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#40
by
A_M_Swallow
on 20 Oct, 2011 23:19
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The VASIMR paper assumed a 12MW power source. At 675W/mē of solar energy density at Mars distance, and assuming an efficiency of 9%, that's an effective energy input of 60.75W/mē. So, you'd need around 200,000mē of effective light gathering surface, i.e. assuming no losses due to light incidence angle. That's roughly a 500m x 500m solar panel or a circle of 520m in diameter. Kind of too big, isn't it?
Yes it is big, but not impossibly big. When the ship is in LEO you may even be able to see the array from the ground.
Solar panels fold up so only a few launches will be needed to lift the array to orbit.
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#41
by
baldusi
on 21 Oct, 2011 14:06
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The VASIMR paper assumed a 12MW power source. At 675W/mē of solar energy density at Mars distance, and assuming an efficiency of 9%, that's an effective energy input of 60.75W/mē. So, you'd need around 200,000mē of effective light gathering surface, i.e. assuming no losses due to light incidence angle. That's roughly a 500m x 500m solar panel or a circle of 520m in diameter. Kind of too big, isn't it?
Yes it is big, but not impossibly big. When the ship is in LEO you may even be able to see the array from the ground.
Solar panels fold up so only a few launches will be needed to lift the array to orbit.
Have you made structural considerations? Pointing considerations? The effects of solar flux push? It's not that it can't be done. The question is if it can be done while keeping the density above 4kW/kg. You might be able to get it with a tension design, but you'd probably need to discard some structured needed during assembly. And you'd need a ship about that long. And the whole structure must be kept pointing to the Sun, else you'd get incidence angle losses.
Then, there's the issue of power distribution. You might have cells, and even panels, with that density. But you not only need a frame, but to transport the electricity. Please remember that you want to transport some 12MW. Let's say that we distribute in 96 segments, that's 125kW at 120V (the natural voltage of a cell is 0.5V, but let's say we group them in 240 cells), that's 1,041 Ampere
. Are you aware of the section that you'd need? What super material will you use that won't weight a lot? If you use a transformer, you'd have to add a lot of weight. And you can't keep it like a cloth, but will have to add structural elements. Individual lightweight cells, even panels, are easy. Whole power systems, are not.
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#42
by
Robotbeat
on 21 Oct, 2011 14:38
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The VASIMR paper assumed a 12MW power source. At 675W/mē of solar energy density at Mars distance, and assuming an efficiency of 9%, that's an effective energy input of 60.75W/mē. So, you'd need around 200,000mē of effective light gathering surface, i.e. assuming no losses due to light incidence angle. That's roughly a 500m x 500m solar panel or a circle of 520m in diameter. Kind of too big, isn't it?
Yes it is big, but not impossibly big. When the ship is in LEO you may even be able to see the array from the ground.
Solar panels fold up so only a few launches will be needed to lift the array to orbit.
Have you made structural considerations? Pointing considerations? The effects of solar flux push? It's not that it can't be done. The question is if it can be done while keeping the density above 4kW/kg. You might be able to get it with a tension design, but you'd probably need to discard some structured needed during assembly. And you'd need a ship about that long. And the whole structure must be kept pointing to the Sun, else you'd get incidence angle losses.
Then, there's the issue of power distribution. You might have cells, and even panels, with that density. But you not only need a frame, but to transport the electricity. Please remember that you want to transport some 12MW. Let's say that we distribute in 96 segments, that's 125kW at 120V (the natural voltage of a cell is 0.5V, but let's say we group them in 240 cells), that's 1,041 Ampere . Are you aware of the section that you'd need? What super material will you use that won't weight a lot? If you use a transformer, you'd have to add a lot of weight. And you can't keep it like a cloth, but will have to add structural elements. Individual lightweight cells, even panels, are easy. Whole power systems, are not.
Yeah, you very well may need a higher voltage than just 120V. Also, there are conductors which could be considerably lighter than copper (for the same resistivity and current), such as those made from Lithium (or is it Sodium or Calcium?). Even Aluminum is lighter than equivalent copper wires.
There's also the possibility (in the further future) of superconducting wires able to have a far higher current carrying capacity (and this keeps increasing as we make solid state physics advances) for the same mass (all inclusive) as copper. Nanotubes can also reportedly carry a lot of current for their mass (though this is still a research area, not yet practical).
Anyway, this is wandering off-topic, but the point is that solar arrays can have pretty darned good specific power inside the asteroid belt (and, as Juno is showing, usable power to Jupiter at least), and that they have lots of room to grow in that area ten or even a hundred times better than current state of the art (which is ~100-150 W/kg at 1AU). Even 4kW/kg at 1.5 AU (i.e. Mars) can't be dismissed out of hand.
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#43
by
Jim
on 03 Nov, 2011 15:31
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Secondly, reduction in consumables and trash generation. If you have a macro gravity environment, it's much easier to e.g. wash and dry clothes and eating utensils, cook with bulk ingredients rather than needing everything in individual packages, etc.
Not really. wash and dry clothes can be done just as easy in zero g.
Eating utensils are not different in zero g.
Bulk cooking is not easier. Requires more ingredients and more logistics. Prepackage is the way to go.
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#44
by
peter-b
on 03 Nov, 2011 15:47
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Not really. wash and dry clothes can be done just as easy in zero g.
Eating utensils are not different in zero g.
Bulk cooking is not easier. Requires more ingredients and more logistics. Prepackage is the way to go.
Can you direct me to any additional information about research that has been done on these topics? I would be fascinated to find out more about it.
I wonder how much mass can be saved on toilet consumables because gravity permits the use of a "normal" toilet...
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#45
by
Jim
on 03 Nov, 2011 19:37
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As for bulk cooking, look at the size of army formation that requires a cook
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#46
by
mike robel
on 03 Nov, 2011 20:09
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Well, my 100 man tank company had 5 cooks. My 72 man tank company had 3 cooks. Of course, I didn't control it directly, it was the S-4's (supply officer's job) and in the field we usually got one hot meal a day (and it was usually a "B" ration which meant generlly canned food).
The other two meals were either C-rations (early) or MRE's (Meal Ready to Eat, which was sometimes thought to be a triple like).
In an assembly area or rest area, you might get two hot meals a day and sometimes they would be "A"s - real food. Usally breakfast and dinner/supper.
Today there are probably even fewer cooks and the hot meal is likely to be a unit ration, sort of like airplane food used to be.
So, I don't see a need for a dedicated cook, but make sure you bring hot sauce and spiced to vary the taste of the food!
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#47
by
peter-b
on 03 Nov, 2011 21:18
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British infantry squad firebases in Helmand (squads of 8-10 men IIRC) have cooked food (they don't eat from ratpacks). They don't have a dedicated cook (squaddies take turns). But I don't recall ever suggesting that a Mars mission should have a ships cook, just that there should be a galley.
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#48
by
Robotbeat
on 03 Nov, 2011 21:45
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British infantry squad firebases in Helmand (squads of 8-10 men IIRC) have cooked food (they don't eat from ratpacks). They don't have a dedicated cook (squaddies take turns). But I don't recall ever suggesting that a Mars mission should have a ships cook, just that there should be a galley.
A galley? A tiny refrigerator/freezer, a food warmer, a tiny microwave, and a tiny toaster oven would be fine, perhaps also an area to wash stuff. It could all fit in a cube 2 feet on a side. Lots of those are also useful for repairs or sample storage or drug storage or tool/utensil sterilization, so they may either serve dual purpose or a similar non-food set may also be needed.
But not a fully galley. Food preparation from bulk food also is quite time-consuming, and the crew will need all the time they can get, at least once at the site.
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#49
by
peter-b
on 03 Nov, 2011 22:21
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A galley? A tiny refrigerator/freezer, a food warmer, a tiny microwave, and a tiny toaster oven would be fine, perhaps also an area to wash stuff. It could all fit in a cube 2 feet on a side. Lots of those are also useful for repairs or sample storage or drug storage or tool/utensil sterilization, so they may either serve dual purpose or a similar non-food set may also be needed.
Sound like exactly what I had in mind.
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#50
by
joek
on 03 Nov, 2011 22:44
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I think there's room, and arguably a place for pre-packaged, semi-bulk, and possibly bulk food store and preparation. While pre-packaged has a number of advantages, you're stuck with whatever was put in the pantry at launch.
THe addition of fresh ingredients and meal variety has been the subject of some NASA research, and part of the rationale is crew morale. Semi-bulk or bulk allows a potentially far greater variety. While not necessarily for every day, maybe a couple days a week or a few days a month is appropriate.
A zero-g bread, rice, bean, etc. cooker (semi-bulk or bulk) sounds feasible (altho I admit I've never considered the problem), and should require very little crew time. Stock the pantry with some pre-packaged ingredients and spices to add to the pot and vary the results..
How about some fresh-baked bread to make that umpteenth pre-packaged eggs-and-sausage, oatmeal or whatever breakfast more palatable? Maybe some fresh-from-the-pot beans or rice (with a dash of cumin and red pepper at your option) to make that 50th Salisbury steak a bit more attractive?
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#51
by
Jim
on 04 Nov, 2011 00:37
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A galley? A tiny refrigerator/freezer, a food warmer, a tiny microwave, and a tiny toaster oven would be fine, perhaps also an area to wash stuff. It could all fit in a cube 2 feet on a side. Lots of those are also useful for repairs or sample storage or drug storage or tool/utensil sterilization, so they may either serve dual purpose or a similar non-food set may also be needed.
Sound like exactly what I had in mind.
That isnt for bulk cooking
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#52
by
Jim
on 04 Nov, 2011 00:39
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British infantry squad firebases in Helmand (squads of 8-10 men IIRC) have cooked food (they don't eat from ratpacks). They don't have a dedicated cook (squaddies take turns). But I don't recall ever suggesting that a Mars mission should have a ships cook, just that there should be a galley.
They don't have the manpower to spare to prepare bulk food like your example
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#53
by
spectre9
on 04 Nov, 2011 02:30
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What exactly is the manpower being used for in the 180 days it will take a crew to get to Mars?
They can't cook one meal?
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#54
by
pathfinder_01
on 04 Nov, 2011 05:07
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What exactly is the manpower being used for in the 180 days it will take a crew to get to Mars?
They can't cook one meal?
With the shuttle and ISS they don't cook meals, they warm them up.
One crew member is given the task of making the meal for the crew(and this job rotates among the crew). Space food is designed to need as little prep. as possible. The bigger issuse is clean up after the meal (stuff floats everywhere) and there are issuses of waste disposal (one upgrade to the shuttle gave the shuttle a garbage compactor).
In space cooking could pose problems (i.e. gravity is quite nice at keeping things contained....). I think for moral reason they might but don't expect complex dishes.
For instance white bread is not allowed due to the crumbs it generates tortillas are prefered.
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#55
by
peter-b
on 04 Nov, 2011 06:30
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In space cooking could pose problems (i.e. gravity is quite nice at keeping things contained....). I think for moral reason they might but don't expect complex dishes.
Well, getting back to the point, I was arguing that
one advantage of providing a centrifugal section for a Mars transit habitat would be the ability to cook real food, with the concomitant crew morale benefits. I still think that the health/acclimatisation benefits would turn out to be the more important factor, however.
I'm still waiting for Jim to back up his supremely confident assertions w.r.t. zero-g space laundry and the packaging efficiency of prepackaged food vs. bulk cooked food. It sounds like there's been some research/experiments done that I'm not aware of, and as I said, I am genuinely interested to learn more...
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#56
by
Patchouli
on 05 Nov, 2011 04:51
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Not really. wash and dry clothes can be done just as easy in zero g.
Eating utensils are not different in zero g.
Bulk cooking is not easier. Requires more ingredients and more logistics. Prepackage is the way to go.
Can you direct me to any additional information about research that has been done on these topics? I would be fascinated to find out more about it.
I wonder how much mass can be saved on toilet consumables because gravity permits the use of a "normal" toilet...
I once saw a concept for a zero G clothes washer proposed for ISS.
As for a toilet they have much better units then the one that went to ISS.
Still for any long 500+ day mission sans landing a centrifuge is probably a necessity.
Really though if you going to hang around Mars for any length of time you might as well land on it and make use of the resources there.
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#57
by
Lampyridae
on 06 Nov, 2011 09:19
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Gravity just makes a lot of things easier. No need to have a fan blowing on your face to prevent you waking up choking in a bubble of your own CO2. Surgery is easier: an astronaut-doctor used to practicing on Earth will have a much easier time of it. No head restraint because your carotid artery bounces your head around when you're trying to sleep. You can actually taste your reconstituted salisbury steak because your head isn't bunged up with fluid.
No explosive flatulence.
Yes, they are astronauts who can suck it up and take risks (most forumites I bet wouldn't hesitate to spend 500 days in zero G if it meant just being in space) but we also need data on AG anyway if we're going out any further than Mars. Also, prolonged exposure to low gravity. That data is in itself valuable.
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#58
by
Jim
on 06 Nov, 2011 12:30
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In space cooking could pose problems (i.e. gravity is quite nice at keeping things contained....). I think for moral reason they might but don't expect complex dishes.
Well, getting back to the point, I was arguing that one advantage of providing a centrifugal section for a Mars transit habitat would be the ability to cook real food, with the concomitant crew morale benefits. I still think that the health/acclimatisation benefits would turn out to be the more important factor, however.
I'm still waiting for Jim to back up his supremely confident assertions w.r.t. zero-g space laundry and the packaging efficiency of prepackaged food vs. bulk cooked food. It sounds like there's been some research/experiments done that I'm not aware of, and as I said, I am genuinely interested to learn more...
Space laundry looks like a front loading washer. there was one designed for the ISS.
Every Mars mission is planned with no centrifuge. Too short of duration to need one.
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#59
by
Patchouli
on 06 Nov, 2011 19:03
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In space cooking could pose problems (i.e. gravity is quite nice at keeping things contained....). I think for moral reason they might but don't expect complex dishes.
Well, getting back to the point, I was arguing that one advantage of providing a centrifugal section for a Mars transit habitat would be the ability to cook real food, with the concomitant crew morale benefits. I still think that the health/acclimatisation benefits would turn out to be the more important factor, however.
I'm still waiting for Jim to back up his supremely confident assertions w.r.t. zero-g space laundry and the packaging efficiency of prepackaged food vs. bulk cooked food. It sounds like there's been some research/experiments done that I'm not aware of, and as I said, I am genuinely interested to learn more...
Space laundry looks like a front loading washer. there was one designed for the ISS.
Every Mars mission is planned with no centrifuge. Too short of duration to need one.
Well that is not entirely correct most Mars mission concepts do have some sort AG usually a tether or in the case of the last serious study the BNTR concept the entire ship acted as a centrifuge during cruise.
Also Mars direct used the old discarded departure stage as a counter weight for ag.
DSH is extremely early and what is shown probably will never fly let alone go to Mars.
The data points that do exist for very long space flights suggest prolonged zero gravity should be avoided.
It's also why I don't see DSH as a serious concept and instead as mostly a political ploy.
If the money for a Mars mission shows up then we may see something that can really go there such as BNTR or Nautilus-X.
. Are you aware of the section that you'd need? What super material will you use that won't weight a lot? If you use a transformer, you'd have to add a lot of weight. And you can't keep it like a cloth, but will have to add structural elements. Individual lightweight cells, even panels, are easy. Whole power systems, are not.
