Quote from: Russel on 02/19/2018 12:53 pmI'm puzzled by the 180 tonne figure just used for the BFS. I'd have thought it required a lot, lot more. Back to the reality of initial scientific/exploratory missions. Its easiest to import hydrogen in the form of liquid methane and simply ISRU the oxygen.Another portable (and non cryogenic) form of hydrogen is common ammonia which is 17% hydrogen by mass and has a room temperature density of 0.73 tonne per m3.In terms of density, liquid methane is 105Kg of hydrogen per m3 and ammonia is 129Kg of hydrogen per m3. Plus it is a source of nitrogen.I'm sorry, I just don't see or support the argument for importing ammonia or liquid methane to the martian surface. This discussion is a distraction, IMHO.Yes, you can transport various gases there in stable forms. And if you do, you are taking many trips to the surface all the way from Earth to collect the necessary ingredients to return once. Until you send up ISRU equipment, you are stuck in this unsustainable and uneconomical paradigm.The necessary gasses are already on Mars in various forms. Identify the path for extracting each (the purpose of this thread), and send the required ISRU equipment instead on early missions.
I'm puzzled by the 180 tonne figure just used for the BFS. I'd have thought it required a lot, lot more. Back to the reality of initial scientific/exploratory missions. Its easiest to import hydrogen in the form of liquid methane and simply ISRU the oxygen.Another portable (and non cryogenic) form of hydrogen is common ammonia which is 17% hydrogen by mass and has a room temperature density of 0.73 tonne per m3.In terms of density, liquid methane is 105Kg of hydrogen per m3 and ammonia is 129Kg of hydrogen per m3. Plus it is a source of nitrogen.
Quote from: sghill on 02/19/2018 01:49 pmQuote from: Russel on 02/19/2018 12:53 pmI'm puzzled by the 180 tonne figure just used for the BFS. I'd have thought it required a lot, lot more. Back to the reality of initial scientific/exploratory missions. Its easiest to import hydrogen in the form of liquid methane and simply ISRU the oxygen.Another portable (and non cryogenic) form of hydrogen is common ammonia which is 17% hydrogen by mass and has a room temperature density of 0.73 tonne per m3.In terms of density, liquid methane is 105Kg of hydrogen per m3 and ammonia is 129Kg of hydrogen per m3. Plus it is a source of nitrogen.I'm sorry, I just don't see or support the argument for importing ammonia or liquid methane to the martian surface. This discussion is a distraction, IMHO.Yes, you can transport various gases there in stable forms. And if you do, you are taking many trips to the surface all the way from Earth to collect the necessary ingredients to return once. Until you send up ISRU equipment, you are stuck in this unsustainable and uneconomical paradigm.The necessary gasses are already on Mars in various forms. Identify the path for extracting each (the purpose of this thread), and send the required ISRU equipment instead on early missions.Curiously your illustration is of MOXIE, which creates Oxygen only. It doesn't generate Hydrogen. Getting ISRU Hydrogen is going to be costly (imported machinery, energy requirements etc) and I've yet to be convince that this really, actually is easier than simply importing Hydrogen.
Quote from: Russel on 07/24/2018 10:48 amQuote from: sghill on 02/19/2018 01:49 pmQuote from: Russel on 02/19/2018 12:53 pmI'm puzzled by the 180 tonne figure just used for the BFS. I'd have thought it required a lot, lot more. Back to the reality of initial scientific/exploratory missions. Its easiest to import hydrogen in the form of liquid methane and simply ISRU the oxygen.Another portable (and non cryogenic) form of hydrogen is common ammonia which is 17% hydrogen by mass and has a room temperature density of 0.73 tonne per m3.In terms of density, liquid methane is 105Kg of hydrogen per m3 and ammonia is 129Kg of hydrogen per m3. Plus it is a source of nitrogen.I'm sorry, I just don't see or support the argument for importing ammonia or liquid methane to the martian surface. This discussion is a distraction, IMHO.Yes, you can transport various gases there in stable forms. And if you do, you are taking many trips to the surface all the way from Earth to collect the necessary ingredients to return once. Until you send up ISRU equipment, you are stuck in this unsustainable and uneconomical paradigm.The necessary gasses are already on Mars in various forms. Identify the path for extracting each (the purpose of this thread), and send the required ISRU equipment instead on early missions.Curiously your illustration is of MOXIE, which creates Oxygen only. It doesn't generate Hydrogen. Getting ISRU Hydrogen is going to be costly (imported machinery, energy requirements etc) and I've yet to be convince that this really, actually is easier than simply importing Hydrogen.What are you talking about? The hydrogen comes from electrolysis of water. If the colonists have access to water, electricity, and a high school chemistry set, they can make as much hydrogen as they want.
Reading the thread I can't quite shake the idea people seem to think they are building a well by handIIRC in several parts of the US people get their water from individual boreholes. Pulling some numbers off the web gives figures around a 200-600 feet with an 8 inch diameter. Such boreholes can be drilled in less than 10 days. A quick check on eBay suggests these run 16HpThis suggests a borehole of < 32 feet is well within the SoA. Building a drilling rig that can do this would be a high energy task by space probe power levels, around 12Kw. You're also looking at quite a heavy package once the drill pipe is included. Obviously the shorter length helps and lowering the drill rate should reduce the Hp requirements. But that's the easy part
Are you saying here that BFS needs an external radiator when parked on the Martian surface?
I found an interesting thing on Exxon's website that might be a consideration for ISRU production of rocket fuel. Last year they announce a breakthrough in a strain of algae with some DNA mods that doubled bio fuel production. The details are outline here:https://news.exxonmobil.com/press-release/exxonmobil-and-synthetic-genomics-report-breakthrough-algae-biofuel-researchUsing sunlight and CO2, both of which are available on Mars, the have doubled the oil production algae can produce. The oil can be run through a traditional refinery. This might open the production of RP-1 on Mars creating another option for ISRU propellant production.From the article: “The major inputs for phototropic algae production are sunlight and carbon dioxide, two resources that are abundant, sustainable and free,” said Oliver Fetzer, Ph.D., chief executive officer at Synthetic Genomics.Exxon is ready to start scaling this technology up to 10,000 barrels a day: https://news.exxonmobil.com/press-release/exxonmobil-and-synthetic-genomics-algae-biofuels-program-targets-10000-barrels-day-202
<snip of algae greenhouse>No, not efficient enough. Pressurized windows are actually more expensive than solar panels.
Algae-based oil might be more valuable as a feedstock for plastics than as fuel, especially given that most rockets proposed for Mars are methalox-based.
Quote from: Robotbeat on 08/23/2018 02:48 pm<snip of algae greenhouse>No, not efficient enough. Pressurized windows are actually more expensive than solar panels.I have next to me a pressurised window that cost me $10/m^2, and is good for several years at >50PSI. It is a 2l cheap lemonade bottle.You might want to lay a UV protective/greenhouse layer of film over the top of this, but pressurised windows, while they can be expensive, can also be inexpensive.
Quote from: speedevil on 08/23/2018 04:04 pmYou might want to lay a UV protective/greenhouse layer of film over the top of this, but pressurised windows, while they can be expensive, can also be inexpensive.Photovoltaics are STILL cheaper. Solar cells, about 20-25% efficient (versus like 1 to 5% for photosynthesis), are about 10.5 cents per watt right now on the spot market. So that's $25 per square meter, or normalized to the efficiency of your PET bottle photosynthesis, about $1-5 per square meter. (solar cells also need a thin protective film and mounting, but comparable to yours... and still simpler since maintenance is about zero.).
You might want to lay a UV protective/greenhouse layer of film over the top of this, but pressurised windows, while they can be expensive, can also be inexpensive.
Quote from: Robotbeat on 08/25/2018 05:21 amQuote from: speedevil on 08/23/2018 04:04 pmYou might want to lay a UV protective/greenhouse layer of film over the top of this, but pressurised windows, while they can be expensive, can also be inexpensive.Photovoltaics are STILL cheaper. Solar cells, about 20-25% efficient (versus like 1 to 5% for photosynthesis), are about 10.5 cents per watt right now on the spot market. So that's $25 per square meter, or normalized to the efficiency of your PET bottle photosynthesis, about $1-5 per square meter. (solar cells also need a thin protective film and mounting, but comparable to yours... and still simpler since maintenance is about zero.).You can only normalise to the efficiency of PV vs photosynthesis, if you are not going to use that power for a greenhouse, and are not growing some sort of edible algae. In principle, biosythetic oil could be part of the diet.But interesting if you're not using it for this.
Much more efficient to convert the electricity into methane (and ammonia, using hydrogen and nitrogen) and then feeding that to single-celled bacteria to produce protein.