H = -22 kcal/mole (exothermic)

    This means that for each metric ton of imported hydrogen, 16 mt of oxygen and 4 mt of methane are produced, precisely matching the 4:1 ratio for the MAV engines and eliminating the need for CO2 electrolysis. The RWGS reactor is virtually identical to the Sabatier reactor, using only a different catalyst, and can use identical compressors and water electrolysis systems. Power consumption for the combination is nearly identical to the Sabatier system alone, since the RWGS system utilizes the Sabatier reaction’s heat, which otherwise would simply be vented as waste.

    Using the table above, the Sabatier mass is essentially duplicated to represent a RWGS reactor, adding about 504 kg to the ISRU system. The filters, compressors, electrolysis machines, etc. would also need to be enlarged slightly to satisfy the demands of the dual reaction, perhaps by about 22 kg each. However, eliminating the need for CO2 electrolysis saves an enormous amount of weight, reducing the total mass of the system to about 3,300 kg. A third RWGS reactor (504 kg, bumping the total to about 3,750 kg) might be used to provide a redundant source of water and/or oxygen, although continuous hydrogen would be needed to make water.

    ------------

    There is also a third option, and it, perhaps, is the most tantalizing of all. The standard RWGS reaction produces CO, which is normally considered a poisonous waste. However, when CO is combined with hydrogen, a substance called “ethylene” results.

    To get ethylene, however, we must start with the RWGS. The reaction is “overloaded” with
    H2 at a 3/1 ratio with CO2 to become:

    6H2
    + 2CO2 + = 2H2O + 4H2 + 2CO
    .

    The water is drawn off and electrolyzed; the O2 is made into LOX and the 2 units of hydrogen are recycled (already cutting the net imported hydrogen needed for future reactions down to 4 units instead of 6).

    Instead of recycling the 4 remaining units of hydrogen and venting the CO, however, the products are sent straight into an ethylene reactor. The ethylene reaction is:

    4H2 + 2CO = C2H4 + 2H2O
    Delta H = -49.4 kcal/mole (exothermic)

    The water is again drawn off and electrolyzed; the O2 is made into LOX and the hydrogen is sent back into the reaction, requiring only 2 units of net hydrogen to be added for each ensuing cycle.



    (This diagram still runs at the original 3/1 ratio as above (after all, 6/2 = 3/1); it has just been simplified to make it easier to understand. Yes, the difference freaked me out too.)

    What’s left is C2H4. What’s left could be termed “liquid gold.”

    First, since ethylene (C2H4), contains half the hydrogen of methane, (CH4), it means that the total amount of hydrogen needed to make the required 5.8 metric tons of non-LOX fuel is cut in half.

    Secondly, ethylene is actually a better fuel than methane. The specific impulse (a measure of momentum gain per unit of fuel, much like mpg in cars) of ethylene in rocket engines is about two seconds higher than methane. The energy density of liquid ethylene is 50% greater than liquid methane, meaning that you’d need 1.5 units of methane to equal the power of one unit of ethylene. This allows you to use smaller (and lighter) fuel tanks on MAVs or rovers while still getting the same amount of power.

    Under a pressure of one atmosphere, ethylene boils at -104° C, a much higher temperature than methane's boiling point of -183° C. The average temperature of Mars is −55 °C, meaning a lot less energy is needed to keep the stuff liquid. Under a few additional atmospheres of pressure, ethylene is essentially storable out in the open, while liquid methane on any part of Mars would still need cryogenic cooling. This reduces the amount of energy needed to cool the fuel – compared to a methane/oxygen system, the power load is cut in half. The smaller temperature difference between the fuel and the outside atmosphere also means that the tanks’ insulation can be thinner and lighter.

    Using ethylene for rocket fuel is just the beginning. It can be used as anesthetic, another thing you don’t have to import from Earth. It is used as a ripening agent for fruits and as a hormone to reduce the germinating time of seeds, allowing astronauts to grow more plants faster.

    Most importantly, however, ethylene forms the basis of the plastics industry that has revolutionized our world. It is the base component of polyethylene and numerous other plastics. A manufacturing plant can take this chemical and work it into films or fabrics to create clothing, large inflatable structures, insulation, or tires, to name a few. Ethylene can be inject-molded to make bottles, cups, tableware, and millions of other little widgets. (Plastic bins, lubricants, sealants, adhesives, tapes…. You name it.)

    I was not able to find mass for the system, but I think it’d be comparable to the RWGS/Sabatier combination. Cryogenic cooling would need less energy, so it might bump the mass of the system down to about 3,200 kg - 3,500 kg.

    -----------------------

    A fourth and final option for ISRU fuel production would be to combine all
    the options – A Sabatier/RWGS reaction(3CO2 + 6H2 = CH4 + 4H2O + 2CO) coupled to an ethylene reactor (4H2 + 2CO = C2H4 + 2H2O). An intermediate step (siphoning off the CH4) and a third water electrolysis machine would be needed between the two reactions to break the 4H2O into 4H2 and 2O2 and send the hydrogen on to the next reactor.

    Products from the entire system are water, O2, methane, and ethylene. The methane could be used as fuel while the ethylene became plastic feedstock.

    There are several limiting factors to this idea. One is complexity. Each tack-on adds another thing that could break. Having all these different processes going on at once – not to mention all the extra equipment needed to make plastic – might not be a good idea for a first mission. This setup might have to wait until a second, third, or fourth mission. The second limiting factor is weight. The Sabatier/RWGS vessel is relatively heavy, and the ethylene reactor would add still more weight. A third electrolysis machine for the intermediate filtering step would add even more weight and draw more power. The third limiting factor is hydrogen supplies. This process recycles far less hydrogen than any other scheme (a net total of 4 units of hydrogen per cycle is needed instead of 2), and might not be sustainable or feasible unless an indigenous source of Martian hydrogen is found (either by electrolyzing Mars water or sucking trace hydrogen from the air).



    System comparison and recommendations

    All of the systems described above – with exception of CO2 electrolysis – have been known and used in operations on Earth since the 1800’s. The challenge now is to shrink and lighten them so that they can be transported and used in space. All of them – with exception for #4 – all require 2 units of hydrogen per cycle, so there is not a large amount of comparison to be gained there.

    The Sabatier reaction is the most well-known and most mature of my three main options. The systems have been built, tested, and are relatively light weight. However, the system does not produce the proper O2:methane fuel ratio, forcing astronauts to bring along another oxygen-making device. The process of CO2 electrolysis itself is relatively new and zirconia cells are still under development. Alternatives to zirconia cells are currently still in prototype stages. RWGS provides oxygen, but it would need yet other source of hydrogen.

    Long-term hydrogen storage itself remains a problem, but it will remain an issue no matter what fuel-making design is finally agreed upon. Research is ongoing, and a solution could be found by 2020, depending on how much money and will is put behind it.

    Like the Sabatier reaction, RWGS has been around for quite a while. However, it is less mature in space-based applications. It has not received as much “press” as Sabatier strategies. However, when RWGS is combined with a Sabatier reaction, the result greatly outperforms the Sabatier/CO2 electrolysis system. “Risky” CO2 electrolysis is eliminated and replaced by two mature, energy-efficient reactions that produce fuel at the needed ratio. This would be my reaction-of-choice if it wasn’t for…

    RWGS with ethylene. Using this system is a moderate risk – RWGS has not been as exhaustively studied as Sabatier, and the ethylene reaction does not appear in as much ISRU literature – but I believe it is a calculated risk that is outweighed by the outstanding returns. Ethylene is simply a better fuel than methane, and it is much easier and lower-cost to store. Ethylene also has many more potential uses than methane, from anesthetic to plant hormone to plastic feedstock.

    In the end, I recommend the RWGS reaction coupled with an ethylene reaction, with the RWGS/Sabatier combination finishing as a close second.





    Sources:

    http://spot.colorado.edu/~meyertr/rwgs/rwgs.html (RWGS and ethylene reactions)

    http://www.clas.ufl.edu/jur/200109/p...er_canton.html (Sabatier)

    isdc2.xisp.net/~kmiller/isdc_archive/fileDownload.php/?link=fileSelect&file_id=19 –

    http://rtreport.ksc.nasa.gov/techrep...t/100/106.html (CO2 electrolysis)

    http://ares.jsc.nasa.gov/marsref/Mars3txt.pdf (ISRU information located on pages 101-105)

    http://nssdc.gsfc.nasa.gov/planetary/mars/marssurf.html (Sabatier, water/CO2 electrolysis)

    Carpe Navi: Because you never know when you'll get to go boating at government expense again.

  7. #7
    Administrator Honored Elder jeriddian's Avatar
    Join Date
    Jun 2006
    Location
    Midland, Texas
    Posts
    7,948
    A most excellent presentation, 'Chutes. I am impressed. I am tempted to let you try to solve some of the conundrums of my profession, for example, developing an effective vector for introduction of gene therapy modalities that can be targeted to specific organ systems without significant misdirection and at minimal risk of detrimental systemic effects elsewhere.
    "Say the Word"

  8. #8
    Registered User Exalted Member Fireand'chutes77's Avatar
    Join Date
    Jan 2005
    Location
    The Old Dominion
    Posts
    2,946
    Quote Originally Posted by jeriddian View Post
    ....developing an effective vector for introduction of gene therapy modalities that can be targeted to specific organ systems without significant misdirection and at minimal risk of detrimental systemic effects elsewhere.
    The most common "vectors" are modified viruses and bacteria, right?

    Hmmm... are there any specific chemical/genetic signatures that are unique to different organ systems? Can we engineer a vector that has a "seeker head" that locks on to just those signatures?

    EDIT: Well, I've turned the essay in. *Raises 4th of July glass of lemonade* Here's to NASA!
    Carpe Navi: Because you never know when you'll get to go boating at government expense again.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •