TripD/etc,What is the purpose of the volume you are creating? Is it just living space?Something that was just brought up again in relation to power demand, and I might as well repeat an observation I made earlier about habitat construction:- The main industrial activity for your settlement, for a long, long time, will be ISRU propellant production. Hence how you get water will be the biggest predictor of the type of equipment, skills, material, etc that you will have available.- OTOH, the biggest requirement for pressurised volume will be agriculture. Many many times the size of your living space.- Hence your living space will be a small side-area off of your agricultural volume, which will be built using whatever equipment you need to get water, and whatever materials are surplus/waste from that process.[Even once you've expanded to the point where specialist housing construction makes sense, this early habitation will still set the standard for later construction, because it will have set the demand for parts/equipment for the first on-Mars manufacturing, and hence be the lowest cost systems available for later development. The size of the Channel Tunnel was ultimately set by the width of the arses of Napoleon's horses, so the joke goes.]People seem to picture everything in reverse order. First your big living area. Then some small ag spaces off the side, tucked out of the way. Then, as an afterthought, somewhere completely out-of-sight, a little module that manufactures propellant.Ludus, at least, puts the water-source first. But he then focuses on living space. Whereas Ag-volume is next, by an order of magnitude.
Ludus, the Amalfi-like giant ice cave is a beautiful concept and it reminds me of Zygote in the Mars trilogy Was that your inspiration?
A village-size habitat that is mostly underground, with distributed hydroponic farming based mostly on artificial light and an energy source that is mostly distributed nuclear (https://www.nasa.gov/directorates/spacetech/kilopower)
What is the purpose of the volume you are creating? Is it just living space?
Quote from: Lumina on 01/14/2018 06:07 pmA village-size habitat that is mostly underground, with distributed hydroponic farming based mostly on artificial light and an energy source that is mostly distributed nuclear (https://www.nasa.gov/directorates/spacetech/kilopower) Sounds great. However, single Kilopower reactor is only 1 to 10 KWe. How many MWe would be required to lets say, have enough artificial light to reliably feed a dozen people on Mars and also fill up a BFS with ISRU propellant? That seems like a lot of Kilopowers..
Well said. Or as Gwynne said at Stanford:Quote from: Fireside Chat with SpaceX President Gwynne Shotwell, October 11, 2017I don't think it's an accident that Elon started the Boring Company, tunnels will be very important in the first steps of living on Mars, before we build domes and terraform.In other words, it won't be just domes, and it won't be just tunnels. It will be both. Domes for growing food. Tunnels for living space that's shielded from space radiation.
I don't think it's an accident that Elon started the Boring Company, tunnels will be very important in the first steps of living on Mars, before we build domes and terraform.
I've read upthread, multiple times, that ISRU propellant energy costs will dominate the power budget.I even probably wrote the same thing.Agriculture, if you need to illuminate large patches of ground, is also MWatt-scale. (Ask any basement pot grower)Earth insolation is 1 kWatt/m2, and I wonder how many m2 are required to feed a person year round.
http://forum.nasaspaceflight.com/index.php?topic=43608.msg1727087#msg1727087 refers to a process which enables you to go from methane -> food at 25% efficiency which might in principle supplement diet and reduce power usage on farming, as it's around 10* as efficient but not very palatable.
Quote from: meekGee on 01/15/2018 02:38 amI've read upthread, multiple times, that ISRU propellant energy costs will dominate the power budget.I even probably wrote the same thing.Agriculture, if you need to illuminate large patches of ground, is also MWatt-scale. (Ask any basement pot grower)Earth insolation is 1 kWatt/m2, and I wonder how many m2 are required to feed a person year round.Plants don't require nearly that amount, for several reasons. (an acre-kilowatt)http://forum.nasaspaceflight.com/index.php?topic=43608.msg1766097#msg1766097 - potatos can feed one person enough calories to live on about 3kW.6kW gets you assorted other plants in the diet quite freely, and 8kW lets you add a bit of meat. (pigs can convert calories in to pork at ~9%). (all average) ISRU, as a comparison, to generate a couple of hundred tons of methane you need about (average) 600kW for a year.So, if you can return 100 people to earth, that's 6kW*year-per person, or about the same for growing a mixed vegetarian diet.http://forum.nasaspaceflight.com/index.php?topic=43608.msg1727087#msg1727087 refers to a process which enables you to go from methane -> food at 25% efficiency which might in principle supplement diet and reduce power usage on farming, as it's around 10* as efficient but not very palatable.
Quote from: Dave G on 01/13/2018 05:23 pmWell said. Or as Gwynne said at Stanford:Quote from: Fireside Chat with SpaceX President Gwynne Shotwell, October 11, 2017I don't think it's an accident that Elon started the Boring Company, tunnels will be very important in the first steps of living on Mars, before we build domes and terraform.In other words, it won't be just domes, and it won't be just tunnels. It will be both. Domes for growing food. Tunnels for living space that's shielded from space radiation.What she said makes it quite clear that tunnels are what we will see in the first years of Mars habitats. "Before we build domes and terraform" distinctly makes domes sound as a far-off thing. ...
the agriculture producing the food, and it adds up to near what that BFS needs, per person.
And what about the machines the person operates? The construction equipment, driving around, excavating soil and ice, processing soil...
Quote from: meekGee on 01/15/2018 03:46 amthe agriculture producing the food, and it adds up to near what that BFS needs, per person.Not quite. Remember that for each crew ship there will be several cargo ships which all need to go back to Earth too. (10:1 was thrown around in the early days.)Quote from: meekGee on 01/15/2018 03:46 amAnd what about the machines the person operates? The construction equipment, driving around, excavating soil and ice, processing soil...I was including that in the "cost of propellant production", not just the propellant manufacture itself. Everything that goes into feeding the beast. That's also what I meant about it dictating the resources you will have available for building pressurised volume. If you need to scrape the regolith, you'll have regolith diggers and haulers, and way too much waste regolith. So cut'n'cover seems obvious. If you are digging underground, you will live in those spaces, because rock-cutters are your main equipment and mines are your primary excavated volume. If you are melting through lightly buried glaciers, that dominates your equipment/volume/thinking. And so on.And I accept that, eventually, broader industry will replace propellant as the main energy users. But the pattern will remain. The largest activity will be industry. The largest pressurised area and second largest power and materials user will be agriculture. The actual living area will be a small add-on, by comparison.
What is the energy budget on earth? I think industry is dominant here (but I'm guessing)[1]... this supports the thesis that it will be that way on Mars too.1 - support factoid, supposedly it takes as much energy to make a car as it does to fuel it for an average lifetime. No cite, just a factoid I remember...
Quote from: Lar on 01/19/2018 03:47 amWhat is the energy budget on earth? I think industry is dominant here (but I'm guessing)[1]... this supports the thesis that it will be that way on Mars too.1 - support factoid, supposedly it takes as much energy to make a car as it does to fuel it for an average lifetime. No cite, just a factoid I remember...Your factoid is off by about a factor of 4. If the car lasts 100,000 miles (and they often last much longer), then the embodied energy is only about 22% of the total energy:http://energyskeptic.com/2015/how-much-energy-does-it-take-to-make-a-car-by-david-fridley-lbl/
So even under the numbers you quote (which I think are a bit optimistic), food at least competes with propellant ISRU.Which would make sense. A person at rest is a constant 100 Watt consumer I believe. Factor in the efficiency of metabolism, and the fact that you're not always at rest, and then the efficiency of the agriculture producing the food, and it adds up to near what that BFS needs, per person.