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#26 2017-06-07 04:52:34

elderflower
Member
Registered: 2016-06-19
Posts: 1,190

Re: Going Solar...the best solution for Mars.

You wouldn't need a hopper for identification of interesting sites in the locality. You only need a drone with a good camera.

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#27 2017-06-07 06:21:12

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Going Solar...the best solution for Mars.

A large part of the power supply for a Manned Mars Mission does need to be available 24/7.  Hotel requirements need to be maintained 24/7, as does power supply to communications and internal computer equipment.  Heating/cooling the habitat must be carried out 24/7, although modest amounts of hot water can be stored.  According to this source, these sorts of loads are anything up to 30kWe.

https://science.nasa.gov/science-news/s … spacepower

Other loads do not necessarily need to be 24/7, although that is always desirable.

•Cooling for propellant tanks might be allowed to vary if the tanks are well insulated and subcooled far beneath saturation pressure at the tank working pressure.  But that reduces the COP of the coolers and may increase insulation mass.

•Vehicle recharging can take place during the day, but that tends to be when you would ideally wish to operate these vehicles.

•Science labs need not be operational full-time, but to get reasonable productivity from the crew, we would ideally need them to operational for 16 hours per day.  Some processes may need to run continuously for days.

•Electrolysis can be carried out intermittently, but to get the same total mass of products, the electrolysis cells must be larger (and more massive) and must operate at higher power levels during operation.  Efficiency is also affected, as these units work most efficiently at high temperatures.

•Propellant production need not take place continuously, but is more efficient if it does.  The process involves electrolysis already mentioned.  The Sabatier reactions take place at high temperatures and substantial amounts of energy will be consumed heating equipment up to operating temperatures.  Compression of atmospheric CO2 is more efficient at night, as the feedstock is colder and denser and less compressor work is needed.  To produce the same amount of propellant in the same amount of time, intermittent production will require a larger propellant plant, as the output per unit time is proportional to plant mass.  High temperature equipment does not well tolerate thermal cycles.  A propellant plant working on an intermittent power supply must be designed to tolerate hundreds if not thousands of thermal cycles without failure.

•ISRU processes like iron smelting are niche applications.  But it is difficult to see why a day-time power excess would be an advantage.  Real life high-temperature processes are not tolerant of thermal cycles and to achieve the best utilisation of invested capital tend to operate continuously on a steady-flow basis.  Maybe you could demonstrate reaction constants for ore reduction at different temperature and CO/H2 gas flow rate using an intermittent supply, but that does simulate a real blast furnace.  What happens if you need to leave the furnace running for 24 hours in order to achieve sufficient ore reduction?  It isn’t much use if your peak solar power only lasts 4 hours.

•Greenhouses could be heated during the day and given sufficient thermal inertia to remain above freezing over night.  But that requires additional mass such as water or phase change materials within the greenhouse to function as a thermal store.  You could use dirt, but it has only half the heat capacity of water.

In short, there are no advantages to having an intermittent power supply.  It can be tolerated, but tolerating it involves both mass and performance penalties elsewhere.  For most things, it would be a lot more convenient to have a continuous 24/7 power supply.  In order to properly assess the relative advantages of nuclear and solar we must either:

1.Compare them like for like, i.e. how much do they both weigh if we use them to produce a 24/7 power supply; or

2.Understand the mass and performance penalty of solar intermittency on the mission as a whole.  We can then compare a solar mission to a nuclear mission as a whole and determine which is the best deal, when all costs and penalties are accounted for.

Since the second is much more difficult to quantify, most mission designers have thus far taken the first approach.  That is the approach most of us have taken on this board.  The second should be attempted for any mission proposal that is beyond concept stage.

Last edited by Antius (2017-06-07 06:57:30)

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#28 2017-06-07 08:35:32

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

Can you really get sustained lift in that low pressure?  I am always a bit sceptical about that. But if it can be done - brilliant!


elderflower wrote:

You wouldn't need a hopper for identification of interesting sites in the locality. You only need a drone with a good camera.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#29 2017-06-07 10:36:33

elderflower
Member
Registered: 2016-06-19
Posts: 1,190

Re: Going Solar...the best solution for Mars.

A drone appears feasible. A quad or hex copter with large diameter rotors compared to earth ones and a very restricted range due to battery weight. Such a device wouldn't lift much of a payload. I would only envisage a camera and UHF transmitter.
A dirigible might also work (Hydrogen isn't flammable on Mars) but again you won't get much of a payload due to the low density of Mars' atmosphere and you need to get hold of some hydrogen or helium to fill it.
You might use catalytic breakdown of hydrazine which would provide a lifting gas mix and a lot of heat to improve your lifting ability, as exhaust, perhaps, from a tiny turbo generator providing motive power and charging batteries. This could only work in low wind speeds.

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#30 2017-06-07 11:39:41

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

You present yet again a set of assertions with nothing to back up your claims about nuclear power being lower mass.  Can you please set out your own thread the mass of a nuclear based energy system (with or without other energy-related mass such as batteries) on a separate thread, so we can actually see what sort of thing you are proposing for an equivalent six person Mission One. Because so far I ain't seen nothing except irrelevant references to core mass and other claims made without citation.


Antius wrote:

A large part of the power supply for a Manned Mars Mission does need to be available 24/7.  Hotel requirements need to be maintained 24/7, as does power supply to communications and internal computer equipment.  Heating/cooling the habitat must be carried out 24/7, although modest amounts of hot water can be stored.  According to this source, these sorts of loads are anything up to 30kWe. https://science.nasa.gov/science-news/s … spacepower.

You're getting a bit desperate now aren't you?  I am setting out the actual quote below so people can see what is and is not said. Nowhere does it say this has to be met as a constant rate of power. It indicates what power you need over the sol. It doesn't even mention what number of people this relates to, and so is essentially meaningless.  In any case it clearly won't be 30kws exactly all through the sol (just take hot water as an example - are you going to heat x litres per minute or are you going to ensure tanks are full when you need them?). That will be the average. Sometimes it will higher, sometimes lower. With my approach the range of energy expended on life support will just be much broader than if you had a nuclear reactor in place.

"Scaling up from the Mars Lander to a human mission on Mars requires more power--about 30 kW to heat and cool a human habitat, run computers and lights, make oxygen, recycle water and recharge the rovers, says Jeff George. For a long mission "we don't have the kind of energetics where you can dash back home [in case of trouble]," adds Gary Martin, assistant associate administrator for Advanced Systems in NASA's Office of Space Flight. "You're building things that have to be ultra reliable, self-healing, and autonomously sense when they're hurt." 

I hope your nuclear reactors are self-healing.

Antius wrote:

Other loads do not necessarily need to be 24/7, although that is always desirable.

Nowhere did the article say the 30 Kws had to be a "24/7".  So your comparison is bogus.

Antius wrote:

Cooling for propellant tanks might be allowed to vary if the tanks are well insulated and subcooled far beneath saturation pressure at the tank working pressure.  But that reduces the COP of the coolers and may increase insulation mass.

If you want to manufacture huge amounts of propellant on Mission One that's your look out. How much energy will you be expending on that? 

Antius wrote:

Vehicle recharging can take place during the day, but that tends to be when you would ideally wish to operate these vehicles.

I can't imagine we will have any bigger than a 100 KwH battery on an exploration Rover. We could easily charge that up in half an hour from the solar energy system I propose. You can either spend the rest of  the sol exploring or, if you are charging up of an afternoon you can take out the Rover the following sol - the idea that people will be out in  rovers exploring and mining every sol is fanciful by the way.  They'll be in the habs most of the time. Of course with a rover, we can in any case  also pack on board a solar power system like megaflex and use it to charge batteries anywhere in principle. You can also power the rover with methane/oxygen or compressed gas.

If you are now saying your Rovers are going to be nuclear powered, please indicate how much the reactor system will mass. If you are charging the batteries from a 100 Kw reactor please indicate when that will happen on a six person mission and how much mass your batteries will be (so we can add to your overall energy system  mass total as I have done) .   

Antius wrote:

Science labs need not be operational full-time, but to get reasonable productivity from the crew, we would ideally need them to operational for 16 hours per day.  Some processes may need to run continuously for days.

You're doing all this off a 100 Kw nuclear system with no batteries? What sort of science are you doing? Or will you have batteries?

Antius wrote:

Electrolysis can be carried out intermittently, but to get the same total mass of products, the electrolysis cells must be larger (and more massive) and must operate at higher power levels during operation.  Efficiency is also affected, as these units work most efficiently at high temperatures.

This applies whether you have nuclear or solar. Not sure what relevance it is.  You haven't produced a budget for your energy use. When are you going to be doing all this stuff? It seems to me you will be limited to 100 Kwes unless you are proposing something beyond the non-existent and untried SAFe 400.

Antius wrote:

Propellant production need not take place continuously, but is more efficient if it does.  The process involves electrolysis already mentioned.  The Sabatier reactions take place at high temperatures and substantial amounts of energy will be consumed heating equipment up to operating temperatures.  Compression of atmospheric CO2 is more efficient at night, as the feedstock is colder and denser and less compressor work is needed.  To produce the same amount of propellant in the same amount of time, intermittent production will require a larger propellant plant, as the output per unit time is proportional to plant mass.  High temperature equipment does not well tolerate thermal cycles.  A propellant plant working on an intermittent power supply must be designed to tolerate hundreds if not thousands of thermal cycles without failure.

I'm not proposing propellant production for Mission One, other than possibly for a small automated rocket hopper which would use the same gas that is used for energy production.

Antius wrote:

ISRU processes like iron smelting are niche applications.  But it is difficult to see why a day-time power excess would be an advantage.  Real life high-temperature processes are not tolerant of thermal cycles and to achieve the best utilisation of invested capital tend to operate continuously on a steady-flow basis.  Maybe you could demonstrate reaction constants for ore reduction at different temperature and CO/H2 gas flow rate using an intermittent supply, but that does simulate a real blast furnace.  What happens if you need to leave the furnace running for 24 hours in order to achieve sufficient ore reduction?  It isn’t much use if your peak solar power only lasts 4 hours.

You simply have a more static, and unadventurous view of the mission from my perspective. Steel making - indeed materials production of all kinds - should absolutely be central to the mission. We need to begin pilot production on a range of industrial materials on Mission One. The peak power available - anything up to 800 Kwes will be very useful.

Antius wrote:

Greenhouses could be heated during the day and given sufficient thermal inertia to remain above freezing over night.  But that requires additional mass such as water or phase change materials within the greenhouse to function as a thermal store.  You could use dirt, but it has only half the heat capacity of water.

Have you never heard of aerogel? Anyway, I think few people are proposing massive energy expenditure on greenhouses for Mission One. For later missions, solar power mirrors the natural light cycle which is useful.


Antius wrote:

In short, there are no advantages to having an intermittent power supply.  It can be tolerated, but tolerating it involves both mass and performance penalties elsewhere.  For most things, it would be a lot more convenient to have a continuous 24/7 power supply.  In order to properly assess the relative advantages of nuclear and solar we must either:

1.Compare them like for like, i.e. how much do they both weigh if we use them to produce a 24/7 power supply; or

2.Understand the mass and performance penalty of solar intermittency on the mission as a whole.  We can then compare a solar mission to a nuclear mission as a whole and determine which is the best deal, when all costs and penalties are accounted for.

Since the second is much more difficult to quantify, most mission designers have thus far taken the first approach.  That is the approach most of us have taken on this board.  The second should be attempted for any mission proposal that is beyond concept stage.

I have produced my mass estimates. You haven't produced yours. Kbd produced a mass estimate for nuclear reactors alone (10 x 10Kwe KiloPower units) - no batteries, no solar, no back up - of 1.5 tonnes per unit, so 15 tonnes for all ten. His estimate not mine.   Do you disagree with that?

The only person who is actually looking to get to Mars in a reasonable timeframe and has the potential wherewithal is Musk and he is sensibly speaking in terms of solar energy.

You are comparing "like with like" on your terms but on my terms a 100 Kwe system cannot match solar's performance. Most of the time the solar energy system will be producing double the number of KWehs per sol.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#31 2017-06-07 11:51:46

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,340

Re: Going Solar...the best solution for Mars.

louis wrote:

You haven't shown that we can't do these things with the current state of technology. Musk is clearly positive about solar energy, but you know better. I have set out one approach which I think covers all angles.

Has Mr. Musk ever sent anyone into space, let alone to another planetary body?

Does Mr. Musk have a giant interplanetary rocket that he can use in a less-than-efficient manner?

Does Mr. Musk, or anyone else for that matter, have any clue about how .38g affects the human body?

Unless the answer to all of those questions is "yes", then reality "knows better".

louis wrote:

You are dodging the question - which is why are you only considering "solar plus imported chemical batteries" rather than solar plus chemical batteries plus methane storage/generation plus ISRU batteries".

I'm not dodging any questions, I'm just not hand waving any solutions that don't even conceptually exist yet.  That is exactly what a robotic methalox plant is.  Collecting water with robots and autonomously operating a cryogen plant for years without replacing any components are two entirely different tasks.  You proposed creating a manufacturing plant on another planet in what is an otherwise random location before you do a day of exploration.  How many water purification plants are built in random locations here on Earth?

louis wrote:

What little problem of mass?  It's you who has the problem with mass since your 10 x 10 Kw KiloPower units come in at 15 tonnes and that is with NO batteries or cabling at all and with no explanation of how they are going to be used.

I never proposed shipping ten Kilopower reactor units to Mars for an exploration mission.  For colonization, which is what you're really talking about here in this thread, is something that follows AFTER we determine what .38g does to the human body.  Nobody knows how that works and anyone who says they do is obviously lying since there have been no long term tests conducted.

louis wrote:

Complexity?  Solar is one of the most straightforward energy technologies going, as Musk points out. Lay it out and plug it in! smile  Methane power generation is one of the best established technologies on Earth.  V. little development required for Mars. Chemical batteries are well understood in a space context.  But "nuclear power plus humans on a planet 100 Kms away over a two year period"?  Well, that is a step into the unknown.  I think it can be done but it will be complex (particularly re deployment and monitoring) and I doubt it will be done without batteries.

You're hand waving development of an autonomous methalox plant for use on Mars.  There are no robotic LOX or LCH4 plants here on Earth, all are serviced regularly by humans, all are very energy-intensive, and none of them have anything remotely resembling the mass restrictions of a plant destined for Mars.

louis wrote:

Cost?  You haven't shown that delivering the sort of system I propose will be less costly than sending a nuclear-based energy system because you haven't shown it is less mass.

Your PV panel and battery concept can't provide more continuous power output with less mass than a fission reactor even when the continuous power requirement is only 10kWe.  Aboard real spacecraft, there were and are relatively high continuous power requirements even for a small number of people.

Space Shuttle - 12kWe to 21kWe, average power consumption 14kWe (typically 6 or 7 onboard)
Cygnus - 3.5kWe (nobody onboard)
Dragon - 5kWe (nobody onboard)
Orion - 11kWe (up to 7 onboard to go to ISS, but normally 3 or 4 onboard for lunar missions)
ISS - 75kWe to 90kWe (typically 3 onboard)

The typical requirements for life support appear to be about 2kWe per person.  I'm sure that varies, but as I've stated before, real spacecraft aren't designed for best case scenarios and none of those spacecraft have ever been on a two year mission in deep space.

louis wrote:

A small robot rocket hopper on Mission One would be invaluable in identifying the locations where the Rover should go, rather than randomly coming across such areas.  I am not saying it is definitely doable on Mission One, but the higher KWeh output of a solar energy system would at least make it a feasible option. How to power the main exploratory Rover is debatable.

JPL is developing a small helicopter drone to explore ahead of land-based robots like the Mars 2020 rover.  Gather information using multiple small airborne robots and then visit sites that contain something of particular interest (higher than average water content, mineral deposits, metals, etc).  We could deploy dozens of these drones for negligible mass since they weigh a couple pounds each.

louis wrote:

The methane plant allows you to expand your energy storage constantly seamlessly. You can't do that with chemical batteries, although chemical battery storage could be expanded through ISRU activity on Mission One. But I think there will be limited space for that (because any ISRU batteries will likely need to be made in the industrial hab), whereas creating gas storage will not be so difficult. We also have to think about the limited available labour time.

As long as you have a local source of water and someone actually builds an autonomous methalox plant that won't break down to begin with, then what you propose could work.

louis wrote:

You're talking about the company that has perfected retro rocket landing of first stage rockets!  Something NASA didn't achieve in 60 years and Space X achieved in 15 from a standing start with no government largesse at the beginning.

Yay, SpaceX!  Now put your pom poms down long enough to realize that he didn't achieve that without help from NASA.  NASA sent people to the moon before Elon Musk was born.  The only reason we can even contemplate sending people to Mars is the continuous effort the agency has put into batteries, solar panels, nuclear power and propulsion, computers, life support technologies, and the wealth of information gathered on human physiology in the environment of space.

louis wrote:

I cannot prove it but it is my judgement that Musk and his teams are well advanced in terms of Mission One planning and will be addressing all the problem areas. Taking along a nuclear reactor will just create a whole host of unnecessary problems for them.

Explain what unnecessary problems you think a nuclear reactor will create.

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#32 2017-06-07 12:16:29

elderflower
Member
Registered: 2016-06-19
Posts: 1,190

Re: Going Solar...the best solution for Mars.

There is no eitherthisorthat option. We need both, and any other we can lay our hands on in a short (few years) period, to equip the Mars exploration expeditions with the best available chances of successful completion, even if something fails due to unforeseen events.

Last edited by elderflower (2017-06-07 12:17:14)

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#33 2017-06-07 16:59:20

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,805

Re: Going Solar...the best solution for Mars.

Correct. WE need nuclear as the basic power source with solar as an ancillary backup. The base will be nuclear, and the rovers will be solar electric.

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#34 2017-06-07 17:44:11

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,348

Re: Going Solar...the best solution for Mars.

The choice of creating a Solar powered emergency Methane Lox battery is definetly something to do as we are expecting to use insitu for the return home rocket if we are going with Mars Direct. So creating the infrastructure for this will take a build up of man's continuing presence.

Thanks for the life support numbers kbd512 and I would agree that depending on uses that the numbers coud be for periods of time done as low as 1 Kw and as high as 3 kW based on my own homes family of 5.

That said if we are using solar for life support the panel count will go up ad so does the battery count in tons to satify that need.

2kW x 25 hr = 50 kwh per person minimum need to which the charging happens in 4 hrs such that the panels need to generate 50Kwh/4 = 12.5 Kw plus for losses in conversion to the batteries output from the panels and more when in use so thats probably more like 15Kw per person. minimum to which during summer there will be an excess of energy from the system to make use of.

Batteries also will need to be a bit bigger than the 50Kw per person as well.

Now for the methane lox battery the losses will make the panels even larger due to the additional steps to create to go with the batteries for some of the off hour drain as we will be making use of the natural cycle of temperature swing.

All of this is going to make a mars colony grow with energy and fuel for return as any surplus can then be used. Sure more tanks in time will be add to the storage as we will want that system to do more as we need more energy it will also add more panels and batteries.

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#35 2017-06-07 18:06:35

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

I don't see electricity generation through methane/oxygen as an "emergency" provision. I see it as part of a holistic approach based on solar power.

I don't accept we need to generate rocket fuel for the Mission One return.  Such considerations only apply if you are rely on a huge lander/ascent vehicle.Keep the ascent vehicle minimal and we can simply land the fuel for that vehicle (probably 8 tonnes in total).

The chemical battery tonnage requirement does not go "up and up" if you have a methane powered generator. But there is in any case no reason why on Mission One the pioneers cannot construct their own batteries with ISRU.

You make the error of assuming all power production is post humans landing. There is nothing to stop us producing energy prior to humans arriving and using that as a storage reserve.

My original post fully allows for conversion losses for both chemical batteries and methane/oxygen storage.

I do agree it is all about creating an energy surplus above and beyond your immediate needs that then allows you to try out new things - industrial processes, manufacture, construction, communications with Earth etc etc .

SpaceNut wrote:

The choice of creating a Solar powered emergency Methane Lox battery is definetly something to do as we are expecting to use insitu for the return home rocket if we are going with Mars Direct. So creating the infrastructure for this will take a build up of man's continuing presence.

Thanks for the life support numbers kbd512 and I would agree that depending on uses that the numbers coud be for periods of time done as low as 1 Kw and as high as 3 kW based on my own homes family of 5.

That said if we are using solar for life support the panel count will go up ad so does the battery count in tons to satify that need.

2kW x 25 hr = 50 kwh per person minimum need to which the charging happens in 4 hrs such that the panels need to generate 50Kwh/4 = 12.5 Kw plus for losses in conversion to the batteries output from the panels and more when in use so thats probably more like 15Kw per person. minimum to which during summer there will be an excess of energy from the system to make use of.

Batteries also will need to be a bit bigger than the 50Kw per person as well.

Now for the methane lox battery the losses will make the panels even larger due to the additional steps to create to go with the batteries for some of the off hour drain as we will be making use of the natural cycle of temperature swing.

All of this is going to make a mars colony grow with energy and fuel for return as any surplus can then be used. Sure more tanks in time will be add to the storage as we will want that system to do more as we need more energy it will also add more panels and batteries.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#36 2017-06-07 18:08:13

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

Why would you do that if nuclear requires more mass? It makes no sense.

Oldfart1939 wrote:

Correct. WE need nuclear as the basic power source with solar as an ancillary backup. The base will be nuclear, and the rovers will be solar electric.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#37 2017-06-07 18:12:53

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

I don't really agree.I think there are basically two energy architectures: nuclear or solar.

Each may involve some minor addition from the other (I am not averse to taking along one or two small RTGs even though I support solar) but they cannot be equal partners because they are v. different approaches. 

I'd rather we selected one of the other rather than try and create some kind of inefficient "middle model".

Obviously I support solar because I think it is human-safe, lower mass, higher power and more flexible.



elderflower wrote:

There is no eitherthisorthat option. We need both, and any other we can lay our hands on in a short (few years) period, to equip the Mars exploration expeditions with the best available chances of successful completion, even if something fails due to unforeseen events.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#38 2017-06-07 18:24:56

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,348

Re: Going Solar...the best solution for Mars.

https://www.inverse.com/article/21492-s … ction-mars

Musk’s presentation neglected to go into detail as to how exactly an ITS propellent-producing facility would work. And bear in mind — Musk thinks 50 to 60 percent of whatever electricity the solar panels are able to generate will go toward propellant production. That’s an insane amount of energy that cannot go toward other things that make day-to-day life in Mars safe and bearable.

http://www.digipac.ca/chemical/mtom/con … atier2.htm

sabatierprocess.gif

http://voitlab.com/courses/thermodynami … en_on_Mars

800px-KennyTran_slide.png

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#39 2017-06-07 18:36:45

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,348

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#40 2017-06-07 18:44:34

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

kbd512 wrote:

Has Mr. Musk ever sent anyone into space, let alone to another planetary body?

Does Mr. Musk have a giant interplanetary rocket that he can use in a less-than-efficient manner?

Does Mr. Musk, or anyone else for that matter, have any clue about how .38g affects the human body?

Unless the answer to all of those questions is "yes", then reality "knows better".

I think we can see where you are coming from kbd. As soon as Space X do get a human into space you will re-frame the question..."Has he ever sent a craft beyond the solar system?" or whatever. Doesn't matter, you are clearly determined to do down this guy...who is a technical genius.

As for .38 gravity I am absolutely sure he's got his team working on that.  Do you really think he is uninterested in the question. Perhaps you are one of those naive people who assume Musk's public utterances are the sum total of his knowledge.

kbd512 wrote:

I'm not dodging any questions, I'm just not hand waving any solutions that don't even conceptually exist yet.  That is exactly what a robotic methalox plant is.  Collecting water with robots and autonomously operating a cryogen plant for years without replacing any components are two entirely different tasks.  You proposed creating a manufacturing plant on another planet in what is an otherwise random location before you do a day of exploration.  How many water purification plants are built in random locations here on Earth?


I have a v. precise location for the landing zone. My preference is Chryse Planitia - 25 north and 30 west.  Not at all random as you can see.

There are hundreds of millions  of AC units on the planet producing water from water vapour in the atmosphere and yet you consider it some sort of gigantic technical feat.


kbd512 wrote:

I never proposed shipping ten Kilopower reactor units to Mars for an exploration mission.  For colonization, which is what you're really talking about here in this thread, is something that follows AFTER we determine what .38g does to the human body.  Nobody knows how that works and anyone who says they do is obviously lying since there have been no long term tests conducted.

Oh dear...sounds like you are one of those "put-it-offers".   The whole point about exploration is that you take calculated risks. There is absolutley no evidence that 0.38 gravity experienced in a weighted suits will be injurious to health. It might be but we don't know. There are plenty of courageous people ready to find out .

So what sort of nuclear power facility would you provide for a party of 6 people? Come on - architecture and tonnage please (with citations) ...you nuclear enthusiasts have gone v. shy on this.


kbd512 wrote:

You're hand waving development of an autonomous methalox plant for use on Mars.  There are no robotic LOX or LCH4 plants here on Earth, all are serviced regularly by humans, all are very energy-intensive, and none of them have anything remotely resembling the mass restrictions of a plant destined for Mars.

You do realise Curiosity undertakes incredibly complex chemistry automatically?

kbd512 wrote:

Your PV panel and battery concept can't provide more continuous power output with less mass than a fission reactor even when the continuous power requirement is only 10kWe.  Aboard real spacecraft, there were and are relatively high continuous power requirements even for a small number of people.

Space Shuttle - 12kWe to 21kWe, average power consumption 14kWe (typically 6 or 7 onboard)
Cygnus - 3.5kWe (nobody onboard)
Dragon - 5kWe (nobody onboard)
Orion - 11kWe (up to 7 onboard to go to ISS, but normally 3 or 4 onboard for lunar missions)
ISS - 75kWe to 90kWe (typically 3 onboard)

The typical requirements for life support appear to be about 2kWe per person.  I'm sure that varies, but as I've stated before, real spacecraft aren't designed for best case scenarios and none of those spacecraft have ever been on a two year mission in deep space.

2 Kws per person (used by the MIT study) is a figure I acknowledge in my original thread.  It amounts to 294 Kwehs per sol. My proposal produces that many times over.


kbd512 wrote:

JPL is developing a small helicopter drone to explore ahead of land-based robots like the Mars 2020 rover.  Gather information using multiple small airborne robots and then visit sites that contain something of particular interest (higher than average water content, mineral deposits, metals, etc).  We could deploy dozens of these drones for negligible mass since they weigh a couple pounds each.

I am all in favour of such helicopter drones if they are feasible. They sound much better than rocket hoppers...but you don't give a link to them sadly...


kbd512 wrote:

As long as you have a local source of water and someone actually builds an autonomous methalox plant that won't break down to begin with, then what you propose could work.

Holey moley we agree! lol



kbd512 wrote:

Yay, SpaceX!  Now put your pom poms down long enough to realize that he didn't achieve that without help from NASA.  NASA sent people to the moon before Elon Musk was born.  The only reason we can even contemplate sending people to Mars is the continuous effort the agency has put into batteries, solar panels, nuclear power and propulsion, computers, life support technologies, and the wealth of information gathered on human physiology in the environment of space.

No one's denying their input, but some of us are querying their rate of input given their access to something like $25 billion pa.  I think with that money I too might produce something impressive. But if you just said to Musk "Here's $250 billion for the next ten years" progress would be staggering and we would be on Mars before you could say boo!  $250 billion!!!!!!!!

kbd512 wrote:

Explain what unnecessary problems you think a nuclear reactor will create.

All sorts - protecting people on earth from fall out if the launch fails, protecting humans in transit to Mars, protecting humans on Mars from radiation, protecting future humans on Mars from radiation, deployment on Mars (some people suggest burying under regolith).  dealing with any functional maintenance issues, the failsafe issue (if you are proposing just one reactor), using labour time to monitor facilities, limited power availability (with solar power is always greater during the day and you can boost it fantastically with stored power...).

Last edited by louis (2017-06-07 18:55:54)


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#41 2017-06-07 18:55:17

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,348

Re: Going Solar...the best solution for Mars.

Here is the helicopter discusion Scouting Mars by Helicopter

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#42 2017-06-07 19:04:09

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

Thanks for that SpaceNut. That digipac diagram is along the lines I was thinking of for the whole process. Clearly in line with the article we need to make it as energy efficient as we can.  Given we will need a good deal of heat on Mars, that will probably help.


SpaceNut wrote:

https://www.inverse.com/article/21492-s … ction-mars

Musk’s presentation neglected to go into detail as to how exactly an ITS propellent-producing facility would work. And bear in mind — Musk thinks 50 to 60 percent of whatever electricity the solar panels are able to generate will go toward propellant production. That’s an insane amount of energy that cannot go toward other things that make day-to-day life in Mars safe and bearable.

http://www.digipac.ca/chemical/mtom/con … atier2.htm

http://www.digipac.ca/chemical/mtom/con … rocess.gif

http://voitlab.com/courses/thermodynami … en_on_Mars

http://voitlab.com/courses/thermodynami … _slide.png


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#43 2017-06-07 20:15:47

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,348

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#44 2017-06-08 03:51:09

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

Thanks for that link SpaceNut,


http://media.nationalgeographic.org/ass … v_2016.pdf

I think that's one of the best graphics I've see regarding a Mars base. They seem to cover just about everything! smile

Couple of points:

1. I don't think we'll need all that mass-intensive alignment support for the solar arrays but they look good!

2. When people here have talked about burying a reactor I hadn't realised that cooling vanes of the type shown in the graphic might be necessary...no doubt someone here will dispute that they are necessary, but if they are then they look hugely mass heavy.

Last edited by louis (2017-06-08 04:37:09)


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#45 2017-06-08 13:33:50

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,340

Re: Going Solar...the best solution for Mars.

louis wrote:

I think we can see where you are coming from kbd. As soon as Space X do get a human into space you will re-frame the question..."Has he ever sent a craft beyond the solar system?" or whatever. Doesn't matter, you are clearly determined to do down this guy...who is a technical genius.

No my point is very simple.  He hasn't put any humans into space yet.  Speculating on what he may or may not be able to achieve, if only he had unlimited funding, is irrelevant to a reality in which unlimited funding doesn't exist.

louis wrote:

As for .38 gravity I am absolutely sure he's got his team working on that.  Do you really think he is uninterested in the question. Perhaps you are one of those naive people who assume Musk's public utterances are the sum total of his knowledge.

The proof that he doesn't have anyone working on this is rather self-evident for people who don't believe in magical thinking.  All space agencies and commercial space transport providers need to know the answer to that question before humans can colonize Mars.  Thus far nobody, as in no humans anywhere ever, to include Elon Musk (he's not a space alien or space travel Jesus, just a human like the rest of us), have tested this.

louis wrote:

I have a v. precise location for the landing zone. My preference is Chryse Planitia - 25 north and 30 west.  Not at all random as you can see.

There are hundreds of millions  of AC units on the planet producing water from water vapour in the atmosphere and yet you consider it some sort of gigantic technical feat.

How many of those AC units are operating at 130,000ft density altitude in CO2?

louis wrote:

Oh dear...sounds like you are one of those "put-it-offers".   The whole point about exploration is that you take calculated risks. There is absolutley no evidence that 0.38 gravity experienced in a weighted suits will be injurious to health. It might be but we don't know. There are plenty of courageous people ready to find out .

Read what I actually proposed doing.  You're starting to sound like Dook.

louis wrote:

So what sort of nuclear power facility would you provide for a party of 6 people? Come on - architecture and tonnage please (with citations) ...you nuclear enthusiasts have gone v. shy on this.

I already provided a mission architecture and tonnages, but you either didn't read my posts or ignored them.  You keep asking for links to things I've already provided.  Read your own threads on this forum and you'll find them.

A Kilopower fission reactor capable of producing 10kWe continuous output weighs 1,545kg and I've posted the same number numerous times in this thread and other threads in response to this nonsense about solar power.  I want to send 2 Kilopower reactors for every 2 astronauts we send to Mars.  The 2 Kilopower reactors provide primary and backup power.  The power plants are part of the cargo delivery cycle that lands before the human delivery cycle.  A solar or permanent battery and homopolar generator powered small tracked rover provides auxiliary power, earth moving capability to bury habitat modules, and a radiation protected transport vehicle (because solar flares, coronal mass ejections, and ions from intergalactic space are real vs imagined radiation threats) to exploration sites of interest.

louis wrote:

You do realise Curiosity undertakes incredibly complex chemistry automatically?

Do you mean to tell me that the nuclear powered rover that always has power, even when the Sun isn't shining, is capable of complex science experiments because it has continuous power?  Whoda thunk it!  Curiosity has 100 watts of power and we couldn't manage that with PV panels and batteries that weighed less than the RTG.

louis wrote:

2 Kws per person (used by the MIT study) is a figure I acknowledge in my original thread.  It amounts to 294 Kwehs per sol. My proposal produces that many times over.

The question of whether or not we can produce methane on Mars only becomes relevant after we determine that humans can live in .38g without serious health effects.  Nobody knows the answer to that question.  Once we do, I'll cheerfully agree to any sort of experimentation with propellant production that you want to do.  Do you understand why NASA hasn't done this yet?  Before the .38g question is answered, Mars is scientifically interesting.

louis wrote:

I am all in favour of such helicopter drones if they are feasible. They sound much better than rocket hoppers...but you don't give a link to them sadly...

You still have Google in the UK.  JPL is working on the helicopter drone so they can drive the Mars 2020 rovers further in a day.

louis wrote:

Holey moley we agree! lol

I guess it's a "surprise" to you that I don't have any problem experimenting, but the experiment is only relevant to colonization AFTER we know how the Martian environment affects human life.  You can believe whatever you want about me.  In my personal life, I like to experiment with batteries and electric generators.  I think solar power and advanced batteries are wonderful things, but they're not mass equivalent replacements for nuclear power, YET.  I advocate for things that are proven to work using technology we have versus what we may or may not one day have.

NASA develops technology portfolios, Louis.  Advanced batteries, advanced fuel cells, advanced RTG's, and small fission reactors are all generally useful additions to their space power technologies portfolio.  IF we can actually live on Mars for a lifetime, then a methalox plant is another generally useful addition to our space power technologies portfolio.  IF NOT, then it's not.  It really is that simple.

louis wrote:

No one's denying their input, but some of us are querying their rate of input given their access to something like $25 billion pa.  I think with that money I too might produce something impressive. But if you just said to Musk "Here's $250 billion for the next ten years" progress would be staggering and we would be on Mars before you could say boo!  $250 billion!!!!!!!!

There's been no talk in Congress about giving Elon Musk $250B to colonize Mars.  We can revisit this matter the very first time someone in our legislature even starts intimating that they might provide serious funding for his efforts.  I would love to put the axe to the military, social, and corporate welfare budgets for this endeavor, which is decidedly more important than killing each other or robbing Peter to pay Paul, but I don't know what to say to my representatives to convince them that we should.  I do call and write on a regular basis, but apart from "thank you for your input", that's the extent of their "support" for this project.

louis wrote:

All sorts - protecting people on earth from fall out if the launch fails, protecting humans in transit to Mars, protecting humans on Mars from radiation, protecting future humans on Mars from radiation, deployment on Mars (some people suggest burying under regolith).  dealing with any functional maintenance issues, the failsafe issue (if you are proposing just one reactor), using labour time to monitor facilities, limited power availability (with solar power is always greater during the day and you can boost it fantastically with stored power...).

I think you're jumping ahead to colonization before we've done any surface exploration of Mars to confirm what our instrumented robots have told us.  I would think our first priority should be getting exploration teams to Mars.  All the speculation in the world isn't worth even the slightest amount of ground truth.

1. We've already proven that your proposed solution is not more mass efficient than Kilopower would be at producing continuous power when the requirement is 10kWe continuous or greater.

2. The peak vs continuous electrical power demand is largely irrelevant if the base requirement is 2kWe per person, as it is for virtually all active spacecraft, irrespective of whether or not they carry humans.  The power problem doesn't improve after humans land on the surface of Mars, it only gets worse than it is in Mars orbit.

3. I think we've finally arrived at your real objection to using nuclear power.  Nuclear power is "black magic" to you.  You can't comprehend how something smaller than a coffee can is able to produce 40 kilowatts of thermal power and 10 kilowatts of electrical power for a couple decades without refueling or refurbishment and it must necessarily be more dangerous than running out of power or making the mission so expensive that we can't do it.

A. Power loss assures death in space no matter what the power source happens to be.  We can't keep a rover the size of an ATV powered with solar panels, even though it moves slower than a human can walk, but somehow when we exponentially increase the electrical power requirement that situation will improve.

B. Humans on Earth are already protected from radiation accidents during launches.  To begin with, unlike a RTG, there's more radioactivity in the grocery store's fresh produce isle than there is in a sub-critical fission reactor.  Eat a few bananas and you've accumulated the same radiation dose you would from standing next to the unshielded sub-critical reactor core for a year.  I'll eat some fruit on your behalf as an homage to your irrational fear of something you clearly know nothing about.

C. Humans on Mars need to be protected from radiation from space.  If there's a radioactive source on the surface of Mars, there's a really simple solution for that.  It's called walking away.

D. Apart from replacing a power cable and turning the reactor on or off, there's not much in the way of maintenance to be done.  Kilopower is to a pressurized water reactor what a lawn mower engine is to a LS6.  Kilopower and PWR's are both nuclear reactors and lawn mower engines and Corvette engines are both internal combustion engines.  All other similarities end there.

Kilopower has a number of unique attributes:

* A solid Uranium-Molybdenum alloy metal core while commercial reactors use ceramic metals that are much more prone to cracking and releasing fission products

* Uses the same Stirling engine technology that was developed for the ASRG (Advanced Stirling Engine Radioisotope Thermal Generators) project that NASA cancelled to provide more funding for Pu238 production

* Uses existing stocks of HEU from DOE whereas RTG's require hundreds of millions to produce more Pu238 in useful quantities

* Uses sealed inert gas coolant and can naturally cool itself even if all coolant loops were completely destroyed or removed as a function of surface area to volume (not going to melt down with or without its coolant loops)

* Has a single control rod that dictates reactivity (as opposed to a more complicated system with multiple control rods or drums)

* Can be shipped in a configuration (neutron reflector removed) that can never go critical, no matter where it lands or what it lands in (sand, sea water, fresh water, or the ground, are all insufficient to cause a criticality if the reflector is removed for shipping to orbit)

* Apart from ensuring that electrical power continues to flow and reviewing logs, nobody is going to monitor the reactors on the ground

* The diameter of the assembled core is about the size of a small bucked, so I assume someone can manage to dig a hole a few inches in diameter and a few inches deep with hand tools, even through rock, and the surface of large rock would be an ideal place to put the reactor

You're starting to sound like those people in Germany who are "reducing their carbon footprint" by building new coal-fired power plants to contend with the fact that PV panels and wind farms are both spectacularly inadequate replacements for nuclear reactors.  Here in the US of A where there are still a handful of people who know how to count, we're trying to build something better.  Kilopower is our little "something better" for use on Mars until those Graphene batteries and PV panels arrive.  When we have something better than Kilopower, we'll start using it.  Until then, "We gots what we gots and we ain't got no more."

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#46 2017-06-09 10:13:24

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Going Solar...the best solution for Mars.

Apologies for not responding sooner.  Between work and family, I get limited free time for hobbies like this.  Louis and others requested information on the Specific power (KWe/Kg) of fast reactor power systems for deployment on Mars.  Here is the information I have been able to find.

I found it difficult to track down detailed design concepts for the SAFE-400 reactor, as most such information is behind paywalls.  I had more luck with Kilopower and SP-100.  The original thin-film solar surface power concept (see below) referenced a specific power of 19W/kg for SP-100 with four Stirling cycle power converters delivering 100kWe.  As the SP-100 is a 2.5MWth reactor system, these arrangements would require using the reactor at only 16% of its rated power, which seems less than efficient.  The second concept was based on the Prometheus design for a lunar based reactor and had specific power of 10W/kg at power levels of 100kWe using a Brayton cycle.

http://systemarchitect.mit.edu/docs/cooper10.pdf

The specific power of space reactors appears to be a strong function of power output – the higher the power output of the system, the higher the specific power.  This study presents a design arrangement for an SP-100 based system producing 550 kWe, with a total system mass of 11,879.9kg.  That is a specific power of 46.3W/Kg.

https://www.osti.gov/scitech/servlets/purl/10181300

This study examine a lunar base power supply using the SP-100 concept and producing 825kWe, with total system mass 20,000kg – 41.25W/kg.

https://ntrs.nasa.gov/archive/nasa/casi … 005714.pdf

Conversely, for very small reactor systems, specific power is low, but increases progressively as power is scaled up (See Table 1 in the link, below).  The Kilopower concept, achieves specific power of 2.5W/kg at 1KWe power level, but that increases to 6.5W/kg at 10KWe output.

https://ntrs.nasa.gov/archive/nasa/casi … 017750.pdf

Page 29 of the link below, provides a useful graphical approximation for system specific mass, for small fast reactors coupled to Brayton cycle generators.  Both surface power concepts and space nuclear electric propulsion concepts are included.

https://ntrs.nasa.gov/archive/nasa/casi … 004957.pdf

•    It can be seen that at power levels as low 10kWe, the specific mass is 350Kg/KWe, corresponding to specific power of 2.9W/Kg.
•    As power scales up to 100KWe, specific mass is 50kg/KWe (20W/Kg).  This compares very closely to what the researchers assumed in the thin-film solar study.
•    As power requirements reach 1MWe, which is the power level required perhaps, for a large base, specific mass declines to ~18kg/KWe (55.6W/Kg).
•    At power levels of 10-100MWe, what might reasonably be required for a colony of 1000-10,000 people, specific mass appears to converge towards 10kg/KWe (100W/Kg).  Presumably at this point, radiator mass dominates the total system mass, as this part of the system obviously cannot realise any scale effects since heat ejected is proportional to radiator area.  As reactor systems scale up, it makes more and more sense to attempt to build the radiators on Mars using local resources.

So, I would suggest that the best choice of power system for a Mars mission / base / colony, etc. is strongly dependant upon the power requirement (nuclear does much better as power scales up) and location, as solar power system mass would increase for locations further from the equator.  There is the added complication that solar power systems including storage have their own specific power curves, with smaller systems having lower specific power than larger systems.

Last edited by Antius (2017-06-09 10:18:04)

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#47 2017-06-09 14:33:04

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

kbd, I guess we’ll have to differ as to whether Space X will have any problems putting humans into space. I doubt it. Human space flight followed on v. quickly from the inauguration of the space era in the late 50s. Musk isn’t performing party tricks. He’s navigating a path to Mars.

It’s not magical thinking to believe Musk and Space X are in all likelihood already working on the challenges of operating in 0.38 gravity.
It’s reasoned speculation. Making a bogeyman out of low gravity is not the way to get to Mars. Likewise extracting water vapour from the Mars atmosphere will not be an amazing technical feat. As far as I can see it involves some pretty standard technology.

So for a six person mission, you would be taking 6 x 10 KWe KiloPower reactors providing (a mere) 60 Kwe. In addition you would have some batteries/homopolar generator (couple of tonnes?).  So it looks your mass for six people would be around 6x 1.54 tonnes plus 2 tonnes. 11.2 tonnes in total. Obviously, if the solar energy system was trimmed from a 100 KWe equivalent to a 60 KWe equivalent,  it would probably be coming in at around 7.5 tonnes, certainly much lower than 11.2 tonnes.

I have never said nuclear can’t do the basic job, so your comments about Curiosity are not relevant.

If Megaflex is 250 w per Kg, I am not sure if you are right about Curiosity’s RTG weighing less than a solar energy solution.  The fuel alone weighs 4.8 Kgs. It’s in a graphite shell and sits in some kind of container (another Kg or so?).  There is also a heat rejection system – not sure if that would be necessary if it was solar powered. The RTG pumps out 100W – so about 2.5 KWhs per day.  .Curiosity has batteries because the 100W is not sufficient for peak demand (precisely the point I was making).  There are 2x 40 ampere-hour batteries. Sounds like around 2kg for those batteries. Looks like the whole system could well be 8 kgs or more. I couldn’t find the mass of the stirling engine.  But I note the MMRTG is designed to produce 125 W electrical power at the start of mission, falling to about 100 W after 14 years. With a mass of 45 kg  the MMRTG provides about 2.8 W/kg of electrical power at beginning of life.  Is this the true amount of energy mass in the Curiosity Rover? A solar version might have 3 Kgs of Mageflex generating 6Kwhs compared with just over 3 Kwhs for the nuclear system. You might have 12 Kgs of batteries on board for the solar energy system.

We can test human ability to cope with 0.38 G with a moon-based experiment. After a zero G flight of 8 months the test crew would live on the Moon for a substantial period, while wearing gravity compensation clothing to make up for the 0.16 G environment.  We can then see how their bodies react. The fact that NASA have conducted no such test shows they are not yet serious about getting to Mars.

Making methane on Mars is more about efficient energy storage not propellant production, but we could of course eventually move into propellant production.

JPL are also working on solar power satellite systems but for some reason that is not considered a viable technology by many here.

NASA is unfocussed and spreads itself too thin in my view.

For me colonisation, or settlement, starts with the first human on Mars. We know a huge amount about ground conditions somewhere like Chryse Planitia and we can build on the current knowledge with pre-landing.  No reason to expect anything that will endanger the setting up of a base.

You claim we've already proven that your proposed solution is not more mass efficient than Kilopower.  See above. I dispute that.
The 2 Kwe per person level can easily be supplied by solar energy system, even in the worst dust storm.

Nuclear black magic! lol I can understand that the “coffee can” is actually a lot bigger and a lot heavier than your description suggests.
We could easily keep an ATV powered with solar panels, had we gone down that design route.  NASA simply chose not to.  Rovers are not to be compared to settlements in any meaningful sense. There is no problem in organising back up power at a static settlement.
Why don’t you eat some plutonium…that would be more convincing than the bananas. smile

A reactor has to be deployed and cabled up.  There may be ways to deploy it without human contact but that will mean more mass I expect. I don’t think maintenance is such an issue with smaller RTGs, especially if you build in some redundancy by bringing in several. Maintenance and back up is more an issue with single nuclear reactor proposals.

I don’t think you’ve established the case that the nuclear/RTG reactor is a lower mass option than solar energy system with methane and chemical batteries.

Last edited by louis (2017-06-09 14:33:26)


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#48 2017-06-09 15:07:15

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

Antius -

Solar panels delivering 19 W per kg?  Surely that is all out of date if we have ATK already achieving space rated systems of 150 w per kg and being close to developing a 250 w per kg system (as confirmed by kbd and SpaceNut).  No wonder you were so convinced that nuclear reactors are a low mass solution.

Even with a reduction in output in comparison with Earth orbital power, you'll be looking at three times that figure of 19W per kg - more like 57 W/kg based on a 150 W per Kg.  For 250 W/kg the figure is an impressive 95 W/kg on Mars.

You appear to be relying on a failed project. I learn from Wikipedia that the SP-100 project never advanced to flight hardware and was terminated in 1994. Why are you trying to build a case on failed projects from 23 years ago?

You seem to be taking a step back from your previous absolute certainty that nuclear reactors are lower mass than solar energy solutions. Good.  I might add that I have never rejected the idea of using nuclear reactors for polar bases on Mars – they would probably be necessary.  But for a Mission One base at a sensible location like Chryse Planitia, a solar energy system will likely come in with a lower mass.

Antius wrote:

Apologies for not responding sooner.  Between work and family, I get limited free time for hobbies like this.  Louis and others requested information on the Specific power (KWe/Kg) of fast reactor power systems for deployment on Mars.  Here is the information I have been able to find.

I found it difficult to track down detailed design concepts for the SAFE-400 reactor, as most such information is behind paywalls.  I had more luck with Kilopower and SP-100.  The original thin-film solar surface power concept (see below) referenced a specific power of 19W/kg for SP-100 with four Stirling cycle power converters delivering 100kWe.  As the SP-100 is a 2.5MWth reactor system, these arrangements would require using the reactor at only 16% of its rated power, which seems less than efficient.  The second concept was based on the Prometheus design for a lunar based reactor and had specific power of 10W/kg at power levels of 100kWe using a Brayton cycle.

http://systemarchitect.mit.edu/docs/cooper10.pdf

The specific power of space reactors appears to be a strong function of power output – the higher the power output of the system, the higher the specific power.  This study presents a design arrangement for an SP-100 based system producing 550 kWe, with a total system mass of 11,879.9kg.  That is a specific power of 46.3W/Kg.

https://www.osti.gov/scitech/servlets/purl/10181300

This study examine a lunar base power supply using the SP-100 concept and producing 825kWe, with total system mass 20,000kg – 41.25W/kg.

https://ntrs.nasa.gov/archive/nasa/casi … 005714.pdf

Conversely, for very small reactor systems, specific power is low, but increases progressively as power is scaled up (See Table 1 in the link, below).  The Kilopower concept, achieves specific power of 2.5W/kg at 1KWe power level, but that increases to 6.5W/kg at 10KWe output.

https://ntrs.nasa.gov/archive/nasa/casi … 017750.pdf

Page 29 of the link below, provides a useful graphical approximation for system specific mass, for small fast reactors coupled to Brayton cycle generators.  Both surface power concepts and space nuclear electric propulsion concepts are included.

https://ntrs.nasa.gov/archive/nasa/casi … 004957.pdf

•    It can be seen that at power levels as low 10kWe, the specific mass is 350Kg/KWe, corresponding to specific power of 2.9W/Kg.
•    As power scales up to 100KWe, specific mass is 50kg/KWe (20W/Kg).  This compares very closely to what the researchers assumed in the thin-film solar study.
•    As power requirements reach 1MWe, which is the power level required perhaps, for a large base, specific mass declines to ~18kg/KWe (55.6W/Kg).
•    At power levels of 10-100MWe, what might reasonably be required for a colony of 1000-10,000 people, specific mass appears to converge towards 10kg/KWe (100W/Kg).  Presumably at this point, radiator mass dominates the total system mass, as this part of the system obviously cannot realise any scale effects since heat ejected is proportional to radiator area.  As reactor systems scale up, it makes more and more sense to attempt to build the radiators on Mars using local resources.

So, I would suggest that the best choice of power system for a Mars mission / base / colony, etc. is strongly dependant upon the power requirement (nuclear does much better as power scales up) and location, as solar power system mass would increase for locations further from the equator.  There is the added complication that solar power systems including storage have their own specific power curves, with smaller systems having lower specific power than larger systems.


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#49 2017-06-09 15:08:29

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,805

Re: Going Solar...the best solution for Mars.

Louis-

You've doubled the mass of 10W KiloPower reactors taken to mars in order to make your numbers sound more "reasonable." There would be 3 reactors taken for a 6 man mission, thereby making the mass 4.62 tonnes.

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#50 2017-06-09 16:09:10

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,652

Re: Going Solar...the best solution for Mars.

Nope, it was kbd who says two reactors for every two people. So 6 for 6.  If it was 3 then you would have a meagre 30 Kwes available. If you recall, this discussion started off with a fair degree of consensus that 100 Kwes for a six person mission would be reasonable target for a 6 person mission. 


Oldfart1939 wrote:

Louis-

You've doubled the mass of 10W KiloPower reactors taken to mars in order to make your numbers sound more "reasonable." There would be 3 reactors taken for a 6 man mission, thereby making the mass 4.62 tonnes.

Last edited by louis (2017-06-09 17:15:37)


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