You are not logged in.
It's the surface area to volume ratio effect. For larger structures there's less surface area per unit of volume. Spheres are optimal but an upper floor needs access.
The Outpost will hold four crew plus equipment, it doesn't need to be huge. Mobile habs seem to have a lot of advantages, but they need extra structure.
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
The Outpost will hold four crew plus equipment, it doesn't need to be huge. Mobile habs seem to have a lot of advantages, but they need extra structure.
Correct but if you plan on establishing more than the 6-month excursions a bigger structure pays off, and a larger lander allows more cargo capacity.
Offline
Turning Moondust Into Air and Water - 5 May 2008 - Planetary Radio interview (about 15mins)
Gerry Sanders, Manager ISRU project, describes in detail NASA's ISRU work and how lunar ISRU helps prepare for Mars.
Overview of ISRU Architecture (PDF) - 14 Jun 2007
Initial ISRU Capabilities to be pursued during early Outpost (first 5 years)
Pilot-scale oxygen production, storage, & transfer capability (replenish consumables)
Pilot-scale water production, storage, & transfer capability – assuming hydrogen source/water is accessible
Excavation & site preparation (i.e. radiation shielding for habitats, landing plume berms, landing area clearance, hole or trench for habitat or nuclear reactor, etc.)
Demonstration of In-situ fabrication and repair demonstration
Mid-Term ISRU Capabilities - Exploration growth (“Hub & Spoke”)
Propellant production for LSAM, robotic sample return, or propulsive Hopper from Outpost
Consumables for long-range pressurized rover
Construction and fabrication demonstrationsPossible Long-Term Lunar Capabilities (Settlement)
In-situ manufacturing and assembly of complex parts and equipment
Habitat and infrastructure construction (surface & subsurface)
In-situ life support – bio support (soil, fertilizers, etc.)
Power generation for Moon and beyond: beaming, helium-3 isotope (3He) mining, etc.
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
Interesting ISRU outline. Broadly, looks OK.
Couple of points:-
1. I can't for the life of me think why you would bother with a nuclear reactor on the moon, given there is no weather there. It is perfect for ultra thin PV film, which already exists and which can no doubt be made even more efficient over the next ten years.
2. I would argue for moving straight into crop production as food is one of the greatest contributors to mass in terms of what needs to be supplied. Once you get your hydroponic facility going waste matter can be recycled into nutritional solutions.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline
1. Because the day night cycle is 2 weeks - with the exception of a few areas of "eternal light" such as near Shackleton crater, the planned location for the Outpost - and even there, there's only solar power for about 80% of the lunar orbit. Nuclear power also can provide the high levels of power for ISRU.
2. For food production water is needed, that's a more critical resource than food and needs to be produced first - ISRU can do it with enough power.
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
1. Well, yes, but there's no reason we can't run with a "peaks of light" location or simply use energy storage. Arriving at the start of a 2 weeks lunar day will provide plenty of opportunity for energy storage. A habitat can in any case run on v. little energy during the lunar night. I would, for a variety of reasons, much prefer to start with the aim of making full use of solar energy.
2. Of course water needs to be produced first. But if we can't begin producing that within a few days of landing, either through tapping a water source or manufacturing it from regolith, then the outlook isn't too good. In other words I would fully expect water to be available in copious quantities at an early stage and therefore also available for agriculture.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline
1. Yes, and that's the current plan, nuclear power isn't being considered for many years. See the sample campaign for the first ten years. Initially crews will only stay for a few weeks and use solar power, when energy storage is available they will extend missions out to six months.
2. Producing water comes after oxygen generation and power. Even if water ice is found in the dark craters it probably won't be used for a while because of the extreme difficulty in extracting and transporting it. Closed life support systems will probably precede ISRU. It seems unlikely that we'll be able to jump ahead to food production early on unless there are rapid advances in ISRU.
More details:
Crew & Habitat Consumables (Crew of 4) .......... Amount (kg/yr)
Oxygen Consumed in Hab by crew & leakage ..........2924.0
EVA oxygen (1kg O2*72 EVAs*4CM/180 days) ..........576.0
Total O2 Needed ...................................................3500.0Nitrogen Makeup N2 for leakage and airlock losses ....554.0
Water Mostly closed loop make-up .............................90.0
No water recycling ................................................3898.2
EVA water (4kg H2O 72 EVAs*4 CM/180 days) ........1152.0Total water (no recycling) ......................................5050.2
Total water (w/ recycling) ......................................1242.0Total Gas Inflate habitat (any gas - one time) .........1800.0
Without recycling the Outpost needs about 9MT of gases and water per year
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
I think the ISS generates about 100 kilowatts of useable electrical energy with about 2500 square meters of PV panels. That works out to about 40 watts per square meter of PV panel or an efficiency of about 3%. Something doesn’t commute in this by almost an order of magnitude.
But, if we figured PV panels could generate 300 watts per square meter (20+% efficiency), 2500 square meters on the moon would produce 750 kilowatts when pointed directly at the sun. 750 kilowatts should be enough electricity for quite a while.
Since the sun moves in the sky, I would think it would be easier to have more (say twice, or even three times as many) PV panels pointing in different directions, rather than try to steer the thing. Such an arrangement would also supply some redundancy, rather than introducing steering solar panels as another critical function.
Five thousand or even ten thousand square meters of PV panels seems quite feasible. Covering for the lunar night would be another problem, but solvable, I would think. Could the things produce any electricity from Earthshine? Paring down operations at night, some storage and a few good imaginative ideas should solve that problem.
So I don’t think nuclear will be necessary on the moon for quite a while.
Bob
Offline
The latest solar cells are about 30% efficient. Given tracking they can produce amazing amounts of power, each ISS pair of solar arrays produces about 30 KW. However the problem is mass, they are big and need more structural support when on the moon, they also need power conditioning and distribution hardware. They will need to be cleaned of lunar dust. So it's a trade of mass, size and performance. A 40 KW reactor has a mass of about 5 MT and operates continuously. Nuclear power will probably be necessary for processing water ice inside a permanently shadowed crater.
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
"The latest solar cells are about 30% efficient."
If solar cells are so efficient, why is it that the ISS solar cells apparently work at about 4%? 100 kilowatts for 2500 square meters?
Bob
Offline
The apparent magnitude of the Sun is -26.73; of the moon -12.6 which means the sun is about 450,000 times brighter than the full moon. (2.512^(26.73-12.6)). The full Earth is about 50 times brighter at the moon than the full moon at the Earth. So full Earthshine would be about 1/9000 as bright as the Sun at Earth. The 750 kilowatt solar power plant on the Moon would generate about 80 watts from the full Earth, if it worked at all.
Well 80 watts is better than nothing. But not much better. Maybe we could have a mirror at the Earth-moon L1, L4 or L5 LaGrange point that would shine sunlight on the solar array? L1 would be about 58,000 kilometers from the moon, I think. L4 or L5 would be about 200,000 kilometers from the moon, but would have stable orbits, unlike L1.
Bob
Offline
Don't forget the difference in albedo, the Earth (0.37) reflects about three the light of the Moon (0.12)
Stellarium tells me the maximum magnitude of the Earth as seen from the Moon is -16.2 and the Moon appears at max magnitude -12.2 from the Earth - a difference of 4 magnitudes or 2.5^4 or about 39 times brighter.
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
"Five thousand or even ten thousand square meters of PV panels seems quite feasible."
I agree Bobunf. In fact with ultra thin PV film and no weather we can cover large areas easily. Although there may be some reduction in efficiency compared with standard solar panels, the reduction in mass would still make the use of film desirable.
Ciclops -
Food production could be conducted on a near closed loop as far as water and nutrition is concerned, supplement with some lunar-sourced nutrients. I think we can move straight into food production. You take hydroponic equipment, water, and nutritional solution and an inflatable facility. The advantage is that once it is up and running you can make proper use of all waste matter - faeces and food scraps to recycle. If you don't have a food production facility, you don't have that recycling opportunity and you are having to resupply from earth. I think you could probably get a useful facility up and running with 200 litres of water. It's better to ship that in if necessary than not to set up crop production.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline
(0.37/0.12)*(12756^2/3474^2)=41.6
Albedo of Earth divided by albebo of moon times the disc of the Earth in square kilometers divided by the disc of the moon = the full Earth should be about 42 times brighter than the full moon.
But the light of the moon is attenuated by the atmosphere of the Earth, whereas Earthshine is not attenuated by any atmosphere. None of the ultraviolet or infrared is cut out. Plus Earth's atmosphere extends the disc several kilometers in every directon, especially if there are clouds.
So the energy received when the Earth is full at the surface of the moon is more than 42 times as much as the energy received on Earth from the full moon—say around 50 times as much.
Bob
Offline
"The latest solar cells are about 30% efficient."
If solar cells are so efficient, why is it that the ISS solar cells apparently work at about 4%? 100 kilowatts for 2500 square meters?
Bob
The 30% refers to the efficiency of converting solar energy into electricity. The ISS arrays were designed and built several years ago, typical silicon cells at that time were about 20% efficient. Today the latest triple junction cells are about 30%. Future cells based on CNT should reach 45%.
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
Or maybe this 30% is like the EPA mileage ratings: "city," "highway," but what we're really interested in "real world."
I hate to be so skeptical, but, if I did the calculating correctly, the best that's been done in the real world is 4%. It's one hell of a leap to 30%.
Grains of salt.
Bob
Offline
Mars Rovers achieved peak performance of 300 watts per hour over 4 hours I believe. I think the panel area was about 1.2 sq. metres giving about 2.5 megawatts per hour four hours for an array covering 10,000 square metres i.e. average 0.4 megawatt per hour over a 24 hour period. But that could probably be doubled with 12 hour operation from static arrays giving 0.8 megawatt per hour average over the whole day/sol. So 800 KWs on a 24 hour basis - a lot of energy.
Given insolation at the earth surface is 1000 watts per square metre ,insolation on Mars is unlikely to be higher (even though the thin atmosphere makes up in large part for the additional distance from the sun). So, I think the Mars Rover panels must have been operating at 30% efficiency or more.
It would be great if we could get some accurate figures on ultrathin PV film. It's difficult to get performance info - but it would probably be a lot less than 30% - 10% might be a reasonable estimate at this stage - giving a figure of about 270KWs for an area 100x100 metres. The mass involved would probably be around 500Kgs. Very good going I would say - and we could cover larger areas if we wished. But we probably need to balance area covered with effective storage. Chemical batteries would be part of the solution. Not sure how easy it would be to manufacture methane on the moon. Need to look into that.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline
"Mars Rovers achieved peak performance of 300 watts per hour over 4 hours I believe. I think the panel area was about 1.2 meters"
I don't think this could be correct. It would be over 50% efficiency, half of which has never been achieved in any application, let alone on a space vehicle using ten year old technology. Solar insolation at Mars orbit (forget any atmospheric effects) is less than 600 watts per square meter.
More grains of salt.
Bob
Offline
From Wikipedia: "the rovers' power supplies hovered between 300 watt-hours and 900 watt-hours per day, depending on dust coverage. "
Looks like I fell victim to the watts v watt-hours beginner's mistake - apologies for that (or it might have been the writer I read did, since i understand the difference!). On a four hour session looks like it was achieving between 75 watts and 225watts.
One point though, with a human mission the figures achieved are likely to be more towards the higher end because we will be able to do something about dust coverage.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline
225 watts would be 32% efficiency. Very hard to believe. Especially since positioning would not always be optimal, there would always be some dust coverage, and this is not even the technology for which 30% efficiency is claimed.
"watt-hours per day"
The sun would be up on Mars at the latitude of the rovers from 10 to 14 hours per day depending on the season and the rover. With very little atmospheric attenuation and optimal positioning, 14 hours could mean 14 hours--efficiency of about 9%.
Try thinking about these things more critically. Develop and treasure alternative competing hypotheses. You're not trying to rally the troops, but, rather, to figure out how this stuff really works.
When you make statements that are clearly incorrect from casual inspection by a lay person, you lose credibility, and the position you advocate losses ground with the people you're trying to convince.
Bob
Offline
Don't be cheeky Bobunf!
I'm v. critical.
However NASA have been very clear that the Mars Rovers operate for only four hours max. a day, so if you want to dispute that you will need to provide some evidence.
See this article for efficiency of over 40% being achieved -
http://www.reuk.co.uk/40-Percent-Effici … Panels.htm
The Mars Rover panels would have been state of the art when designed in 2000-2002 I guess. So would not seem impossible for them to achieve 30% around that time I think.
I have just seen an efficiency claim for ultra thin of over 19% which is also v. encouraging.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline
“Mars Rovers operate for only four hours max. a day”
Why do you suppose that is? Union rules?
The reason is that Spirit and Opportunity don’t have enough electricity to operate any longer. The rest of the day is spent charging the batteries so the rovers don’t freeze overnight. You’re confusing operating time with charging time.
We’re back to 9% efficiency, which is better than the 4% of ISS.
Bob
Offline
Bobunf -
I think it's you who are confused. They are charging the batteries for the 4 hours (and they do to a certain extent track the sun). For the rest of the time they are on the move. That's my understanding.
No, we're at 30% plus efficiency I think. It's just for a limited time.
I'll see if I can get you a citation because obviously you're not going to believe my recollections.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline
The reason is that Spirit and Opportunity don’t have enough electricity to operate any longer. The rest of the day is spent charging the batteries so the rovers don’t freeze overnight. You’re confusing operating time with charging time.
We’re back to 9% efficiency, which is better than the 4% of ISS.
This is getting way OT, however maybe this helps.
The rover was powered by a combination of solar arrays and rechargeable batteries. The solar panel provides 30 strings of triple junction cells (gallium indium phosphorus, gallium arsenide, and germanium) covering 1.3 square meters, which produced about 800 to 900 W hours per sol at the beginning of the MER mission. Each rover had two reference solar cells, one that measures short circuit current and another that measures open circuit voltage. Due to the change in season from late southern summer to early southern autumn, and the degradation in performance due to dust deposition, the energy produced by this array dropped to about 600 W h per sol, 90 sols after landing. Energy was stored in two 8 A h lithium ion rechargeable batteries to provide over 400 W h of energy to support rover peak power operations and provide auxiliary heating and operations overnight.
Currently MER Spirt is producing 237 watt-hours per sol, just enough to do 90 mins of science per sol. Spirit is not moving at all, it's been sitting tilted towards the Sun for weeks because of its low power levels. Opportunity is much further south and has more power, it has other problems but has enough power to move.
Now back to discussion of the Lunar Outpost please ...
[color=darkred]Let's go to Mars and far beyond - triple NASA's budget ![/color] [url=irc://freenode#space] #space channel !! [/url] [url=http://www.youtube.com/user/c1cl0ps] - videos !!![/url]
Offline
Thanks Ciclops for that info which is helpful.
However this debate isn't completely at a tangent. We're trying I think to establish the sort of photovoltaic efficiency that could be achieved in an operational (as opposed to laboratory) environment. Given as far as I am aware there have been hardly any relevant missions to the lunar surface in recent times, we do have to draw on Mars experience to get an idea of what can be achieved. There's a big difference between the 30% plus I am claiming and the 9% Bobunf is putting forward.
Do you have any info on what efficiency levels (as opposed to watt hours) have been achieved on Mars?
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
Offline