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#26 2017-05-22 18:04:59

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

GW - There are several key decisions that will determine Mars's future. This is one of them. 

"There are other things that simply cannot be done that way,  or else people die!" Well quite, so why on Earth would you depend on a single nuclear power facility which may fail?  Even two is doubtful in my view. There may be some issue about operation on Mars which is not apparent prior to the Mission. Are you really not going to go with major battery storage?

GW Johnson wrote:

Here's a notion I hope is resolved before men go to Mars,  but WILL get resolved regardless shortly after,  at some cost in lives,  if not resolved properly before that first trip. 

Some things work quite well as solar-powered items,  especially if not needed at night,  which reduces the battery size you need.  It would be easier to just bring those devices than to string the power line from a nuke plant.  And there's nothing wrong with that,  as long as you can do without whatever-this-toy-is for the weeks- or months-long duration of a major Martian dust storm,  such as the one that covered the entire planet for months in 1969 when our first orbiter (Mariner 9?) arrived. 

There are other things that simply cannot be done that way,  or else people die!  You need these things night and day,  and you need them regardless of whether the daytime sun is obscured or not.  Solar simply cannot do that job,  because the battery gets ridiculous very,  very quickly.  Thus,  there is simply NO excuse not to rig those things to a nuke generator.  Period.  End of issue.

What that really means is you take a mix of both power supplies,  each tailored to how critical continuous operation is. 

So I suggest:  accept reality.  Just get on with it.  Nuke and solar.

Otherwise,  you might as well be arguing about how many angels can sit on the head of a pin. 

GW


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

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#27 2017-05-22 18:20:07

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,756
Website

Re: Louis' Solar Power Strategy

No,  batteries work well enough,  if you can afford to ship them there.  There's a point where shipping a nuke power plant becomes easier.  That point has to do with how critical continuous power is,  not the amount of power. 

That being said,  nuke reactors have actually been very reliable,  3 very public failures notwithstanding.  Use the SAFE-400,  and just ship enough of them to do whatever KW or MW you think you need.  That gives you the redundancy to counter any individual failures.  And as I said,  some things are better done as solar PV items. 

But,  if you apply the US Navy criteria instead of commercial or NASA criteria,  you won't have any nuke generator failures.  There has been no power failure or radiation containment failure of a standard US Navy nuke power reactor,  not since the very first one went to sea in 1954.  Not even two ship sinkings caused a leak,  and the reactors did NOT cause the ship sinkings. 

The ONLY exception was an experimental sodium-cooled reactor in the submarine USS Seawolf SSN-585 in 1956.  That unit had radioactive sodium fires from leaks,  and was replaced with a pressurized-water reactor.  No more troubles at all,  for a nice long service life for that boat. 

The two sinkings were submarines USS Thresher SSN-593 in 1963,  and USS Scorpion SSN-589 in 1968.  Those wrecks have been monitored closely ever since.  No leaks.  The fail-safe designs were quite good.  We're talking about wrecks that struck hard bottom at over 100 mph,  in 8-12 thousand feet of water.  That's a pretty demanding fail-safe design. 

Hyman Rickover was a real bastard to work for,  but he got the safety thing right.  We are indebted eternally to him for that. 

GW

Last edited by GW Johnson (2017-05-22 18:30:44)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#28 2017-05-22 18:38:15

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

On nuclear powered submarines there are staff dedicated to reactor control and maintenance. I don't know how many but even if it's only two people, with shifts, that could amount to 4 or even 6 people. 

http://rickcampbellauthor.com/styled/index.html#topic4

I think a lot of easy assumptions are being made about the Safe-400 which as far as I know has never been built.


GW Johnson wrote:

No,  batteries work well enough,  if you can afford to shp them there. 

That being said,  nuke reactors have actually been very reliable,  3 very public failures notwithstanding.  Use the SAFe-400,  and ship enough of them to do whatever KW or MW you think you need.  That gives you the redundancy to counter any individual failures.

But,  if you apply the US Navy criteria instead of commercial or NASA,  you won't have any failures.  There has been no power failure or radiation containment failure of a US Navy nuke power reactor,  since the very first one went to sea in 1954.  Not even two ship sinkings caused a leak,  and the reactors did NOT cause the ship sinkings. 

GW


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

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#29 2017-05-22 19:00:26

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,390

Re: Louis' Solar Power Strategy

I can only say that I understand submarines GW and safety, with the newest class still going to the same measures for safety. Each refurbishment and overhaul is different but they are quite the machine.

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#30 2017-05-22 19:17:34

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,390

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#31 2017-05-22 20:48:02

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,110

Re: Louis' Solar Power Strategy

louis wrote:

How small are these nuclear reactors? Have any ever been built? Or are you referring to RTGs?  Has the Safe-400 actually been built (I can't find anything on the net suggesting it has) - so is this an untried design?

We've already covered this topic.

Core Dimensions and System Masses:

Kilopower 1kWe reactor: 4.5" D x 9.5" L (600kg, complete system, 4m in length, complete system, uses UMo fuel from DOE-NNSA)

Kilopower 10kWe reactor: 6" D x 11" L (1800kg, complete system, 4m in length, complete system, uses UMo fuel from DOE-NNSA)

DOE is spending less than $10M per year for all components and contracts (for Stirling electric generators, control electronics, etc).

SAFE-400 100kWe reactor: 12" D x 20" L (512kg, core only, 2t to 2.5t for the complete system; mass variability comes from using new vs old generation radiator technology being developed for space nuclear power, uses HEU fuel)

There's a non-linear relationship between total system mass and output for anyone who doesn't willfully ignore it.  The radiators are by far the largest component of the reactor.  The shielding is the highest mass component of the reactor.  The same is not true of solar power.

louis wrote:

Electricity from solar can easily be stored in batteries.  The reason it isn't done on Earth much is because it is an expensive option. The revenue cost of providing battery storage on Mars will be zero for Mission One. Cost doesn't come into it.  Lithium batteries can store nearly 12Kwhs per Kg. So a tonne will give you 12000 KWhs. Power can also be stored as methane and overnight as hot water or heated bricks. The intermittent nature of solar power is a red herring in terms of judging the overall effectiveness of the system.

Lithium-ion batteries don't store 12kWh/kg nor anything close to it.  Try 250Wh/kg or .25kWh/kg.  That's our best commercial tech.  Thank you, Panasonic and Tesla.  Graphene promises 1kWh/kg and that's supposed to be commercial tech this year.  The 250Wh/kg Lithium-ion batteries translates to 48,000kg of to store 12,000KWh using a naive calculation that consumes 100% of rated capacity, which will destroy any type of battery you care to name off.  Therefore, the real battery mass is 60,000kg to store 12MWh and that doesn't include mass for more storage capacity for electric heating of the batteries, packaging, or control electronics.  80% DoD is what you get with Lithium-ion.  You can drain 100% of rated capacity of capacitors, but not batteries.

Even with 1kWh/kg Graphene batteries, do you not see how ridiculous it is to try to store 12MWh of electricity in batteries?  It's silly.  A 4MWe reactor might weigh 12t, which is exactly what a 12MWh capacity Graphene battery would weigh, except that the fission reactor pumps out 4MWe continuously and the physical core dimension are literally just a few inches greater than SAFE-400 using HEU fuel.

Let's compare that with current solar panel technology from ATK, which is the absolute best that money can buy for space power.  The panels themselves are 7kg per kWe.  Those are actual numbers from the actual manufacturer of real space solar panel hardware that can survive both launches and reentries on Mars and is flight proven for that specific purpose.

4,000,000 Watts / 1,000 Watts = 4,000 of the 1kWe PV arrays from Orbital ATK

4,000 * 7kg/kWe = 28,000kg of PV panels to produce 4MWe for 12 hours per day in Earth orbit

You only get about 43% of the solar irradiance received in Earth orbit on the surface of Mars, so to actually produce 4MWe at any point in time during the day, you need an equivalent of a little more than 65,100kg worth of solar panels.

That's 125,100kg for a ridiculous 4MWe (on Mars) PV array and a 12MWh capacity Lithium-ion battery system or 80,100kg with the Graphene-based 12MWh capacity battery.  If we have that type of payload capacity to expend on this Mars colony just to provide electrical power, then we can afford to ship completely shielded nuclear reactors that produce 4MWe 24/7 and still come out ahead on the mass budget.  The math doesn't work out in favor of solar power and NASA's engineers already know this.

The solar concentrators or solar thermal systems that you and I made reference to, which I know from actual use here on Earth are viable alternatives to molten salt reactors, are still substantially more massive than molten salt fission reactors that provide equivalent output but arguably easier to build if resource consumption (steel, concrete, salts) to construct them is not a constraint and the materials are locally sourced.

louis wrote:

Not sure why you think nuclear reactors are such a great option longer term. At one of our major UK nuclear facilities, Sellafield, there are 10,000 people employed!!! That's how labour intensive a nuclear power industry is.  A solar power satellite microwave beam system could be pretty much completely automated.

That's how labor intensive a nuclear fuel reprocessing plant for half the world is.  This is just another non-example of how labor intensive a space reactor power system would actually be.  While they're at it, UK's government decided to build three new reactors at Sellafield to produce 7% of the UK's electrical power requirement.  If you're reprocessing the fuel into usable isotopes, then you may as well stick it back in a reactor.

louis wrote:

Geothermal works fantastically well in Iceland...so it if is a practical option on Mars, there's no reason to think it won't work well there.

Great.  Let's find one of those on Mars.  Have we found one yet?

louis wrote:

It sounds to me like you are going to condemn the people of Mars to being dependent on energy imports from Earth for many years  as there is no way that they will be able to manufacture nuclear power facilities.

PV panels and batteries condemn people on Mars to energy imports from Earth.  The nuclear reactors in naval ships operate for decades at a time between refueling.  The length of time between commissioning and decommissioning is largely a part of the reactor design.  If we started using molten salt reactors here on Earth, then what would the Uranium mining companies have to sell the reactor operators?  It's an economics model that revolves around a well-known concept here in the US of A called "planned obsolescence".  Maybe you've heard of it.

louis wrote:

Furthermore, given the absolute necessity of life support on Mars, if your nuclear reactor fails, the people die. Or are you going to invest in battery technology as  well.

We'd invest in multiple nuclear reactors.

This solar power for everything nonsense just doesn't work in the real world.  It's not about what I want or believe, it's just what basic math tells me using what I already know about solar power, nuclear power, and batteries.  Orbital ATK is not lying.  DOE is not lying.  Panasonic is not lying.  Things cost what they cost, they weigh what they weigh, and they produce what they produce.  We gots what we gots and we ain't got no more.

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#32 2017-05-22 21:00:56

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,796

Re: Louis' Solar Power Strategy

Louis-

Wishful thinking is nice; you can make all your dreams come true. In your dreams. We're trying here to deal with the real situation, and Mars is hard enough without making things unwieldy with tons of solar panels, and batteries.

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#33 2017-05-23 03:56:24

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

kbd has admitted you have to arrive with multiple nuclear reactors. How many and how much will they weigh? When I last looked into this, it seemed to me the nuclear option was going to require several tonnes. A fail safe nuclear based option with flexibilty (enabling rover exploration) would probably be several tonnes. I've read a reference to the SAFE-400 reactor weighing 500 kgs. But of course, that's unlikely to be the total mass for a Mars mission.

But I do come back to the point that I can't find any reference to the SAFE-400 having been built. Here's relevant link:

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

We are told:

The Multi-Mission RTG (MMRTG) uses eight GPHS units with a total of 4.8 kg of plutonium oxide producing 2 kW thermal which can be used to generate some 110 watts of electric power, 2.7 kWh/day.


The MIT study suggested a figure of 100KwE for a fully realised first mission of six people. So about 2450 KwHs. That would suggest well over 900 Kgs if it scales up proportionally. But that is without "human-proofing".  I know kbd is suggesting it doesn't scale in proportion - but then you have the "putting all your eggs in one basket" issue. And if you do put all your eggs in one big nuclear reactor then  I think you need a second one for fail safeness.  With all the accompanying electrical equipment, cabling,  packaging and safety features, I very much doubt you are going to provide an effective solution for under 5 tonnes. I can see this creeping up to ten tonnes.

I have to emphasise again, I am not dogmatic on this. Pre-landing a couple of small RTGs sounds like  sensible back up to me. But I would definitely focus the energy system on PV.

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

Why don't you set out in detail the mass requirement for a nuclear powered based first mission?



Oldfart1939 wrote:

Louis-

Wishful thinking is nice; you can make all your dreams come true. In your dreams. We're trying here to deal with the real situation, and Mars is hard enough without making things unwieldy with tons of solar panels, and batteries.


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

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#34 2017-05-23 04:43:57

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

So - assuming these reactors are human-proofed (which I am not sure is the case) - you basically have a choice between:

(a) an inflexible low tonnage nuclear power scenario, where you take two "big" SAFE-400 (not yet built as far as I can tell) reactors at 5 tonnes or

(b) a more flexible high tonnage nuclear scenario where perhaps you take ten 10 Kwe reactors at 18 tonnes.

This is of course ignoring add ons like cabling, protective material in Rovers and so on. We also don't have details on whether these reactors really need to be monitored in a Mars mission context, as they are on a nuclear submarine. It's one thing having a nuclear reactor in an inanimate robot craft. Quite different if humans are involved.

Geothermal and methane capture are longer term options. If they are viable, they are infinitely preferable to nuclear reactors.

In terms of energy storage, my approach would be focused on pre-landing methane production rather than chemical battery storage.

We can get 13 KwHs per kg of methane - maybe stored at 0.4 kg per litre. At minimum KwE (12 KwEs) that's nearly 54,000 KwHs for 100 sols equals about 7,600 litres of methane to be stored.  Having looked up cylinder weights, we can store those at 3.9 tonnes but presumably at a lower tonnage with larger cylinders - my guess would be around 2 tonnes. But I suspect there may be alternative methods of storage in the cold conditions on Mars (e.g. clathrate style storage - needs to be researched).

Chemical battery storage is more about ensuring a few days' survival at minimal energy use in the event something goes wrong with the energy generation/methane storage system. Even on the basis of 1 KwH storage per kg, a tonne of batteries will provide that protection.
Overnight energy storage is not a real problem as much of the life support energy usage can take place during the day, and hot water can be stored overnight.

kbd512 wrote:
louis wrote:

How small are these nuclear reactors? Have any ever been built? Or are you referring to RTGs?  Has the Safe-400 actually been built (I can't find anything on the net suggesting it has) - so is this an untried design?

We've already covered this topic.

Core Dimensions and System Masses:

Kilopower 1kWe reactor: 4.5" D x 9.5" L (600kg, complete system, 4m in length, complete system, uses UMo fuel from DOE-NNSA)

Kilopower 10kWe reactor: 6" D x 11" L (1800kg, complete system, 4m in length, complete system, uses UMo fuel from DOE-NNSA)

DOE is spending less than $10M per year for all components and contracts (for Stirling electric generators, control electronics, etc).

SAFE-400 100kWe reactor: 12" D x 20" L (512kg, core only, 2t to 2.5t for the complete system; mass variability comes from using new vs old generation radiator technology being developed for space nuclear power, uses HEU fuel)

There's a non-linear relationship between total system mass and output for anyone who doesn't willfully ignore it.  The radiators are by far the largest component of the reactor.  The shielding is the highest mass component of the reactor.  The same is not true of solar power.

louis wrote:

Electricity from solar can easily be stored in batteries.  The reason it isn't done on Earth much is because it is an expensive option. The revenue cost of providing battery storage on Mars will be zero for Mission One. Cost doesn't come into it.  Lithium batteries can store nearly 12Kwhs per Kg. So a tonne will give you 12000 KWhs. Power can also be stored as methane and overnight as hot water or heated bricks. The intermittent nature of solar power is a red herring in terms of judging the overall effectiveness of the system.

Lithium-ion batteries don't store 12kWh/kg nor anything close to it.  Try 250Wh/kg or .25kWh/kg.  That's our best commercial tech.  Thank you, Panasonic and Tesla.  Graphene promises 1kWh/kg and that's supposed to be commercial tech this year.  The 250Wh/kg Lithium-ion batteries translates to 48,000kg of to store 12,000KWh using a naive calculation that consumes 100% of rated capacity, which will destroy any type of battery you care to name off.  Therefore, the real battery mass is 60,000kg to store 12MWh and that doesn't include mass for more storage capacity for electric heating of the batteries, packaging, or control electronics.  80% DoD is what you get with Lithium-ion.  You can drain 100% of rated capacity of capacitors, but not batteries.

Even with 1kWh/kg Graphene batteries, do you not see how ridiculous it is to try to store 12MWh of electricity in batteries?  It's silly.  A 4MWe reactor might weigh 12t, which is exactly what a 12MWh capacity Graphene battery would weigh, except that the fission reactor pumps out 4MWe continuously and the physical core dimension are literally just a few inches greater than SAFE-400 using HEU fuel.

Let's compare that with current solar panel technology from ATK, which is the absolute best that money can buy for space power.  The panels themselves are 7kg per kWe.  Those are actual numbers from the actual manufacturer of real space solar panel hardware that can survive both launches and reentries on Mars and is flight proven for that specific purpose.

4,000,000 Watts / 1,000 Watts = 4,000 of the 1kWe PV arrays from Orbital ATK

4,000 * 7kg/kWe = 28,000kg of PV panels to produce 4MWe for 12 hours per day in Earth orbit

You only get about 43% of the solar irradiance received in Earth orbit on the surface of Mars, so to actually produce 4MWe at any point in time during the day, you need an equivalent of a little more than 65,100kg worth of solar panels.

That's 125,100kg for a ridiculous 4MWe (on Mars) PV array and a 12MWh capacity Lithium-ion battery system or 80,100kg with the Graphene-based 12MWh capacity battery.  If we have that type of payload capacity to expend on this Mars colony just to provide electrical power, then we can afford to ship completely shielded nuclear reactors that produce 4MWe 24/7 and still come out ahead on the mass budget.  The math doesn't work out in favor of solar power and NASA's engineers already know this.

The solar concentrators or solar thermal systems that you and I made reference to, which I know from actual use here on Earth are viable alternatives to molten salt reactors, are still substantially more massive than molten salt fission reactors that provide equivalent output but arguably easier to build if resource consumption (steel, concrete, salts) to construct them is not a constraint and the materials are locally sourced.

louis wrote:

Not sure why you think nuclear reactors are such a great option longer term. At one of our major UK nuclear facilities, Sellafield, there are 10,000 people employed!!! That's how labour intensive a nuclear power industry is.  A solar power satellite microwave beam system could be pretty much completely automated.

That's how labor intensive a nuclear fuel reprocessing plant for half the world is.  This is just another non-example of how labor intensive a space reactor power system would actually be.  While they're at it, UK's government decided to build three new reactors at Sellafield to produce 7% of the UK's electrical power requirement.  If you're reprocessing the fuel into usable isotopes, then you may as well stick it back in a reactor.

louis wrote:

Geothermal works fantastically well in Iceland...so it if is a practical option on Mars, there's no reason to think it won't work well there.

Great.  Let's find one of those on Mars.  Have we found one yet?

louis wrote:

It sounds to me like you are going to condemn the people of Mars to being dependent on energy imports from Earth for many years  as there is no way that they will be able to manufacture nuclear power facilities.

PV panels and batteries condemn people on Mars to energy imports from Earth.  The nuclear reactors in naval ships operate for decades at a time between refueling.  The length of time between commissioning and decommissioning is largely a part of the reactor design.  If we started using molten salt reactors here on Earth, then what would the Uranium mining companies have to sell the reactor operators?  It's an economics model that revolves around a well-known concept here in the US of A called "planned obsolescence".  Maybe you've heard of it.

louis wrote:

Furthermore, given the absolute necessity of life support on Mars, if your nuclear reactor fails, the people die. Or are you going to invest in battery technology as  well.

We'd invest in multiple nuclear reactors.

This solar power for everything nonsense just doesn't work in the real world.  It's not about what I want or believe, it's just what basic math tells me using what I already know about solar power, nuclear power, and batteries.  Orbital ATK is not lying.  DOE is not lying.  Panasonic is not lying.  Things cost what they cost, they weigh what they weigh, and they produce what they produce.  We gots what we gots and we ain't got no more.


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

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#35 2017-05-23 06:01:54

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

Re: Louis' Solar Power Strategy

louis wrote:

So - assuming these reactors are human-proofed (which I am not sure is the case) - you basically have a choice between:

(a) an inflexible low tonnage nuclear power scenario, where you take two "big" SAFE-400 (not yet built as far as I can tell) reactors at 5 tonnes or

(b) a more flexible high tonnage nuclear scenario where perhaps you take ten 10 Kwe reactors at 18 tonnes.

Louis, nuclear reactors are not inflexible.

The baseline scenario assumes a constant 24/7 generation of 100KWe because that is what is desirable for things like propellant production.  If you have spent a lot of money building and shipping a piece of equipment to Mars (i.e. propellant plant), you get the most out of that investment if you run it continuously.  It is not a necessity, but it is always economically desirable.  Otherwise, you must either build a larger plant with higher peak power output, or you must wait longer for the same output.

If power requirements are variable, a base / mission, etc. could ramp the power output of a reactor down and would extend core life.  We do actually do that sometimes with reactors on Earth, but it is undesirable, because the capital and operating costs of plants are the same regardless of power output and fuel is relatively cheap.  So it is more efficient to use a low-capital but expensive fuel generating option (i.e. gas turbines) to meet fluctuating loads.

In terms of reliability, it is true that shutting down a base nuclear reactor would be problematic as it would represent a large proportion of power supply going off line.  To reduce the probability of this, the original Mars Direct planned for a 2MWth, 0.1MWe reactor power system, as this used thermoelectric generators with few if any moving parts.  Heat removal in the reactor core would have been through natural convection.  So it is hard to see what could go wrong.  Using Stirling engines one gets a much superior thermal efficiency at the expense of some moving parts.  So failure is possible, but a reliable design would include multiple Stirling units, removing the potential for common cause failure.  Then again, solar power systems shut down uncontrollably between sunset and sunrise.  You need energy storage to get around that problem.  The original Mars Direct scenario included a 5KWe solar power system, presumably to provide stay-alive power in the event of a reactor malfunction or catastrophic loss of stored propellants.


louis wrote:

In terms of energy storage, my approach would be focused on pre-landing methane production rather than chemical battery storage.

Louis, you are talking about building an additional spacecraft and effectively mounting an entire additional mission, just to support an aesthetic decision over energy architecture. 

I will answer your other points later, as my lunch break is about to run out.

Last edited by Antius (2017-05-23 06:08:35)

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#36 2017-05-23 08:38:00

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

Antius - You and the other nuclear enthusiasts here appear reluctant to give a detailed mass breakdown for the total mass of a nuclear-based energy system, including any mass required to ensure the safety of human beings.

Also, you seem reluctant to state in detail how automated these systems will be, or whether members of the crew will need to monitor, control or maintain them (as happens on nuclear submarines). For me, this is another crucial issue.

Propellant production is not an essential requirement of Mission One. If that is the logic for nuclear, it is poor logic.

Power requirements will be very variable in my judgement.  With a solar power approach, that will be perfectly natural.  When solar energy is at its greatest, that is when industrial experiments will be undertaken and when life support energy usage will be greatest.

Being 100 million kms away, we cannot afford a "why should it go wrong" attitude. We have to assume all systems can go wrong.


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

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#37 2017-05-23 09:46:18

Terraformer
Member
From: Lancashire
Registered: 2007-08-27
Posts: 3,163
Website

Re: Louis' Solar Power Strategy

Lithium batteries can store nearly 12Kwhs per Kg.

Not the ones in regular use. Maybe a theoretical device could (based on..?), but the ones we actually have available only store 1/50th of that, ~240 Wh/kg.

At one of our major UK nuclear facilities, Sellafield, there are 10,000 people employed!!! That's how labour intensive a nuclear power industry is.

The Vanguard class submarines only carry 135 people, and they're not all engaged in keeping the reactor going.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#38 2017-05-23 10:59:39

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,756
Website

Re: Louis' Solar Power Strategy

What I suggested was that the first crews need to take both solar and nuclear power.  Self-contained solar for this and that provides a ready-to use item right out-of-the-box.  But there are some critical needs for power that cannot wait for the sun to shine bright enough,  and as has already been pointed out,  battery energy storage densities are still fairly low,  although quite a bit better now than the old lead-acid batteries still in your cars. 

I don't know how well the SAFE-400 can be scaled up,  or how reliable that design is going to be.  The small ones are still being run experimentally,  and as far as I can tell,  no MWe-scale units have ever been built.  But I would think that with concerted effort,  a 100-KWe-scale design could be made ready and characterized for reliability,  on a time scale of about 5 years.  Without that effort,  never. 

As for submarine reactor systems requiring "tending",  no they do not.  Ship and submarine systems are NOT (I repeat NOT!!!) like commercial power plant units.  They are monitored remotely,  by a tiny minority of the crew.  All of the propulsion machinery (not just the reactor) is aft of a shielding bulkhead.  No one goes back there while the system operates.  The reactor compartment itself is even more heavily shielded,  and no one ever goes in there until the unit is refueled or recycled. 

THAT's the kind of reactor system I would like to send to Mars. I don't know if SAFE-400 is that kind of a design or not,  but I rather doubt it.  NASA is not the USN.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#39 2017-05-23 11:46:10

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,796

Re: Louis' Solar Power Strategy

Everything on this first human mission must be as "fail-safe," and "idiot proof" as possible. My personal position is as GW and Robert Zubrin have indicated: take both solar and nuclear. I, for one, would be unwilling to stake my life on having clear Martian skies for both base power requirements and production of Oxygen (and still--Methane) for a return flight, without that nuclear backup. That needs to be decided by the individual on the mission designated as "pilot in command." Going to Mars is not an enviro-fest of ecofreaks, but the most important voyage of discovery ever undertaken by humans since Columbus sailed west, "off the edge of the Earth."

For those not involved in Aviation as pilots, Pilot in Command is a position not taken lightly, and has ultimate authority on board an airplane as does a ship's master/Captain at sea.

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#40 2017-05-23 12:47:16

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,110

Re: Louis' Solar Power Strategy

Louis,

Your power provisioning strategy is based on technologies that don't exist.  There are no 12kWh/kg batteries in the real world.  If there were, nobody in their right mind would be driving a car with an internal combustion engine.  Thin film solar panels are still experimental.  I expect the technology to be commercially available in about 5 years or so, but right now it's still experimental.  We haven't found any geothermal vents on Mars.  To make LOX and LCH4, you need a LOT of power.  I did the math to show you what things would weigh.  That is what the batteries and solar panels alone would weigh without packaging, insulation, charge controller electronics, or power cables.

I gave you masses for Kilopower reactors that DOE-NNSA is actively developing.  Those masses include the core, shielding, radiators, and Stirling electric generators.  Apart from the radiator panels, these things are tiny.  The core dimensions won't change.  The cores use commercial low-enriched Uranium and have one moving part to control criticality, which is why these designs weigh so much, relative to output.  DOE-NNSA didn't throw darts at a dart board to decide how large the reactor would be or what it would weigh.  Every component in the reactor is using very well established principles of nuclear, thermodynamic, and electrical engineering.

One small correction, Kilopower is now using HEU.  The first concepts were LEU.  Also, the total development cost is projected at $10M over 3 years, not $10M per year.

Kilopower 10kWe mass breakdown:

Core: 235kg (UMo fuel, BeO reflector, Na heat pipes)
Shielding: 547kg (LiH/W)
Everything Else: 763kg (Stirling generators, radiators, electronics, structures)
Total: 1,545kg

The reactor requires a 28VDC 1 AH battery to bring the plant on line.  I think we can manage that.

If you really believe that anything that can go wrong, will go wrong, then you have to assume that electric battery heaters and charge controllers will fail and that solar power output drops substantially during dust storms.  Solar power alone is a losing proposition, from a mass perspective, if substantial 24/7 electrical power output is required.

Hot water storage to generate power at night?  You're still throwing out ideas without thinking about what's involved.

The math simply does not work in favor of solar power for high output requirements.  It's not about what I want, it's about how the real world works right now.  If it was the other way around, I would be advocating for solar power, but it's not.

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#41 2017-05-23 18:04:30

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,390

Re: Louis' Solar Power Strategy

Just in case this is missed in the other topic
Slide 5 of this link does a nice job of showing all types of power levels to duration...
5595_files/Electrical Power Subsystem_v2.ppt

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#42 2017-05-23 18:45:50

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

Yes, thanks for the correction.  I definitely got that wrong about battery storage!  3.5 Kwh/kg does seem within reach but lets run with 250 watt hours per Kg.

Overall on Mission One, I think for a solar based strategy you might need 2 tonnes of batteries in various configuration - providing about 500 KwHs of storage.  That will give you a direct source of emergency energy for a couple of sols in the extremely unlikely event of all round failure in other systems, giving you time to address the failures and make a repair or engage back up energy. 

Based on Zubrin's work, a machine of about 250kg could produce enough methane and oxygen over just under 6 years to provide emergency power (29400 KweHs) for 100 sols at 3.5 Kwe power usage, constant.  You would have to store that gas of course.  The tanks might mass at a couple of tonnes.

https://en.wikipedia.org/wiki/Sabatier_ … nt_on_Mars

At Chryse Planitia water could be extracted from the atmosphere at about 3kgs per sol for 10KWe constant.

However, robot rover harvesting of water ice (a 500 kg rover could no doubt easily throughput 100 kgs of regolith per sol and harvest 6 kgs per sol at somewhere like Chryse Planitia where water ice is about 6% of the surface regolith) will be more productive in all likelihood.

I need to look into this in more detail, but I think under this approach you might need to pre-land maybe 2 tonnes of equipment,  a tonne's worth of rovers, 2tonnes of gas tank (unless there is a better way of storing the product),  a tonne of batteries, and maybe a tonne of PV panelling to get a working system in place. So perhaps 7 tonnes in all.  Of course, this isn't just a power guarantee - once people land, all this equipment can have a continuing role to play in supporting the mission (and subsequent missions) e.g. in providing water for farming and human usage and in providing methane (e.g. for use on exploration mission or with automated "rocket hoppers"). A nuclear reactor is only good at being a nuclear reactor.

So if 7 tonnes is a reasonable ball park figure, then on top of that (with a PV-based approach), I would be talking about bringing in a further 5 tonnes of PV panelling and associated equipment to ensure a constant 100Kwe, bringing the total mass of the energy/water production system to 12 tonnes. 

There's room for perhaps another 3 tonnes expended on back up energy in the form of an RTG, maybe an iron fuel steam turbine and maybe a machine for CO and oxygen combustion.

I wasn't suggesting overnight hot water storage for power production, simply for human hygiene and kitchen usage and for heating. I was  observing that you don't need to provide power for hot water or heating through the night. Same goes for life support. You don't have to separate out oxygen and other gases during nighttime.
 
Even in the worst dust storm conditions imaginable the system would still be delivering 10 Kwes and the 100 sol emergency supply could contribute a top up of 2 Kwe over 600 sols.

kbd512 wrote:

Louis,

Your power provisioning strategy is based on technologies that don't exist.  There are no 12kWh/kg batteries in the real world.  If there were, nobody in their right mind would be driving a car with an internal combustion engine.  Thin film solar panels are still experimental.  I expect the technology to be commercially available in about 5 years or so, but right now it's still experimental.  We haven't found any geothermal vents on Mars.  To make LOX and LCH4, you need a LOT of power.  I did the math to show you what things would weigh.  That is what the batteries and solar panels alone would weigh without packaging, insulation, charge controller electronics, or power cables.

I gave you masses for Kilopower reactors that DOE-NNSA is actively developing.  Those masses include the core, shielding, radiators, and Stirling electric generators.  Apart from the radiator panels, these things are tiny.  The core dimensions won't change.  The cores use commercial low-enriched Uranium and have one moving part to control criticality, which is why these designs weigh so much, relative to output.  DOE-NNSA didn't throw darts at a dart board to decide how large the reactor would be or what it would weigh.  Every component in the reactor is using very well established principles of nuclear, thermodynamic, and electrical engineering.

One small correction, Kilopower is now using HEU.  The first concepts were LEU.  Also, the total development cost is projected at $10M over 3 years, not $10M per year.

Kilopower 10kWe mass breakdown:

Core: 235kg (UMo fuel, BeO reflector, Na heat pipes)
Shielding: 547kg (LiH/W)
Everything Else: 763kg (Stirling generators, radiators, electronics, structures)
Total: 1,545kg

The reactor requires a 28VDC 1 AH battery to bring the plant on line.  I think we can manage that.

If you really believe that anything that can go wrong, will go wrong, then you have to assume that electric battery heaters and charge controllers will fail and that solar power output drops substantially during dust storms.  Solar power alone is a losing proposition, from a mass perspective, if substantial 24/7 electrical power output is required.

Hot water storage to generate power at night?  You're still throwing out ideas without thinking about what's involved.

The math simply does not work in favor of solar power for high output requirements.  It's not about what I want, it's about how the real world works right now.  If it was the other way around, I would be advocating for solar power, but it's not.


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

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#43 2017-05-23 22:52:44

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,796

Re: Louis' Solar Power Strategy

The total mass of your solar power system, batteries included, would be better allocated to additional food and habitat . Sorry. You're just barking up the wrong tree. A 6 man mission (round trip) requires some 9+ metric tonnes of food (based on a 550 day planetary stay, and 360 days of travel aboard spacecraft. Add in 2 SAFE-400 nuke reactors for redundancy at 3.5 metric tonnes. So...for 12.5 metric tonnes equal to your solar array and not nearly enough batteries, we get enough food and power for the entire mission with 6 pioneers/astronauts.

As GW has pointed out--solar is highly suspect when there is a year-long Martian dust storm capable of obscuring a large %age of the incident light.

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#44 2017-05-24 03:08:13

elderflower
Member
Registered: 2016-06-19
Posts: 1,149

Re: Louis' Solar Power Strategy

Problem here ,Oldfart, is that the two reactors are identical. For real reliability you need multiple technologies launched on different vehicles and confirmed as landed safely near one another. Otherwise there is the possibility of common mode failure due to whatever you didn't think of, or dismissed as too unlikely.

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#45 2017-05-24 04:12:12

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

Too logical, Mr Spock.

The problem with making food-through-farming a big element of Mission One is that you are then making it another failsafe item...Any farm project big enough to feed the pioneers is going to require a lot of mass in itself and will suck up a lot of energy. If it relies on ambient light it will fail in a dust storm and your pioneers will starve .  If it's all done on artificial lighting, then you are talking about a huge power intake, probably the equivalent of the amount of light that falls on a 60,000 sq. metre patch on Earth in the temperate zone about 100,000 KweHs equivalent a day I would think. A SAFE-400 gives about 2400 KWehs! Bit of a difference there!! You might be able to reduce the 100,000 KWHs through careful crop choice and crop rotation (but you are then adding huge layers of complexity to Mission One and probably also restricting diet hugely) but you won't get anywhere near 2400 KWeHs.

While I accept that a normal food intake would be around 9 tonnes, let's remember (a) some foods (e.g. olive oil) are hugely more densely calorific than others and we can bias our food intake to them, thus cutting down on tonnage (b) if we use dehydrated food as a substantial part of the diet we can get that 9 tonnes down to 6 (c) about 20% of the total food load can stay in the transit vehicle.

I'd say that an assumed  9 tonne overall food load could be reduced to maybe 3 tonnes to the Mars surface using (a), (b) and (c).

Oldfart1939 wrote:

The total mass of your solar power system, batteries included, would be better allocated to additional food and habitat . Sorry. You're just barking up the wrong tree. A 6 man mission (round trip) requires some 9+ metric tonnes of food (based on a 550 day planetary stay, and 360 days of travel aboard spacecraft. Add in 2 SAFE-400 nuke reactors for redundancy at 3.5 metric tonnes. So...for 12.5 metric tonnes equal to your solar array and not nearly enough batteries, we get enough food and power for the entire mission with 6 pioneers/astronauts.

As GW has pointed out--solar is highly suspect when there is a year-long Martian dust storm capable of obscuring a large %age of the incident light.


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

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#46 2017-05-24 04:39:27

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

Re: Louis' Solar Power Strategy

Here is a detailed design description for a 100KWe (1.2MWth) reactor system.  I havn't had time to look at it in detail, but here are the basics.  Total mass is 6.5 tonnes, about 2te of which is shielding and 0.9te of which is the 1km power transmission cable and 0.5te is the radiator.  Presumably, for a Martian base able to locate the reactor core at the bottom of a pit, shielding and transmission mass could be eliminated.

https://stuff.mit.edu/afs/athena/course … Report.pdf

Shielding options that do not appear to have been explored in detail are (1) Dry ice condensed from the Martian atmosphere; (2) Water condensed from the Martian atmosphere.  A system designed to operate and build a shield from these materials would presumably save considerable mass.

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#47 2017-05-24 04:50:44

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

I guess it could be transited separately from the crew - but that will add some mass (a separate transit craft).

There seems to be a consensus that you need at least two since it would be arrogant folly to assume they can't malfunction. So without shielding that is 9 tonnes and with shielding it is 13 tonnes.

Many advocates of nuclear say they still want to take small RTGs, PV panelling and chemical batteries to provide needed flexibility. You're probably talking about at least 2 tonnes if you want to build in that back up and flexibility.

You will still need to source water , but you will have to use different machinery from your nuclear reactor, not the same machinery as used in the methane manufacture process(so at least another couple of tonnes I'm thinking). For purposes of comparison we really need to look at total energy system + total water sourcing (or recycling).  And of course all that has to be done in the context of what you are going to do on Mission One.


Antius wrote:

Here is a detailed design description for a 100KWe (1.2MWth) reactor system.  I havn't had time to look at it in detail, but here are the basics.  Total mass is 6.5 tonnes, about 2te of which is shielding and 0.9te of which is the 1km power transmission cable and 0.5te is the radiator.  Presumably, for a Martian base able to locate the reactor core at the bottom of a pit, shielding and transmission mass could be eliminated.

https://stuff.mit.edu/afs/athena/course … Report.pdf

Shielding options that do not appear to have been explored in detail are (1) Dry ice condensed from the Martian atmosphere; (2) Water condensed from the Martian atmosphere.  A system designed to operate and build a shield from these materials would presumably save considerable mass.


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

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#48 2017-05-24 06:45:23

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,796

Re: Louis' Solar Power Strategy

What I have stated in the past is a combination of BOTH solar and nuclear. Nuclear is for the main base, but having solar panels available and part of the structure of the rovers and outlying stations also makes sense.

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#49 2017-05-24 13:07:45

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

Re: Louis' Solar Power Strategy

louis wrote:

There seems to be a consensus that you need at least two since it would be arrogant folly to assume they can't malfunction. So without shielding that is 9 tonnes and with shielding it is 13 tonnes.

Many advocates of nuclear say they still want to take small RTGs, PV panelling and chemical batteries to provide needed flexibility. You're probably talking about at least 2 tonnes if you want to build in that back up and flexibility.

Louis, the mission does not necessarily need two reactors.  There are many faults that could result in mission failure.  Reactor faults are only one category.  If the probability of failure is small compared to all other mission related risks, it doesn't make sense to double power supply mass.

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#50 2017-05-24 13:20:23

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,339

Re: Louis' Solar Power Strategy

That's your view but I am not sure everyone who wants nuclear backs you on that.  I think it would be arrogant folly to assume your single reactor will not malfunction.

There are some risks that have to be taken e.g. launch...you can't have a back up launch, as it were. Likewise, meteorite strikes - they could damage any surface base.

But, food, energy, life support should not involve major risks. They should all be backed up.


Antius wrote:
louis wrote:

There seems to be a consensus that you need at least two since it would be arrogant folly to assume they can't malfunction. So without shielding that is 9 tonnes and with shielding it is 13 tonnes.

Many advocates of nuclear say they still want to take small RTGs, PV panelling and chemical batteries to provide needed flexibility. You're probably talking about at least 2 tonnes if you want to build in that back up and flexibility.

Louis, the mission does not necessarily need two reactors.  There are many faults that could result in mission failure.  Reactor faults are only one category.  If the probability of failure is small compared to all other mission related risks, it doesn't make sense to double power supply mass.


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

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