New Mars Forums

Official discussion forum of The Mars Society and MarsNews.com

You are not logged in.

Announcement

Announcement: We've recently made changes to our user database and have removed inactive and spam users. If you can not login, please re-register.

#1 2019-10-01 17:59:33

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Methane backup not nuclear vs solar

SpaceNut
Edit This topic has started with content which the other was not created for.

Yes, Louis. I'm looking ahead to the far future w/r asteroid mining; but it WILL take place once Mars is adequately developed. But you HAVE overlooked the major resource on the Moon, and that's He-3. Today--worthless, as we do not yet have fusion energy generation. But maybe--just maybe--in 10 years, we could see viable fusion reactors running, and He-3 is the fuel of choice. At that juncture, He-3 becomes financially viable at $2 Million per kg (today's prices).

Offline

#2 2019-10-01 19:06:08

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,669

Re: Methane backup not nuclear vs solar

Calliban, the riches for return on going to mars will be there as we have done quite a good geological touch with regards to mars chemistry. and there are enough simularities to say that we will find in time gold, silver, nickle plus more.

He3 is the new gold of the moon for the chances of building nuclear on mars or in space as its not coming from earth so no need to cry wolf on the launching of it to orbit....

The mars prize will be harder to obtain but it can be done once we have the initial toehold the James town of the new world mars....

Online

#3 2019-10-02 03:12:18

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

I was aware people mention He3 a lot! But I remain highly sceptical about hot fusion becoming technically viable in the next few years...it's always been 10 years away in my lifetime! lol

Oldfart1939 wrote:

Yes, Louis. I'm looking ahead to the far future w/r asteroid mining; but it WILL take place once Mars is adequately developed. But you HAVE overlooked the major resource on the Moon, and that's He-3. Today--worthless, as we do not yet have fusion energy generation. But maybe--just maybe--in 10 years, we could see viable fusion reactors running, and He-3 is the fuel of choice. At that juncture, He-3 becomes financially viable at $2 Million per kg (today's prices).


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

Offline

#4 2019-10-02 07:22:10

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Re: Methane backup not nuclear vs solar

Louis-
I've heard about fusion being available in the "next XX years" for a long time, too. It's really a matter of money and effort made. Most of the work is being carried out at Livermore National Laboratory in California, but continues to languish from indifferent funding by the US Department of Energy. The key isn't getting ignition, but achieving a sustainable reaction. Take the progress NASA makes in comparison to SpaceX and Blue Origin as a comparable. Until some private company gets super-involved, things will drag on and on in government labs. No real deadlines or incentives.
The initial reactors will be Tritium-Deuterium facilities, but these generate a highly radioactive infrastructure over time; the advantage of He3 based systems is NO FREE NEUTRON flux! The nuclear chemistry is much more favorable and infinitely less polluting, since more energy is released, and without the free neutron.

Offline

#5 2019-10-02 10:59:14

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

Our Prime Minister in the UK was today claiming in his party conference speech that scientists at Harwell here were "on the verge" of commercialising hot fusion...yeah, believe it when I see it!


Oldfart1939 wrote:

Louis-
I've heard about fusion being available in the "next XX years" for a long time, too. It's really a matter of money and effort made. Most of the work is being carried out at Livermore National Laboratory in California, but continues to languish from indifferent funding by the US Department of Energy. The key isn't getting ignition, but achieving a sustainable reaction. Take the progress NASA makes in comparison to SpaceX and Blue Origin as a comparable. Until some private company gets super-involved, things will drag on and on in government labs. No real deadlines or incentives.
The initial reactors will be Tritium-Deuterium facilities, but these generate a highly radioactive infrastructure over time; the advantage of He3 based systems is NO FREE NEUTRON flux! The nuclear chemistry is much more favorable and infinitely less polluting, since more energy is released, and without the free neutron.


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

Offline

#6 2019-10-02 11:55:42

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,077
Website

Re: Methane backup not nuclear vs solar

The government-supported research into fusion began about 1950 in the US.  It has been "10 or 15 years away" for 69 years now.  If I was you,  I wouldn't be holding my breath over it.

What that really means is you go with what you got in-hand.  You do not wait for fusion.  For electricity in space or on other worlds,  there is solar,  there is nuclear fission,  and if you requirement is pitifully low,  there is radioisotope generation. 

You put some sort of base or settlement anywhere out there (on Mars,  the moon,  or in space),  and you will need LOTS of electricity.  Which means there is solar and there is nuclear fission.  Fuel cells are a converter,  NOT a source.

Under most circumstances in airless environments,  solar is not intermittent,  excepting whatever day/night cycles there might be.  Those can be a problem if you cannot afford the batteries (and their upkeep and replacement) to get through the nights.  The moon is such with 14 days of daylight,  followed by 14 days of darkness. 

Mars has only a 24-ish hour day/night cycle, so the battery problem is no worse than using solar here on Earth.  But quite unlike Earth,  Mars can have dust storms that blot out 95+% of daylight insolation,  for multiple months at a time.  That is what finally "killed" the Opportunity rover. 

MOST of the dust storms are NOT that bad,  but ones that bad happen frequently enough to make it a dead certainty a manned outpost WILL see them!

So on Mars,  you can use solar,  yes,  but you had better have a credible backup.  That's nuclear fission,  no ifs,  ands,  or buts. 

There are NO hardware items you can go buy that would burn LOX and LCH4 to make electricity,  there are only rocket engines that burn it to make thrust,  and not yet very many of them.  That's not to say there couldn't be,  but how many years do you want to wait before someone decides to develop one,  and how many more years do you want to wait while he develops it into a usable product?

Besides,  on Mars,  you already have a critical need for that LOX and LCH4 as rocket propellant.  Or else no one ever comes home. 

That,  taken together,  is why Louis is wrong about solar-only on Mars.  You MUST have both solar and nuclear fission. You take enough fission to get you through the night,  and wee bit more.  Then add sufficient solar for the higher daytime electricity demand.  You hunker down at minimal activity on fission during the dust storms. 

If you increase the proportion of fission in your electricity source mix,  then you can still maybe make a little propellant,  even during a worst-case dust storm. Fuel cells might (or might not) be the battery you need for your solar.  There are certainly the "battery" you want for your rovers.

That's not really hard to understand. 

GW

Last edited by GW Johnson (2019-10-02 12:03:06)


GW Johnson
McGregor,  Texas

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

Offline

#7 2019-10-02 12:58:54

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Re: Methane backup not nuclear vs solar

GW-Last year I had a conversation with a friend I see only intermittently; he's a lead Ph.D. Physicist at Lawrence Livermore National Laboratory, and has been working on the "ignition" problem for years. His complaint was as usual: not enough money to build "XYZ." A bigger and more powerful Tokamak. They can get ignition on small scale, but to sustainable reaction due to confinement constraints. They aren't that far away, but not close enough to count on anything in the next 5-10 years (decades??).

Offline

#8 2019-10-02 13:18:17

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

I am proposing solar plus methane-oxygen not solar plus batteries. That provides a total and secure energy architecture.  There will be chemical batteries as well but the system won't depend on them.

This is really only a critical issue on Mission One. Later missions will land at the base and find plenty of energy storage immediately available (most likely in methane-oxygen form with generators in place).

For Mission One I propose that the pioneers land with a dedicated supply on board of methane and oxygen and two methane-oxygen electricity generators (20Kw each, 250kg mass per generator). The Starship will land with charged batteries for life support systems.  The methane-oxygen generation won't be required immediately even if they land in the middle of a worst case dust storm scenario. Another point to remember is that the 4 cargo Starships will have been standing on the surface and recharging their powerful fin batteries (total of 2,400 KWhs), that can be used as a power supply on the surface.

All in all there will be plenty of energy available to set up the base. Once the base is set up, solar arrays can be deployed. The first tranche would ATK-style fan arrays that open automatically. Even in the worst case dust storm, the PV equipment will be generating at least 20% of the seasonal norm (with dust accumulation) and such low levels of insolation do not last for more than a few days .  After a few sols, the pioneers should be able to lay out the rest of the PV array within 10 sols, supervising robot rovers. 


GW Johnson wrote:

The government-supported research into fusion began about 1950 in the US.  It has been "10 or 15 years away" for 69 years now.  If I was you,  I wouldn't be holding my breath over it.

What that really means is you go with what you got in-hand.  You do not wait for fusion.  For electricity in space or on other worlds,  there is solar,  there is nuclear fission,  and if you requirement is pitifully low,  there is radioisotope generation. 

You put some sort of base or settlement anywhere out there (on Mars,  the moon,  or in space),  and you will need LOTS of electricity.  Which means there is solar and there is nuclear fission.  Fuel cells are a converter,  NOT a source.

Under most circumstances in airless environments,  solar is not intermittent,  excepting whatever day/night cycles there might be.  Those can be a problem if you cannot afford the batteries (and their upkeep and replacement) to get through the nights.  The moon is such with 14 days of daylight,  followed by 14 days of darkness. 

Mars has only a 24-ish hour day/night cycle, so the battery problem is no worse than using solar here on Earth.  But quite unlike Earth,  Mars can have dust storms that blot out 95+% of daylight insolation,  for multiple months at a time.  That is what finally "killed" the Opportunity rover. 

MOST of the dust storms are NOT that bad,  but ones that bad happen frequently enough to make it a dead certainty a manned outpost WILL see them!

So on Mars,  you can use solar,  yes,  but you had better have a credible backup.  That's nuclear fission,  no ifs,  ands,  or buts. 

There are NO hardware items you can go buy that would burn LOX and LCH4 to make electricity,  there are only rocket engines that burn it to make thrust,  and not yet very many of them.  That's not to say there couldn't be,  but how many years do you want to wait before someone decides to develop one,  and how many more years do you want to wait while he develops it into a usable product?

Besides,  on Mars,  you already have a critical need for that LOX and LCH4 as rocket propellant.  Or else no one ever comes home. 

That,  taken together,  is why Louis is wrong about solar-only on Mars.  You MUST have both solar and nuclear fission. You take enough fission to get you through the night,  and wee bit more.  Then add sufficient solar for the higher daytime electricity demand.  You hunker down at minimal activity on fission during the dust storms. 

If you increase the proportion of fission in your electricity source mix,  then you can still maybe make a little propellant,  even during a worst-case dust storm. Fuel cells might (or might not) be the battery you need for your solar.  There are certainly the "battery" you want for your rovers.

That's not really hard to understand. 

GW


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

Offline

#9 2019-10-02 13:45:34

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Re: Methane backup not nuclear vs solar

Louis-
I really didn't want this discussion to devolve into another solar power versus nuclear discussion, but I need to state now that your proposal for methane-oxygen as a substitute for nuclear is absurd. We don't need another experimental power supply to contend with, and any methane produced will be required facilitate the trips back to Earth. Re-read what GW has written in the section you quoted. You are violating one of Musk's basic rules by making things overly complicated. A small portable nuclear reactor as suggested by Dr. Zubrin is EXACTLY  what is required for Mars Base Alpha. We're talking about human survival--the crew needs energy for all life support functions, and if a massive storm swamps the solar farm--everybody dies. Not if we have that Kilopower unit up and running.

I'm trying very hard to remain civil in our discussion.

Offline

#10 2019-10-02 16:24:54

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,669

Re: Methane backup not nuclear vs solar

methane oxygen combustion means that you are slowly losing the air for backup to breath with for when power is not working. Not to meantion you now are eating into the ships ability to leave on schedule. Solar and batteries can not be left in a charging mode for ever Louis they will not be able to be cycled enough to allow for proper charging if you are waiting for a human crew to use the system. This will kill the batteries....

Online

#11 2019-10-02 16:50:30

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

That doesn't make sense Space Nut. If you take a Kilopower nuclear reactor you are taking up payload mass. I am suggesting you take methane and oxygen as part of the payload mass but don't take a Kilopower nuclear reactor, so there's a saving there.

We can argue about the exact mass numbers but that is how it works. It's just nonsense to talk about "losing air for backup".

As for the solar power charging of batteries in other Starships...just disconnect until a few weeks before the human passenger Starship is due to land. All these things are possible.

I used to get all these objections thrown at me about retro landing on Mars...now everyone seems to accept it. I used to be told it was impossible to do a pass around Earth when you enter at hypersonic speed - not so much now Musk says it's possible!

I think all these objections about solar power are really motivated by nothing more than enthusiasm for nuclear. 



SpaceNut wrote:

methane oxygen combustion means that you are slowly losing the air for backup to breath with for when power is not working. Not to meantion you now are eating into the ships ability to leave on schedule. Solar and batteries can not be left in a charging mode for ever Louis they will not be able to be cycled enough to allow for proper charging if you are waiting for a human crew to use the system. This will kill the batteries....


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

Offline

#12 2019-10-02 17:44:19

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,669

Re: Methane backup not nuclear vs solar

A kilowatt reactor will run for decades but methane oxygen plus the generator to create the power will last just days....
Nothing will be able to disconnect the batteries that are powered from them...

Online

#13 2019-10-03 08:56:39

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Re: Methane backup not nuclear vs solar

The minimum size nuke reactor has varied according to which of Zubrin's plans you look at, but more recently he calls for a 100 Kwe reactor. This could generate enough electric power to manufacture methane and hydrolyze water for oxygen, in addition to supplying a steady stream of energy for life support systems (heating, rover recharge, water and waste systems, cooking, lab operations). This is able to provide 25 hours around the clock energy even in Martian night. Such a reactor might weigh from 4,500 to 7,000 pounds; call it from 2 to 3.5 metric Tonnes. This is the total weight of a system capable of providing power for the base for years; 3.5 metric Tonnes of methane and oxygen would last maybe a month if called upon to generate power for a Mars Base Alpha., but the quantity would be reduced by the mass of the power generation apparatus and tankage involved.
The numbers simply do NOT support use of methane/oxygen as a backup energy plan. Chemical energy production is in distant last place when compared to fission.

Last edited by Oldfart1939 (2019-10-03 08:57:28)

Offline

#14 2019-10-03 12:24:18

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

A methane generator will last for decades.

We have no information on how much a Kilopower reactor will actually mass in practice and how it will be deployed.



SpaceNut wrote:

A kilowatt reactor will run for decades but methane oxygen plus the generator to create the power will last just days....
Nothing will be able to disconnect the batteries that are powered from them...


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

Offline

#15 2019-10-03 13:42:38

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Re: Methane backup not nuclear vs solar

Louis-

But the fuel WON'T. See for reference: Post #31

The generator hasn't been designed yet, Louis. As GW stated. The generator may last but it will take an enormous amount of methane and LOX to fuel it. The Kilopower unit is undergoing NASA testing as we dither around here on this website. It will be ready by time Starship flies.
Your methane-oxygen system is currently a fantasy. I'm using mass estimates based on the NASA initial mass data.   

We have agreed on a lot of topics--but this isn't one of them.

Last edited by Oldfart1939 (2019-10-03 15:54:12)

Offline

#16 2019-10-03 17:01:16

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

It doesn't need to last forever. 

Under the Space X mission about 500 tons is being delivered to Mars.

Let's suppose that out of that allowance we have 30 tons of methane useable with 60 tons of oxygen for combustion.

There's 15.4 KwHs of energy in 1 Kg of methane = 462,000 KwHs for 30 tons of methane. At 40% efficiency that would provide 184,800 KwHes. That would be enough to provide 10Kwe constant power for 754 sols. 10 Kwe constant is a generous allowance. I suspect the pioneers could survive in their hab on 2Kwes.

Do we really need that much outward bound methox storage? I'd say no.  Probably 100 sols at 10 Kwe constant would be a good marker. That would give a requirement of about 4 tons of methane with 8 tons of oxygen, so 12 tons of mass.

The reason I don't think we need anything more, is that (with the Space X mission) you will have six Starships on the surface. The four cargo Starships will have landed two years previously, and dust storms or not will have been recharging their batteries from their external PV panels. For each Starship the fin batteries set will store about 400 KwHs. I expect there will be additional battery storage in other parts of the craft, so let's say 500KwHs per Starship, so that will be a total of 2000KwHs of storage at the surface (another 40 sols at emergency power levels).

Furthermore it will be possible in the first 100 sols, dust storm or not, to begin deploying the solar arrays. Even in the worst dust storm you are going to get 20% of the norm (that's allowing for dust accumulation).  You will gradually be ramping up generation.

Now, all I have ever heard of with regard to the Kilopower units is that they will be deployed on the surface, and not in the Starship (the reason being that if you don't do it that way, you have a radiation hazard on board, unless you then provide elaborate screening).

So, on that basis, you could land on the surface and not have a supplemental energy source on board. That surely is worse than having a working methane-fuelled generator on board.

Oldfart1939 wrote:

Louis-

But the fuel WON'T.

The generator hasn't been designed yet, Louis. As GW stated. The generator may last but it will take an enormous amount of methane and LOX to fuel it. The Kilopower unit is undergoing NASA testing as we dither around here on this website. It will be ready by time Starship flies.
Your methane-oxygen system is currently a fantasy. I'm using mass estimates based on the NASA initial mass data.   

We have agreed on a lot of topics--but this isn't one of them.


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

Offline

#17 2019-10-03 18:11:04

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,669

Re: Methane backup not nuclear vs solar

The generators can not run continously and must have maintenance to keep it going which means we will need serveral backup methane generators which are very simular to the natural and propane gas ones here on earth.
The ratings of the output of a generator is give as a max level but its not capable to running at that level but only for short peak periods. typically they are run at 70% output power levels to ensure that they do not over heat.

Here is a typical 22kw unit

  • NG Fuel Consumption @ 50% Load 216 ft³/hr
    NG Fuel Consumption @ 100% Load 310 ft³/hr
    LP Fuel Consumption @ 50% Load 2.56 gallons/hr
    LP Fuel Consumption @ 100% Load 3.87 gallons/hr

So if we used say 5 gallons hr then for a day we will use 125 a day and for a week 875 a week which is the typical tank on earth for home use of 1,000 gallons.

https://www.convertunits.com/from/ton/to/gallon+[U.S.]+of+LPG
10 ton to gallon [U.S.] of LPG = 415.25305 gallon [U.S.] of LPG

ouch we are dead

Online

#18 2019-10-03 20:16:03

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Re: Methane backup not nuclear vs solar

The major point here is Methane and Oxygen are the trip home for the new Martians. I can't see using a critical resource, particularly in the case of a major planetary dust storm which has cut production if depending on solar, to facilitate a trip back to Earth. The sheer size of teh Starships has made fuel production THE priority for energy produced in situ.

Offline

#19 2019-10-03 20:37:42

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,709

Re: Methane backup not nuclear vs solar

SpaceNut,

At full load your example 22kW LPG generator consumes 1 gallon of LPG per hour for every 5,684 Watts of output.  That'd be 8,760 gallons over the course of a year to produce 49.8MWh worth of electricity.  Each gallon of LPG weighs about 4.2 pounds, so 36,792 pounds of LPG over the course of a year.

Each 10kWe output KiloPower fission reactor weighs 3,300 pounds.  That 8,760 gallons of initial LPG fuel equates to the mass of a little over 11 of those 10kWe KiloPower units.  If we ran all 11 reactors at 75% of their rated output, that'd be 82.5kW.  For the same weight of fuel required to generate 49.8MWh over a year's time, those 11 KiloPower units would produce 772.7MWh.  That presumes we obtain all oxidizer from the Martian atmosphere for zero additional weight penalty associated with additional production capacity and storage of the fuel and oxidizer.  We could store both in Starship's propellant tanks, obviously, but we'd also require additional input power to keep our cryogens frosty.  For the mass of the fuel alone, those dinky little fission reactors produce 14.5 times as much output for equivalent initial fuel mass.

If you can afford to take 8,760 gallons of anything with you to Mars, it should be potable water.

Louis is in denial about how well this would work in practice.

As always, power production is the name of the game.  If I could devote 50t of mass to power provisioning, it would be photovoltaics and fission reactors.  The use of fuel cells and batteries would be relegated to powering specific pieces of equipment.  Since equipment is needed during the day when humans can see, the batteries would be recharged at night when most people will be sleeping.  If it was also possible to deploy reasonably sized solar power satellites in orbit that always receive full Sun and aren't subject to degradation associated with surface conditions, then I'd transmit power to microwave power collector on the surface, which have minimal associated mass.  The technical problems with deployment and operation of a massive surface photovoltaic array in a severely dusty and abrasive environment are negated, the power equipment that is taken to the surface takes decades to degrade appreciably, and the overall mass of the power provisioning solution is minimized.  The solar power satellites have the added capability of repositioning their beams to transmit power to a secondary site where water must be extracted.  Their power could also be used to flash evaporate water from icy regolith.

Offline

#20 2019-10-03 21:07:58

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,890

Re: Methane backup not nuclear vs solar

kbd512-
Thanks, you saved me the drudgery of doing the energy calculations that Louis refuses to accept in portraying his system as hopeless. It also kept me from saying something negative about how things operate in reality. The difference in power provided from nuclear versus chemical reactions is on many orders of magnitude differential. One only needs remember the comparisons in explosive potential--megatons of TNT versus a single nuke weighing about a ton (of which only a small fraction is fissile material).
It seems that the anti-nuclear lobby and propaganda has done an effective job at discouraging use of nuclear energy.

Last edited by Oldfart1939 (2019-10-03 21:08:57)

Offline

#21 2019-10-03 21:40:52

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,669

Re: Methane backup not nuclear vs solar

Another aspect of the math is that the equation if run backwards suggests that we will need even more energy to make our fuel and oxidizer than what I once thought. Engine efficiency is about 25% so 88kw plus is what the fuel and oxidizer of energy stored had before use and to get that from mars since these are both energy intense processes for gaining both from soils and air we are going to need a high concentration of water for each scoop to make the energy levels required drop.

Online

#22 2019-10-04 00:24:34

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

The generators I was referencing are 20 Kwe output (250 Kg mass).  Take 3 if you're concerned about maintenance.

I don't know about your figures as I work in Kgs and KwH but obviously a 22 Kw unit would be producing a lot more than 10 Kwe and that 10 Kwe figure (more like 15Kwe on your 70% output) would in itself be extremely "generous" in terms of ticking over at the base. What  would 10 Kwe be required for? Some minimal heating would be  required but heat loss in an areogelled hab would be v. minimal in Mars's v. low pressure atmosphere and of course six human bodies would be producing quite a lot of heat themselves. Life support would probably be maxing at something like 2Kwe average.

SpaceNut wrote:

The generators can not run continously and must have maintenance to keep it going which means we will need serveral backup methane generators which are very simular to the natural and propane gas ones here on earth.
The ratings of the output of a generator is give as a max level but its not capable to running at that level but only for short peak periods. typically they are run at 70% output power levels to ensure that they do not over heat.

Here is a typical 22kw unit

  • NG Fuel Consumption @ 50% Load 216 ft³/hr
    NG Fuel Consumption @ 100% Load 310 ft³/hr
    LP Fuel Consumption @ 50% Load 2.56 gallons/hr
    LP Fuel Consumption @ 100% Load 3.87 gallons/hr

So if we used say 5 gallons hr then for a day we will use 125 a day and for a week 875 a week which is the typical tank on earth for home use of 1,000 gallons.

https://www.convertunits.com/from/ton/to/gallon+[U.S.]+of+LPG
10 ton to gallon [U.S.] of LPG = 415.25305 gallon [U.S.] of LPG

ouch we are dead


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

Offline

#23 2019-10-04 00:28:01

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

The background info I have read suggests the engine efficiency is at least 38%.

As for methane and oxygen production on Mars, it doesn't matter how inefficient the process is, in terms of a Space X mission that's the only way to get back. 

For the energy architecture I am proposing, you would simply "top up" your energy storage via methox as a byproduct of having to produce methox for the return journey.

SpaceNut wrote:

Another aspect of the math is that the equation if run backwards suggests that we will need even more energy to make our fuel and oxidizer than what I once thought. Engine efficiency is about 25% so 88kw plus is what the fuel and oxidizer of energy stored had before use and to get that from mars since these are both energy intense processes for gaining both from soils and air we are going to need a high concentration of water for each scoop to make the energy levels required drop.


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

Offline

#24 2019-10-04 00:48:23

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

(a) You need to be clear if this Kilopower machine is operating on the Starship or not. If it is, it's radioactive on a crewed ship and that raises issues of health and safety, and presumably would require heavy shielding.

(b) If you've not going to operate your Kilopower unit on the Starship, then it is irrelevant to how much power you have available on the Starship in the event of an emergency on landing.

(c) There's no point in comparing the output of the Kilopower unit with the output of equivalent methane generation alone to judge the effectiveness of my proposed energy system. I am proposing solar plus methane, not methane alone. So compare the overall KWe output.

(d) We have no idea how much the Kilpower unit will mass if it is going to be actively used on the Starship, because then, as far as I can see, you will need radiation shielding.

(e) If it's not being used on the Starship it's of no relevance to the emergency scenario involving the crew on the Starship.

(f) I'm not saying I'm accepting Spacenut's figures (I'll take a look at those). They don't match with mine. His efficieny percentage of 25% appears wrong from what I have read.

(g) Musk is already proposing large battery storage on the Starships, in order to actuate the fins (400 Kwhes IIRC). Presumably rovers will also have large battery storage as well. So, whether you wish it or not, there will be quite a large battery capacity built into the mission.


kbd512 wrote:

SpaceNut,

At full load your example 22kW LPG generator consumes 1 gallon of LPG per hour for every 5,684 Watts of output.  That'd be 8,760 gallons over the course of a year to produce 49.8MWh worth of electricity.  Each gallon of LPG weighs about 4.2 pounds, so 36,792 pounds of LPG over the course of a year.

Each 10kWe output KiloPower fission reactor weighs 3,300 pounds.  That 8,760 gallons of initial LPG fuel equates to the mass of a little over 11 of those 10kWe KiloPower units.  If we ran all 11 reactors at 75% of their rated output, that'd be 82.5kW.  For the same weight of fuel required to generate 49.8MWh over a year's time, those 11 KiloPower units would produce 772.7MWh.  That presumes we obtain all oxidizer from the Martian atmosphere for zero additional weight penalty associated with additional production capacity and storage of the fuel and oxidizer.  We could store both in Starship's propellant tanks, obviously, but we'd also require additional input power to keep our cryogens frosty.  For the mass of the fuel alone, those dinky little fission reactors produce 14.5 times as much output for equivalent initial fuel mass.

If you can afford to take 8,760 gallons of anything with you to Mars, it should be potable water.

Louis is in denial about how well this would work in practice.

As always, power production is the name of the game.  If I could devote 50t of mass to power provisioning, it would be photovoltaics and fission reactors.  The use of fuel cells and batteries would be relegated to powering specific pieces of equipment.  Since equipment is needed during the day when humans can see, the batteries would be recharged at night when most people will be sleeping.  If it was also possible to deploy reasonably sized solar power satellites in orbit that always receive full Sun and aren't subject to degradation associated with surface conditions, then I'd transmit power to microwave power collector on the surface, which have minimal associated mass.  The technical problems with deployment and operation of a massive surface photovoltaic array in a severely dusty and abrasive environment are negated, the power equipment that is taken to the surface takes decades to degrade appreciably, and the overall mass of the power provisioning solution is minimized.  The solar power satellites have the added capability of repositioning their beams to transmit power to a secondary site where water must be extracted.  Their power could also be used to flash evaporate water from icy regolith.


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

Offline

#25 2019-10-04 00:59:51

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,868

Re: Methane backup not nuclear vs solar

I think you're misunderstanding what I propose. Firstly, you take the 12 tons of methox with you , so at that point you are not tapping into propellant production. You would only need to tap in to propellant production if you deplete that emergency store - itself a very, very unlikely scenario. But assuming you had to replenish the store entirely, 12 tons out of 1000 tons over say a 600 sol production period would be about 7 sols' worth of production. Or, to put it another way, you would just run your propellant production facility for another 7 sols.  You are going to have to build in a wide margin of safety in any case ie propellant production will have to be completed well in advance of departure date. So these things are at the margins and amount to keeping the propellant production facility going for a few sols longer than would otherwise be the case (but still v. unlikely you would need to do so).

Oldfart1939 wrote:

The major point here is Methane and Oxygen are the trip home for the new Martians. I can't see using a critical resource, particularly in the case of a major planetary dust storm which has cut production if depending on solar, to facilitate a trip back to Earth. The sheer size of teh Starships has made fuel production THE priority for energy produced in situ.


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

Offline

Board footer

Powered by FluxBB