Author Topic: Internal Combustion Engines (ICEs) on the Moon  (Read 135245 times)

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #20 on: 01/05/2014 02:13 am »
Look up pumped storage for example - you convert power to "potential energy". Entirely doable by moving in-situ available mass.

So you propose to pump water up to a reservoir high on a mountain during the day, and then letting it run down in the night? It could work, but the piping is going to mass a lot--you'd pretty much have to do it with ISRU materials somehow; and, given the 1/6 g gravity on the Moon, the same amount of head on the Moon is going to deliver a lot less power than you would have on Planet Earth...
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Offline Lee Jay

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #21 on: 01/05/2014 02:16 am »
The power system on a battery powered rover consists of a BIG battery and an electric motor; using an ICE, the power system consists of the electric motor, a small battery, a small generator/starter, a small ICE, a fuel tank, AND the fuel.

Presumably a gaseous hydrogen tank?  Figure 5% mass fraction for that.

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #22 on: 01/05/2014 02:27 am »
The power system on a battery powered rover consists of a BIG battery and an electric motor; using an ICE, the power system consists of the electric motor, a small battery, a small generator/starter, a small ICE, a fuel tank, AND the fuel.

Presumably a gaseous hydrogen tank?  Figure 5% mass fraction for that.

Well, I was thinking hydrogen peroxide since that's what the MoonEx lander proposes to use. The tank would be relatively simple then. The only question is how many kg of H2O2 you would need to run a 400 W ICE for 24 hours....
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Offline joek

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #23 on: 01/05/2014 02:34 am »
Yes, I was thinking of mainly mobile, mass-limited applications (rovers/miners). However, consider perhaps the early stages of a lunar base that must survive 2 weeks of darkness. Batteries would be the most efficient end-to-end system, at least as far as electricity is concerned, but you'd have to haul in a huge load of batteries, most likely from Earth. Any heating you did would have to come from electric heaters, and any shaft power you needed would require electric motors.

Not exactly comparable, but worth a note ... There is a guy in the Pacific Northwest who has a home on a remote island in the Orcas San Juan's.*  No access to the grid.  He set up a solar array with battery storage (deep cycle marine).  That wasn't enough for him, and the cost of additional battery storage was significant (not just the cost of the batteries, but hauling them to a remote location, and the volume required to house them).

So he installed an electrolysis system to harvest excess solar energy beyond what he could store in the batteries and store it as H2, with fuel cells to then recover the energy and generate electricity from the stored H2.  The end-to-end efficiency of the H2 system sucks (IIRC ~7%), but it allowed him to harvest the excess energy when it was available and use it for "peak demand" or when solar/battery was tapped out.


* He had/has a web site documenting his efforts.  If anyone is interested I'll try and find it.
edit: found it: http://www.siei.org/
« Last Edit: 01/05/2014 08:32 am by joek »

Offline savuporo

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #24 on: 01/05/2014 02:35 am »
So you propose to pump water up to a reservoir high on a mountain during the day, and then letting it run down in the night?
No.
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Offline go4mars

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #25 on: 01/05/2014 02:43 am »
* He had/has a web site documenting his efforts.  If anyone is interested I'll try and find it.
Yes please.
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Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #26 on: 01/05/2014 03:10 am »
* He had/has a web site documenting his efforts.  If anyone is interested I'll try and find it.
Yes please.

Ditto!

Well, I was thinking hydrogen peroxide since that's what the MoonEx lander proposes to use. The tank would be relatively simple then. The only question is how many kg of H2O2 you would need to run a 400 W ICE for 24 hours....

We can put some numbers to this: that paper attached a few posts back said the specific energy of H2O2 when the exhaust is condensed water is 2.9 MJ/kg, whereas the specific energy when the water is vapor is only 1.6 MJ/kg (compared to ~13 MJ/kg for GH2/GO2), which isn't so hot, but at least its is a monopropellant that doesn't need an oxidizer.

Now if the thing could run for 24 hours at 200 W, that would basically double the loiter time for the proposed RPM. So we work backwards from there.

Assuming 30% efficiency, then the specific energy of H2O2 available for shaft energy is 0.48 MJ/kg.

Next, 200W * 24 hr = 4800 Whr = ~17 MJ.

Thus, one would need 17.3 MJ / 0.48 MJ/kg = 36 kg of H2O2.

Well, I guess that's yet another argument for using LH2/LO2 for landers! GH2/GO2 ICE could run for 24 hours at 200 W using only 4.4 kg of propellant.... :(

ETA: If the ICE was engineered really well, perhaps an efficiency of 40% could be squeezed out. Also, some versions of the RPM I've seen only call for 100 W; presumably some of this must be used for thermal management. Thus, one could probably get away with a 75 W ICE and use the "waste" heat for thermal management. If you did all those things, the rover could run for 24 hours using only 10 kg of residual H2O2. If you used hydrazine, you could probably run for 24 hours on 5 kg (or 1.2 kg of GH2/GO2).

That seems more reasonable. With luck, depending on how much margin was left over, you could get 2 or 3 fill-ups...
« Last Edit: 01/05/2014 03:33 am by Warren Platts »
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Offline joek

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #27 on: 01/05/2014 08:45 am »
* He had/has a web site documenting his efforts.  If anyone is interested I'll try and find it.
Yes please.
Ditto!
found it & updated original post; see: http://www.siei.org/

Offline HappyMartian

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #28 on: 01/05/2014 08:55 am »
Cost effectiveness suggests a long-term and efficient international power and communication option.

There are probably at least a dozen excellent ice and frozen gas candidate craters in the north polar region and maybe as many in the south polar region that need to be explored by an inexpensive robotic rover.

Several countries have or will soon have the technical ability to land a small rover near or in one of those permanently shadowed polar craters.

American space law instructs NASA to do international missions in cis-lunar space and cis-lunar space is clearly defined in that law to include the surface of the Moon.

Countries with a large Lander might choose to land several inexpensive rovers at the same time, and then those rovers would proceed to travel in different directions to nearby craters.

I have nothing against the idea of using an ICE in some situations.

However for robotic rover missions in permanently shadowed regions, or PSRs, and other regions that are almost PSRs, ICEs are not the best solution for the needed efficient extended exploration and communication requirements of the small rovers. Instead, we need very long international missions that are somewhat similar to that of the small Opportunity rover on Mars.

Solar power is available in orbit, but that is a considerable distance from those inexpensive rovers.

Nonetheless, a constellation of eight small communication/power sats in a polar orbit should be able to maintain intervals of regular communication and also beam sufficient infrared laser power on an intermittent basis to several small robotic rovers in the polar regions of the Moon.


"Lockheed Martin and LaserMotive recently demonstrated the capabilities of an innovative laser power system to extend the Stalker Unmanned Aerial System (UAS) flight time to more than 48 hours. This increase in flight duration represents an improvement of 2,400 percent."
From: Laser Powers Lockheed Martin's Stalker UAS For 48 Hours  July 16, 2012
At: http://www.spacedaily.com/reports/Laser_Powers_Lockheed_Martins_Stalker_UAS_For_48_Hours_999.html


"Following the wind tunnel test, Lockheed and LaserMotive Inc. performed a series of outdoor tests with the laser powering system the next month. The flight tests went successfully, and accomplishments included:
Demonstrating net positive power to the Stalker in flight, at ranges up to 600 meters.
Proving that the laser did not damage the Stalker and that the addition of the laser receiver did not impact its normal flight operations or aerodynamics.
Operating multiple test flights in a range of desert conditions (day and night, high temperatures, and strong winds), demonstrating the ruggedness of the Stalker-mounted laser receiver power system.
The beam director tracking the receiver for long periods, with centimeter accuracy at 500 meters, despite turbulence and aircraft maneuvers."

From: Lockheed Martin Stalker    Wikipedia
At: http://en.wikipedia.org/wiki/Lockheed_Martin_Stalker


"Testing will continue once the LaserMotive-built 'horse trailer-sized' laser apparatus has shrunk down to something suitably small for tactical operations, which Coontz describes ideally as the size of two travel suitcases put together."

From: AUVSI: Lockheed Stalker offers improved endurance  By Zach Rosenberg   August 13, 2013 
At: http://www.flightglobal.com/news/articles/auvsi-lockheed-stalker-offers-improved-endurance-389385/
   

A constellation of small power/communication sats in a Lunar polar orbit could be quite useful for providing both intermittent laser beamed power and high data communication links for a twenty-year-long Lunar polar small robotic rover campaign to extensively explore both polar regions.


"'There are actually a number of 'frozen orbits' where a spacecraft can stay in a low lunar orbit indefinitely. They occur at four inclinations: 27º, 50º, 76º, and 86º'—the last one being nearly over the lunar poles."

From: Bizarre Lunar Orbits
At: http://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit/



Other higher polar orbits may be preferable, and should be considered, in examining the best technical option.


Note also the power requirements of the 185 kilogram Opportunity, MER-B (Mars Exploration Rover – B) that continues in 2014 on a mission that began when it landed on Mars on January 25, 2004.


"Solar arrays generate about 140 watts for up to four hours per Martian day (sol) while rechargeable lithium ion batteries store energy for use at night. Opportunity's onboard computer uses a 20 MHz RAD6000 CPU with 128 MB of DRAM, 3 MB of EEPROM, and 256 MB of flash memory. The rover's operating temperature ranges from −40 to +40 °C (−40 to 104 °F) and radioisotope heaters provide a base level of heating,"

From: Opportunity (rover)   Wikipedia
At: http://en.wikipedia.org/wiki/Opportunity_%28rover%29


Radioisotope heaters similar to those on Opportunity could provide sufficient heat to maintain each small international Lunar rover in a temporary warm sleep mode even if the recharging of the batteries with laser beamed infrared light doesn't occur or is sometimes reduced due to a foreseen or unplanned interruption of normal beaming and communication operations.

Edited. 
« Last Edit: 01/05/2014 09:19 am by HappyMartian »
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Offline A_M_Swallow

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #29 on: 01/05/2014 09:14 am »
On a long term off-Earth mission the steam produced by the ICE will need recycling.  So the complexity and mass of the condenser, water tank and water need including.

Why would a long-term mission need to recycling the water produced by the ICE? It's not like you can recycle the water back into hydrogen and oxygen, and robotic missions have no need for water. Now if you were talking about a manned mission recovering the waste water might make sense but that wasn't mentioned.

If you do not recycle then the vehicle will run out of fuel.  Water can be converted back into hydrogen and oxygen using electrolysis.  The electrolysis could be powered by solar electricity back at a base/surface.

Water on the Moon appears to be concentrated at the polls.  An aluminum mine could be on the lunar equator, making water very expensive.

Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #30 on: 01/05/2014 06:33 pm »
I think ICE is a better choice for PSRs but to be fair, a solar powered rover (or later, digger, driller, hauler, maintenance mech for the ISRU, etc. etc.) might well "dip in" to the PSR to do some work, then "climb back out" by traveling back to sunlight, and get recharged and then go back in, many many times... as long as nothing bad happened.

That is the plan for RPM: to do one "dip in", climb out, recharge, and then go for broke as long as it lasts within the PSR.

Quote
The higher energy density of the H2 ICE means it has a lot more dwell time before it has to refuel, IMHO anyway.

There's a few things going on here: energy density is energy per unit volume (J/m3), and then there's specific energy, which is energy per unit mass (J/kg). And then there's specific power, which is the amount of power that can be delivered per unit mass (W/kg). H2 has great specific energy, but lousy energy density, which is its biggest disadvantage since it requires gigantic fuel tanks for the amount of energy you get.

Here's a table that compares GH2/GO2 (pressurized up to 300 bar) versus H2O2. Kind of surprised that the energy density of the GH2/GO2 compares well with the H2O2 if I did the math right...

fuelGH2/GO2   H2O2
MJ/kg131.6
GJ/m^3    2.92.3
kg/m^3    2221450

Of course a 1 m3 tank (actually 2 tanks) for GH2/GO2 is going to be a lot more massive than a single tank for liquid H2O2.

The thing about specific power is that you need to take into account both the mass and density of the power plant in addition to the fuel mass. Thus as you go piling on the fuel, your specific power goes to zero (since rated power is more or less constant), and the specific energy of the combined engine/fuel system goes to the specific energy of the fuel. (See attached "Ragone" plot).

Thus, the problem for small rovers is the volume of the tank. For big mining equipment, you want to pile on as much high specific energy as you can, volume be damned as much as possible. Next step is to figure out how much fuel is required for a 300 hp excavator to run for 10 hours....
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Offline Lar

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #31 on: 01/05/2014 07:45 pm »
Interesting info, Warren. Does energy density get any better if you are using liquid H2 and O2 in the tanks and combusting the boiloff? It may take more energy to make the fuel for refilll (since you have to chill it to liquefy it) but energy out in the sun might be worth spending profligately if it improves energy density.

I have this visual of a digger (with smaller tanks) pulling a trailer 3x the size it is with big fuel tanks on it :) Of course all that complexity adds mass and failure points.
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Offline Lar

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #32 on: 01/05/2014 07:46 pm »
I think ICE is a better choice for PSRs but to be fair, a solar powered rover (or later, digger, driller, hauler, maintenance mech for the ISRU, etc. etc.) might well "dip in" to the PSR to do some work, then "climb back out" by traveling back to sunlight, and get recharged and then go back in, many many times... as long as nothing bad happened.

That is the plan for RPM: to do one "dip in", climb out, recharge, and then go for broke as long as it lasts within the PSR.

Why is that the plan? Why not dip in multiple times?
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Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #33 on: 01/05/2014 08:21 pm »
I think ICE is a better choice for PSRs but to be fair, a solar powered rover (or later, digger, driller, hauler, maintenance mech for the ISRU, etc. etc.) might well "dip in" to the PSR to do some work, then "climb back out" by traveling back to sunlight, and get recharged and then go back in, many many times... as long as nothing bad happened.

That is the plan for RPM: to do one "dip in", climb out, recharge, and then go for broke as long as it lasts within the PSR.

Why is that the plan? Why not dip in multiple times?

I'm guessing its because they're afraid of getting stuck and losing the rover. The goal is to get at least 1 or 2 cores from relatively deep within the PSR, and that's going to be a suicide mission. So they want to minimize the risk of losing the rover on multiple shallow excursions into the crater. The first "dip in" is mainly a sort of reconnaissance mission to help form a plan of action once the batteries are fully recharged.

Interesting info, Warren. Does energy density get any better if you are using liquid H2 and O2 in the tanks and combusting the boiloff? It may take more energy to make the fuel for refilll (since you have to chill it to liquefy it) but energy out in the sun might be worth spending profligately if it improves energy density.

I have this visual of a digger (with smaller tanks) pulling a trailer 3x the size it is with big fuel tanks on it :) Of course all that complexity adds mass and failure points.

I think the BMW site said their "Hydrogen 7" car (which runs on LH2) can pack 75% more energy per volume than they could with a 300 bar GH2 tank. Haven't yet crunched the numbers myself. Of course H2 ICEs on Planet Earth don't have to bring their own oxidizer....

I figured for a 200 kW excavator to run for 10 hours, it would take about 1385 kg of H2+O2 to run:

Energy density of H2/O2 = 13 MJ/kg
Efficiency = 40%
Available energy density = 5.2 MJ/kg
200 kW * 36,000 s = 7200 MJ
7200 MJ / 5.2 MJ/kg = ~1385 kg

Which seems like a LOT....
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Offline R7

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #34 on: 01/05/2014 09:27 pm »
I figured for a 200 kW excavator to run for 10 hours, it would take about 1385 kg of H2+O2 to run:

Energy density of H2/O2 = 13 MJ/kg

That appears to be using 8:1 O/F stoichiometric mixture, 1/9th of hydrogen's ~120MJ/kg LHV. As you wrote earlier IVF ICE runs 1:1 rich, only 1/16th of total propellant mass is burned. 120MJ/kg / 16 = 7.5MJ/kg.

The good news is 200kW terrestrial excavators are quite big 30+ ton machines and in 1/6th gee you could use that power to move even bigger machine. Traditionally a lot of energy is wasted into heat by not trying to recover it when you lower or turn the boom. Substantial amount of that can be recovered by regenerative breaking (see terrestrial example).
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Offline Warren Platts

Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #35 on: 01/05/2014 09:56 pm »
I figured for a 200 kW excavator to run for 10 hours, it would take about 1385 kg of H2+O2 to run:

Energy density of H2/O2 = 13 MJ/kg

That appears to be using 8:1 O/F stoichiometric mixture, 1/9th of hydrogen's ~120MJ/kg LHV. As you wrote earlier IVF ICE runs 1:1 rich, only 1/16th of total propellant mass is burned. 120MJ/kg / 16 = 7.5MJ/kg.

I'm getting something somewhat different. The chemical equation would be:

1/2 O2 + 8 H2 = 1 H2O + 7 H2

if these were moles, the mass equation would be:

16 g O2 + 16 g H2 = 18 g H2O + 14 g H2

Thus, if I'm doing it right, the latter 14 g H2 don't contribute anything to the reaction energy, so it's 14 g/32 g = 0.4375. Hence, 13 MJ/kg * 0.4375 = 5.7 MJ/kg. And 40% of that is ~2.3 MJ/kg -- almost back down to H2O2!

However, there could be a magic means of recovering the unused H2. Presumably, a big excavator would use LH2/LO2. And by running a mass ration of 1.0, you're exhaust gases are several hundred degrees less than they would be if you were burning a stoichiometric mixture (mass ration 8.0). Thus, run the exhaust through an expansion valve for some adiabatic cooling, then through a heat exchanger within the LO2 tank--since you need GO2, and the boiloff within a shaded crater is going to be less than the demands of the ICE. This will cool the exhaust enough to condense out the H2O, but obviously not enough to liquefy the GH2, so the exhaust then gets cycled back to the fuel injectors, and back into the combustion chambers. Of course, this is all conceptual at this stage. I haven't put any numbers to it yet....

Quote
The good news is 200kW terrestrial excavators are quite big 30+ ton machines and in 1/6th gee you could use that power to move even bigger machine. Traditionally a lot of energy is wasted into heat by not trying to recover it when you lower or turn the boom. Substantial amount of that can be recovered by regenerative breaking (see terrestrial example).

Yes, I was also looking at a similar excavator made by Caterpillar, the 336 EH HYBRID. They claim that regenerative braking can reduce fuel consumption by up to 33% over the similar non-hybrid model. The other good thing is that such a big unit has room to put huge fuel tanks. We're probably looking at tanks at least as big as 4 times the size of the terrestrial models (which are 163.8 gallons).

@ Lars: I like the idea of a trailer to hold extra fuel for a prospecting rover! It's sort of like staging for rockets....
« Last Edit: 01/05/2014 11:11 pm by Warren Platts »
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Offline savuporo

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #36 on: 01/05/2014 11:35 pm »
I dont know how to put this exactly but .. with all these figures of 40% efficiencies ( which are fiction anyway ) etc and 100 kilowatt outputs, people dont realize that you are effectively pumping 60kw of heat directly into a closed system somewhere, continously, and all the rest of 40kw ends up as heat too. Or as anyone that is briefly familiar with thermal design of spacecraft would say, "in this house, we obey the laws of  thermodynamics!"

Good luck building heat pumps and radiators ( convection cooling is not terribly effective in vacuum )

All the theoretical energy density figures of fuel sources are pretty much meaningless in a real system design.
« Last Edit: 01/05/2014 11:40 pm by savuporo »
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Offline A_M_Swallow

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #37 on: 01/05/2014 11:47 pm »
{snip}
Good luck building heat pumps and radiators ( convection cooling is not terribly effective in vacuum )

All the theoretical energy density figures of fuel sources are pretty much meaningless in a real system design.

Sounds like we will have to pump the gasses to the surface.  A hot mixture of steam, water, hydrogen, hydrogen monoxide, hydrogen peroxide and oxygen may need pipes made from stainless steel.

Offline savuporo

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #38 on: 01/05/2014 11:57 pm »
Sounds like we will have to pump the gasses to the surface.  A hot mixture of steam, water, hydrogen, hydrogen monoxide, hydrogen peroxide and oxygen may need pipes made from stainless steel.
Brilliant engineering ! Wikipedia says that lunar surface is 12% iron so thats perfect.
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Offline joek

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Re: Internal Combustion Engines (ICEs) on the Moon
« Reply #39 on: 01/06/2014 02:48 am »
I dont know how to put this exactly but .. with all these figures of 40% efficiencies ( which are fiction anyway ) etc and 100 kilowatt outputs, people dont realize that you are effectively pumping 60kw of heat directly into a closed system somewhere, continously, and all the rest of 40kw ends up as heat too. Or as anyone that is briefly familiar with thermal design of spacecraft would say, "in this house, we obey the laws of  thermodynamics!"

Good point. I was trying to make a similar point over in the MCT-Mars fast transit thread but hadn't really thought about the implications for Lunar surface systems.  Obviously depends on several factors; for in-space deployable radiators some numbers to chew on:*
1. Current state (e.g., ISS)
- 14.64kg/m2 (given)
- 2.2m2/kW (given)
= ~32kg/kW
2. Near term ("with investment")
- 10kg/m2 (given)
- 2.2m2/kW (given)
= ~22kg/kW
3. Long term ("may approach")
- 2.5kg/m2 (given)
- 2.2m2/kW (not given, but implied)
= ~5.5kg/kW (given)

* Fast Transits to Mars Using Electric Propulsion, John W. Dankanich et. al., AIAA 2010-6771
« Last Edit: 01/06/2014 02:49 am by joek »

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