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OK let's assume an artificial 1G rocket ship is a slam dunk, easy-to-do, no-risk kind of enterprise...and focus on your other claims.
Space X certainly don't reveal all the research they are doing until they've done it. Is there anything about Musk's career that suggests that he isn't pretty thorough when it comes to developing a product? Not to my mind. He may stray into areas that prove more complex than might have been supposed e.g. strapping 3 rockets together to make the F9H but generally he has a good record I would say. I am sure Space X have already started looking at ISRU in some detail.
Personally, I don't think making propellant will be that difficult, given the extent of Space X's cargo delivery (800 tonnes). Where exactly do you think the difficulty will lie? I can see only one: water sourcing. But there are a number of approaches to that.
As an alternative, what about the hydrogen solution (as originally proposed by Zubrin)...why not take the hydrogen with the BFR cargo flights? If my calculations are right, to make 1000 tonnes of propellant/fuel you need about 68 tonnes of hydrogen (hydrogen being about 25% of methane by weight and methane being about 27% of the propellant/fuel total). If Space X take the hydrogen do they really need the water? The carbon and the oxygen can come from concentrated CO2, from the atmosphere. They maybe need to produce the remaining gases at about 2 tonnes per sol or about 81 kgs per annum/1.35kg per minute or 22 grams per second. Is that impossbile?
I wouldn't be surprised if Space X take hydrogen with them as a failsafe against failure to find the predicted water resources.
Trying to develop ships that take humans to Jupiter would be a brake on progress at this stage. If we create a human settlement on Mars we can then hop to Ceres and from there to Jupiter, if we wish, using the BFR/BFS technology. Musk has made that point. Why spend tens of billions on developing an NTR when you already have the solution?
My understanding is the BFR-BFS system would be able to deliver at least 150 tonnes a time to the Moon, given that amount can be delivered to Mars.
So to deal with your three alleged weak points:
1) "The lack of artificial gravity".
I don't myself think this is a serious weak point. Your characterisation of astronauts being reduced to zombie status is not very helpful. Polyakov was walking with help immediately after leaving his capsule (then without aid, a few hours later) and that was after 437 days in zero G. His bone loss over that period was 7%. Remarkably low. Clearly any crew member selected to be a pioneer to Mars needs to be in that sort of range and you can test for that before they head for Mars. And don't forget the mission took place in 1995. I would be surprised if space medicine hasn't moved on if only marginally. Incidentally I don't think it's correct to say astronauts suffer from osteoporosis. My research suggests osteopenia is the correct term.
2) "The tail-landing which needs a perfect knowledge of the stability of the terrain"
Well we know tail landing can be done on Earth (though only of a booster stage so far, not the equivalent of a BFS). The amount of data gathered by Mars satellites and rovers is incredibly detailed. NASA has identified hard surface, low dust areas on Mars suited to landing. Cargo flights will land two years in advance of the human flights. There will be every opportunity for rovers to investigate the site and perhaps lay down a smooth landing sheet marked with an X.
3) "The ISRU which needs a prefect knowledge of the alleged buried glaciers in equatorial latitudes"
Well as discussed above...I am not sure that identifying buried glaciers is necessary to ensure propellant production. Water can be sourced from ice-rich regolith and also the atmosphere. Or hydrogen can be taken separately to be combined with carbon for methane or oxygen for water, CO2 having been extracted from the atmosphere.
louis wrote:It sounded like you were referencing more the negative health effects of zero/micro-gravity, rather than the challenge of re-entry at Mars transfer velocities, since you were talking of the necessity of spinning the ship during transit to avoid a dead crew...
I referred both the issues: the reentry is the more lethal, but even with an orbit-orbit ship I prefer artificial gravity because I would like to have an healthy crew to explore an unknown planet, rather than a crew of almost seek zombie-walking people with osteoporosis, anemia, impaired vision and muscular hypotrophy.
louis wrote:You want a spinning ship that then hits the Earth's atmosphere at such a hyperspeed, returning from Mars? Doesn't sound like a good idea to me.
You can find a way to pair two ships and spinning them, then separate and de-spin them before entry. But my preference lies with a NTR orbit-to-orbit spaceship, able to spin during coasting, that do all propulsive maneuvers. If we find a way to develop some kind of mini-magnetosphere that may shield even from GCR - there are many interesting researches on the issue - we will have a ship that can bring us almost every were in the solar system, from Mercury to the moons of Jupiter.
louis wrote:I am not suggesting we ignore the issue of high G re-entry. Musk is clearly aware of the problem...
https://www.youtube.com/watch?v=2AaTfQcte8U
He doesn't spell out in detail what the solution is but it appears to be a combination of high performance heat shield and propulsive landing. Space X appears to think they can keep G forces down to 2-3 on return to Earth, which the crew should be able to cope with.
In a previous post GW has answered this topic far better than I could do.
Anyway, Musk is far from going to Mars, because it will pass many years before he will have a reliable ISRU-device, able to produce 1100 metric tons of LOX-LCH4 (I still don't know if the SpaceX guys have just started the R & D for the ISRU).
Probably, in waiting for the ISRU-device, the BFR will be used to go to the Moon - it has enough delta-V to do it, after refueling in elliptical orbit - where the transfer time is too short to have microgravity health problems. It can deliver 20-30 tons of stuff on the Moon surface every mission, that can be used to build a Moon-base.So, to recap, IMHO, SpaceX Mars Mission has three main week-points:
1) the lack of artificial gravity
2) the tail-landing which needs a perfect knowledge of the stability of the terrain
3) the ISRU which needs a prefect knowledge of the alleged buried glaciers in equatorial latitudes
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Take water as there is no hydrogen boiloff issue to contend with and you are guarenteed to be able to make fuel for the return which leaves just the 2 issues to resolve. Evebn taking along half og the water spread out in the 2 bfr would allow for a quicker creation of fuel even if only half as much water can be found where we land.
While the tower of pisa is not a rocket it does illustrate how mass on a soft surface will give and if a rocket heat does melt the underlying surface ice then we will topple over. A wide base leg to hieght ratio is required to compensate for the landing with large landing pads to distribute that mass. Now down to just 1...
Artifical gravity to what level is needed as we are not doing the experiment in space, where we can vary the amount to be able to tell if we can be safe with a mars, lunar of some value that is higher than either of these to guarentee healthy crew members on return to earth. So do the work to find out in order to resolve the issues to zero.....
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I think Musk is going to surprise people with something like that - taking a lot of hydrogen or water or oxygen as part of the 800 tonnes delivered to Mars. I am coming to that view, from looking at how much the energy system takes up -that can't be more than 200 tonnes.
Emergency supplies (air and water) maybe 50 tonnes. You've still got 550 tonnes spare. Maybe 50 tonnes of food supplies. OK that's now 500 tonnes left. Medical supplies? Can that be more than 10 tonnes? I don't think so. 490 left. What else? I am struggling to think, but let's assume it's a 100 tonnes of stuff I forgot, that's still 390 tonnes left and that could mean hydrogen, or water or whatever to aid propellant production.
Take water as there is no hydrogen boiloff issue to contend with and you are guarenteed to be able to make fuel for the return which leaves just the 2 issues to resolve. Evebn taking along half og the water spread out in the 2 bfr would allow for a quicker creation of fuel even if only half as much water can be found where we land.
While the tower of pisa is not a rocket it does illustrate how mass on a soft surface will give and if a rocket heat does melt the underlying surface ice then we will topple over. A wide base leg to hieght ratio is required to compensate for the landing with large landing pads to distribute that mass. Now down to just 1...
Artifical gravity to what level is needed as we are not doing the experiment in space, where we can vary the amount to be able to tell if we can be safe with a mars, lunar of some value that is higher than either of these to guarentee healthy crew members on return to earth. So do the work to find out in order to resolve the issues to zero.....
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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OK let's assume an artificial 1G rocket ship is a slam dunk, easy-to-do, no-risk kind of enterprise...and focus on your other claims.
Nobody else here is claiming that anything about this mission is easy. Anyone waving around a magic wand saying that they've solved all the problems is immediately suspect. Everyone else is claiming that 0g to any substantial level of gravity above that is pretty rough on the crew without a rigorous exercise program and properly designed seating arrangement. Crews that return to Earth aren't expected to do much except recover and attend media events. It's a different story on Mars. Alternating between laying down in bed and puking because your eyes tell you one thing and your inner ears tell you another is not an option.
Space X certainly don't reveal all the research they are doing until they've done it. Is there anything about Musk's career that suggests that he isn't pretty thorough when it comes to developing a product? Not to my mind. He may stray into areas that prove more complex than might have been supposed e.g. strapping 3 rockets together to make the F9H but generally he has a good record I would say. I am sure Space X have already started looking at ISRU in some detail.
In order to do the mission they say they want to do, they need to demonstrate a plant with the capacity to produce enough propellant to refuel BFS in some reasonable amount of time. NASA and their contractors still haven't figured this out and they've been working on the problem long before SpaceX ever existed. Maybe they're just lazy or not very bright, but I kinda doubt it. Meanwhile, the Proton OnSite M400 O2/H2 PEM fuel cell that can supply enough propellant is a commercial product that anyone with enough money can purchase. The state of development for LOX/LH2 technologies that split water is far beyond LOX/LCH4.
Personally, I don't think making propellant will be that difficult, given the extent of Space X's cargo delivery (800 tonnes). Where exactly do you think the difficulty will lie? I can see only one: water sourcing. But there are a number of approaches to that.
Do you design CH4 production plants that use CO2 in dusty deserts and sea water? If so, then why not show everyone else how it's done?
I'm a lot more concerned about running dusty CO2 through a ceramic with a temperature of around 1,000C and plating out the cell than I am about obtaining water, presuming the claim of 1 quart of water per cubic foot of regolith is true. If the claim is not true, then the entire process quickly becomes far more problematic, no matter what propellants are selected.
As an alternative, what about the hydrogen solution (as originally proposed by Zubrin)...why not take the hydrogen with the BFR cargo flights? If my calculations are right, to make 1000 tonnes of propellant/fuel you need about 68 tonnes of hydrogen (hydrogen being about 25% of methane by weight and methane being about 27% of the propellant/fuel total). If Space X take the hydrogen do they really need the water? The carbon and the oxygen can come from concentrated CO2, from the atmosphere. They maybe need to produce the remaining gases at about 2 tonnes per sol or about 81 kgs per annum/1.35kg per minute or 22 grams per second. Is that impossbile?
Bringing LH2 from Earth is a prudent backup plan, at least for the first missions, but then you're back to storing tons LH2. A 100nm thick Reduced Graphene Oxide bi-layer coating the storage tanks is virtually impenetrable to O2, H2, CH4, and most other liquid rocket propellants. RGO bi-layers solves embrittlement and oxidation problems because the propellant never touches the composite structure. There's no substantial change in mass, so coat the entire thing, inside and out, just to be sure. If we're back to storing LH2, we come back to my point about using LCH4 vs LH2. LH2 provides a substantial performance improvement, the fuel it's light, and it requires a single and presently available technology set for ISPP. The tanks are not substantially bigger for equivalent performance. If IVF is incorporated, the total tankage volume will be very comparable.
I wouldn't be surprised if Space X take hydrogen with them as a failsafe against failure to find the predicted water resources.
It’s worth considering. The use of H2O may be somewhat problematic since 9kg of water are required to get 1kg of H2 in an ideal case. That means 243t of H2O would be required to obtain the 27t of H2 for LOX/LCH4. I think I’d rather deal with storing 27t of LH2, considering the mass differential. We’re going to find out how well SOXE works on Mars when the 2020 rover arrives. If it works well, then great. We have our LOX solution for Mars and LOX/LCH4 becomes a lot more realistic. If it doesn’t work or the filter clogs, then this could be problematic.
Trying to develop ships that take humans to Jupiter would be a brake on progress at this stage. If we create a human settlement on Mars we can then hop to Ceres and from there to Jupiter, if we wish, using the BFR/BFS technology. Musk has made that point. Why spend tens of billions on developing an NTR when you already have the solution?
This is another straw man argument. If, for whatever reason, BFS can’t land on Mars and needs to come back to Earth, then the ability to bring the crew back in good physical condition becomes a requirement. In that case, they’re in space for 2 years, not 3 months. I’ve no idea why we’re even talking about NTR now that we have X3. NTR does not solve any human habitation requirement issues. It’s still a minimum of 3 months of microgravity.
My understanding is the BFR-BFS system would be able to deliver at least 150 tonnes a time to the Moon, given that amount can be delivered to Mars.
This remains untested. The rockets being landed are just about empty when they land. There’s no heavy payload up top to support on a column of thrust. This could easily be tested with a Falcon booster and a dummy payload simulator.
So to deal with your three alleged weak points:
1) "The lack of artificial gravity".
I don't myself think this is a serious weak point. Your characterisation of astronauts being reduced to zombie status is not very helpful. Polyakov was walking with help immediately after leaving his capsule (then without aid, a few hours later) and that was after 437 days in zero G. His bone loss over that period was 7%. Remarkably low. Clearly any crew member selected to be a pioneer to Mars needs to be in that sort of range and you can test for that before they head for Mars. And don't forget the mission took place in 1995. I would be surprised if space medicine hasn't moved on if only marginally. Incidentally I don't think it's correct to say astronauts suffer from osteoporosis. My research suggests osteopenia is the correct term.
All the statements about your thoughts and beliefs have already been tested. Polyakov is a sample size of 1. In statistics, a sample size of 1 means nothing whatsoever. It’s a data point. That’s it. You can use whatever terminology you want, but the bone mass of astronauts can degrade by as much as 1% per month. That’s results from real testing conducted by NASA, not suppositions or personal beliefs.
2) "The tail-landing which needs a perfect knowledge of the stability of the terrain"
Well we know tail landing can be done on Earth (though only of a booster stage so far, not the equivalent of a BFS). The amount of data gathered by Mars satellites and rovers is incredibly detailed. NASA has identified hard surface, low dust areas on Mars suited to landing. Cargo flights will land two years in advance of the human flights. There will be every opportunity for rovers to investigate the site and perhaps lay down a smooth landing sheet marked with an X.
Landings of full laden C-130’s are only permitted after an Airman checks the soil compaction with a hand probe to ensure that the Herc won’t sink, flip, and explode when it lands. I’m less concerned with regolith compaction than I am with landing on uneven terrain or the fact that all tail sitters with narrow landing gear are inherently unstable. The limits need to be modeled and tested. A series of Falcon booster tests would go a long way towards quelling any bad feelings I have over this aspect of the flight. If the vehicle remains controllable with the payload mass simulator installed and can land on less than perfect terrain, I’ll withdraw this objection. A concrete block or steel ship deck is not a substitute for less than perfectly level ground.
3) "The ISRU which needs a prefect knowledge of the alleged buried glaciers in equatorial latitudes"
Well as discussed above...I am not sure that identifying buried glaciers is necessary to ensure propellant production. Water can be sourced from ice-rich regolith and also the atmosphere. Or hydrogen can be taken separately to be combined with carbon for methane or oxygen for water, CO2 having been extracted from the atmosphere.
This is another assertion that remains to be tested. A test mission that obtains cubic meter chunks of regolith is required to assure that there is indeed as much surface water as we think there is. We’ve only gone a few centimeters into the regolith. Is there more or less water slightly deeper than that? If we can locate blocks of ice to extract, then why not go directly after our best sources of water?
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Never mind excess water, if we are talking about hundreds of tonnes just take the methane and generate only the LOX on site. Then you don't need the methane reactor, nor the equipment to power it. Oxygen is more easily split from CO2, leaving CO which is vented, than it is from water. Much more simple and less to go wrong.
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If it's not abundantly clear yet, you don't plan for optimal scenarios. You plan for the worst case scenarios and work your way backwards. If everything functions correctly on a ship, then you don't need flotation devices, but they're still required on all ships.
A true ITV might require 3 BFS flights to construct. The payload volume, rather than mass, is the principle constraint. Thereafter, 1 BFS flight can load the ITV.
A true ITV has the following characteristics or features:
* will serve equally well as an orbital station by adding more modules
* capacity is upgradeable with more spinning wheels to hold more people and more solar cells for more power
* detachable habitation and engineering modules enable swapping of the engineering or habitation module, if required, for repairs or contingency use, such as transfer of the ITV-C's engineering module to the ITV-P for the return flight
* purpose built to provide artificial gravity and radiation protection (aluminum - well tested but not optimal, composite - fairly well tested and lighter than aluminum but degrades over time from exposure, or inflatable structures - least well tested but most promising at the moment, with non-structural BNNT fabric liners and PE water tanks for solar flare protection)
* minimizes fuel mass by using electric propulsion, so more of the delivered tonnage is useful payload (things that will go to the surface of Mars for the purposes of exploring and colonizing Mars)
* no artificial mass constraints imposed on rocket stages that demand low inert mass fractions (mass is not unlimited, but it doesn't have to go from the surface of the Earth to the surface of Mars and back again, a major advantage when the cost and complexity of a vehicle that can do that is considered)
* delta-V capability to abort to Earth (without refueling)
* delta-V capability to establish circular low orbits (without refueling)
* no requirement to refuel at Mars, but still could if desirable (Did I mention that there's no refueling until after you return to Earth?)
* ascent vehicle only has to make low orbit (reduces the mass of the propellants that must be sourced from Mars)
* ascent vehicle only has to bleed off 3.8km/s to land (reduces the structural mass of the vehicle and the mass of the propellants that must be shipped from Earth)
* heat shield mass and reusability of the descent vehicle (lower reentry velocities at Mars means a lighter heat shield can be used and the heat shield experiences less extreme heating during reentry, increasing the maintainability of the TPS)
* capability to use multiple types of descent vehicles (BFS for lots of passengers or heavy cargo, HIAD-equipped Cygnus for light cargo, escape pods)
None of the problems with going to Mars are made up problems. Giving the crew no other possible option except to execute a perfect reentry and landing on Mars (they obviously can't come back to Earth, either, since they're going too fast for Earth to be there when they get back) doesn't give me a warm fuzzy about the design characteristics of this BFS-only mission.
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OK let's assume an artificial 1G rocket ship is a slam dunk, easy-to-do, no-risk kind of enterprise...and focus on your other claims.
Space X certainly don't reveal all the research they are doing until they've done it. Is there anything about Musk's career that suggests that he isn't pretty thorough when it comes to developing a product? Not to my mind. He may stray into areas that prove more complex than might have been supposed e.g. strapping 3 rockets together to make the F9H but generally he has a good record I would say. I am sure Space X have already started looking at ISRU in some detail.
Personally, I don't think making propellant will be that difficult, given the extent of Space X's cargo delivery (800 tonnes). Where exactly do you think the difficulty will lie? I can see only one: water sourcing. But there are a number of approaches to that.
As an alternative, what about the hydrogen solution (as originally proposed by Zubrin)...why not take the hydrogen with the BFR cargo flights? If my calculations are right, to make 1000 tonnes of propellant/fuel you need about 68 tonnes of hydrogen (hydrogen being about 25% of methane by weight and methane being about 27% of the propellant/fuel total). If Space X take the hydrogen do they really need the water? The carbon and the oxygen can come from concentrated CO2, from the atmosphere. They maybe need to produce the remaining gases at about 2 tonnes per sol or about 81 kgs per annum/1.35kg per minute or 22 grams per second. Is that impossbile?
I wouldn't be surprised if Space X take hydrogen with them as a failsafe against failure to find the predicted water resources.
If you want to bring hydrogen from Earth, you have also to consider the boil-off losses. So you have to bring more hydrogen than you have calculated and this inevitably reduces the amount of payload you can deliver on Mars surface. Sure you can project and develop a new zero-boil-off cryocooler able to work either in the void or on Mars surface, but this takes years of R&D, and if it breaks down you surely lost the crew (take in mind that even Robert Zubrin didn't bet the lives of the astronauts on ISRU: in fact, he proposed to send an unmanned rocket and send the crewed one only WHEN and IF the refueling had been completed.)
Trying to develop ships that take humans to Jupiter would be a brake on progress at this stage. If we create a human settlement on Mars we can then hop to Ceres and from there to Jupiter, if we wish, using the BFR/BFS technology. Musk has made that point. Why spend tens of billions on developing an NTR when you already have the solution?
I'm not so sure that BFR will be the final solution for space exploration.
My understanding is the BFR-BFS system would be able to deliver at least 150 tonnes a time to the Moon, given that amount can be delivered to Mars.
The rocket equation says NO.
You cannot do a direct entry on the moon, using the atmospheric drag to kill the delta-V, like on Mars, and you have to do all the maneuvers propulsively.
The outward journey from LEO to Moon surface takes 5.9 km/s of delta-V and the inward journey from Moon surface to TEI takes 2.8 km/s. You enter from TEI in the Earth atmosphere, using the drag to slow down, but then you needs almost 1 km/s for a safe propulsive landing, so the total delta-V of the mission is 9.7 km/s.
The BFR has an empty mass of 85 ton, brings 1100 tons of LOX-LCH4, and its rockets have a vacuum exhaust velocity of 3.675 km/s. So without payload, the total delta-V of the BFR is almost 9.68 km/s (I've not take count that the sea-level exhaust velocity is less than the vacuum one).
So even going to the Moon without payload, the BFR will likely run out propellant during the final landing. You can mitigate this issue by refueling in an elliptical orbit, to spare 1.275 km/s for the TMI and have only 4.675 km/s of outward journey, but even in this case, you can land on the Moon almost 85 tons (that's also very good.)
Take in mind that an elliptic rendez-vous is difficult to perform and was never tested, but it's not impossible. So the BFR can go to the Moon, but is surely not optimized for this kind of mission, where a ship-plus-lander architecture would be better suited.
So to deal with your three alleged weak points:
1) "The lack of artificial gravity".
I don't myself think this is a serious weak point. Your characterisation of astronauts being reduced to zombie status is not very helpful. Polyakov was walking with help immediately after leaving his capsule (then without aid, a few hours later) and that was after 437 days in zero G. His bone loss over that period was 7%. Remarkably low. Clearly any crew member selected to be a pioneer to Mars needs to be in that sort of range and you can test for that before they head for Mars. And don't forget the mission took place in 1995. I would be surprised if space medicine hasn't moved on if only marginally. Incidentally I don't think it's correct to say astronauts suffer from osteoporosis. My research suggests osteopenia is the correct term.
According to NASA, the mean bone loss in microgravity is almost 1.5%/month, and you have from 8.5 to 6 months for the outward journey 8.5 months for the inward journey plus 18 months on Mars surface at 3.9 gee, where the bone loss might something between 0%/month in the better case scenario and 1.5%/month in the worst case scenario: it's unethical to bet on the skin of the astronauts, so, in absence of data, we are forced to consider the worst case scenario as true (I don't want to talk about the risk of kidney stones due high level of calcium in urine).
You can mitigate the bone loss using biphosphonate drugs, but then you have to deal with the frozen-bone syndrome, where bone calcium is almost normal, but bones broke suddenly because micro-fracture don't heal and bone trabeculae are not well oriented to cope with the loads.
I remember that Italian astronaut Samantha Cristoforetti, after spending 200 days on ISS, needed to take the shower sitting on a chair because she was unable to do it standing up. So she said in an interview.
Are you sure you want an astronaut in so poor physical condition to explore an alien planet?
2) "The tail-landing which needs a perfect knowledge of the stability of the terrain"
Well we know tail landing can be done on Earth (though only of a booster stage so far, not the equivalent of a BFS). The amount of data gathered by Mars satellites and rovers is incredibly detailed. NASA has identified hard surface, low dust areas on Mars suited to landing. Cargo flights will land two years in advance of the human flights. There will be every opportunity for rovers to investigate the site and perhaps lay down a smooth landing sheet marked with an X.
You cannot see from orbit if a terrain is good for landing and even an unmanned rover cannot predict if one leg of the BFR, in time, will ted to sink more than the others.
3) "The ISRU which needs a prefect knowledge of the alleged buried glaciers in equatorial latitudes"
Well as discussed above...I am not sure that identifying buried glaciers is necessary to ensure propellant production. Water can be sourced from ice-rich regolith and also the atmosphere. Or hydrogen can be taken separately to be combined with carbon for methane or oxygen for water, CO2 having been extracted from the atmosphere.
You have to process a huge amount of regolith with the right stuff: but to develop it you needs a perfect knowledge of the amount of water that the regolith has in the place you will land. So the issue is the same: you need a perfect knowledge of what you will find in your landing place.
The problem is that what we know now is not enough to bet human lives on it.
So if we really want to make a Mars mission in the next 10-15 years, we have to do it only with the technology we have now, and with all the propellant and the stuff we bring from Earth, and avoiding the risk we just know. So an orbit-to-orbit spinning ship using storable hypergolic propellant (NTO-MMH) and propellant depot sent in mars orbit with electric propulsion together with Mars landers.
In the next 20 years we can upgrade our orbit-to-orbit spaceship with solid core nuclear thermal propulsion and zero-boil-off cryocoolers for LH2, then with gas-core NTR.
Last edited by Quaoar (2018-06-25 09:42:42)
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If you want to bring hydrogen from Earth, you have also to consider the boil-off losses. So you have to bring more hydrogen than you have calculated and this inevitably reduces the amount of payload you can deliver on Mars surface. Sure you can project and develop a new zero-boil-off cryocooler able to work either in the void or on Mars surface, but this takes years of R&D, and if it breaks down you surely lost the crew (take in mind that even Robert Zubrin didn't bet the lives of the astronauts on ISRU: in fact, he proposed to send an unmanned rocket and send the crewed one only WHEN and IF the refueling had been completed.)
The boil off issue needs looking into. Boil off is allowed to reduce pressure. So I think it's more a question of determining what strength of pressure container would be required to prevent boil off. But if we do have to make allowance for that so be it. Perhaps you need to take 100 tonnes rather than 68 tonnes...
I'm not so sure that BFR will be the final solution for space exploration.
It definitely won't be the final word in space exploration. But I could see it being the workhouse of solar system exploration for the next 30 years.
The rocket equation says NO.
You cannot do a direct entry on the moon, using the atmospheric drag to kill the delta-V, like on Mars, and you have to do all the maneuvers propulsively.
The outward journey from LEO to Moon surface takes 5.9 km/s of delta-V and the inward journey from Moon surface to TEI takes 2.8 km/s. You enter from TEI in the Earth atmosphere, using the drag to slow down, but then you needs almost 1 km/s for a safe propulsive landing, so the total delta-V of the mission is 9.7 km/s.
The BFR has an empty mass of 85 ton, brings 1100 tons of LOX-LCH4, and its rockets have a vacuum exhaust velocity of 3.675 km/s. So without payload, the total delta-V of the BFR is almost 9.68 km/s (I've not take count that the sea-level exhaust velocity is less than the vacuum one).
So even going to the Moon without payload, the BFR will likely run out propellant during the final landing. You can mitigate this issue by refueling in an elliptical orbit, to spare 1 km/s for the TMI and have only 4.9 km/s of outward journey, but even in this case, you can land on the Moon almost 50 tons (that's quite good.)
Take in mind that an elliptic rendez-vous is difficult and was never tested, but it's not impossible. So the BFR can go to the Moon, but is surely not optimized for this kind of mission, where a ship-plus-lander architecture would be better suited.
Well if it's only 50 tonnes - more than your original estimate of 20-30 tonnes - it's still good. You could definitely build a Moon base with a few BFSs being landed on the Moon.
According to NASA, the mean bone loss in microgravity is almost 1.5%/month, and you have from 8.5 to 6 months for the outward journey 8.5 months for the inward journey plus 18 months on Mars surface at 3.9 gee, where the bone loss might something between 0%/month in the better case scenario and 1.5%/month in the worst case scenario: it's unethical to bet on the skin of the astronauts, so, in absence of data, we are forced to consider the worst case scenario as true (I don't want to talk about the risk of kidney stones due high level of calcium in urine).
You can mitigate the bone loss using biphosphonate drugs, but then you have to deal with the frozen-bone syndrome, where bone calcium is almost normal, but bones broke suddenly because micro-fracture don't heal and bone trabeculae are not well oriented to cope with the loads.
I remember that Italian astronaut Samantha Cristoforetti, after spending 200 days on ISS, needed to take the shower sitting on a chair because she was unable to do it standing up. So she said in an interview.
Are you sure you want an astronaut in so poor physical condition to explore an alien planet?
Your comments are very misleading, based probably on old data. Read this study:
https://onlinelibrary.wiley.com/doi/ful … /jbmr.1948
Here is a key quote:
"Coincident with the change from using iRED to ARED, the average monthly loss in aBMD decreased from roughly 1.0% (n = 24 iRED users) to 0.3% to 0.5% per month (n = 11 ARED users to‐date, unpublished NASA data)."
So the baseline is 1% per month and with the latest exercise regimes (some five years ago) we see a reduction to 0.3% to 0.5%. We know there are genetic variations in people's responses, so I think it is reasonable to take the 0.3% figure, since you will be able to test and select your crew. So with a 0.3% per month figure you would see a total 9% bone loss rate on a 30 month mission (and that is assuming the loss rate continued on Mars which is highly unlikely, especially if we use weighted suits). I think in reality a figure of around 6% is much more likely.
Sitting for your first shower after zero G flight is just a sensible precaution.
You cannot see from orbit if a terrain is good for landing and even an unmanned rover cannot predict if one leg of the BFR, in time, will ted to sink more than the others.
Are you really up to speed on what these satellites can do? - it's not just the visual spectrum...they use infrared, lasers, all sorts of techniques to assess the ground. They can in any case resolve images down to 10s cms.
You have to process a huge amount of regolith with the right stuff: but to develop it you needs a perfect knowledge of the amount of water that the regolith has in the place you will land. So the issue is the same: you need a perfect knowledge of what you will find in your landing place.
The problem is that what we know now is not enough to bet human lives on it.
Well I am sure Space X on not going to gamble on this.
On an 800 tonne mission you don't have to gamble. If you are getting consistent water signatures across the board from regolith in a particular area, it's going to be there, in the vicinity of your landing site. They can travel with several robot mining vehicles.
In a 5% water rich regolith area that would mean to get 900 tonnes of water you would have to dig up a minimum of about 18000 tonnes of water. Over a 450 sol mission, that would be 40 tonnes a sol - say 8 tonnes per hour over a working sol of 5 hours. That's 133 kgs per minute. Spread that over say three robot mining rovers, that would be 44 Kgs per minute. Sounds doable to me.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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The boil off issue needs looking into. Boil off is allowed to reduce pressure. So I think it's more a question of determining what strength of pressure container would be required to prevent boil off. But if we do have to make allowance for that so be it. Perhaps you need to take 100 tonnes rather than 68 tonnes...
Boil-off depends from heat leakage into the tank from the ambient and from the exothermic conversion from ortho-H2 to para-H2. Above the critical temperature of 33°K you cannot liquefying the vapor by compression, so you cannot have zero boil-off by only increasing the tank strength - otherwise you would be able to maintain liquid hydrogen at room temperature and you would probably win the Nobel Prize - but you need to actively cool your LH2 with a cryocooler: there are an interesting project of cryocooler for for the NTR-Copernicus, but it's designed to work in space, not on the surface of Mars. Anyway it's not impossible to build, but needs some year of R & D.
Well if it's only 50 tonnes - more than your original estimate of 20-30 tonnes - it's still good. You could definitely build a Moon base with a few BFSs being landed on the Moon.
I firstly calculate it using a less eccentric refueling orbit, then I used a more eccentric one, sparing 1.275 km/s of delta-V and lowering the TEI delta-V to 4.675 km/s. With this high-eccentric - but even more difficult - refueling orbit I calculate that the BFR could land 85 metric tons of payload on the Moon. That is very good to build a moon base. I think the Moon will be likely the first destination of the BFR in waiting for the ISRU-device.
Your comments are very misleading, based probably on old data. Read this study:
https://onlinelibrary.wiley.com/doi/ful … /jbmr.1948
Here is a key quote:
"Coincident with the change from using iRED to ARED, the average monthly loss in aBMD decreased from roughly 1.0% (n = 24 iRED users) to 0.3% to 0.5% per month (n = 11 ARED users to‐date, unpublished NASA data)."
So the baseline is 1% per month and with the latest exercise regimes (some five years ago) we see a reduction to 0.3% to 0.5%. We know there are genetic variations in people's responses, so I think it is reasonable to take the 0.3% figure, since you will be able to test and select your crew. So with a 0.3% per month figure you would see a total 9% bone loss rate on a 30 month mission (and that is assuming the loss rate continued on Mars which is highly unlikely, especially if we use weighted suits). I think in reality a figure of around 6% is much more likely.
Just a moment please. You have to read the whole article, not just quote the brute data as the word of God.
This study was performed on 8 astronauts using the ARED, 3 of them also taking biphsophonate, who are probably the 3 marks over the 0 in the plot, that have raised the mean. Without them, the mean is lower: almost 0.75%/month in the femur neck, and quite better in the lumbar spine. But if you look at the data from the Mir astronauts, who had neither ARED nor biphosphonate, you can see that there is also a huge amount of variability and some individual has no bone loss at all (just take in mind that the data where mainly obtained by DXA that is less reliable than QCT in eventuating the real bone strength).
So we can conclude that genetic variability plays an important role in microgravity bone loss, and that ARED may be useful to mitigate it. But 8 astronauts are a too little sample to assert definitive results and further studies are needed (that's almost what the authors said).
In a future we can probably identify the genetic pattern of people with microgravity-resistant bones, and use it as a selection criteria for the astronauts, but we cannot do it now. And, above all, you cannot extrapolate the data of a 8-people-sample to predict the effective bone loss of the astronauts in a Mars mission.
And please, consider also that the bone-loss is only one of the many issues of microgravity body damage (impair immune responsiveness, retinal and optic nerve damage, anemia, hearth hypotrophy...)
Are you really up to speed on what these satellites can do? - it's not just the visual spectrum...they use infrared, lasers, all sorts of techniques to assess the ground. They can in any case resolve images down to 10s cms.
So USAF guys are primitives because they still send a man to test the ground before landing a C-130.
Well I am sure Space X on not going to gamble on this.
On an 800 tonne mission you don't have to gamble. If you are getting consistent water signatures across the board from regolith in a particular area, it's going to be there, in the vicinity of your landing site. They can travel with several robot mining vehicles.
In a 5% water rich regolith area that would mean to get 900 tonnes of water you would have to dig up a minimum of about 18000 tonnes of water. Over a 450 sol mission, that would be 40 tonnes a sol - say 8 tonnes per hour over a working sol of 5 hours. That's 133 kgs per minute. Spread that over say three robot mining rovers, that would be 44 Kgs per minute. Sounds doable to me.
Data obtained from infrared spectroscopy that sees OH groups, that likely belong to water, but may also be part of other compounds. But assuming it's all water, you also have to know exactly how deep the water layer is, because you don't want to process a hundred and a hundred of square kilometers to make your return propellant.
Last edited by Quaoar (2018-06-26 00:56:31)
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Quaoar,
1. Yes, tank strength/ambient temperature would seem to be the issue. It sounds like a soluble problem to me but whether it's more efficient to simply take more hydrogen, and allow boil off, I don't know.
2. Well the data might necessarily be from a small sample, but it didn't agree with your alarmist narrative. I think if you combine crew selection (for genetically suitable types) with space medicine and exercise regimes you are going to manageable results. Remember as well this data is as far as I know prior to some more recent innovations that are being trialled involving low pressure surrounds for lower body exercise. Also, no doubt, space medicine continues to improve. I think achieve a Polyakov-style figure of 0.5% per month is definitely achievable but could probably be improved upon.
3. I think the NASA analysis of water content is more subtle than you suggest. They look at all sorts of data, combining geological analysis (e.g. recent crate impacts) with satellite data. Of course there can be no absolute guarantee of accuracy until you get there. Which perhaps argues for taking hydrogen feed with you.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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1. Yes, tank strength/ambient temperature would seem to be the issue. It sounds like a soluble problem to me but whether it's more efficient to simply take more hydrogen, and allow boil off, I don't know.
On Mars surface boil off would be much more than in space, so you probably need a good cryocooler, which imply a nuclear reactor, but you surely need a megawatt range nuclear reactor if you want to produce 1100 ton of propellant. So the cryocooler might be the best solution.
2. Well the data might necessarily be from a small sample, but it didn't agree with your alarmist narrative. I think if you combine crew selection (for genetically suitable types) with space medicine and exercise regimes you are going to manageable results. Remember as well this data is as far as I know prior to some more recent innovations that are being trialled involving low pressure surrounds for lower body exercise. Also, no doubt, space medicine continues to improve. I think achieve a Polyakov-style figure of 0.5% per month is definitely achievable but could probably be improved upon.
We still don't now what is the right genetic pattern. In the next fifty years we can also have space-compliant GM astronauts, who will be microgravity and cosmic-ray resistant. The problem is only about WHEN do you want to do your Mars mission.
If you want to do it in 2070, it may be OK. But if you want to do it in 2030-35, you have to realize that we still don't know many issues, so a correct precautionary principe might be to assume the worst-case scenario as true and to use the state of the art of the current technology to cope with it (read spinning ship).
It's a question of ethic: if you want to spare the money of a spinning ship, you have to delay your mission to 2050-60 and use these years to gain a better knowledge of the many microgravity diseases and how to cope with them.
3. I think the NASA analysis of water content is more subtle than you suggest. They look at all sorts of data, combining geological analysis (e.g. recent crate impacts) with satellite data. Of course there can be no absolute guarantee of accuracy until you get there. Which perhaps argues for taking hydrogen feed with you.
I never said there is no water: I think that there is water and probably we will find even some life form. I only said that you cannot bet on it until you have the certainty that water is really there. So for the first mission it's wiser to bring hydrogen from Earth, like also Zubrin had planned for his Mars Direct.
Last edited by Quaoar (2018-06-26 06:27:54)
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I would be most interested to see what sort of propellant production equipment Musk has in mind. It's not in his presentations. I therefore suspect he is banking on others to supply this equipment.
Whatever it is, it needs a good field trial on a place like Baffin Island or the Antarctic Dry Valleys. Should look like an equipment package mounted on a skid or skids. Something we can take to the field trial location, plumb up, and hit the "on" switch. Then step back for a couple of years and watch what happens.
We'll need massive bottled CO2 to simulate the Martian atmosphere in this trial. It probably won't be a field trial of ice recovery. Ice is easier-had on Baffin Island or in the Dry Valleys than it will be on Mars. Ice is stable on the surface here, not on Mars. That will be a different field trial.
GW
Last edited by GW Johnson (2018-06-26 13:54:56)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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We don't need megawatts of power from a nuclear reactor to cool the propellants. The product from the ISPP plant can be cooled in cycles or phases. A continuous end-to-end process is the only type that demands megawatts of power. Since there is no proven way to extract water from subsurface glaciers, there's no requirement for this type of process. You accumulate product (O2/H2/CH4) in tanks and when you have enough product to further process, then you start cooling it.
I proposed the use of nuclear reactors, not because I think a continuous process is necessary or desirable, but because I'm concerned about relying on any single technology, including nuclear technology, to provide all electrical power to sustain life. The combination of more insulation for cryogen tanks and the removal of waste heat with cryocoolers is sufficient to keep cryogenic propellants cold. Moreover, a small internal combustion engine that provides the power, as it does for IVF, is sufficient for that purpose.
Solar power is abundantly available in space and the electrical power required to remove waste heat from a properly insulated propellant tank or depot, even a very large LH2 tank, is such a small figure as to be a minor nuisance. Existing cryocooler technology is sufficient for LOX/LCH4, but the pedestrian Isp from that propellant combination and added ISPP plant complexity is not desirable because we're basically starting from a fundamentals standpoint with the overall design of the plant. It's entirely doable, but requires more time and funding. We don't make LCH4 on Earth at any significant scale using the Sabatier reaction because we can pump CH4 out of the ground and liquefy it. On the other hand, most if not all, of our advanced cryogen storage and combustion technology is centered around LH2.
It took about 10 years of continuous effort to produce ZBO coolers for LH2 and we're just to the point to where we're ready to start testing the flight prototypes in space. NASA is still working on the Sabatier technology for industrial scale CH4 production. In another 5 to 10 years, we might have something ready for testing on Mars. I fail to see why we wouldn't make a bee-line towards the best propellants and most well-developed propulsion technologies available. At present, that's LOX/LH2, RL-10, J-2, and RS-25. We've been using those technologies for many decades and LH2 provides the best performance achievable with cryogenic chemical rocket propellant technology.
CH4 is nothing new, but we're much closer to being able to make Sulfur free kerosene (RP-2) at an industrial scale using CO2 and H2O than we are to making LOX from CO2 SOXE and CH4 from the Sabatier reaction. In time, we'll be able to make CH4, too. Development on that is slow, but steady, and tracking towards target production rates. Zubrin's system required 16.8kWh to make 1kg of CH4 using LH2 brought from Earth. He theorized that the system could be twice as efficient and would then require 17MWh to make 1t of CH4, again using LH2 from Earth. NASA state-of-the-art is using special microliths to dramatically improve efficiency and production rate. If they don't have this ready to go after years of R&D, I can guarantee that SpaceX doesn't, either.
Required Reading for Aspiring Rocket Propellant Chemists:
IGNITION! by Dr. John Drury Clark
On the surface of Mars, solar power is available during the day and small ICE's can provide the power required at night for a nominal loss of propellant. Alternatively, nuclear power provides the power at night and no propellant is lost from running ICE's or simply permitting boil-off to occur.
Here's what a real cryoplant looks like:
Integrated Refrigeration and Storage for Advanced Liquid Hydrogen Operations
Technology Development Roadmap:
Cryogenic Fluid Management - Technology Development Roadmaps
Testing Overview, Results, and Discussion:
Cryogenic Boil-Off Reduction System Testing
NASA Cryogenic Propellant Systems Technology Development and Potential Opportunities for Discussion
Technical Details of the Implementation Hardware:
In-Space Cryogenic Propellant Storage Applications for a 20 W at 20 K Cryocooler
Demonstration of a High-Capacity Cryocooler for Zero Boil-Off Cryogen Storage in Space
Basic Ideas and Concepts:
Broad Area Cooler Concepts for Cryogenic Propellant Tanks
Cryocoolers for HTS Power Applications (note use of magnetic bearings for turbomachinery and no oil or other lubricants):
Cooling and Cryocoolers for HTS Power Applications
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If Musk tries to buy the propellant plant from any competitor he will be paying through the nose for it, talk about cost plus.....
I do not think that the Hydrogen for the reactor is cryro but it is under pressure entering the system from what I remember.
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SpaceNut,
There's nobody to simply "buy" this sort of technology from. Anyone you could buy it from would want to see it in operation on Mars since that's what everyone working on this technology set is talking about using it for. For all practical purposes, only NASA and their contractors are actually working on it in a serious way. ZBO is likely a hard requirement for keeping the header tanks sub-cooled for 3 months. I don't think insulation alone is sufficient.
You're correct in your statement that a Sabatier reactor uses gaseous H2. The reason for delivering liquid H2 is densification for transport and the fact that LH2 is pretty light. I suppose that a pair of BFS could deliver the 243t of H2O required to send 1 BFS home. If you're carrying 62% of the water in an Olympic sized swimming pool, but still short the O2 required and must supply it using Martian CO2, then you're probably better off figuring out how to deliver the 27t of LH2.
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The more I look at this, the more I am thinking, why on earth take on the risk and difficulty of water sourcing, when you can take your hydrogen feed with you (as Zubrin suggested, a long time ago)?
I think for a BFS that means you need about 60 tonnes of hydrogen...with boil off (assuming you can't stop boil off, but you might be able to) maybe you'd need to take 100 tonnes but that's still very manageable on an 600/800 tonnes cargo mission and you would be making mass savings on water mining rovers and equipment and so on, probably in the tens of tonnes. That also frees you to focus on a safe landing site, rather than a site that provides both safe landing and water sources.
Anyone care to argue the case that the hydrogen feed approach is flawed?
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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I think you have to take your fuel feedstock with you on the first mission. If you land some place hard and level, there's probably not much water there. Ultimately, if there's no water anywhere near where you decided to set up shop, then there's little possibility of permanent settlement there. Recycling alone is not efficient enough to inhibit all water losses. However, water is not more important than landing in one piece. It doesn't matter how much water exists where you land if you die on impact. That could be fixed with a better landing gear design or a better lander design. Given the tonnage of propellant thrown away on a BFS mission, throwing an inflatable heat shield away is just noise. That's why I said the lander design is wrong for Mars. BFS may be perfect for landing on a concrete or steel pad, neither of which exist on Mars, but could be built there, or some functional equivalent built there, so BFS can land without issue.
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Yes, I would only be proposing this as a Mission One solution. Later Missions could begin water processing in earnest.
I think as long as your water source is within say 100 Km of your landing site, then I don't think this is a huge problem. I think robo-mining of water ice or water laden regolith is definitely within our technological capability.
To get a 100 tonnes of hydrogen you might have to shift 22000 of regolith at 5% water. If your prime water source area was say 50 kms
away, then a fleet of rover trucks with say 4 tonne loads working 8 hour "shifts" per load and travelling at 25Kms per hour could each transport 12 tonnes per truck per sol, so you would probably be able to cope with that with a team of 5 trucks - to allow for some maintenance.
This would require the creation of boulder-free road trails which allow trucks to travel as fast as 25km per hour.
Of course that would not be necessary if it were possible to build a landing platform in the water source area. That might be less difficult than seems but it might be a Mission 2 or 3 task. I am think of a pretty substantial metal structure that could be adjusted to provide a completely level platform for landing. You'd also have to deploy dust suppression techniques in the area if it is otherwise dusty.
I think you have to take your fuel feedstock with you on the first mission. If you land some place hard and level, there's probably not much water there. Ultimately, if there's no water anywhere near where you decided to set up shop, then there's little possibility of permanent settlement there. Recycling alone is not efficient enough to inhibit all water losses. However, water is not more important than landing in one piece. It doesn't matter how much water exists where you land if you die on impact. That could be fixed with a better landing gear design or a better lander design. Given the tonnage of propellant thrown away on a BFS mission, throwing an inflatable heat shield away is just noise. That's why I said the lander design is wrong for Mars. BFS may be perfect for landing on a concrete or steel pad, neither of which exist on Mars, but could be built there, or some functional equivalent built there, so BFS can land without issue.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Louis-
Another proposal which does not look at the energy penalty imposed through trucking solids 100 miles. One must look at the entire thermodynamic system, and not chirp around the edges with further energy drains.
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I don't think energy will be a major problem for the early colony - whether it's solar or nuclear based.
If we've got about 36 round trips of 100 kms to move a total of about 48 tonnes (of water rich regolith) per sol, that would be about 640KwHs per sol. However, you might process the water out of the regolith at your water source site.
A round trip of 200 kms would, I agree probably be a bit extreme but round trips of 100 Kms could be manageable.
I am not particularly proposing this. I am just pointing out really that we have a number of competing priorities in the first few missions. Safe landing has to come first, over a convenient proximate water resource. I would favour hydrogen feed for Mission One. But for Missions Two and Three you might want to start processing water for propellant.
The easiest way to deal with some of these competing priorities is to up the energy provision.
I would hope though that we can find somewhere with a safe landing site (solid fairly flat rock, with few boulders, and relatively dust free) which is close (say within 10 Kms of a good water resource).
After Mission One, you might treat the safe landing site as your spaceport and simply tow cargo to the water resource centre where you would develop your settlement. However you would still need propellant storage at your spaceport.
Louis-
Another proposal which does not look at the energy penalty imposed through trucking solids 100 miles. One must look at the entire thermodynamic system, and not chirp around the edges with further energy drains.
Last edited by louis (2018-06-27 18:14:28)
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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If we are going to send seed resources for the first mission and possibly even the second would mean that we could also send storable propellants as well which could be an even greater store than what could be send and still be there long after the cycle times for a next launch but then again whats stopping that mission?
1. What level of AG is still needed for a complete misson question that needs an answer.
2. Perfecting radiational shielding for complete mission.
3. select power source for each leg of mission to be sure of survival
Everything else is tonnage to set up future options and science plus exploration growing with each mission to mars.
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Louis,
Mission Zero is that robotic ISPP demonstration I proposed. That mission involves one or two Cygnus landers that demonstrate all of these new technologies. If that works semi-autonomously, then it'll still work at greater scale when humans are available to intervene. If it doesn't work, then humans don't add much to the equation. We can't have people in suits basket weaving to set up solar arrays. The power, propellant, and life support equipment mostly needs to take care of itself. In other words, it just has to work, period.
I agree 100% about not taking chances with BFS. No mission commander worth his salt will hazard his ship or his crew without good cause. Nothing else matters if BFS doesn't land in one piece. We need a rock solid and reasonably flat location to land on. It may or may not be in an ideal location to retrieve water rich regolith, but that's a secondary concern.
SpaceNut,
1. 1g is required. That's what humans evolved with. If we can change tens of thousands of years of human evolution in a matter of days, then feel free to substitute any other number that magic wand can adapt human physiology to.
2. Use what works. We know that water, Hydrogen-rich plastics and fabrics, and BNNT work quite well. We know that metals create secondary particle showers that can cause as much or more damage than the energetic particles that impacted the metal. Active radiation shielding technologies are, as yet, untested in space. As a function of the thermal environment in space, Aluminum alloy with a heavy BNNT liner or PE water tank liner to absorb the secondaries is as good as it gets at present. I may change my opinion on that after we get some test data back from BEAM regarding materials fatigue from thermal cycling and micrometeoroid strikes. If it turns out that multi-layered fabrics work better than aluminum cans with fabric liners, then so be it.
3. There's no serious dispute about using solar power in deep space in the inner solar system. The spacecraft is constantly bathed in solar radiation. The new thin film arrays are exceptionally light and resistant to tears or punctures and radiation, so let's use that. Any attempt to store megawatt-hours of power in batteries using current generation technology on the surface of Mars is a fool's errand. There are reliable and durable batteries that can supply power at night for life support as a function of the minimal continuous power requirements and manageable transient or peak loads. Some sort of dissimilar technology should provide backup electrical power for life support. My preference is nuclear because no chemical fuels have to be transported to Mars or acquired on Mars. However, small gas turbines are reliable and durable. If we're taking many tons of H2 with us, then a stock of O2/H2 or O2/CH4 micro turbogenerators is an acceptable backup power source.
As I've told Louis before, I'm agnostic on whether or not any particular form of electrical power generation technology is included. However, I'm not agnostic about running out of power. There can be no loss of power, at all or ever. If that requirement can reasonably be met by a combination of solar panels, batteries, and gas turbines, then I'm good with that. If there are issues with that, then the only other logical choice is nuclear. The more I learn about fuel cells, the less impressed I am with the durability of the technology. Sometimes fuel cells work great and sometimes they don't work at all. That said, the technology is improving along with all other forms of energy generation and storage.
My objection to megawatt-hour scale batteries is that anything drawing that much current requires an active thermal management system and there is no way around that. The mass of the batteries is 50% or less of the solution.
The ISS Lithium-Ion ORU's have ten 155Wh/kg batteries per pack. Each cell weighs 3.53kg, or 35.3kg per pack. However, the entire ORU weighs 198kg. That's without the 39kg heater plate that secures the pack to the ISS truss structure. You could substitute 1,000Wh/kg batteries and it not save much mass. The mass driver is clearly not the battery itself. It's all the packaging around it. Now you know why fuel cells, despite reliability issues, still have a place in space applications.
International Space Station Lithium-Ion Battery Start-Up
This is what a thermal runaway test produced for those packs:
Assessment of International Space Station (ISS) Lithium-ion Battery Thermal Runaway (TR)
International Space Station Lithium‐Ion Main Battery Thermal Runaway Propagation Test
The packaging contained the failure, but still destroyed the entire pack and out-gassed. That is why when someone says, let's put megawatt-hour Lithium-Ion battery packs inside the cargo bay, my response is "Oh, hell no!".
Some bright young lad may say, we could use composites for the containment. My response is "Great, now we have a combustible casing, due to the binders that glue the carbon fiber together, that still weighs more than the batteries inside it."
I'm not entertaining any of this magical thinking about what a space applications battery actually weighs. The fact of the matter is that the packaging solution is always a multiple of the mass of the batteries inside. The more Wh/kg you cram into a battery pack, the more it begins to imitate an explosive device if that energy is instantly released from a short within a cell or a cell penetration from space debris or rough handling.
The BOL watt-hours stored by the ISS ORU pack is 5,471.5Wh for 35.3kg. The Tesla 2170 cells would store 8,825Wh for the same mass. If the battery was completely drained, the pack's life would be drastically shorter, but let's do the math on what it would take to provide 7.5kW during 12 hours of darkness.
7.5kW * 12hrs = 90kWh
90kWh / 8.825kWh = 10.198 ORU's with 2170 cells
Let's round that to 10. Each ORU has a mass of 237kg with the heater plate assembly for thermal regulation, so 10 ORU's have a mass of 2,370kg. We're absolutely draining and killing these batteries well within 2 years, too. In order to maintain acceptable cell life (at least 4 years, in my mind), we need to double the number of ORU's. This is why production beats storage. For double the ORU mass, we get a pair of the 10kWe KiloPower reactors, a megawatt class solar array, and the wiring. BFS is a POWERFUL rocket, so I mandate a minimum separation distance of 5km for all other surface equipment. Any power plant must be at least that far away. Furthermore, all surface equipment should be shielded using regolith berms.
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Louis,
Mission Zero is that robotic ISPP demonstration I proposed. That mission involves one or two Cygnus landers that demonstrate all of these new technologies. If that works semi-autonomously, then it'll still work at greater scale when humans are available to intervene. If it doesn't work, then humans don't add much to the equation. We can't have people in suits basket weaving to set up solar arrays. The power, propellant, and life support equipment mostly needs to take care of itself. In other words, it just has to work, period.
I agree 100% about not taking chances with BFS. No mission commander worth his salt will hazard his ship or his crew without good cause. Nothing else matters if BFS doesn't land in one piece. We need a rock solid and reasonably flat location to land on. It may or may not be in an ideal location to retrieve water rich regolith, but that's a secondary concern.
My feeling about the Space X mission architecture is that the 2022 cargo element will be in effect proving mission for the human mission that follows two years later. However, I personally don't believe any humans will head for Mars before a serious analogue mission to the Moon takes place. Crucially, Musk has made clear the BFR can undertake lunar surface missions.
SpaceNut,
1. 1g is required. That's what humans evolved with. If we can change tens of thousands of years of human evolution in a matter of days, then feel free to substitute any other number that magic wand can adapt human physiology to.
We need to distinguish between 1G on Earth, artificial (spinning) 1G, and weighted 1G. I think weighted 1G (on Mars) is being underrated here, on this site. It will in my view solve the muscle/bone loss issue. We are then left with heart muscle atrophy (probably partially resolve by weighted 1G creating pressure on internal organs), immune system deterioation and visual acuity problems (overstated in my view). Immunity is not really an issue in a small colony on Mars. It could only become a serious issue back on Earth and so far there has been no evidence of early death among astronauts subjected to long periods of zero G.
2. Use what works. We know that water, Hydrogen-rich plastics and fabrics, and BNNT work quite well. We know that metals create secondary particle showers that can cause as much or more damage than the energetic particles that impacted the metal. Active radiation shielding technologies are, as yet, untested in space. As a function of the thermal environment in space, Aluminum alloy with a heavy BNNT liner or PE water tank liner to absorb the secondaries is as good as it gets at present. I may change my opinion on that after we get some test data back from BEAM regarding materials fatigue from thermal cycling and micrometeoroid strikes. If it turns out that multi-layered fabrics work better than aluminum cans with fabric liners, then so be it.
It think the radiation issue is largely resolved and I would not be looking to pioneers undertaking prolonged EVAs.
3. There's no serious dispute about using solar power in deep space in the inner solar system. The spacecraft is constantly bathed in solar radiation. The new thin film arrays are exceptionally light and resistant to tears or punctures and radiation, so let's use that. Any attempt to store megawatt-hours of power in batteries using current generation technology on the surface of Mars is a fool's errand. There are reliable and durable batteries that can supply power at night for life support as a function of the minimal continuous power requirements and manageable transient or peak loads. Some sort of dissimilar technology should provide backup electrical power for life support. My preference is nuclear because no chemical fuels have to be transported to Mars or acquired on Mars. However, small gas turbines are reliable and durable. If we're taking many tons of H2 with us, then a stock of O2/H2 or O2/CH4 micro turbogenerators is an acceptable backup power source.
There are all sorts of handling and management issues with nuclear power, not least whether anyone would be happy to have radioactive material showered over them in the event of a Challenger style disaster. I agree we definitely should take along generators to use methane or other fuels.
As I've told Louis before, I'm agnostic on whether or not any particular form of electrical power generation technology is included. However, I'm not agnostic about running out of power. There can be no loss of power, at all or ever. If that requirement can reasonably be met by a combination of solar panels, batteries, and gas turbines, then I'm good with that. If there are issues with that, then the only other logical choice is nuclear. The more I learn about fuel cells, the less impressed I am with the durability of the technology. Sometimes fuel cells work great and sometimes they don't work at all. That said, the technology is improving along with all other forms of energy generation and storage.
This is one reason why you have to have at least two cables running from any energy system - well separated. The potential for human error makes one cable too vulnerable (think of a tired driver taking a rover over a cable and breaking it). It is also why I am a little suspicious of nuclear generators driving stirling engines. Everything I have read about stirling engines suggests they are relatively unreliable.
My objection to megawatt-hour scale batteries is that anything drawing that much current requires an active thermal management system and there is no way around that. The mass of the batteries is 50% or less of the solution.
The ISS Lithium-Ion ORU's have ten 155Wh/kg batteries per pack. Each cell weighs 3.53kg, or 35.3kg per pack. However, the entire ORU weighs 198kg. That's without the 39kg heater plate that secures the pack to the ISS truss structure. You could substitute 1,000Wh/kg batteries and it not save much mass. The mass driver is clearly not the battery itself. It's all the packaging around it. Now you know why fuel cells, despite reliability issues, still have a place in space applications.
Aren't there ways of using the cold ambient temperature on Mars to cool battery facilities?
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Louis,
Analogue Missions
An analogue mission to the moon would make a lot of sense. However, the moon doesn't adequately simulate the environment on Mars. A robotic mission to Mars that uses all of the technologies we want to use on Mars is a cheaper and highly realistic simulation of how the technology would perform at significant scale.
Artificial Gravity
Chris has already explained how they attempt to load the bodies of the astronauts during exercise to deal with de-conditioning from microgravity. It's partially successful. He thinks another two generations of the exercise equipment will produce the desired results, but admits that they have no complete solution at the present time. He specifically stated that exercise does not adequately contend with the loss of bone mass and muscle in the upper legs and pelvic girdle, both of which are required to walk. Spin gravity, or artificial acceleration, can and does produce 1g of acceleration at a rotational rate that is acceptable to human physiology when the radius of rotation is 50m+. The Earth itself also produces spin gravity, but at a much greater radius. The other problems you think are overstated, such as visual acuity, are just your opinion, not based in the reality that the astronauts have to deal with when they return to Earth or set foot on another planet.
Issues with Space Nuclear Power and Propulsion
It doesn't seem to me that you have much of an understanding of how nuclear power works, how the containment systems for space nuclear power generation systems work, nor why some of the types of failure modes you described are impossible. You do realize that a nuclear reactor is far less radioactive than any RTG is during launch, right? RTG's have been aboard rockets that exploded during launch. The core, the part that contains the radioactive material, were recovered intact from the sea bed and re-flown on a subsequent mission. There was no radiation leak, nor damage to the containment.
"All sorts of handling and management issues" is a broad sweeping statement that says nothing because it means nothing. Either define precisely what you mean, or I'll conclude that you've no idea what you're talking about and are just saying things based upon irrational fear of the unknown. That's precisely one of the things that Chris Hadfield says that real astronauts don't do. If they don't understand something, then they educate themselves. This is the exact opposite of what the general public does and the reason "Joe off the street" is not a NASA astronaut.
Stirling engines of the type NASA's contractors have provided are exceptionally reliable. Reading articles about primitive designs from many decades ago or stuff people cooked up in their garages is not a good indicator of how reliable and durable modern Stirling engines are. The materials, seals, bearings, and all other aspects of modern designs are far more reliable than past designs have ever been. Designs for use on Earth often attempt to emulate piston-powered internal combustion engines, which has a dramatic effect on reliability. If that's what you've been reading about, then just know that those designs have very little in common with the designs that NASA uses. There are no connecting rods in the designs NASA uses because they don't translate linear motion into circular motion to turn a crank shaft to spin a generator. A free piston travels back and forth through a coil of wire in the NASA designs to generate electricity. Some designs are superior to others when absolute reliability is a consideration and that's all there is to it.
Furthermore, if BFS is so unreliable that a Challenger-style launch accident is probable, then there's no way that hundreds of people will fly aboard BFS and there is essentially no chance of colonizing Mars at that point. BFS has a few real design issues, like the landing gear width and extremely low structural mass fraction, and that's already been pointed out numerous times by numerous people. Those issues are basic physics that no amount of magical thinking will overcome.
Surface Power System Vulnerabilities
If a power cable is accidentally cut, then splice in a new wire segment to continue conducting electricity. That's how it's done here on Earth. There is nothing magical about using two wires when both wires run between the same power source and the same powered device.
Battery Thermal Management in a Vacuum or Near-Vacuum
The primary issues with battery management are containment of individual cell failures, keeping the battery warm enough for optimal charge and discharge, and also keeping the battery cool during periods of heavy current draw. The systems aboard ISS are well insulated and the mass of the aluminum cage surrounding the batteries serves as a thermal sink for cooling during discharge at much lower current draw rates.
Those PDF's I posted illustrate exactly what happens during a cell penetration in a vacuum, which is essentially what the atmosphere on the surface of Mars is. The result was destruction of the entire battery pack since the cells are not individually contained within the pack. Individual cell containment would make the packaging even heavier. We've already seen what happens to the Tesla Model S battery packs when one of the cells is shorted internally (manufacturing defect) or punctured (damaged by an operational event). The entire battery and the vehicle it was mounted in was destroyed.
If the problems with the Lithium in the liquid electrolyte are solved, then active thermal management is still required to regulate temperature. The dominant method of heat transport in a vacuum or near vacuum is radiation. Heat can be transferred into a heavy Aluminum heat sink and radiated away into the vacuum. That's exactly what ISS does. That's exactly what KiloPower does. Earth's thick atmosphere makes convective cooling using fans and comparatively small heat sinks relatively easy. That heat transport mechanism does not apply to the moon and Mars.
If you properly insulate a battery, then it retains heat well. If you draw a lot of current from a battery in operation, then what are you doing? You're increasing the rate of the chemical reaction that produces electrical power. What does increasing the rate of the chemical reaction do? It generates more heat. Lithium-Ion batteries don't function well (can't charge or discharge nearly as fast without cell damage or destruction) in extremely hot and cold environments. So, how do you get rid of the heat? You either poorly insulate the battery or you have a large and heavy system that transfers the heat, via radiation, to the surrounding environment. If the battery technology wasn't severely affected by cold and hot environments, then this wouldn't be as much of a problem. Unfortunately, all of our batteries work best near room temperature and the moon and Mars spend very little time near room temperature.
Closing Remarks
There are no free lunches to be had here, no matter what power generation and storage technologies are selected. However, generating power is still a lot easier than storing it with current battery technology when mass is at a premium. On every mission into space, mass is severely restricted. If you had more mass to play with, then you're still better off with more food, water, radiation protection, power generation equipment vs power storage equipment, and spare parts to repair whatever inevitably fails. BFS won't change the calculus of how to best plan for a mission. It's more likely to deliver enough tonnage to contend with fudge factors associated with mission mass estimates. If some little widget used has a little more mass than anticipated, then a DARPA level engineering effort isn't required to redesign the widget or everything else on the mission. That's the major improvement I think BFS will provide.
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Louis,
Analogue Missions
An analogue mission to the moon would make a lot of sense. However, the moon doesn't adequately simulate the environment on Mars. A robotic mission to Mars that uses all of the technologies we want to use on Mars is a cheaper and highly realistic simulation of how the technology would perform at significant scale.
Well in many ways being on the Moon is more challenging than being on Mars. But I think the key element would be to assess the effects of zero G and low G over a 2.5 year mission. You could probably shorten the analogue mission to maybe 1.5 years and still get some reasonable informative data I would think.
You would also fly your elite Mars crew pool in Earth orbit for a few months to assess their bone and muscle loss and make sure they can cope with space.
Artificial Gravity
Chris has already explained how they attempt to load the bodies of the astronauts during exercise to deal with de-conditioning from microgravity. It's partially successful. He thinks another two generations of the exercise equipment will produce the desired results, but admits that they have no complete solution at the present time. He specifically stated that exercise does not adequately contend with the loss of bone mass and muscle in the upper legs and pelvic girdle, both of which are required to walk. Spin gravity, or artificial acceleration, can and does produce 1g of acceleration at a rotational rate that is acceptable to human physiology when the radius of rotation is 50m+. The Earth itself also produces spin gravity, but at a much greater radius. The other problems you think are overstated, such as visual acuity, are just your opinion, not based in the reality that the astronauts have to deal with when they return to Earth or set foot on another planet.
That's exercise in zero G. Exercise in 1G weighted suits on Mars will I am sure lead to bone and muscle recovery...because that's what happens when astronauts return to Earth. So the way I see it, your risk factor is the six months in zero G travelling each way.
Issues with Space Nuclear Power and Propulsion
It doesn't seem to me that you have much of an understanding of how nuclear power works, how the containment systems for space nuclear power generation systems work, nor why some of the types of failure modes you described are impossible. You do realize that a nuclear reactor is far less radioactive than any RTG is during launch, right? RTG's have been aboard rockets that exploded during launch. The core, the part that contains the radioactive material, were recovered intact from the sea bed and re-flown on a subsequent mission. There was no radiation leak, nor damage to the containment."All sorts of handling and management issues" is a broad sweeping statement that says nothing because it means nothing. Either define precisely what you mean, or I'll conclude that you've no idea what you're talking about and are just saying things based upon irrational fear of the unknown. That's precisely one of the things that Chris Hadfield says that real astronauts don't do. If they don't understand something, then they educate themselves. This is the exact opposite of what the general public does and the reason "Joe off the street" is not a NASA astronaut.
Stirling engines of the type NASA's contractors have provided are exceptionally reliable. Reading articles about primitive designs from many decades ago or stuff people cooked up in their garages is not a good indicator of how reliable and durable modern Stirling engines are. The materials, seals, bearings, and all other aspects of modern designs are far more reliable than past designs have ever been. Designs for use on Earth often attempt to emulate piston-powered internal combustion engines, which has a dramatic effect on reliability. If that's what you've been reading about, then just know that those designs have very little in common with the designs that NASA uses. There are no connecting rods in the designs NASA uses because they don't translate linear motion into circular motion to turn a crank shaft to spin a generator. A free piston travels back and forth through a coil of wire in the NASA designs to generate electricity. Some designs are superior to others when absolute reliability is a consideration and that's all there is to it.
Furthermore, if BFS is so unreliable that a Challenger-style launch accident is probable, then there's no way that hundreds of people will fly aboard BFS and there is essentially no chance of colonizing Mars at that point. BFS has a few real design issues, like the landing gear width and extremely low structural mass fraction, and that's already been pointed out numerous times by numerous people. Those issues are basic physics that no amount of magical thinking will overcome.
I will accept the admonition! However, I think sometimes people speak about nuclear generators as though there are no moving parts and they can't fail, whereas clearly there are and they can, as much as anything else with moving parts, especially in the challenging environment of Mars. Nevertheless, I am sure NASA work to the highers standards regarding reliability.
Surface Power System Vulnerabilities
If a power cable is accidentally cut, then splice in a new wire segment to continue conducting electricity. That's how it's done here on Earth. There is nothing magical about using two wires when both wires run between the same power source and the same powered device.
Not necessarily that easy. Maybe an EVA would be involved...at least an hour required to get into your spacesuit and do all the checks...Plus you've got to locate where problem is if you aren't sure where it is...I am not being overdramatic, but just stressing that relying on one power source can be dangerous. At a minimum you need several days' storage within the hab I think, to give you the time to identify the problem.
Closing Remarks
There are no free lunches to be had here, no matter what power generation and storage technologies are selected. However, generating power is still a lot easier than storing it with current battery technology when mass is at a premium. On every mission into space, mass is severely restricted. If you had more mass to play with, then you're still better off with more food, water, radiation protection, power generation equipment vs power storage equipment, and spare parts to repair whatever inevitably fails. BFS won't change the calculus of how to best plan for a mission. It's more likely to deliver enough tonnage to contend with fudge factors associated with mission mass estimates. If some little widget used has a little more mass than anticipated, then a DARPA level engineering effort isn't required to redesign the widget or everything else on the mission. That's the major improvement I think BFS will provide.
Mission design is definitely all about mass balance but also keeping the ISRU relatively low. But Mission One also has to think about Missions Two and Three - if this is to be a colonisation effort.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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