Light weight nuclear reactor, updating Mars Direct

SpaceNut · 2016-01-18 20:20:42

We have been discussing the Small Nuclear reactors for use in an RV sized rover for Mars and it would seem that the SAFE-400 or small is in the ball park for use but its in need of modifications for Mars use.

We all know that we need a robust power sources in the range of 10 to 200 kWe. Fission systems are well suited to provide safe, reliable, and economic power within this range. The Heatpipe Power System (HPS) is one possible approach for producing near-term, low-cost, space fission power. We have talked about the SAFE-400 which is a 400-kW thermal reactor. Its design couples to a 100-kWe Brayton gas power system. Details of the SAFE-400 are that it contains 127 identical molybdenum (Mo) modules. A Mo/sodium heatpipe is at the center of each module, surrounded by three Mo tubes that each contain a rhenium-clad uranium-nitride fuel pin. Fission energy is conducted from the fuel pins to the heatpipes, which then carry the heat to a heatpipe-to-gas heat exchanger.

The Safe Affordable Fission Engine (SAFE) Test Series April 3 - 5, 2001 NASA/JPL/MSFC/UAH 12th Annual Advanced Space Propulsion Workshop

The Role of Nuclear Power and Nuclear Propulsion in the Peaceful Exploration of Space

kbd512 · 2016-01-22 18:11:22

The passive cooling system of SAFE-400 is a nice design feature from a simplicity standpoint, but to operate it on Mars the radiators must be attached to the reactor in a deployed configuration or the radiators require some sort of deployment mechanism. SAFE-400 requires a 100m2 to 150m2 radiator. That's not unworkably large, but large enough that radiator deployment is likely required.

Obviously Mars has an atmosphere, even if it is rather thin, and it may make sense to use an open loop active cooling system that sucks in the Martian atmosphere and compresses or liquefies it for use as a coolant in an open loop. It's either that or figure out how to package delicate radiators to avoid damage from EDL. Although it's obvious that any mechanical part can fail, and we'd love to avoid mechanical complexity if possible, I think an active cooling system mitigates some of the operational issues with packaging and deployment of large surface area radiators.

Irrespective of any radiator operational use issues, shielding is also required to operate the reactor anywhere near the habitat. The SAFE-400 working group was not concerned with reactor shielding, but obviously any use of the reactor in close proximity to humans or electronics requires it.

I think the best solution, if unattractive from a mass requirement, is to properly shield the reactor so that humans can briefly work on the reactor while it is in operation. Exclusion zones should not extend more than 5M from the reactor and any habitat placed 25M from the reactor should not require any additional shielding to protect against radiation from the reactor.

More importantly, I think the reactor must be transportable to assure that the reactor is available to the crew, in the event that the lander or habitat lands off-course.

RobertDyck · 2016-01-22 19:08:17

Transportable: Mars Direct included the SP-100 reactor. That plan included an autonomous truck to deliver the reactor to a crater, drop it in the bottom so the regolith of the crater walls are radiation shielding. Obviously that means the crater and any ground close enough to see down into the crater is the exclusion zone. I suggested a simplification: instead of a truck to transport the reactor (once), bolt mobility equipment identical to the Curiosity rover. That is wheels, motors, suspension arms, navigation camera (nav cam), and autopilot computer. No science instruments. That means you won't have a separate truck, but it's a way to reduce launch mass.

GW Johnson · 2016-01-25 11:25:05

I read on another thread that most of the electric propulsion schemes demand something close to 200 kW electric. That suggests a scaled-up SAFE 400 design of about 800-1000 kW thermal (at the same indicated 25% conversion efficiency) would produce 200-250 kW electric. That's enough to add an electric thruster engine to the conventional engines we need for impulsive burn efficiency.

If you build a long baton shape of a vehicle, and put your hab at one end and the reactor at the other (with a shadow shield), then you have a spinnable design for artificial gravity. Put your electric propulsion at the spin center. The modules that make up the baton are mostly propellant tanks and other supplies, that help with the shielding issue.

I'd put the conventional engines at either the reactor end or the hab end, to put their large thrust through the axis of the stack, which makes good structural sense. The stack needs to be modules in parallel as well as series, so that empties can be jettisoned, although I hate losing equipment if I can avoid it.

That kind of vehicle is an orbit-to-orbit transport, with impulsive chemical rocket departure and arrival burns, plus electric propulsion to speed up the long transits each way. It is fundamentally a potentially-reusable design, as well. The same vehicle could take you pretty much anywhere in the inner solar system, at least from the asteroid belt inward.

We have chemical rockets, we have more than one kind of electric thrusters, we are getting very close to practical hab designs, we have dockable module technology. I'm guessing scaling up a SAFE 400 is not that difficult. All we need is a lander and the surface-stay gear.

There's nothing here that cannot be done, and probably could have been done some time ago.

GW

SpaceNut · 2016-01-25 17:31:02

I am not sure why we are trying to dump all that thermal heat from a reactor when it could be used to power a sterling engine generator or other power creating methods...Is the heat level to low for use?

RobertDyck · 2016-01-25 18:36:39

Any power generator required a strong temperature difference. So anything that obstructs heat flow will reduce power generated. But you should be able to use the heat for something mild, like heating a greenhouse. Would that significantly obstruct heat flow?

GW Johnson · 2016-01-25 19:18:15

My understanding of the SAFE 400 is that the reactor generates heat, which is carried to the generating rig by heat pipes. The generating rig is some kind of a heat engine, just not a naval or commercial steam loop rig. All (and I do mean ALL) heat engines are subject to the laws of thermodynamics. Their conversion efficiencies will fall between two bounds: upper bound is Carnot efficiency = 1 - Tcold/Thot. The lower bound is zero. Few real devices come anywhere close to Carnot efficiency.

The numbers I saw discussed above for the SAFE 400 said it was 400 KW thermal, and put out 100 KW electric, for a conversion efficiency of 100 KW/400 KW = 25%. That ain't bad for a small device, and it's significantly better than your car at best-mileage cruise. Even the giant 1000-1200 MW electric steam loop rigs at power plants rarely exceed 40% efficiency. These efficiencies are indirectly scale-dependent: bigger is usually at least slightly better.

GW

Last edited by GW Johnson (2016-01-25 19:18:48)

SpaceNut · 2016-01-25 20:04:25

Radiating heat of 400 kw into a vaccumn or into mars is not quite the same for the same reactor as Mars can wick the heat from the radiator while the emptiness of a vaccumn is done by mass obsorbtion....

http://www.chromalox.com/catalog/resour … iquids.pdf

http://www.pumpschool.com/applications/hightemp.asp

http://www.thermaltransfersystems.com/p … angers.Pdf

http://www.rotron.com/techcorner/cooling-flow.aspx

http://www.thermo-dynamics.com/pdfiles/ … _guide.pdf

GW Johnson · 2016-01-26 10:28:02

Physics says that in space your only option to shed heat is by radiation, via the Stefan-Boltzmann law. With SAFE-400, that would be about 300 KW thermal to be radiated, and you have to radiate it at the "Tcold" waste temperature from the heat engine (likely near liquid water temperatures). It radiates to deep space at 4 K, except if the radiating surface faces the sun, where it won't work well, if at all.

It's easier on Mars, as radiation, convection, and conduction are all available. Convection is awfully weak because the air density is so low. But you can spread a big hot mat on the ground and conduct heat into the cold ground, by conduction. There will be a contact resistance, but it will work. Burial of the hot mat is even better. This would be more suited to something stationary, though. Radiation is less effective than in deep space, because your background receiving sink is no longer 4 K.

Qrad = sig e A (Trad^4 - Tsink^4), where sig is the Stefan-Boltzmann constant, e is your emissivity (0 to 100%, better as close to 100% as possible), and A is the area of your radiating surface. If you know Qrad, and the appropriate temperatures, the equation sizes your radiating area A. The equation uses absolute temperatures. Most folks these days do it metric in deg K.

GW

SpaceNut · 2016-01-26 20:59:23

Stefan-Boltzmann law and what describes the power radiated from a black body in terms of its temperature. This I have had some basic knowledge of with in terms of sensing and transmitting of thermal energy. Also with regards to solar energy for hot water ect....

So we need a good calculator to solve for what we need for a radiator....

http://hyperphysics.phy-astr.gsu.edu/hb … tefan.html

Here is the way more complex math for those that can follow it...and thats not me....
https://en.wikipedia.org/wiki/Stefan%E2 … tzmann_law

This how we see it from the standpoint of a sun
http://www.teachastronomy.com/astropedi … tzmann-Law

So from what we know from your equation Qrad = 400 kw where e= 5.6703x10^-8 w / m^2 K^4 the stefan constant, the A =area which is an unknown at this point, ( Trad^4 - T sink ^4) will vary due to T sink changes during the day to night on Mars....so unless we can modulate the rods to reduce power output during the day to lessen the Trad^4 we are going to have a problem with trying to create a fixed area radiator, oh an sig is sort of like the efficiency rating of the ratiator to do the job.

http://cmex.ihmc.us/data/catalog/Surfac … tTemp.html

The temperature on Mars may reach a high of about 70 degrees Fahrenheit (20 degrees Celsius) at noon, at the equator in the summer, or a low of about -225 degrees Fahrenheit (-153 degrees Celsius) at the poles. In the mid-latitudes, the average temperature would be about -50 degrees Celsius with a nighttime minimum of -60 degrees Celsius and a summer midday maximum of about 0 degrees Celsius.

Oldfart1939 · 2017-01-02 14:06:42

I'm not making a new contribution to this thread, but simply bringing it forward for some possible inclusion in a possible new "Mars Development Flow Chart" thread. I'm not a big supporter of a Solar Panels only approach. Power is needed during dust storm cycles.

Oldfart1939 · 2017-01-02 16:36:08

After skimming thorough this thread, it seems as though the SAFE-400 reactor is a possible candidate for an early SpaceX Red Dragon mission to Mars?
In my analysis of any construction of a Mars base/colony, one of the first requirements for any progress at all will be availability of ample electric power. The mobility option described above in post #128 seems to be a way of moving this to an operating location. This would not be used in an early Methylox generation protocol, but a pre-positioned power source for the first base.

SpaceNut · 2017-01-02 17:44:48

Here are a few more links for what I know about nuclear which is not must....

EVIDENCE FOR A LARGE, NATURAL, PALEO-NUCLEAR REACTOR ON MARS from thorium and potassium detection.

Abstract Nuclear Design of the SAFE-400a Space Fission Reactor

https://www.researchgate.net/publicatio … on_reactor

http://www.world-nuclear.org/informatio … space.aspx

Based on small mass this might be a good choice to drop to mars in a modified for landing Dragon of course it will need cabling and other supports to make it workable for Mars Insitu methane production....

kbd512 · 2017-01-09 21:55:17

SpaceNut,

Is there any reason why pressure operated valves can't change the volume of the coolant loop to stabilize the operating temperature of the reactor?

SpaceNut · 2017-01-10 19:40:54

I know of thermostaic valves such as the 1 used in your car cooling system but a pressure controled valve uses a sensor and electronincs to control the valve. I am not aware of a direct controlled pressure valve but I do not see why it could not be one as that is what we do when we are use pressure regulated air with spring loaded tension.

Fluids in piping are restricted to wall pressure max at a flow rate for the diameter of the pipe with the wicking rate from fluid controlled by the metal and thickness of it. Adding Fins or a mass obsorber changes these rates a bit. Another way to achieve more surface is to add multiple parallel paths of tubing for the fluid to flow through.

This is simular but oposite to how solar thermal works as well with the flat plate collectors with the longer the path and with slow flow rates the hotter the working fliud gets.

elderflower · 2017-01-11 11:11:22

Self acting pressure control valves are actually common, Spacenut.. They normally have a diaphragm subject to the controlled pressure, opposed by a spring. Pressure increase pushes the diaphragm and closes the valve until the new pressure balances with the spring force again.
These devices depend on a flow through them to generate a drop in pressure.

SpaceNut · 2017-06-25 17:21:26

The proposed FSP system uses a low temperature, uranium dioxide-fueled, liquid metal-cooled fission reactor coupled to free-piston Stirling converters. System Concepts for Affordable Fission Surface Power

A notional lunar outpost power profile was assumed at 30 kWe for the first 5 years and 80 kWe for 15 years thereafter. Which would mean sending several of these to be used for the specific life support function with surplus going towards exploration.

RobertDyck · 2017-10-01 16:22:20

Another update to Mars Direct. Could we use a "sky crane" like Curiosity? Mars Direct was developed in the last quarter of 1989, and first half of 1990, presentation to NASA in June 1990. That first hab had a single deck. Description included a rover, but where would the rover go? Later that same year Robert Zubrin added a lower deck with garage for the rover. I presume the first version would sling the rover under the hab, nestled between landing engines, held by cables that could lower with a winch. The problem with that is rocks kicked up by rocket exhaust could damage the rover. Notice the Apollo lunar rover was contained in a storage compartment, protected from rocks.

But Curiosity was able to land without any storage compartment; dropped by cables from a sky crane that stayed high enough that it didn't kick up rocks. If we use a sky crane, could we sling the rover under the hab? Just protected by the heat shield during transit, no storage compartment? That would reduce the lower deck to nothing but air lock, stairway to the upper deck, life support equipment, and storage for surface equipment including inflatable greenhouse.
MEDLI-MSL-Curiosity-thrusters-Mars-planetary-entry-atmosphere-sky-crane-NASA.jpg

Image from year 2000 movie "Mission to Mars".

Or should we stick to integrated landing rockets, like the Apollo LM? We would still use rockets off to the side, like Mars Phoenix, rather than one single big engine like Apollo. That allows a central storage compartment for the rover. With integrated landing rockets, you don't need the structure of sky crane, but surface equipment and the rover must be protected instead of just slung on the bottom. However, a compartment could be pressurized for use as a laboratory the size of a single-car garage. It would be packed full during transit, but empty on the surface.

louis · 2017-10-01 16:40:49

I think Space X are going to make all our speculations irrelevant. I can't see anything wrong with Musk's plan, from a technical point of view, and he will be delivering huge tonnages to Mars. Power will be provided from a solar energy system. Why would we rely on a Sky Crane if we can deliver 150 tonnes to the Mars surface with a propulsive landing? Musk is so far ahead of the game as well, that he will have at least 5 and probably more like 10 years' head start over everyone else. Why would anyone invest in a system that will never deliver anything like Space X tonnages?

RobertDyck wrote:

Another update to Mars Direct. Could we use a "sky crane" like Curiosity? Mars Direct was developed in the last quarter of 1989, and first half of 1990, presentation to NASA in June 1990. That first hab had a single deck. Description included a rover, but where would the rover go? Later that same year Robert Zubrin added a lower deck with garage for the rover. I presume the first version would sling the rover under the hab, nestled between landing engines, held by cables that could lower with a winch. The problem with that is rocks kicked up by rocket exhaust could damage the rover. Notice the Apollo lunar rover was contained in a storage compartment, protected from rocks.
http://canada.marssociety.org/winnipeg/charts/marsdirect/hab.png http://matus1976.com/local_mirrors/mars_direct_plan/Scientific_American_Mars_Direct_files/0300zubrin5.gif
But Curiosity was able to land without any storage compartment; dropped by cables from a sky crane that stayed high enough that it didn't kick up rocks. If we use a sky crane, could we sling the rover under the hab? Just protected by the heat shield during transit, no storage compartment? That would reduce the lower deck to nothing but air lock, stairway to the upper deck, life support equipment, and storage for surface equipment including inflatable greenhouse.
http://1x57.com/wp-content/uploads/2011 … e-NASA.jpg
Image from year 2000 movie "Mission to Mars".
http://alanschuyler.files.wordpress.com … w-mars.jpg
Or should we stick to integrated landing rockets, like the Apollo LM? We would still use rockets off to the side, like Mars Phoenix, rather than one single big engine like Apollo. That allows a central storage compartment for the rover. With integrated landing rockets, you don't need the structure of sky crane, but surface equipment and the rover must be protected instead of just slung on the bottom. However, a compartment could be pressurized for use as a laboratory the size of a single-car garage. It would be packed full during transit, but empty on the surface.

RobertDyck · 2017-10-01 17:28:51

louis wrote:

I think Space X are going to make all our speculations irrelevant. I can't see anything wrong with Musk's plan, from a technical point of view, and he will be delivering huge tonnages to Mars. Power will be provided from a solar energy system. Why would we rely on a Sky Crane if we can deliver 150 tonnes to the Mars surface with a propulsive landing? Musk is so far ahead of the game as well, that he will have at least 5 and probably more like 10 years' head start over everyone else. Why would anyone invest in a system that will never deliver anything like Space X tonnages?

SpaceX plans have two major flaws. 1) How do you pay for that giant rocket? 2) and more important: His system requires a propellant depot BEFORE the first rocket lands. How do you get a propellant production facility and depot work before anything arrives?

I keep saying, we need something the size of Mars Direct first. Then build a base with propellant production facilities and storage depot capable of refuelling the giant SpaceX transport. You'll also need living quarters and life support for those first 100 settlers. All set up before the first SpaceX transport.

SpaceNut · 2017-10-01 20:34:51

The more that I see the Mars habitat lander the more I think that we can go with a smaller crew using a modified Cygnus module of course modified to land. I did find a mars curiosity simulator at this page https://www.khanacademy.org/partner-con … simulation

This would be for the mars landing and skycrane....

louis · 2017-10-02 04:34:01

He needs 4 Mars ships to get humans going on Mars over 7 years. I think he could do it for maybe $10 billion, remembering that a lot of the development costs e.g. propulsive landing technology and the fuel tank has already been covered, and that costs will be shared with other projects (e.g. lunar tourism and ISS servicing) . That could be raised through a variety of sources (I've given some indicative figures):

1. Reinvested Space X profits. ($2.5 billion or about $357 million pa)

2. Commercial sponsorship. ($1.5 billion or $214 million pa)

3. Selling exclusive TV and other media rights e.g. to Netflix. ($1.5 billion or $214 million pa).

4. Borrowing. ($1 billion or about $142 million pa)

5. Personal investment by Musk and others. ($1 billion or $142 million pa)

6. Selling space and support for 100 scientific experiments. (£1 billion or $142 million pa)

7. Creating a new Mars Consortium and invite investors to come on board. ($1.5 billion or 214 million pa).

I didn't take away the message that the propellant plant needs to be operational before the Mars ships arrive. The first two will be cargo. They can stay on Mars in perpetuity if necessary. When humans land they unload the cargo ships which presumably have the propellant manufacturing facility on board. I thought the aim was then to manufacture the necessary propellant for the return journey at the point.

These will be pretty big facilities capable of manufacturing tonnes of propellant per sol would be my understanding.

The great thing about Musk's approach is that with such huge tonnages delivered to the planet, this can be a very safe mission, with a lot of redundancy built in - it kind of simplifies everything.

I would have gone for a smaller mission first as well, a few years back. I think it could have been done any time in the last 20 years but I think now - given they start constructing the first Mars ship in 2018 - we are on a different track.

RobertDyck wrote:

louis wrote:
I think Space X are going to make all our speculations irrelevant. I can't see anything wrong with Musk's plan, from a technical point of view, and he will be delivering huge tonnages to Mars. Power will be provided from a solar energy system. Why would we rely on a Sky Crane if we can deliver 150 tonnes to the Mars surface with a propulsive landing? Musk is so far ahead of the game as well, that he will have at least 5 and probably more like 10 years' head start over everyone else. Why would anyone invest in a system that will never deliver anything like Space X tonnages?
SpaceX plans have two major flaws. 1) How do you pay for that giant rocket? 2) and more important: His system requires a propellant depot BEFORE the first rocket lands. How do you get a propellant production facility and depot work before anything arrives?
I keep saying, we need something the size of Mars Direct first. Then build a base with propellant production facilities and storage depot capable of refuelling the giant SpaceX transport. You'll also need living quarters and life support for those first 100 settlers. All set up before the first SpaceX transport.

Oldfart1939 · 2017-10-05 09:21:04

I hate to rain on Elon's parade, but never does he mention anything about dealing with microgravity disease. It's one thing to "think big," but he's overlooking many of the real issues that have not yet been addressed properly. If he is able to pull this off--and I'm not saying he can't--it will be one of the greatest steps ever taken by private enterprise.

louis · 2017-10-05 10:24:21

I agree he has little to say about microgravity disease but (a) experience shows he does tend to be rather thorough in his projects and (b) there is lots of evidence that the dangers of microgravity have been exaggerated. At Elon plans to put people on a planet where we can simulate 1G (with weighted suits) whereas Lockeed Martin have a rubbish proposal for a "multiple foray" expedition to Mars which will mean they stay in zero G for nearly all the time!

Oldfart1939 wrote:

I hate to rain on Elon's parade, but never does he mention anything about dealing with microgravity disease. It's one thing to "think big," but he's overlooking many of the real issues that have not yet been addressed properly. If he is able to pull this off--and I'm not saying he can't--it will be one of the greatest steps ever taken by private enterprise.

GW Johnson · 2017-10-05 11:04:49

Louis & Oldfart1939:

I don't think artificial gravity issue is either over-hyped or under-hyped. I know for a fact that we humans know nothing about gravity's effects on the body except at the two endpoints: 0 and 1 gee. There has to be a spectrum of increasing deleterious effects as gravity is reduced from 1 to 0 gee, but we know nothing about the shape of those curves between those two endpoints. I say curves (plural) because the various effects likely will not respond the same way. Murphy's Law says so.

What NASA and Musk are "counting on" is that partial gee will be "therapeutic enough" to tolerate the deleterious effects on the moon and on Mars for long exposures, potentially lifetimes. NASA is further counting on exercise and medicines to counter 0-gee effects for long flight time exposures, longer than roughly a year, which is far short of a trip to Mars and back, and trivial compared to a lifetime spent by a colonist.

But we already DO NOT keep people on ISS longer than a year, and preferably not longer than 6 months. There is probably a very good medical reason for that, which they (NASA) don't like publicized, apparently. Because nobody talks about it, except folks like us in discussions like these.

Musk is reducing the 0-gee exposures with higher energy trips: 3 to 6 months, versus a nominal 8.5 months for a min-energy transfer orbit, and that is very smart. But like NASA, he is "counting on" 0.38 gee being "enough" to tolerate the reduced-gee effects. We have precisely ZERO data to support that bet, but it really isn't such a bad bet. Any colonists on Mars are going to live the rest of their lives dealing with whatever the effects of 0.38 gee finally prove to be. Regardless.

So we might as well go out there and start finding out "for sure" what those effects are. While not doing those things we already know are stupid. My bet is there's a whole lot more stupid things we still don't know about, than there are stupid things we already do know about. The "trick" is to uncover them before we commit to lifetimes of exposure.

I know people and their habits and attitudes well enough to know that Mars colonists would probably go to the gym every day to work out, but are very unlikely to wear weighted suits all day, every day. That inherent feeling of confinement from such a suit goes against everything that we are, psychologically.

GW

Last edited by GW Johnson (2017-10-05 11:07:33)

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#126 2016-01-18 20:20:42

Re: Light weight nuclear reactor, updating Mars Direct

#127 2016-01-22 18:11:22

Re: Light weight nuclear reactor, updating Mars Direct

#128 2016-01-22 19:08:17

Re: Light weight nuclear reactor, updating Mars Direct

#129 2016-01-25 11:25:05

Re: Light weight nuclear reactor, updating Mars Direct

#130 2016-01-25 17:31:02

Re: Light weight nuclear reactor, updating Mars Direct

#131 2016-01-25 18:36:39

Re: Light weight nuclear reactor, updating Mars Direct

#132 2016-01-25 19:18:15

Re: Light weight nuclear reactor, updating Mars Direct

#133 2016-01-25 20:04:25

Re: Light weight nuclear reactor, updating Mars Direct

#134 2016-01-26 10:28:02

Re: Light weight nuclear reactor, updating Mars Direct

#135 2016-01-26 20:59:23

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#136 2017-01-02 14:06:42

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#137 2017-01-02 16:36:08

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#138 2017-01-02 17:44:48

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#139 2017-01-09 21:55:17

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#140 2017-01-10 19:40:54

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#141 2017-01-11 11:11:22

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#142 2017-06-25 17:21:26

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#143 2017-10-01 16:22:20

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#144 2017-10-01 16:40:49

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#145 2017-10-01 17:28:51

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#146 2017-10-01 20:34:51

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#148 2017-10-05 09:21:04

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